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  • 1. Alexanderson, Helena
    et al.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cronin, Thomas M.
    Funder, Svend
    Ingólfsson, Ólafur
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Landvik, Jon Y.
    Löwemark, Ludvig
    Mangerud, Jan
    März, Christian
    Möller, Per
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Spielhagen, Robert F.
    An Arctic perspective on dating Mid-Late Pleistocene environmental history2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, p. 9-31Article in journal (Refereed)
    Abstract [en]

    To better understand Pleistocene climatic changes in the Arctic, integrated palaeoenvironmental andpalaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologicage control are required, not least for correlation to extra-Arctic records. In this paper we discuss,from an Arctic perspective, methods and correlation tools that are commonly used to date ArcticPleistocene marine and terrestrial events. We review the state of the art of Arctic geochronology, withfocus on factors that affect the possibility and quality of dating, and support this overview by examples ofapplication of modern dating methods to Arctic terrestrial and marine sequences.Event stratigraphy and numerical ages are important tools used in the Arctic to correlate fragmentedterrestrial records and to establish regional stratigraphic schemes. Age control is commonly provided byradiocarbon, luminescence or cosmogenic exposure ages. Arctic Ocean deep-sea sediment successionscan be correlated over large distances based on geochemical and physical property proxies for sedimentcomposition, patterns in palaeomagnetic records and, increasingly, biostratigraphic data. Many of theseproxies reveal cyclical patterns that provide a basis for astronomical tuning.Recent advances in dating technology, calibration and age modelling allow for measuring smallerquantities of material and to more precisely date previously undatable material (i.e. foraminifera for 14C,and single-grain luminescence). However, for much of the Pleistocene there are still limits to the resolutionof most dating methods. Consequently improving the accuracy and precision (analytical andgeological uncertainty) of dating methods through technological advances and better understanding ofprocesses are important tasks for the future. Another challenge is to better integrate marine andterrestrial records, which could be aided by targeting continental shelf and lake records, exploringproxies that occur in both settings, and by creating joint research networks that promote collaborationbetween marine and terrestrial geologists and modellers.

  • 2. Anderson, Leif G.
    et al.
    Björk, Göran
    Holby, Ola
    Jutterström, Sara
    Mörth, Carl Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark.
    Semiletov, Igor
    Stranne, Christian
    Stöven, Tim
    Tanhua, Toste
    Ulfsbo, Adam
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Shelf-Basin interaction along the East Siberian Sea2017In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 13, no 2, p. 349-363Article in journal (Refereed)
    Abstract [en]

    Extensive biogeochemical transformation of organic matter takes place in the shallow continental shelf seas of Siberia. This, in combination with brine production from sea-ice formation, results in cold bottom waters with relatively high salinity and nutrient concentrations, as well as low oxygen and pH levels. Data from the SWERUS-C3 expedition with icebreaker Oden, from July to September 2014, show the distribution of such nutrient-rich, cold bottom waters along the continental margin from about 140 to 180 degrees E. The water with maximum nutrient concentration, classically named the upper halocline, is absent over the Lomonosov Ridge at 140 degrees E, while it appears in the Makarov Basin at 150 degrees E and intensifies further eastwards. At the intercept between the Mendeleev Ridge and the East Siberian continental shelf slope, the nutrient maximum is still intense, but distributed across a larger depth interval. The nutrient-rich water is found here at salinities of up to similar to 34.5, i.e. in the water classically named lower halocline. East of 170 degrees E transient tracers show significantly less ventilated waters below about 150 m water depth. This likely results from a local isolation of waters over the Chukchi Abyssal Plain as the boundary current from the west is steered away from this area by the bathymetry of the Mendeleev Ridge. The water with salinities of similar to 34.5 has high nutrients and low oxygen concentrations as well as low pH, typically indicating decay of organic matter. A deficit in nitrate relative to phosphate suggests that this process partly occurs under hypoxia. We conclude that the high nutrient water with salinity similar to 34.5 are formed on the shelf slope in the Mendeleev Ridge region from interior basin water that is trapped for enough time to attain its signature through interaction with the sediment.

  • 3.
    Barrientos, Natalia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen
    Lear, Caroline
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl-Magnus
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mg/Ca ratios in late Quaternary benthic foraminifera from the central Arctic OceanManuscript (preprint) (Other academic)
  • 4.
    Barrientos, Natalia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lear, Caroline
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Muschitiello, Francesco
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    de Boer, Agatha
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cronin, Thomas
    Semiletov, Igor
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Late Holocene variability in Arctic Ocean Pacific Water inflow through the Bering StraitManuscript (preprint) (Other academic)
  • 5.
    Barrientos, Natalia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Miller, Clint
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Brüchert, Volker
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Johansson, Carina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Post-recovery dissolution of calcareous microfossils in sediments from a highly productive Arctic marine environmentManuscript (preprint) (Other academic)
  • 6.
    Barrientos, Natalia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lear, Caroline H.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cronin, Thomas M.
    Gukov, Aleksandr Y.
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Arctic Ocean benthic foraminifera Mg/Ca ratios and global Mg/Ca-temperature calibrations: New constraints at low temperatures2018In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 236, p. 240-259Article in journal (Refereed)
    Abstract [en]

    We explore the use of Mg/Ca ratios in six Arctic Ocean benthic foraminifera species as bottom water palaeothermometers and expand published Mg/Ca-temperature calibrations to the coldest bottom temperatures (<1 °C). Foraminifera were analyzed in surface sediments at 27 sites in the Chukchi Sea, East Siberian Sea, Laptev Sea, Lomonosov Ridge and Petermann Fjord. The sites span water depths of 52–1157 m and bottom water temperatures (BWT) of −1.8 to +0.9 °C. Benthic foraminifera were alive at time of collection, determined from Rose Bengal (RB) staining. Three infaunal and three epifaunal species were abundant enough for Mg/Ca analysis. As predicted by theory and empirical evidence, cold water Arctic Ocean benthic species produce low Mg/Ca ratios, the exception being the porcelaneous species Quinqueloculina arctica. Our new data provide important constraints at the cold end (<1 °C) when added to existing global datasets. The refined calibrations based on the new and published global data appear best supported for the infaunal species Nonionella labradorica (Mg/Ca = 1.325 ± 0.01 × e^(0.065 ± 0.01 × BWT), r2 = 0.9), Cassidulina neoteretis (Mg/Ca = 1.009 ± 0.02 × e^(0.042 ± 0.01 × BWT), r2 = 0.6) and Elphidium clavatum (Mg/Ca = 0.816 ± 0.06 + 0.125 ± 0.05 × BWT, r2 = 0.4). The latter is based on the new Arctic data only. This suggests that Arctic Ocean infaunal taxa are suitable for capturing at least relative and probably semi-quantitative past changes in BWT. Arctic Oridorsalis tener Mg/Ca data are combined with existing O. umbonatus Mg/Ca data from well saturated core-tops from other regions to produce a temperature calibration with minimal influence of bottom water carbonate saturation state (Mg/Ca = 1.317 ± 0.03 × e^(0.102 ± 0.01 BWT), r2 = 0.7). The same approach for Cibicidoides wuellerstorfi yields Mg/Ca = 1.043 ± 0.03 × e^(0.118 ± 0.1 BWT), r2 = 0.4. Mg/Ca ratios of the porcelaneous epifaunal species Q. arctica show a clear positive relationship between Mg/Ca and Δ[CO32−] indicating that this species is not suitable for Mg/Ca-palaeothermometry at low temperatures, but may be useful in reconstructing carbonate system parameters through time.

  • 7. Chiu, Pin-Yao
    et al.
    Chao, Weng-Si
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Li, Hong-Chun
    Löwemark, Ludvig
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    New constraints on Arctic Ocean Mn stratigraphy from radiocarbon dating on planktonic foraminifera2017In: Quaternary International, ISSN 1040-6182, E-ISSN 1873-4553, Vol. 447, p. 13-26Article in journal (Refereed)
    Abstract [en]

    Variations in the abundance of manganese (Mn) in Arctic Ocean sediments are used as a tool to identify glacial and interglacial periods. This study aims to provide new insight into the applicability of Mn as a stratigraphic tool in the topmost sediment and to investigate the occurrence of Mn peaks in sediments within the range of radiocarbon dating. In combination with variations in ice-rafted debris (IRD), radiocarbon dating is used to better constrain the stratigraphic occurrence of Mn peaks, and the synchroneity between multiple records, especially during the late glacial and the Holocene. We find that a hiatus spanning MIS 2 is widely observed in most of our cores, resulting in a merging of Mn peaks of Holocene age and the later part of MIS 3. The Holocene Mn peak is usually high amplitude but short, while the MIS 3 Mn peak has a lower amplitude and is protracted. Where preserved, MIS 2 sediments form a 2-3 cm thick layer characterized by a light color, low Mn content, sparse IRD and low foraminiferal abundance. IRD variations provide a powerful tool to identify the boundary of the Holocene and late MIS 3 in cores with a MIS 2 hiatus. Because the IRD content displays a general increment from the start of MIS 3, and both the Holocene and MIS 2 show small IRD variations, the end of MIS 3 can be pinpointed to the point of decrease in IRD. The hiatus of MIS 2 is widely observed in our cores, suggesting extensive persistent sea ice coverage during the peak of the last glacial cycle, with sharply reduced sedimentation throughout the Arctic Ocean. Identifying similar events during previous glacial periods may be an important step towards constructing longer and more accurate chronologies for Arctic Ocean sediments.

  • 8.
    Coxall, Helen K.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Huck, Claire E.
    Huber, Matthew
    Lear, Caroline H.
    Legarda-Lisarri, Alba
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sliwinska, Kasia K.
    van de Flierdt, Tina
    de Boer, Agatha M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Zachos, James C.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Export of nutrient rich Northern Component Water preceded early Oligocene Antarctic glaciation2018In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 11, no 3, p. 190-196Article in journal (Refereed)
    Abstract [en]

    The onset of the North Atlantic Deep Water formation is thought to have coincided with Antarctic ice-sheet growth about 34 million years ago (Ma). However, this timing is debated, in part due to questions over the geochemical signature of the ancient Northern Component Water (NCW) formed in the deep North Atlantic. Here we present detailed geochemical records from North Atlantic sediment cores located close to sites of deep-water formation. We find that prior to 36 Ma, the northwestern Atlantic was stratified, with nutrient-rich, low-salinity bottom waters. This restricted basin transitioned into a conduit for NCW that began flowing southwards approximately one million years before the initial Antarctic glaciation. The probable trigger was tectonic adjustments in subarctic seas that enabled an increased exchange across the Greenland-Scotland Ridge. The increasing surface salinity and density strengthened the production of NCW. The late Eocene deep-water mass differed in its carbon isotopic signature from modern values as a result of the leakage of fossil carbon from the Arctic Ocean. Export of this nutrient-laden water provided a transient pulse of CO2 to the Earth system, which perhaps caused short-term warming, whereas the long-term effect of enhanced NCW formation was a greater northward heat transport that cooled Antarctica.

  • 9. Cronin, Thomas M.
    et al.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gemery, Laura
    Toomey, Michael
    Semiletov, Igor
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Deglacial sea level history of the East Siberian Sea and Chukchi Sea margins2017In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 13, no 9, p. 1097-1110Article in journal (Refereed)
    Abstract [en]

    Deglacial (12.8-10.7 ka) sea level history on the East Siberian continental shelf and upper continental slope was reconstructed using new geophysical records and sediment cores taken during Leg 2 of the 2014 SWERUS-C3 expedition. The focus of this study is two cores from Herald Canyon, piston core SWERUS-L2-4-PC1 (4-PC1) and multicore SWERUS-L2-4-MC1 (4-MC1), and a gravity core from an East Siberian Sea transect, SWERUS-L2-20-GC1 (20GC1). Cores 4-PC1 and 20-GC were taken at 120 and 115m of modern water depth, respectively, only a few meters above the global last glacial maximum (LGM; similar to 24 kiloannum or ka) minimum sea level of similar to 125-130 meters below sea level (m b.s.l.). Using calibrated radiocarbon ages mainly on molluscs for chronology and the ecology of benthic foraminifera and ostracode species to estimate paleodepths, the data reveal a dominance of river-proximal species during the early part of the Younger Dryas event (YD, Greenland Stadial GS-1) followed by a rise in river-intermediate species in the late Younger Dryas or the early Holocene (Preboreal) period. A rapid relative sea level rise beginning at roughly 11.4 to 10.8 ka (similar to 400 cm of core depth) is indicated by a sharp faunal change and unconformity or condensed zone of sedimentation. Regional sea level at this time was about 108m b.s.l. at the 4-PC1 site and 102m b.s.l. at 20-GC1. Regional sea level near the end of the YD was up to 42-47m lower than predicted by geophysical models corrected for glacio-isostatic adjustment. This discrepancy could be explained by delayed isostatic adjustment caused by a greater volume and/or geo-graphical extent of glacial-age land ice and/or ice shelves in the western Arctic Ocean and adjacent Siberian land areas.

  • 10. Dowdeswell, J. A.
    et al.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hogan, K. A.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Evans, J.
    Hell, Benjamin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Marcussen, C.
    Noormets, R.
    O'Cofaigh, C.
    Sellén, Emma
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sölvsten, M.
    High-resolution geophysical observations of the Yermak Plateau and northern Svalbard margin: Implications for ice-sheet grounding and deep-keeled icebergs2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3518-3531Article in journal (Refereed)
    Abstract [en]

    High-resolution geophysical evidence on the seafloor morphology and acoustic stratigraphy of the Yermak Plateau and northern Svalbard margin between 79°20′ and 81°30′N and 5° and 22°E is presented. Geophysical datasets are derived from swath bathymetry and sub-bottom acoustic profiling and are combined with existing cores to derive chronological control. Seafloor landforms, in the form of ice-produced lineations, iceberg ploughmarks of various dimensions (including features over 80 m deep and down to about 1000 m), and a moat indicating strong currents are found. The shallow stratigraphy of the Yermak Plateau shows three acoustic units: the first with well-developed stratification produced by hemipelagic sedimentation, often draped over a strong and undulating internal reflector; a second with an undulating upper surface and little acoustic penetration, indicative of the action of ice; a third unit of an acoustically transparent facies, resulting from debris flows. Core chronology suggests a MIS 6 age for the undulating seafloor above about 580 m. There are several possible explanations, including: (a) the flow of a major grounded ice sheet across the plateau crest from Svalbard (least likely given the consolidation state of the underlying sediments); (b) the more transient encroachment of relatively thin ice from Svalbard; or (c) the drift across the plateau of an ice-shelf remnant or megaberg from the Arctic Basin. The latter is our favoured explanation given the evidence currently at our disposal.

  • 11. Flink, Anne E.
    et al.
    Noormets, Riko
    Fransner, Oscar
    Hogan, Kelly A.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Past ice flow in Wahlenbergfjorden and its implications for late Quaternary ice sheet dynamics in northeastern Svalbard2017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 163, p. 162-179Article in journal (Refereed)
    Abstract [en]

    Wahlenbergfjorden is a fjord situated in the western part of Nordaustlandet in northern Svalbard. It leads into the 400 m deep Hinlopen Strait located between Nordaustlandet and Spitsbergen. High-resolution multibeam bathymetric and sub-bottom data, as well as sediment cores are used to study the past extent and dynamics of glaciers in Wahlenbergfjorden and western Nordaustlandet. The submarine landform assemblage in Wahlenbergfjorden consists of landforms characteristic of subglacial, ice marginal and proglacial conditions. Glacial lineations indicate that Wahlenbergfjorden was occupied by streaming ice during the LGM and most likely acted as an ice stream onset zone. Westward ice flow in the fjord merged with the ice stream in Hinlopen Strait. Absence of ice recessional landforms in outer Wahlenbergfjorden suggests relatively fast deglaciation, possibly by flotation of the glacier front in the deeper parts of the fjord. The inner part of Wahlenbergfjorden and Palanderbukta are characterized by De Geer moraines, indicating episodic retreat of a grounded glacier front. In Palanderbukta, longer still stands of the glacier terminus resulted in the formation of larger terminal moraine ridges. The inner part of Wahlenbergfjorden was deglaciated prior to 11.3 +/- 55 Cal. ka BP. The submarine landform assemblages in front of Bodleybreen, Etonbreen, Idunbreen, Frazerbreen and Aldousbreen confirm that these glaciers have surged at least once during the Holocene.

  • 12. Fransner, O.
    et al.
    Noormets, R.
    Flink, A. E.
    Hogan, K. A.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Glacial landforms and their implications for glacier dynamics in Rijpfjorden and Duvefjorden, northern Nordaustlandet, Svalbard2017In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 32, no 3, p. 437-455Article in journal (Refereed)
    Abstract [en]

    Observations of subglacial landforms yielding the configuration and dynamics of former ice-flows have for the first time been made in Rijpfjorden and Duvefjorden, Nordaustlandet, Svalbard, using sub-bottom acoustic, swath-bathymetric data and sediment cores. Five acoustic-stratigraphic units were distinguished suggesting the presence of a complete glacial-postglacial succession in the central fjord basins. C-14 ages from the sediments indicate that the inner Rijpfjorden and central Duvefjorden were deglaciated before ca. 10.6 cal ka BP and 11.0 cal ka BP, respectively. Maximum sediment thickness in Rijpfjorden and Duvefjorden is 26 m, resulting in sediment accumulation rates of ca. 66 cm ka(-1). The landform record suggests that the ice streaming in both fjords was topographically controlled. The considerably deeper basin and higher elongation ratios of the crag-and-tails in Duvefjorden are linked to the faulted bedrock and possibly to somewhat larger ice stream and/or more focused ice-flow compared to that in Rijpfjorden. De Geer moraines suggest slower retreat of a grounded ice margin from shallow areas of Rijpfjorden. In deeper areas of the fjords, the glaciers were probably floating, resulting in the lack of ice-marginal transverse landforms. The ice margin retreat from these areas was probably relatively rapid and dominated by calving.

  • 13. Gemery, Laura
    et al.
    Cronin, Thomas M.
    Poirier, Robert K.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark.
    Barrientos, Natalia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Johansson, Carina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Koshurnikov, Andrey
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Central Arctic Ocean paleoceanography from similar to 50 ka to present, on the basis of ostracode faunal assemblages from the SWERUS 2014 expedition2017In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 13, no 11, p. 1473-1489Article in journal (Refereed)
    Abstract [en]

    Late Quaternary paleoceanographic changes at the Lomonosov Ridge, central Arctic Ocean, were reconstructed from a multicore and gravity core recovered during the 2014 SWERUS-C3 Expedition. Ostracode assemblages dated by accelerator mass spectrometry (AMS) indicate changing sea-ice conditions and warm Atlantic Water (AW) inflow to the Arctic Ocean from similar to 50 ka to present. Key taxa used as environmental indicators include Acetabulastoma arcticum (perennial sea ice), Polycope spp. (variable sea-ice margins, high surface productivity), Krithe hunti (Arctic Ocean deep water), and Rabilimis mirabilis (water mass change/AWinflow). Results indicate periodic seasonally sea-ice-free conditions during Marine Isotope Stage (MIS) 3 (similar to 57-29 ka), rapid deglacial changes in water mass conditions (15-11 ka), seasonally sea-ice-free conditions during the early Holocene (similar to 10-7 ka) and perennial sea ice during the late Holocene. Comparisons with faunal records from other cores from the Mendeleev and Lomonosov ridges suggest generally similar patterns, although sea-ice cover during the Last Glacial Maximum may have been less extensive at the new Lomonosov Ridge core site (similar to 85.15 degrees N, 152 degrees E) than farther north and towards Greenland. The new data provide evidence for abrupt, large-scale shifts in ostracode species depth and geographical distributions during rapid climatic transitions.

  • 14.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Swärd, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ananyev, Roman
    Chernykh, Denis
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Multiple re-advances of a Lake Vättern outlet glacier during Fennoscandian Ice Sheet retreat, south-central Sweden2015In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 44, no 4, p. 619-637Article in journal (Refereed)
    Abstract [en]

    Lake Vättern represents a critical region geographically and dynamically in the deglaciation of the Fennoscandian Ice Sheet. The outlet glacier that occupied the basin and its behaviour during ice-sheet retreat were key to the development and drainage of the Baltic Ice Lake, dammed just west of the basin, yet its geometry, extent, thickness, margin dynamics, timing and sensitivity to regional retreat forcing are rather poorly known. The submerged sediment archives of Lake Vättern represent a missing component of the regional Swedish deglaciation history. Newly collected geophysical data, including high-resolution multibeam bathymetry of the lake floor and seismic reflection profiles of southern Lake Vättern, are used here together with a unique 74-m sediment record recently acquired by drill coring, and with onshore LiDAR-based geomorphological analysis, to investigate the deglacial environments and dynamics in the basin and its terrestrial environs. Five stratigraphical units comprise a thick subglacial package attributed to the last glacial period (and probably earlier), and an overlying > 120-m deglacial sequence. Three distinct retreat-re-advance episodes occurred in southern Lake Vättern between the initial deglaciation and the Younger Dryas. In the most recent of these, ice overrode proglacial lake sediments and re-advanced from north of Visingsö to the southern reaches of the lake, where ice up to 400 m thick encroached on land in a lobate fashion, moulding crag-and-tail lineations and depositing till above earlier glacifluvial sediments. This event precedes the Younger Dryas, which our data reveal was probably restricted to north-central sectors of the basin. These dynamics, and their position within the regional retreat chronology, indicate a highly active ice margin during deglaciation, with retreat rates on average 175 m a(-1). The pronounced topography of the Vättern basin and its deep proglacial-dammed lake are likely to have encouraged the dynamic behaviour of this major Fennoscandian outlet glacier.

  • 15.
    Hanslik, Daniela
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Björck, Svante
    Lund University, Department of Geology.
    Sellén, Emma
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Fornaciari, Eliana
    University of Padova, Department of Geosciences.
    Skog, Göran
    Lund University, Department of Geology.
    Quaternary Arctic Ocean sea ice variations and deep water isolation times2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3430-3441Article in journal (Refereed)
    Abstract [en]

    A short sediment core retrieved from a local depression forming an intra basin on the Lomonosov Ridge during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX) contains a record of the Marine Isotope Stages (MIS) 1-3 showing exceptionally high abundances of calcareous microfossils during parts of MIS 3. Based on radiocarbon dating, linear sedimentation rates of 7-9 cm/ka persist during the last deglaciation. Last Glacial Maximum (LGM) is partly characterized by a hiatus. Planktic foraminiferal abundance variations of Neogloboquadrina pachyderma sinistral and calcareous nannofossils reflect changes in Arctic Ocean summer sea ice coverage and probably inflow of subpolar North Atlantic water. Marine reservoir ages of 1400 years or more, at least during the last deglaciation, seem plausible from calibration of the radiocarbon ages using modeled reservoir corrections from previous studies in combination with the microfossil abundance record of the studied core. Paired benthic-planktic radiocarbon dated foraminiferal samples indicate a slow decrease in age difference between surface and bottom waters from the Late Glacial to the Holocene, suggesting circulation and ventilation changes.

  • 16. Hilton, Robert G.
    et al.
    Galy, Valier
    Gaillardet, Jerome
    Dellinger, Mathieu
    Bryant, Charlotte
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Groecke, Darren R.
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bouchez, Julien
    Calmels, Damien
    Erosion of organic carbon in the Arctic as a geological carbon dioxide sink2015In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 524, no 7563, p. 84-U162Article in journal (Refereed)
    Abstract [en]

    Soils of the northern high latitudes store carbon over millennial timescales (thousands of years) and contain approximately double the carbon stock of the atmosphere(1-3). Warming and associated permafrost thaw can expose soil organic carbon and result in mineralization and carbon dioxide (CO2) release(4-6). However, some of this soil organic carbon may be eroded and transferred to rivers(7-9). If it escapes degradation during river transport and is buried in marine sediments, then it can contribute to a longer-term (more than ten thousand years), geological CO2 sink(8-10). Despite this recognition, the erosional flux and fate of particulate organic carbon (POC) in large rivers at high latitudes remains poorly constrained. Here, we quantify the source of POC in the Mackenzie River, the main sediment supplier to the Arctic Ocean(11,12), and assess its flux and fate. We combine measurements of radiocarbon, stable carbon isotopes and element ratios to correct for rock-derived POC10,13,14. Our samples reveal that the eroded biospheric POC has resided in the basin for millennia, with a mean radiocarbon age of 5,800 +/- 800 years, much older than the POC in large tropical rivers(13,14). From the measured biospheric POC content and variability in annual sediment yield(15), we calculate a biospheric POC flux of 2.2(-0.9)(+1.3) teragrams of carbon per year from the Mackenzie River, which is three times the CO2 drawdown by silicate weathering in this basin(16). Offshore, we find evidence for efficient terrestrial organic carbon burial over the Holocene period, suggesting that erosion of organic carbon-rich, high-latitude soils may result in an important geological CO2 sink.

  • 17.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Anderson, John B.
    Nitsche, Frank O.
    Dowdeswell, Julian A.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Mohammad, Rezwan
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Alley, Richard B.
    Anandakrishnan, Sridhar
    Eriksson, Björn
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kirshner, Alexandra
    Fernandez, Rodrigo
    Stolldorf, Travis
    Minzoni, Rebecca
    Majewski, Wojciech
    Geological record of ice shelf break-up and grounding line retreat, Pine Island Bay, West Antarctica2011In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 39, no 7, p. 691-694Article in journal (Refereed)
    Abstract [en]

    The catastrophic break-ups of the floating Larsen A and B ice shelves (Antarctica) in 1995 and 2002 and associated acceleration of glaciers that flowed into these ice shelves were among the most dramatic glaciological events observed in historical time. This raises a question about the larger West Antarctic ice shelves. Do these shelves, with their much greater glacial discharge, have a history of collapse? Here we describe features from the seafloor in Pine Island Bay, West Antarctica, which we interpret as having been formed during a massive ice shelf break-up and associated grounding line retreat. This evidence exists in the form of seafloor landforms that we argue were produced daily as a consequence of tidally influenced motion of mega-icebergs maintained upright in an iceberg armada produced from the disintegrating ice shelf and retreating grounding line. The break-up occurred prior to ca. 12 ka and was likely a response to rapid sea-level rise or ocean warming at that time.

  • 18.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Andreassen, Karin
    Bjarnadóttir, Lilja Rün
    Dove, Dayton
    Dowdeswell, Julian A.
    England, John H.
    Funder, Svend
    Hogan, Kelly
    Ingólfsson, Ólafur
    Jennings, Anne
    Krog Larsen, Nikolaj
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Landvik, Jon Y.
    Mayer, Larry
    Mikkelsen, Naja
    Möller, Per
    Niessen, Frank
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Polyak, Leonid
    Nørgaard-Pedersen, Niels
    Stein, Ruediger
    Arctic Ocean glacial history2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, p. 40-67Article in journal (Refereed)
    Abstract [en]

    While there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the Arctic Ocean, a holistic view on the Northern Hemisphere's late Quaternary ice-sheet extent and their impact on ocean and sea-ice dynamics remains to be established. Here we aim to provide a step in this direction by presenting an overview of Arctic Ocean glacial history, based on the present state-of-the-art knowledge gained from field work and chronological studies, and with a specific focus on ice-sheet extent and environmental conditions during the Last Glacial Maximum (LGM). The maximum Quaternary extension of ice sheets is discussed and compared to LGM. We bring together recent results from the circum-Arctic continental margins and the deep central basin; extent of ice sheets and ice streams bordering the Arctic Ocean as well as evidence for ice shelves extending into the central deep basin. Discrepancies between new results and published LGM ice-sheet reconstructions in the high Arctic are highlighted and outstanding questions are identified. Finally, we address the ability to simulate the Arctic Ocean ice sheet complexes and their dynamics, including ice streams and ice shelves, using presently available ice-sheet models. Our review shows that while we are able to firmly reject some of the earlier hypotheses formulated to describe Arctic Ocean glacial conditions, we still lack information from key areas to compile the holistic Arctic Ocean glacial history.

  • 19.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Björck, Svante
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Swärd, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lif, Arne
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ampel, Linda
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Koyi, Hemin
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Major earthquake at the Pleistocene-Holocene transition in Lake Vattern, southern Sweden2014In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 42, no 5, p. 379-382Article in journal (Refereed)
    Abstract [en]

    Lake Vattern, Sweden, is within a graben that formed through rifting along the boundary between two Precambrian terrains. Geophysical mapping and geological coring show that substantial tectonic movements along the Lake Vattern graben occurred at the very onset of the Holocene. This is evident from deformation structures in the soft sediment accumulated on the lake floor. Our interpretation of these structures suggests as much as 13 m of vertical tectonic displacements along sections of a >80-km-long fault system. If these large displacements are from one tectonic event, Lake Vattern must have had an earthquake with seismic moment magnitudes to 7.5. In addition, our geophysical mapping shows large landslides along sections of the steep lake shores. Pollen analysis of sediment infillings of some of the most prominent sediment deformation structures places this major seismic event at the Younger Dryas-Preboreal transition, ca. 11.5 ka. We suggest that this event is mainly related to the rapid release of ice-sheet load following the deglaciation. This paleoseismic event in Lake Vattern ranks among the larger known intraplate tectonic events in Scandinavia and attests to the significance of glacio-isostatic unloading.

  • 20.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Anderson, Leif
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Björk, Göran
    Cronin, Thomas M.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Koshurnikov, Andrey
    Mayer, Larry
    Noormets, Riko
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of New Hampshire, USA.
    Ananiev, Roman
    Barrientos Macho, Natalia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cherniykh, Denis
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Eriksson, Björn
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gemery, Laura
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Jerram, Kevin
    Johansson, Carina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Khortov, Alexey
    Mohammad, Rezwan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Semiletov, Igor
    Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation2016In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7, article id 10365Article in journal (Refereed)
    Abstract [en]

    The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions41-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (similar to 140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening.

  • 21.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Dowdeswell, J. A.
    Mayer, L.
    Polyak, L.
    Colleoni, Florence
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Anderson, L. G.
    Björk, G.
    Darby, D.
    Eriksson, Björn
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hanslik, Daniela
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hell, Benjamin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Marcussen, C.
    Sellén, Emma
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wallin, T.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    An Arctic Ocean ice shelf during MIS 6 constrained by new geophysical and geological data2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3505-3517Article in journal (Refereed)
    Abstract [en]

    The hypothesis of floating ice shelves covering the Arctic Ocean during glacial periods was developed in the 1970s. In its most extreme form, this theory involved a 1000 m thick continuous ice shelf covering the Arctic Ocean during Quaternary glacial maxima including the Last Glacial Maximum (LGM). While recent observations clearly demonstrate deep ice grounding events in the central Arctic Ocean, the ice shelf hypothesis has been difficult to evaluate due to a lack of information from key areas with severe sea ice conditions. Here we present new data from previously inaccessible, unmapped areas that constrain the spatial extent and timing of marine ice sheets during past glacials. These data include multibeam swath bathymetry and subbottom profiles portraying glaciogenic features on the Chukchi Borderland, southern Lomonosov Ridge north of Greenland, Morris Jesup Rise, and Yermak Plateau. Sediment cores from the mapped areas provide age constraints on the glaciogenic features. Combining these new geophysical and geological data with earlier results suggests that an especially extensive marine ice sheet complex, including an ice shelf, existed in the Amerasian Arctic Ocean during Marine Isotope Stage (MIS) 6. From a conceptual oceanographic model we speculate that the cold halocline of the Polar Surface Water may have extended to deeper water depths during MIS 6 inhibiting the warm Atlantic water from reaching the Amerasian Arctic Ocean and, thus, creating favorable conditions for ice shelf development. The hypothesis of a continuous 1000 m thick ice shelf is rejected because our mapping results show that several areas in the central Arctic Ocean substantially shallower than 1000 m water depth are free from glacial influence on the seafloor.

  • 22.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark.
    Cronin, Thomas M.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Anderson, Leif G.
    Barrientos, Natalia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Björk, Göran
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    de Boer, Agatha
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mayer, Larry A.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Rattray, Jayne E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of New Hampshire, USA.
    Semiletov, Igor
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Post-glacial flooding of the Bering Land Bridge dated to 11 cal ka BP based on new geophysical and sediment records2017In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 13, no 8, p. 991-1005Article in journal (Refereed)
    Abstract [en]

    The Bering Strait connects the Arctic and Pacific oceans and separates the North American and Asian landmasses. The presently shallow (similar to 53 m) strait was exposed during the sea level lowstand of the last glacial period, which permitted human migration across a land bridge today referred to as the Bering Land Bridge. Proxy studies (stable isotope composition of foraminifera, whale migration into the Arctic Ocean, mollusc and insect fossils and paleobotanical data) have suggested a range of ages for the Bering Strait reopening, mainly falling within the Younger Dryas stadial (12.9-11.7 cal ka BP). Here we provide new information on the deglacial and post-glacial evolution of the Arctic-Pacific connection through the Bering Strait based on analyses of geological and geophysical data from Herald Canyon, located north of the Bering Strait on the Chukchi Sea shelf region in the western Arctic Ocean. Our results suggest an initial opening at about 11 cal ka BP in the earliest Holocene, which is later than in several previous studies. Our key evidence is based on a well-dated core from Herald Canyon, in which a shift from a near-shore environment to a Pacific-influenced open marine setting at around 11 cal ka BP is observed. The shift corresponds to meltwater pulse 1b (MWP1b) and is interpreted to signify relatively rapid breaching of the Bering Strait and the submergence of the large Bering Land Bridge. Although the precise rates of sea level rise cannot be quantified, our new results suggest that the late deglacial sea level rise was rapid and occurred after the end of the Younger Dryas stadial.

  • 23. Kremer, A.
    et al.
    Stein, R.
    Fahl, K.
    Ji, Z.
    Yang, Z.
    Wiers, S.
    Matthiessen, J.
    Forwick, M.
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Chen, J.
    Snowball, I.
    Changes in sea ice cover and ice sheet extent at the Yermak Plateau during the last 160 ka - Reconstructions from biomarker records2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 182, p. 93-108Article in journal (Refereed)
    Abstract [en]

    The Yermak Plateau is located north of Svalbard at the entrance to the Arctic Ocean, i.e. in an area highly sensitive to climate change. A multi proxy approach was carried out on Core PS92/039-2 to study glacial interglacial environmental changes at the northern Barents Sea margin during the last 160 ka. The main emphasis was on the reconstruction of sea ice cover, based on the sea ice proxy IP25 and the related phytoplankton - sea ice index PIP25. Sea ice was present most of the time but showed significant temporal variability decisively affected by movements of the Svalbard Barents Sea Ice Sheet. For the first time, we prove the occurrence of seasonal sea ice at the eastern Yermak Plateau during glacial intervals, probably steered by a major northward advance of the ice sheet and the formation of a coastal polynya in front of it. Maximum accumulation of terrigenous organic carbon, IP25 and the phytoplankton biomarkers (brassicasterol, dinosterol, HBI III) can be correlated to distinct deglaciation events. More severe, but variable sea ice cover prevailed at the Yermak Plateau during interglacials. The general proximity to the sea ice margin is further indicated by biomarker (GDGT) - based sea surface temperatures below 2.5 degrees C.

  • 24. Löwemark, L.
    et al.
    März, C.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Arctic Ocean Mn-stratigraphy: genesis, synthesis and inter-basin correlation2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, p. 97-111Article in journal (Refereed)
    Abstract [en]

    Across the Arctic Ocean, late Quaternary deep marine sediments are characterized by the occurrence of brownish layers intercalated with yellowish to olive gray sediments. These layers show enhanced levels of bioturbation, peaks in Mn content, and typically contain elevated abundances of planktonic and benthic micro-and nannofossils. It was early surmised that these layers were deposited under interglacial conditions and that their cyclical downcore occurrence could be correlated to the global benthic oxygen isotope curve. However, the synchronicity of Mn layers with interglacial conditions and the underlying mechanisms responsible for their formation remain controversial. Here we compile and synthesize findings of the last decades with several recent studies that shed light on issues such as the sources of Mn to the Arctic Ocean, the processes and pathways for Mn to the deep sea, the chemical processes active in the sediment, and the spatial and temporal distribution of Mn-rich layers in Arctic deep marine sediments. Budget calculations show that about 90% of Mn input to the Arctic Ocean originates from Arctic rivers or coastal erosion, two sources effectively shut down during mid-to late Quaternary glacial intervals by continental ice sheets blocking or redirecting the rivers and vast subaerial exposure of the shelf areas. Thus, the strong late Quaternary interglacial-glacial cyclicity in Mn content is clearly an input-related signal, and only secondarily influenced by chemical processes in the water column and in the sediment. On the shelves, the Mn undergoes repeated geochemical recycling caused by the high organic carbon content in the sediments before it is ultimately exported to the deep basins where scavenging processes in the water column effectively bring the Mn to the sea floor in the form of Mn (oxyhydr)oxides. The close synchronicity with enhanced bioturbation and elevated micro and nannofossil abundances shows that the Mn peaks are preserved at a stratigraphic level closely corresponding to the interglacial intervals. However, under certain biogeochemical conditions, Mn (oxyhydr)oxides may diagenetically become both dissolved and re-precipitated deep in the sediments, as shown by pore water analyses and X-ray radiograph studies. Dissolution is particularly conspicuous in late Quaternary sediments from the Lomonosov Ridge, where in rapidly deposited coarse grained intervals (diamictons) with elevated total organic carbon (TOC) contents, Mn appears almost completely removed from within the glacial sediments, and also the surrounding interglacial sediments. Correspondingly, bundles of closely spaced, mm-thick, Mn-rich horizontal bands are observed in sediment otherwise devoid of indicators for interglacial conditions, suggesting that these bands were purely formed by diagenetic processes redistributing the Mn from deeper sediment layers. This type of diagenetic Mn redistribution within the sediment can be recognized in XRF-core scanner data combined with sedimentological information from X-ray radiographs, while pore water data are highly promising if clear diagenetic features in the sediment are missing. With this increasing ability to recognize intervals where a diagenetic overprint exists in the Mn record, the recently improved understanding of the Mn cycle in the Arctic Ocean provides a conceptual paleoenvironmental framework in which carefully applied Mn stratigraphy can provide a powerful correlation tool, when combined with other paleoceanographic proxies and sedimentological data.

  • 25. Miller, Clint M.
    et al.
    Dickens, Gerald R.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Johansson, Carina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Koshurnikov, Andrey
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Muschitiello, Francesco
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pore water geochemistry along continental slopes north of the East Siberian Sea: inference of low methane concentrations2017In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, no 12, p. 2929-2953Article in journal (Refereed)
    Abstract [en]

    Continental slopes north of the East Siberian Sea potentially hold large amounts of methane (CH4/in sediments as gas hydrate and free gas. Although release of this CH4 to the ocean and atmosphere has become a topic of discussion, the region remains sparingly explored. Here we present pore water chemistry results from 32 sediment cores taken during Leg 2 of the 2014 joint Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3) expedition. The cores come from depth transects across the slope and rise extending between the Mendeleev and the Lomonosov ridges, north of Wrangel Island and the New Siberian Islands, respectively. Upward CH4 flux towards the seafloor, as inferred from profiles of dissolved sulfate (SO42-), alkalinity, and the delta C-13 of dissolved inorganic carbon (DIC), is negligible at all stations east of 143 degrees E longitude. In the upper 8m of these cores, downward SO42- flux never exceeds 6.2 mol m(-2) kyr(-1), the upward alkalinity flux never exceeds 6.8 mol m(-2) kyr(-1), and delta C-13 composition of DIC (delta C-13-DIC) only moderately decreases with depth (3.6% m 1 on average). Moreover, upon addition of Zn acetate to pore water samples, ZnS did not precipitate, indicating a lack of dissolved H2S. Phosphate, ammonium, and metal profiles reveal that metal oxide reduction by organic carbon dominates the geochemical environment and supports very low organic carbon turnover rates. A single core on the Lomonosov Ridge differs, as diffusive fluxes for SO42- and alkalinity were 13.9 and 11.3 mol m(-2) kyr(-1), respectively, the delta C-13-DIC gradient was 5.6% m(-1), and Mn2+ reduction terminated within 1.3 m of the seafloor. These are among the first pore water results generated from this vast climatically sensitive region, and they imply that abundant CH4, including gas hydrates, do not characterize the East Siberian Sea slope or rise along the investigated depth transects. This contradicts previous modeling and discussions, which due to the lack of data are almost entirely based on assumption.

  • 26.
    O'Regan, Matt
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Barrientos, Natalia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cronin, Thomas M.
    Gemery, Laura
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Mayer, Larry A.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Noormets, Riko
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark.
    Semiletov, Igor
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of New Hampshire, USA.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The De Long Trough: A newly discovered glacial trough on the East Siberian continental margin2017In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 13, no 9, p. 1269-1284Article in journal (Refereed)
    Abstract [en]

    Ice sheets extending over parts of the East Siberian continental shelf have been proposed for the last glacial period and during the larger Pleistocene glaciations. The sparse data available over this sector of the Arctic Ocean have left the timing, extent and even existence of these ice sheets largely unresolved. Here we present new geophysical mapping and sediment coring data from the East Siberian shelf and slope collected during the 2014 SWERUS-C3 expedition (SWERUS-C3: Swedish - Russian - US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions). The multibeam bathymetry and chirp sub-bottom profiles reveal a set of glacial landforms that include grounding zone formations along the outer continental shelf, seaward of which lies a > 65m thick sequence of glacio-genic debris flows. The glacial landforms are interpreted to lie at the seaward end of a glacial trough - the first to be reported on the East Siberian margin, here referred to as the De Long Trough because of its location due north of the De Long Islands. Stratigraphy and dating of sediment cores show that a drape of acoustically laminated sediments covering the glacial deposits is older than similar to 50 cal kyr BP. This provides direct evidence for extensive glacial activity on the Siberian shelf that predates the Last Glacial Maximum and most likely occurred during the Saalian (Marine Isotope Stage (MIS) 6).

  • 27.
    O`Regan, Matt
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hill, Philip
    Hilton, Robert
    Muschitiello, Francesco
    Swärd, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Early Holocene sea level in the Canadian Beaufort Sea constrained by radiocarbon dates from a deep borehole in the Mackenzie Trough, Arctic Canada2018In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 47, no 4, p. 1102-1117Article in journal (Refereed)
    Abstract [en]

    Deglacial and Holocene relative sea level (RSL) in the Canadian Beaufort Sea was influenced by the timing and extent of glacial ice in the Mackenzie River corridor and adjacent coastal plains. Considerable evidence indicates extensive ice cover in this region of northwestern Canada during the Late Wisconsinan. However, no absolute ages exist to constrain maximum RSL lowering before the late Holocene (4.2-0ka). In 1984, the Geological Survey of Canada drilled an 81.5-m-deep borehole in the western Mackenzie Trough at 45m water depth (MTW01). The lower 52.5m of the borehole was interpreted as a deltaic progradational sequence deposited during a period of rising sea level. The upper 29m was described as foraminifer-bearing marine sediments deposited after transgression of the site, when RSL rose above similar to-74m. Here, we present radiocarbon measurements from MTW01, acquired from benthic foraminifera, mollusc fragments and particulate organic carbon in the >63m fraction (POC>63m) in an attempt to constrain the chronology of sediments within this borehole and date the timing of transgression. The deepest carbonate macrofossil was acquired from 8m above the transgressive surface (equivalent to 21m b.s.l.), where mollusc fragments returned a date of 9400 +180-260cal. a BP (2 sigma). This provides the oldest constraint on Holocene sea-level lowering in the region, and implies that transgression at this site occurred prior to the early Holocene. Ages obtained from the lower 52.5m of the borehole are limited to POC>63m samples. These indicate that progradational sediments were deposited rapidly after 24820 +390-380cal. a BP (2 sigma). Due to the incorporation of older reworked organic matter, the actual age of progradation is likely to be younger, occurring after Late Wisconsinan glacial ice retreated from the coast.

  • 28.
    O'Regan, Matt
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Forwick, Matthias
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Moran, Kathryn
    Mosher, David
    Seafloor cratering and sediment remolding at sites of fluid escape2015In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 43, no 10, p. 895-898Article in journal (Refereed)
    Abstract [en]

    Episodic fluid escape from marine sediments results from overpressure development and pressure release, and can occur slowly through geologic time or catastrophically. Morphological features in regions of fluid seepage include doming, mud volcanism, cratering, and pockmark formation. Vertical sediment mobilization and surface erosion are considered the principal mechanisms for these topographic changes. However, the impact of mobilization on the geotechnical properties of sediments has not been explicitly considered. Here we develop a one-dimensional numerical subsidence model that incorporates the well-established behavior of remolded fine-grained cohesive sediments. We use this to show that if subsurface overpressure results in the mobilization of sediments, large settlements (20%-35% reduction in volume) can occur when overpressure dissipates. This presents a novel mechanism to explain changes in seafloor and subsurface topography in areas of fluid escape, while highlighting an important interplay between subsurface fluid flow and the geotechnical properties of fine-grained cohesive sediments.

  • 29.
    O'Regan, Matt
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Preto, Pedro
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Swärd, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Geotechnical and sedimentary evidence for thick-grounded ice in southern Lake Vättern during deglaciation2016In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 138, no 2, p. 355-366Article in journal (Refereed)
    Abstract [en]

    A 74-meter Late Pleistocene to Holocene sedimentary sequence was recovered from southern Lake Vattern in the autumn of 2012. At approximate to 54m below the lake floor, shear strength and high-resolution bulk density measurements suggest the presence of an unconformity in the varved proglacial clays. Incremental load consolidation tests reveal highly overconsolidated sediments below this level. Preconsolidation pressures for the underlying sediments are between 1250 and 2100kPa, up to approximate to 1700kPa more than the current in-situ effective stress. The highly overconsolidated sediments indicate either substantial erosion (the removal of 215-360m of sediment), or consolidation under a large grounded ice mass sitting up to 230m above paleo-lake level. Glaciotectonic deformation in underlying sediments supports the interpretation of a grounded ice mass. It is likely that this horizon is either contemporaneous with or older than the Levene moraine, formed between 13.4 and 13.8ka. In the approximate to 30m of overlying proglacial clays, there is no further evidence for grounded ice, indicating that any ice advance to southern Lake Vattern during the Younger Dryas would have been limited to an extremely thin ice tongue.

  • 30.
    O'Regan, Matt
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glacial geological implications of overconsolidated sediments on the Lomonosov Ridge and Yermak Plateau2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3532-3544Article in journal (Refereed)
    Abstract [en]

    With the coupled use of multibeam swath bathymetry, high-resolution subbottom profiling and sediment coring from icebreakers in the Arctic Ocean, there is a growing awareness of the prevalence of Quaternary ice-grounding events on many of the topographic highs found in present water depths of <1000 m. In some regions, such as the Lomonosov Ridge and Yermak Plateau, overconsolidated sediments sampled through either drilling or coring are found beneath seismically imaged unconformities of glacigenic origin. However, there exists no comprehensive analysis of the geotechnical properties of these sediments, or how their inferred stress state may be related to different glacigenic processes or types of ice-loading. Here we combine geophysical, stratigraphic and geotechnical measurements from the Lomonosov Ridge and Yermak Plateau and discuss the glacial geological implications of overconsolidated sediments. The degree of overconsolidation, determined from measurements of porosity and shear strength, is shown to result from consolidation and/or deformation below grounded ice and, with the exception of a single region on the Lomonosov Ridge, cannot be explained by erosion of overlying sediments. We demonstrate that the amount and depth of porosity loss associated with a middle Quaternary (790–950 thousand years ago – ka) grounding on the Yermak Plateau is compatible with sediment consolidation under an ice sheet or ice rise. Conversely, geotechnical properties of sediments from beneath late Quaternary ice-groundings in both regions, independently dated to Marine Isotope Stage (MIS) 6, indicate a more transient event commensurate with a passing tabular iceberg calved from an ice shelf.

  • 31.
    O'Regan, Matt
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Moran, Kate
    University of Rhode Island.
    Deep-water methane hydrates in the Arctic Ocean: Re-assessing the significance of a shallow BSR on the Lomonosov Ridge2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, ISSN 115, B05102, 13 PP., 2010, Vol. 115Article in journal (Refereed)
    Abstract [en]

    Recently published multi-channel seismic data from the Lomonosov Ridge image a reversed polarity bottom-simulating reflector (BSR) tentatively attributed to the presence of deepwater marine hydrates and recognized throughout a survey area exceeding 100,000 km2. In addition to the importance of these findings for estimating Arctic hydrate reserves, if shown to correspond to the base of the hydrate stability zone, this seismic marker could provide a means for expanding spatial cover of heat flow data in deepwater settings of the Amerasian Basin, where little is known about the tectonic origin and nature of plate boundaries. As an initial test on the validity of this assumption, we develop a petrophysical model using sediments collected from circumpolar regions of the Lomonosov Ridge to derive an estimate of surface heat flow patterns from the BSR. The results show that the BSR inferred geothermal gradient and surface heat flow are exceedingly high when compared to published regional measurements. Although potential errors in the analysis may explain some of this discrepancy, the observation that the BSR remains at a constant sub-bottom depth despite large variations in water depths (> 2400 m) and relative sedimentation rates provides additional evidence that it cannot mark the base of the hydrate stability zone. A further understanding of its origin requires a more detailed investigation of the existing seismic data and highlights the need for renewed collection of heat flow data from the Arctic Ocean.

  • 32.
    O'Regan, Matt
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Preto, Pedro
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Koshurnikov, Andrey
    Surface heat flow measurements from the East Siberian continental slope and southern Lomonosov Ridge, Arctic Ocean2016In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 17, no 5, p. 1608-1622Article in journal (Refereed)
    Abstract [en]

    Surface heat flow data in the Arctic Ocean are needed to assess hydrocarbon and methane hydrate distributions, and provide constraints into the tectonic origins and nature of underlying crust. However, across broad areas of the Arctic, few published measurements exist. This is true for the outer continental shelf and slope of the East Siberian Sea, and the adjoining deep water ridges and basins. Here we present 21 new surface heat flow measurements from this region of the Arctic Ocean. On the Southern Lomonosov Ridge, the average measured heat flow, uncorrected for effects of sedimentation and topography, is 574 mW/m(2) (n=4). On the outer continental shelf and slope of the East Siberian Sea (ESS), the average is 5710 mW/m(2) (n=16). An anomalously high heat flow of 20328 mW/m(2) was measured at a single station in the Herald Canyon. With the exception of this high heat flow, the new data from the ESS are consistent with predictions for thermally equilibrated lithosphere of continental origin that was last affected by thermotectonic processes in the Cretaceous to early Cenozoic. Variability within the data likely arises from differences in radiogenic heat production within the continental crust and overlying sediments. This can be further explored by comparing the data with geophysical constraints on sediment and crustal thicknesses.

  • 33.
    O'Regan, Matthew
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Deglacial sedimentation and the origin of deep-keeled icebergs in the Beaufort Sea2012In: APEX Sixth International Conference and Workshop: Quaternary Glacial and Climate Extremes, Oulu: Oulun yliopisto , 2012, p. 72-72Conference paper (Other academic)
  • 34.
    O'Regan, Matthew
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sellén, Emma
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Middle to late Quaternary grain size variations and sea-ice rafting on the Lomonosov Ridge2014In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 33, p. 23672-Article in journal (Refereed)
    Abstract [en]

    Sea ice and icebergs are the dominant transport agents for sand-sized material to the central Arctic Ocean. However, few studies have investigated concurrent changes in the silt-sized fraction of Arctic sediments. Here we present an analysis of the coarse fraction content and silt grain size composition from middle and late Quaternary sediments recovered from the Lomonosov Ridge, in the central Arctic Ocean. A significant shift in the grain size record occurs at the marine isotope stage (MIS) 6/7 boundary, where larger amplitude variability in the sand fraction is seen in glacial and stadial periods. Below the MIS6/7 boundary, variations in the coarse fraction content are less pronounced, but prominent changes in the silt size fraction appear to define glacial and interglacial periods. Throughout the record, the percent weight of sortable silt in the fine fraction (SS % wt(fines)), sortable silt mean size, and coarse silt content all increase as the >63 mu m % wt content increases. This is consistent with observations of grain size spectra obtained from modern sea-ice samples, and indicates a strong overprint from sea ice on the silt distribution. The mechanism by which this sea-ice signal is preserved in the sediments across glacial and interglacial periods remains unclear. We suggest that the coarsening of silt-sized material during glacial periods could be attributed to either the entrainment of larger size fractions during suspension/anchor ice formation when sea levels are lowered, or diminished input and advection of fine fraction material during glacial periods.

  • 35.
    O'Regan, Matthew
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    St John, Kristen
    James Madison University.
    Moran, Kathryn
    University of Rhode Island.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    King, John
    University of Rhode Island.
    Haley, Brian A.
    IFM-GEOMAR, Leibniz Institute of Marine Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Frank, Martin
    IFM-GEOMAR, Leibniz Institute of Marine Sciences.
    Röhl, Ursula
    Bremen University.
    Plio-Pleistocene trends in ice rafted debris on the Lomonosov Ridge2010In: Quaternary International, ISSN 1040-6182, E-ISSN 1873-4553, Vol. 19, no 1-2, p. 168-176Article in journal (Refereed)
    Abstract [en]

    Although more than 700 sediment cores exist from the Arctic Ocean, the Plio-Pleistocene evolution of the basin and its marginal seas remains virtually unknown. This is largely due the shallow penetration of most of these records, and difficulties associated with deriving chronologies for the recovered material. The Integrated Ocean Drilling Program's (IODP) Expedition 302 (Arctic Coring Expedition, ACEX) recovered 197 m of Neogene/Quaternary sediment from the circumpolar regions of the Lomonosov Ridge. As detailed analyses of this material emerge, research is beginning to formulate a long-term picture of paleoceanographic changes in the central Arctic Ocean. This paper reviews the ACEX Plio-Pleistocene age model, identifies uncertainties, and addresses ways in which these may be eliminated. Within the established stratigraphic framework, a notable reduction in the abundance of ice rafted debris (IRD) occurs in the early part of the Pleistocene and persists until Marine Isotope Stage 6 (MIS 6). Therefore, while global oceanographic proxies indicate the gradual growth of terrestrial ice-sheets during this time, IRD delivery to the central Arctic Ocean remained comparatively low and stable. Within the resolution of existing data, the Pleistocene reduction in IRD is synchronous with predicted changes in both the inflow of North Atlantic and Pacific waters, which in modern times are known to exert a strong influence on sea ice stability.

  • 36.
    Pearce, Christof
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark.
    Varhelyi, Aron
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Muschitiello, Francesco
    Stockholm University, Faculty of Science, Department of Geological Sciences. Columbia University, USA; Bjerknes Centre for Climate Research, Norway.
    Barrientos, Natalia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cronin, Thomas M.
    Gemery, Laura
    Semiletov, Igor
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    The 3.6 ka Aniakchak tephra in the Arctic Ocean: a constraint on the Holocene radiocarbon reservoir age in the Chukchi Sea2017In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 13, no 4, p. 303-316Article in journal (Refereed)
    Abstract [en]

    The caldera-forming eruption of the Aniakchak volcano in the Aleutian Range on the Alaskan Peninsula at 3.6 cal kyr BP was one of the largest Holocene eruptions worldwide. The resulting ash is found as a visible sediment layer in several Alaskan sites and as a cryptotephra on Newfoundland and Greenland. This large geographic distribution, combined with the fact that the eruption is relatively well constrained in time using radiocarbon dating of lake sediments and annual layer counts in ice cores, makes it an excellent stratigraphic marker for dating and correlating mid-late Holocene sediment and paleoclimate records. This study presents the outcome of a targeted search for the Aniakchak tephra in a marine sediment core from the Arctic Ocean, namely Core SWERUS-L2-2-PC1 (2PC), raised from 57m water depth in Herald Canyon, western Chukchi Sea. High concentrations of tephra shards, with a geochemical signature matching that of Aniakchak ash, were observed across a more than 1.5m long sediment sequence. Since the primary input of volcanic ash is through atmospheric transport, and assuming that bioturbation can account for mixing up to ca. 10 cm of the marine sediment deposited at the coring site, the broad signal is interpreted as sustained reworking at the sediment source input. The isochron is therefore placed at the base of the sudden increase in tephra concentrations rather than at the maximum concentration. This interpretation of major reworking is strengthened by analysis of grain size distribution which points to ice rafting as an important secondary transport mechanism of volcanic ash. Combined with radiocarbon dates on mollusks in the same sediment core, the volcanic marker is used to calculate a marine radiocarbon reservoir age offset Delta R = 477 +/- 60 years. This relatively high value may be explained by the major influence of typically carbon-old Pacific waters, and it agrees well with recent estimates of Delta R along the northwest Alaskan coast, possibly indicating stable oceanographic conditions during the second half of the Holocene. Our use of a volcanic absolute age marker to obtain the marine reservoir age offset is the first of its kind in the Arctic Ocean and provides an important framework for improving chronologies and correlating marine sediment archives in this region. Core 2PC has a high sediment accumulation rate averaging 200 cm kyr(-1) throughout the last 4000 years, and the chronology presented here provides a solid base for high-resolution reconstructions of late Holocene climate and ocean variability in the Chukchi Sea.

  • 37. Polyak, Leonid
    et al.
    Alley, Richard B.
    Andrews, John T.
    Brigham-Grette, Julie
    Cronin, Thomas M.
    Darby, Dennis A.
    Dyke, Arthur S.
    Fitzpatrick, Joan J.
    Funder, Svend
    Holland, Marika
    Jennings, Anne E.
    Miller, Gifford H.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Savelle, James
    Serreze, Mark
    St John, Kristen
    White, James W. C.
    Wolff, Eric
    History of sea ice in the Arctic2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 15-16, p. 1757-1778Article in journal (Refereed)
    Abstract [en]

    Arctic sea-ice extent and volume are declining rapidly. Several studies project that the Arctic Ocean may become seasonally ice-free by the year 2040 or even earlier. Putting this into perspective requires information on the history of Arctic sea-ice conditions through the geologic past. This information can be provided by proxy records from the Arctic Ocean floor and from the surrounding coasts. Although existing records are far from complete, they indicate that sea ice became a feature of the Arctic by 47 Ma, following a pronounced decline in atmospheric pCO(2) after the Paleocene-Eocene Thermal Optimum, and consistently covered at least part of the Arctic Ocean for no less than the last 13-14 million years. Ice was apparently most widespread during the last 2-3 million years, in accordance with Earth's overall cooler climate. Nevertheless, episodes of considerably reduced sea ice or even seasonally ice-free conditions occurred during warmer periods linked to orbital variations. The last low-ice event related to orbital forcing (high insolation) was in the early Holocene, after which the northern high latitudes cooled overall, with some superimposed shorterterm (multidecadal to millennial-scale) and lower-magnitude variability. The current reduction in Arctic ice cover started in the late 19th century, consistent with the rapidly warming climate, and became very pronounced over the last three decades. This ice loss appears to be unmatched over at least the last few thousand years and unexplainable by any of the known natural variabilities.

  • 38. Roberts, Andrew P.
    et al.
    Florindo, Fabio
    Larrasoana, Juan C.
    O'Regan, Matthew A.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Zhao, Xiang
    Complex polarity pattern at the former Plio-Pleistocene global stratotype section at Vrica (Italy): Remagnetization by magnetic iron sulphides2010In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 292, no 02-jan, p. 98-111Article in journal (Refereed)
    Abstract [en]

    The Vrica section in Calabria, southern Italy, was the global stratotype for the Pliocene-Pleistocene boundary until this boundary was redefined in 2009. Several paleomagnetic investigations have been carried out at Vrica to determine the age of the formerly defined Pliocene-Pleistocene boundary, which was a key calibration point for the astronomical polarity timescale (APTS). Each study has documented a complex polarity pattern at and above the top of the Olduvai subchron and in relation to the existence of the so-called Vrica subchron. When constructing the APTS, two alternative interpretations for the Vrica section were proposed, neither of which could be conclusively supported. Authigenic growth of magnetic iron sulphide minerals was proposed to explain the complex magnetic polarity record. Availability of a fresh 50-m sediment core enabled us to test this possibility. Our magnetostratigraphic record is similar to that of previous studies, but it is also complex above the Olduvai subchron. We confirm abundant occurrences of authigenic greigite and pyrrhotite, along with detrital titanomagnetite. Authigenic monoclinic pyrrhotite indicates growth significantly later than deposition, and greigite can grow at any time during diagenesis, depending on the availability of dissolved iron and sulphide. The spatially variable magnetic polarity pattern at Vrica is therefore interpreted to have resulted from post-depositional magnetic iron sulphide formation at variable times. Tectonism along the Calabrian arc provides a plausible mechanism for forcing reducing fluids through the sediments, thereby supplying the dissolved ions needed to produce late diagenetic sulphide growth and remagnetization. The complex magnetostratigraphic record at Vrica was taken into account when the APTS was developed, and alternative interpretations result in a maximum age difference of 50 kyr for the upper Olduvai reversal. Our results therefore do not undermine the APTS. Rather, they explain the complex magnetic polarity pattern at this globally important location and highlight the importance of remagnetization processes in such sediments.

  • 39.
    Sellén, Emma
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Spatial and temporal ArcticOcean depositional regimes: a key to the evolution of ice and current patterns2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3644-3664Article in journal (Refereed)
    Abstract [en]

    Sediment physical properties measured in cores from all the major ridges and plateaus in the central Arctic Ocean were studied in order to analyze the spatial and temporal consistency of sediment depositional regimes during the Quaternary. In total, six physiographically distinct areas are outlined. In five of these, cores can be correlated over large distances through characteristic patterns in sediment physical properties. These areas are (1) the southern Mendeleev Ridge, (2) the northern Mendeleev Ridge and Alpha Ridge, (3) the Lomonosov Ridge, (4) the Morris Jesup Rise and (5) the Yermak Plateau. Averaged downhole patterns in magnetic susceptibility, bulk density and lithostratigraphy were compiled to establish a composite stratigraphy for each area. In the sixth physiographic area, the Chukchi Borderland, repeated ice-grounding during recent glacial periods complicates the stratigraphy and prevents the compilation of a composite stratigraphy using the studied material. By utilizing published age models for the studied cores we are able to show that the northern Mendeleev Ridge and Alpha Ridge have the lowest average late Quaternary sedimentation rates, while intermediate sedimentation rates prevail on the southern Mendeleev Ridge and the Morris Jesup Rise. The second highest sedimentation rate is observed on the Lomonosov Ridge, whereas the average sedimentation rate on the Yermak Plateau is more than twice as high. The close correlation of physical properties within each area suggests uniform variations in sediment transport through time, at least throughout the later part of the Quaternary. The unique stratigraphic characteristics within each area is the product of similar past depositional regimes and are key for furthering our understanding of the evolution of ice drift and current patterns in the central Arctic Ocean.

  • 40. Shephard, G. E.
    et al.
    Wiers, Steffen
    Bazhenova, Evgenia
    Perez, Lara F.
    Mejia, Luz Maria
    Johansson, Carina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    A North Pole thermal anomaly? Evidence from new and existing heat flow measurements from the central Arctic Ocean2018In: Journal of Geodynamics, ISSN 0264-3707, E-ISSN 1879-1670, Vol. 118, p. 166-181Article in journal (Refereed)
    Abstract [en]

    Constraining the thermal evolution of the Arctic Ocean is hampered by notably sparse heat flow measurements and a complex tectonic history. Previous results from the Lomonosov Ridge in the vicinity of the North Pole, and the adjacent central Amundsen Basin reveal varied values, including those higher than expected considering plate cooling or simple uniform stretching models. Furthermore, in the vicinity of the North Pole an anomalously slow velocity perturbation exists in upper mantle seismic tomography models. However, whether these observations are related to a thermal anomaly in the mantle remains unknown. We present new heat flow results gathered from 17 sediment cores acquired during the Arctic Ocean 2016 and SWERUS-C3 expeditions on the Swedish icebreaker Oden. Three sites located on oceanic lithosphere in the Amundsen Basin between 7 degrees W-71E degrees reveal surface thermal conductivity of 1.07-1.26 W/mK and heat flow in the order of 71-95 mW/m(2), in line-with or slightly higher (1-21 mW/m(2)) than expected from oceanic heat flow curves. These results contrast with published results from further east in the Amundsen Basin, which indicated surface heat flow values up to 2 times higher than predicted from oceanic crustal cooling models. Heat flow of 49-61 mW/m(2) was recovered from the Amerasia Basin. Sites from the submerged continental fragments of the Lomonosov Ridge and Marvin Spur recovered heat flow in the order of 53-76 and 51-69 mW/m(2) respectively. When considering the additional potential surface heat flux from radiogenic heat production in the crust, these variable measurements are broadly in line with predictions from uniform extension models for continental crust. A seismically imaged upper mantle velocity anomaly in the central Arctic Ocean may arise from a combination of compositional and thermal variations but requires additional investigation. Disentangling surface heat flow contributions from crustal, lithospheric and mantle processes, including variable along-ridge rifting rates and timing, density and phase changes, conductive and advective dynamics, and regional tectonics, requires further analysis.

  • 41.
    Stranne, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O`Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Conductive heat flow and nonlinear geothermal gradients in marine sediment—observations from Ocean Drilling Program boreholes2016In: Geo-Marine Letters, ISSN 0276-0460, E-ISSN 1432-1157, Vol. 36, no 1, p. 25-33Article in journal (Refereed)
    Abstract [en]

    A basic premise in marine heat flow studies is that the temperature gradient varies with depth as a function of the bulk thermal conductivity of the sediments. As sediments become more deeply buried, compaction reduces the porosity and causes an increase in the bulk thermal conductivity. Therefore, while the heat flow may remain constant with depth, the thermal gradient is not necessarily linear. However, it has been argued that measurements showing increased sediment thermal conductivity with burial depth may be caused by a horizontal measurement bias generated by increasing anisotropy in sediments during consolidation. This study reanalyses a synthesis of Ocean Drilling Program data from 186 boreholes, and investigates the occurrence of nonlinear geothermal gradients in marine sediments. The aim is to identify whether observed downhole changes in thermal conductivity influence the measured temperature gradient, and to investigate potential errors in the prediction of in-situ temperatures derived from the extrapolation of near-surface thermal gradients. The results indicate that the measured thermal conductivity does influence the geothermal gradient. Furthermore, comparisons between shallow measurements (<10 m) from surface heat flow surveys and the deeply constrained temperature data from 98 ODP boreholes indicate that the shallow gradients are consistently higher by on average 19 °C km–1. This is consistent with higher porosity and generally lower thermal conductivity in near-seafloor sediments, and highlights the need to develop robust porosity–thermal conductivity models to accurately predict temperatures at depth from shallow heat flow surveys.

  • 42.
    Stranne, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Center for Coastal & Ocean Mapping/Joint Hydrographic Center, USA.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Dickens, Gerald R.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Rice University, USA.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Miller, C.
    Preto, Pedro
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Dynamic simulations of potential methane release from East Siberian continental slope sediments2016In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 17, no 3, p. 872-886Article in journal (Refereed)
    Abstract [en]

    Sediments deposited along continental margins of the Arctic Ocean presumably host large amounts of methane (CH4) in gas hydrates. Here we apply numerical simulations to assess the potential of gas hydrate dissociation and methane release from the East Siberian slope over the next 100 years. Simulations are based on a hypothesized bottom water warming of 3 degrees C, and an assumed starting distribution of gas hydrate. The simulation results show that gas hydrate dissociation in these sediments is relatively slow, and that CH4 fluxes toward the seafloor are limited by low sediment permeability. The latter is true even when sediment fractures are permitted to form in response to overpressure in pore space. With an initial gas hydrate distribution dictated by present-day pressure and temperature conditions, nominally 0.35 Gt of CH4 are released from the East Siberian slope during the first 100 years of the simulation. However, this CH4 discharge becomes significantly smaller (approximate to 0.05 Gt) if glacial sea level changes in the Arctic Ocean are considered. This is because a lower sea level during the last glacial maximum (LGM) must result in depleted gas hydrate abundance within the most sensitive region of the modern gas hydrate stability zone. Even if all released CH4 reached the atmosphere, the amount coming from East Siberian slopes would be trivial compared to present-day atmospheric CH4 inputs from other sources.

  • 43.
    Stranne, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Center for Coastal and Ocean Mapping/Joint Hydrographic Center, USA.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Modeling fracture propagation and seafloor gas release during seafloor warming-induced hydrate dissociation2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 16, p. 8510-8519Article in journal (Refereed)
    Abstract [en]

    The stability of marine methane hydrates and the potential release of methane gas to the ocean and atmosphere have received considerable attention in the past decade. Sophisticated hydraulic-thermodynamic models are increasingly being applied to investigate the dynamics of bottom water warming, hydrate dissociation, and gas escape from the seafloor. However, these models often lack geomechanical coupling and neglect how overpressure development and fracture propagation affect the timing, rate, and magnitude of methane escape. In this study we integrate a geomechanical coupling into the widely used TOUGH+Hydrate model. It is shown that such coupling is crucial in sediments with permeability 10(-16)m(2), as fracture formation dramatically affects rates of dissociation and seafloor gas release. The geomechanical coupling also results in highly nonlinear seafloor gas release, which presents an additional mechanism for explaining the widely observed episodic nature of gas flares from seafloor sediments in a variety of tectonic and oceanographic settings.

  • 44.
    Stranne, Christian
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Center for Coastal and Ocean Mapping/Joint Hydrographic Center, USA.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Overestimating climate warming-induced methane gas escape from the seafloor by neglecting multiphase flow dynamics2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 16, p. 8703-8712Article in journal (Refereed)
    Abstract [en]

    Continental margins host large quantities of methane stored partly as hydrates in sediments. Release of methane through hydrate dissociation is implicated as a possible feedback mechanism to climate change. Large-scale estimates of future warming-induced methane release are commonly based on a hydrate stability approach that omits dynamic processes. Here we use the multiphase flow model TOUGH+hydrate (T+H) to quantitatively investigate how dynamic processes affect dissociation rates and methane release. The simulations involve shallow, 20-100m thick hydrate deposits, forced by a bottom water temperature increase of 0.03 degrees Cyr(-1) over 100years. We show that on a centennial time scale, the hydrate stability approach can overestimate gas escape quantities by orders of magnitude. Our results indicate a time lag of>40years between the onset of warming and gas escape, meaning that recent climate warming may soon be manifested as widespread gas seepages along the world's continental margins.

  • 45.
    Swärd, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ampel, Linda
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ananyev, Roman
    Chernykh, Denis
    Flodén, Tom
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kylander, Malin E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Preto, Pedro
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Regional deglaciation and postglacial lake development as reflected in a 74m sedimentary record from Lake Vättern, southern Sweden2016In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 138, no 2, p. 336-354Article in journal (Refereed)
    Abstract [en]

    The withdrawal of the Late Weichselian ice sheet and rapid isostatic uplift in southern Scandinavia led to the entrainment of large volumes of melt water within the proglacial Baltic Ice Lake (BIL). The eventual western outpost of BIL, Lake Vattern, has been a focal point for studying the dynamic retreat history of the Late Weichselian ice sheet in south central Sweden. This part of the deglacial history is described from an abundance of terrestrial studies, but, to date, no complimentary long sediment cores from Lake Vattern have been available. Here, we present the results from a unique, 74m borehole in southern Lake Vattern that recovered a Late Pleistocene to Holocene sedimentary sequence. Physical and chemical analyses of the sediment and pore water, together with geophysical mapping, reveal glacial as well as postglacial imprints implying an oscillating ice sheet margin, evidence for neotectonic activity and one or more marine incursions into the lake during deglaciation. We attribute the glaciotectonic deformation of the sediments at 54m below the lake floor to an ice readvance that likely occurred at the same time or before the advance that formed the Levene moraine (approximate to 13.8-13.4cal.kaBP). After this event, potential readvances were likely restricted to a more northerly position in the basin. We identify the final drainage of the BIL, but find evidence for an earlier marine incursion into the Vattern basin (approximate to 13.0cal.kaBP), indicating water exchange between the North Atlantic and the Baltic Ice Lake during the late Allerod.

  • 46.
    Swärd, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Björck, Svante
    Stockholm University, Faculty of Science, Department of Geological Sciences. Lund University, Sweden.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kylander, Malin E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    A chronology of environmental changes in the Lake Vättern basin from deglaciation to its final isolation2018In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 47, no 2, p. 609-624Article in journal (Refereed)
    Abstract [en]

    During and after deglaciation, Lake Vättern developed from a proglacial lake situated at the westernmost rim of the Baltic Ice Lake (BIL), into a brackish water body connecting the North Sea and the Baltic Sea, and finally into an isolated freshwater lake. Here we present geochemical and mineralogical data from a 70‐m composite sediment core recovered in southern Lake Vättern. Together with a radiocarbon age model of this core, we are able to delineate the character and timing of the different lake stages. In addition to a common mineralogical background signature seen throughout the sediment core, the proglacial sediments bear a calcite imprint representing ice‐sheet transported material from the limestone bedrock that borders the lake basin in the northeast. The proglacial fresh to brackish water transition is dated to 11 480±290 cal. a BP and is in close agreement with other regional chronologies. The brackish period lasted c. 300 years and was followed by a c. 1600 year freshwater period before the Vättern basin became isolated from the Initial Littorina Sea. Decreasing detrital input, increasing δ13C values and the appearance of diatoms in the upper 15 m of the sediment succession are interpreted as an overall increase in biological productivity. This mode of sedimentation continues until the present and is interpreted to mark the final isolation of the lake at 9530±50 cal. a BP. Consequently, the isolation of Lake Vättern was not an outcome of the Ancylus Lake regression, but rather because of ongoing continental uplift in the early Littorina period.

  • 47.
    Swärd, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hilton, Robert
    Vogt, Christoph
    Andersson, Per
    Mineral and isotopic (Nd, Sr) of fine-grained deglacial and Holocene sediments from the Mackenzie Trough, Arctic CanadaManuscript (preprint) (Other academic)
  • 48.
    Swärd, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Semiletov, Igor
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Tarras, Henrik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sedimentary proxies for Pacific water inflow through the Herald Canyon, western Arctic OceanManuscript (preprint) (Other academic)
  • 49. Wegner, Carolyn
    et al.
    Bennett, Katrina E.
    de Vernal, Anne
    Forwick, Matthias
    Fritz, Michael
    Heikkila, Maija
    Lacka, Magdalena
    Lantuit, Hugues
    Laska, Michal
    Moskalik, Mateusz
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pawlowska, Joanna
    Prominska, Agnieszka
    Rachold, Volker
    Vonk, Jorien E.
    Werner, Kirstin
    Variability in transport of terrigenous material on the shelves and the deep Arctic Ocean during the Holocene2015In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 34, article id 24964Article in journal (Refereed)
    Abstract [en]

    Arctic coastal zones serve as a sensitive filter for terrigenous matter input onto the shelves via river discharge and coastal erosion. This material is further distributed across the Arctic by ocean currents and sea ice. The coastal regions are particularly vulnerable to changes related to recent climate change. We compiled a pan-Arctic review that looks into the changing Holocene sources, transport processes and sinks of terrigenous sediment in the Arctic Ocean. Existing palaeoceanographic studies demonstrate how climate warming and the disappearance of ice sheets during the early Holocene initiated eustatic sea-level rise that greatly modified the physiography of the Arctic Ocean. Sedimentation rates over the shelves and slopes were much greater during periods of rapid sea-level rise in the early and middle Holocene, as a result of the relative distance to the terrestrial sediment sources. However, estimates of suspended sediment delivery through major Arctic rivers do not indicate enhanced delivery during this time, which suggests enhanced rates of coastal erosion. The increased supply of terrigenous material to the outer shelves and deep Arctic Ocean in the early and middle Holocene might serve as analogous to forecast changes in the future Arctic.

  • 50. Werner, Kirstin
    et al.
    Fritz, Michael
    Morata, Nathalie
    Keil, Kathrin
    Pavlov, Alexey
    Peeken, Ilka
    Nikolopoulos, Anna
    Findlay, Helen S.
    Kedra, Monika
    Majaneva, Sanna
    Renner, Angelika
    Hendricks, Stefan
    Jacquot, Mathilde
    Nicolaus, Marcel
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sampei, Makoto
    Wegner, Carolyn
    Arctic in Rapid Transition: Priorities for the future of marine and coastal research in the Arctic2016In: Polar Science, ISSN 1873-9652, E-ISSN 1876-4428, Vol. 10, no 3, p. 364-373Article in journal (Refereed)
    Abstract [en]

    Understanding and responding to the rapidly occurring environmental changes in the Arctic over the past few decades require new approaches in science. This includes improved collaborations within the scientific community but also enhanced dialogue between scientists and societal stakeholders, especially with Arctic communities. As a contribution to the Third International Conference on Arctic Research Planning (ICARPIII), the Arctic in Rapid Transition (ART) network held an international workshop in France, in October 2014, in order to discuss high-priority requirements for future Arctic marine and coastal research from an early-career scientists (ECS) perspective. The discussion encompassed a variety of research fields, including topics of oceanographic conditions, sea-ice monitoring, marine biodiversity, land-ocean interactions, and geological reconstructions, as well as law and governance issues. Participants of the workshop strongly agreed on the need to enhance interdisciplinarity in order to collect comprehensive knowledge about the modern and past Arctic Ocean's geo-ecological dynamics. Such knowledge enables improved predictions of Arctic developments and provides the basis for elaborate decision-making on future actions under plausible environmental and climate scenarios in the high northern latitudes. Priority research sheets resulting from the workshop's discussions were distributed during the ICARPIII meetings in April 2015 in Japan, and are publicly available online.

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