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  • 1. 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.

  • 2. Erbs-Hansen, Dorthe Reng
    et al.
    Knudsen, Karen Luise
    Gary, Anthony Cavedo
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jansen, Eystein
    Holocene climatic development in Skagerrak, eastern North Atlantic: Foraminiferal and stable isotopic evidence2012In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 22, no 3, p. 301-312Article in journal (Refereed)
    Abstract [en]

    A high-resolution multiproxy study of core MD99-2286 reveals a highly variable hydrographic environment in the Skagerrak from 9300 cal. yr BP to the present. The study includes foraminiferal faunas, stable isotopes and sedimentary parameters, as well as temperature and salinity reconstructions of a c. 29 m long radiocarbon-dated core record. The multivariate technique fuzzy c-means was applied to the foraminiferal counts, and it was extremely valuable in defining subtle heterogeneities in the foraminiferal faunal data corresponding to hydrographic changes. The major early-/mid-Holocene (Littorina) transgression led to flooding of large former land areas in the North Sea, the opening of the English Channel and Danish straits, and initiation of the modern circulation system. This is reflected by fluctuating C/N values and an explosive bloom of Hyalinea balthica. A slight indication of ameliorated conditions between 8000 and 5750 cal. yr BP is related to the Holocene Thermal Maximum. A subsequent increase in freshwater/Baltic water influence between 5750 and 4350 cal. yr BP is reflected by dominance of Bulimina marginata and depleted delta O-18 values. The Neoglacial cooling (after 4350 cal. yr BP) is seen in the Skagerrak as enhanced turbidity, increasing TOC values and short-term changes in an overall Cassidulina laevigata-dominated fauna suggesting a prevailing influence of Atlantic waters. This is in agreement with increased strength of westerly winds, as recorded for this period. The last 2000 years were also dominated by Atlantic Water conditions with generally abundant nutrient supply. However, during warm periods, particularly the 'Medieval Warm Period'and the modern warming, the area was subject to a restriction in the supply of nutrients and/or the nutrient supply had a more refractory character.

  • 3. Erbs-Hansen, Dorthe Reng
    et al.
    Knudsen, Karen Luise
    Gary, Anthony Cavedo
    Jansen, Eystein
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Scao, Vincent
    Lambeck, Kurt
    Late Younger Dryas and early Holocene palaeoenvironments in the Skagerrak, eastern North Atlantic: a multiproxy study2011In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 40, no 4, p. 660-680Article in journal (Refereed)
    Abstract [en]

    A high-resolution study of palaeoenvironmental changes through the late Younger Dryas and early Holocene in the Skagerrak, the eastern North Atlantic, is based on multiproxy analyses of core MD99-2286 combined with palaeowater depth modelling for the area. The late Younger Dryas was characterized by a cold ice-distal benthic foraminiferal fauna. After the transition to the Preboreal (c. 11 650 cal. a BP) this fauna was replaced by a Cassidulina neoteretis-dominated fauna, indicating the influence of chilled Atlantic Water at the sea floor. Persisting relatively cold bottom-water conditions until c. 10 300 cal. a BP are presumably a result of an outflow of glacial meltwater from the Baltic area across south-central Sweden, which led to a strong stratification of the water column at MD99-2286, as also indicated by C. neoteretis. A short-term peak in the C/N ratio at c. 10 200 cal. a BP is suggested to indicate input of terrestrial material, which may represent the drainage of an ice-dammed lake in southern Norway, the Glomma event. After the last drainage route across south-central Sweden closed, c. 10 300 cal. a BP, the meltwater influence diminished, and the Skagerrak resembled a fjord with a stable inflow of waters from the North Atlantic through the Norwegian Trench and a gradual increase in boreal species. Full interglacial conditions were established at the sea floor from c. 9250 cal. a BP. Subsequent warm stable conditions were interrupted by a short-term cooling around 8300-8200 cal. a BP, representing the 8.2 ka event.

  • 4. Eriksson, Jerker
    et al.
    Löwemark, Ludvig
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    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.
    Holmgren, Hanna
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Andersson, Per
    Schöberg, Hans
    Wallner, Karin
    Persson, Per-Olov
    Weichselian ice dammed lakes: New geochemical evidence for a rapidly deposited event-layer in the Eurasian Arctic Basin2012In: : APEX Sixth International Conference and Workshop: Quaternary Glacial and Climate Extremes / [ed] Ninna Immonen, Martin Jakobsson, Juha Pekka Lunkka, Kari Strand, Oulu: Oulun yliopisto , 2012, p. 48-48Conference paper (Other academic)
  • 5.
    Freire, Francis
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mayer, Larry
    Egilsson, Arnar
    Thorsteinsson, Tomas
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    High resolution mapping of offshore and onshore glaciogenic features in metamorphic bedrock terrain, Melville Bay, northwestern Greenland2015In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 250, p. 29-40Article in journal (Refereed)
    Abstract [en]

    Geomorphological studies of previously glaciated landscapes are important to understand how ice sheets and glaciers respond to rapidly changing climate. Melville Bay, in northwestern Greenland, contains some of the most sensitive but least studied ice sheet sectors in the northern hemisphere, where the bathymetric knowledge previously was restricted to a few sparsely distributed single beam echo soundings. We present here the results of high-resolution, geomorphological mapping of the offshore and onshore landscapes in Melville Bay using multibeam sonar and satellite data, at 5- and 10-m resolutions respectively. The results show a similar areally-scoured bedrock-dominated landscape with a glacially modified cnoc-and-lochan morphology on the inner shelf (150-500 m depth) and on the nearby exposed coast. This is manifested by the presence of U-shaped troughs, moutonee-type elongated landforms, stoss-and-lee forms, and streamlined features. The submarine landscape shows features that are characteristic of bedrock in folded, faulted, and weathered metamorphic terrain, and, to a lesser extent, glacially molded bedforms; while coastal landforms exhibit higher relief, irregular-shaped basins, and more subdued fracture valleys. Although generally similar, the onshore and offshore landscapes contain examples of distinctly different landform patterns, which are interpreted to reflect a longer exposure to long-term deep weathering as well as to more recent periglacial weathering processes on land. The spatial variability in the distribution of landforms across the landscape in both study areas is mostly attributed to differences in lithological properties of the bedrock. The lack of sediment cover on the inner shelf is likely a result of a capacity for sediment erosion and removal by the West Greenland Current flowing northward over the area in combination with limited sediment supply from long sea ice-cover seasons. The distribution and orientation of the landforms in the offshore part indicate ice movement toward the NW, and suggests that this area acted as a tributary or onset region for the major paleo ice stream that formed the present day Melville Bay Trough.

  • 6.
    Freire, Francis
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jafri, Rooh Ullah
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Acoustic evidence of a submarine slide in the deepest part of the Arctic, the Molloy Hole2014In: Geo-Marine Letters, ISSN 0276-0460, E-ISSN 1432-1157, Vol. 34, no 4, p. 315-325Article in journal (Refereed)
    Abstract [en]

    The western Svalbard continental margin contains thick sediment sequences with areas known to contain gas hydrates. Together with a dynamic tectonic environment, this makes the region prone to submarine slides. This paper presents results from geophysical mapping of the deepest part of the high Arctic environment, the Molloy Hole. The mapping includes multibeam bathymetry, acoustic backscatter and sub-bottom profiling. The geophysical data reveal seabed features indicative of sediment transport and larger-scale mass wasting. The large slide scar is here referred to as the Molloy Slide. It is located adjacent to the prominent Molloy Hole and Ridge system. The slide is estimated to have transported >65 km(3) of sediments over the deep axial valley of the Molloy Ridge, and further into the Molloy Hole. A unique feature of this slide is that, although its run-out distance is relatively short (<5 km), it extends over an enormous vertical depth (>2,000 m) as a result of its position in a complex bathymetric setting. The slide was most likely triggered by seismic activity caused by seafloor spreading processes along the adjacent Molloy Ridge. However, gas-hydrate destabilization may also have played a role in the ensuing slide event.

  • 7.
    Freire, Francis
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Initial Results from Seafloor Characterization of Arctic and Antarctic Margins using Multibeam Backscatter2012In: Arctic Palaeoclimate and its Extremes: APEX VI / [ed] Ninna Immonen, Martin Jakobsson, Juha Pekka Lunkka, Kari Strand, Oulu: University of Oulu , 2012, p. 51-51Conference paper (Other academic)
    Abstract [en]

    The seafloor of high-latitude Polar margins is characterized by various submarine glacigenic landforms whose shape and texture were created, and subsequently modified, by ice. These glaciogenic landforms together with deposited seafloor sediments serve as a record of the past glacial history. The Multibeam Echo Sounder (MBES) technology provides a tool to map and study submarine glaciogenic landforms and seafloor texture. MBES bathymetric images have afforded scientists a way to understand many glacial processes such as iceberg movements, advance and retreat patterns of ice sheets, and polar underwater currents, among others. Aside from measuring the bathymetry, MBES systems also record the returned intensity, or backscatter, of the acoustic pulse. Recent developments have shown that the backscatter information can be used to distinguish/classify differences in the surface sediment types. Here we present the preliminary results of an analysis of backscatter data aimed to characterize sediment types at locations of the Arctic and Antarctic margins mapped with Swedish icebreaker Oden and the installed Kongsberg EM122, 12 kHz, deep water MBES. We apply the Angular Range Analysis (ARA) method that is included in the Geocoder Backscatter processing algorithm [Fonseca and Mayer, 2007]. The results are correlated with other geophysical data and core samples to ground-truth the resulting seafloor maps.

  • 8.
    Freire, Francis
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Zingerlersen, Karl
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Paleo-ice stream behavior inferred from cross-shelf troughs and submarine glaciogenic debris flows along the west Greenland continental marginManuscript (preprint) (Other academic)
  • 9. Gowan, Evan J.
    et al.
    Zhang, Xu
    Khosravi, Sara
    Rovere, Alessio
    Stocchi, Paolo
    Hughes, Anna L. C.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mangerud, Jan
    Svendsen, John-Inge
    Lohmann, Gerrit
    A new global ice sheet reconstruction for the past 80000 years2021In: Nature Communications, E-ISSN 2041-1723, Vol. 12, no 1, article id 1199Article in journal (Refereed)
    Abstract [en]

    The evolution of past global ice sheets is highly uncertain. One example is the missing ice problem during the Last Glacial Maximum (LGM, 26000-19000 years before present) - an apparent 8-28 m discrepancy between far-field sea level indicators and modelled sea level from ice sheet reconstructions. In the absence of ice sheet reconstructions, researchers often use marine delta O-18 proxy records to infer ice volume prior to the LGM. We present a global ice sheet reconstruction for the past 80000 years, called PaleoMIST 1.0, constructed independently of far-field sea level and delta O-18 proxy records. Our reconstruction is compatible with LGM far-field sea-level records without requiring extra ice volume, thus solving the missing ice problem. However, for Marine Isotope Stage 3 (57000-29000 years before present) - a pre-LGM period - our reconstruction does not match proxy-based sea level reconstructions, indicating the relationship between marine delta O-18 and sea level may be more complex than assumed. The configuration of past ice sheets, and therefore sea level, is highly uncertain. Here, the authors provide a global reconstruction of ice sheets for the past 80,000 years that allows to test proxy based sea level reconstructions and helps to reconcile disagreements with sea level changes inferred from models.

  • 10. Gowan, Evan J.
    et al.
    Zhang, Xu
    Khosravi, Sara
    Rovere, Alession
    Stocchi, Paolo
    Hughes, Anna L. C.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mangerud, Jan
    Svendsen, John-Inge
    Lohmann, Gerrit
    Reply to: Towards solving the missing ice problem and the importance of rigorous model data comparisons2022In: Nature Communications, E-ISSN 2041-1723, Vol. 13, no 1, article id 6264Article in journal (Refereed)
  • 11. Graham, Alastair G. C.
    et al.
    Dutrieux, Pierre
    Vaughan, David G.
    Nitsche, Frank O.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Larter, Robert D.
    Jenkins, Adrian
    Seabed corrugations beneath an Antarctic ice shelf revealed by autonomous underwater vehicle survey: Origin and implications for the history of Pine Island Glacier2013In: Journal of Geophysical Research: Earth Surface, ISSN 2169-9011, Vol. 118, no 3, p. 1356-1366Article in journal (Refereed)
    Abstract [en]

    [1] Ice shelves are critical features in the debate about West Antarctic ice sheet change and sea level rise, both because they limit ice discharge and because they are sensitive to change in the surrounding ocean. The Pine Island Glacier ice shelf has been thinning rapidly since at least the early 1990s, which has caused its trunk to accelerate and retreat. Although the ice shelf front has remained stable for the past six decades, past periods of ice shelf collapse have been inferred from relict seabed “corrugations” (corrugated ridges), preserved 340 km from the glacier in Pine Island Trough. Here we present high-resolution bathymetry gathered by an autonomous underwater vehicle operating beneath an Antarctic ice shelf, which provides evidence of long-term change in Pine Island Glacier. Corrugations and ploughmarks on a sub-ice shelf ridge that was a former grounding line closely resemble those observed offshore, interpreted previously as the result of iceberg grounding. The same interpretation here would indicate a significantly reduced ice shelf extent within the last 11 kyr, implying Holocene glacier retreat beyond present limits, or a past tidewater glacier regime different from today. The alternative, that corrugations were not formed in open water, would question ice shelf collapse events interpreted from the geological record, revealing detail of another bed-shaping process occurring at glacier margins. We assess hypotheses for corrugation formation and suggest periodic grounding of ice shelf keels during glacier unpinning as a viable origin. This interpretation requires neither loss of the ice shelf nor glacier retreat and is consistent with a “stable” grounding-line configuration throughout the Holocene.

  • 12.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, Department of Physical Geography.
    Avery, Rachael S.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Regnéll, Carl
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Tylmann, Karol
    Footprint of the Baltic Ice Stream: geomorphic evidence for shifting ice stream pathways2024In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 53, no 1, p. 4-26Article in journal (Refereed)
    Abstract [en]

    The Baltic Ice Stream, a large fast-flowing sector of the last Fennoscandian Ice Sheet that occupied the present-day Baltic Sea basin, was first conceptualized in the earliest days of glacial geological research in Scandinavia. Landform and sedimentological evidence from the terrestrial margins support the concept and numerical ice-sheet models demonstrate its existence and possible evolution. However, with evidence for the Baltic Ice Stream thus far limited to the terrestrial periphery, its true form, scale, function, and role in deglaciation have proven enigmatic. Here we present geomorphological evidence directly from the Baltic seabed that confirms the existence of and sheds light on the behaviour of the Baltic Ice Stream. Based on an extensive collection of high-, moderate- and low-resolution bathymetric terrain models covering a large proportion of the Baltic Sea floor, and complemented by LiDAR-data for the Baltic islands, we have identified and mapped >20 000 individual subglacial bedforms, meltwater landforms and grounding line landforms. We reconstruct a six-stage sequence of ice flow and retreat, finding that streaming was persistent in the Baltic but that pathways were variable in extent, timing and duration: different sectors of the Baltic exhibit asynchronous streaming and out-of-phase grounding line changes. During deglaciation, grounding line readvances occurred in both the southwestern and the northern Baltic Proper, and, while abundant iceberg ploughmarks attest to calving as a significant ice loss mechanism, lobate margins suggest supply to the Baltic catchment was consistently high. Our reconstruction is limited by a fragmentary geomorphic record. Here we put forward a first hypothesis for how the Baltic Ice Stream evolved, and hope it stimulates new geomorphic, stratigraphical and core data collection to extend the landform record, provide insights into subglacial and grounding line processes, and constrain the chronology for Baltic Ice Stream flow and retreat.

  • 13.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Anderson, John B.
    Ice-flow switching and East/West Antarctic Ice Sheet roles in glaciation of the western Ross Sea2012In: Geological Society of America Bulletin, ISSN 0016-7606, E-ISSN 1943-2674, Vol. 124, no 11-12, p. 1736-1749Article in journal (Refereed)
    Abstract [en]

    The long-term behavior of the East and West Antarctic Ice Sheets, and their respective responses to forcing provide essential context for assessment of modern dynamic changes in ice-flow regimes and ice-sheet and shelf margins. The western Ross Sea discharges ice from both the East and West Antarctic Ice Sheets, and the paleoglacial record from this region is therefore valuable in unraveling their long-term behavior. New, high-resolution multibeam bathymetric data reveal snapshots of well-preserved glacial landforms on the seafloor around Ross Island and McMurdo Sound. Glacial lineations, grounding zone wedges, draped recessional moraines, and meltwater channels record a series of different ice-flow events in the region, contradictions between which require major phases of ice-flow reorganization. From the glacial geomorphology, we reconstruct a four-stage model of ice-flow evolution for the last glacial cycle, consisting of: (1) northeastward flow into the Ross Sea from McMurdo Sound; (2) westward flow from the Ross Sea, around Ross Island, and onto the Victoria Land coast and coastal seafloor trough; (3) a deglacial phase of ice-sheet thinning, minor shifts in flow, and grounding line retreat into McMurdo Sound; and (4) grounding line pinning on Ross Island during regional retreat, uncoupling of a remnant Ross Island ice cap, and local oscillation of Victoria Land outlet glaciers. We find that East Antarctic Ice Sheet ice discharge had a strong influence on ice-flow geometry in this part of the Ross Sea during the last glacial stage, but that it was not necessarily in phase with the behavior of the West Antarctic Ice Sheet. It is similarly evident that the ice streams that drained the Ross Sea over the continental shelf at the Last Glacial Maximum did not all operate synchronously, and exerted different drawdown power at different times. Finally, we conclude that Ross Island acts as an important pinning point in the Ross Sea ice-sheet-shelf system, stabilizing grounding line retreat and encouraging lasting ice-shelf development.

  • 14.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Late Glacial and Holocene paleoceanography in the Skagerrak from high-resolution grain size records2005In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 222, no 3-4, p. 344-369Article in journal (Refereed)
    Abstract [en]

    High-resolution grain size analyses of the AMS 14C-dated, 32 m long core MD99-2286 from the northeastern Skagerrak were performed in order to study late Glacial and Holocene paleoceanographic and sedimentary changes. All ages in this study are given in calibrated thousand years before present (= AD 1950), abbreviated ‘kyr’, unless otherwise noted.

    The distinct ending of IRD (ice rafted debris) in core MD99-2286, which was retrieved from a location down current from the final calving ice margin in the region, indicates that iceberg calving in the Skagerrak ended between 10.6 and 10.2 kyr.

    A clay-rich sequence in core MD99-2286, deposited between 11.3 and 10.3 kyr, is attributed to outflow from the Baltic basin across south central Sweden. The sequence is correlated to similar units from cores along the Swedish west coast. The onset of this clay-rich deposition occurs progressively later in cores further south along the coast, supporting a previous hypothesis that differential glacio-isostatic uplift caused a southward migration of the Baltic outflow from the Otteid-Stenselva to the Göta Älv outlet.

    A distinct coarsening towards younger sediments in core MD99-2286 indicates a hydrographic shift at 8.5 kyr, which is correlated to a shift previously reported in the Skagerrak, Kattegat and the Norwegian Channel. This shift reflects the establishment of the modern circulation system in the eastern North Sea, as a consequence of the opening of the English Channel and the Danish straits and increased Atlantic water inflow, and the subsequent development of the South Jutland Current. A general trend of coarsening, poorer sorting and increasing variability from 8.5 kyr until the present indicates increasing strength and influence of the variable South Jutland Current.

    A series of changes from ca. 6.3 to ca. 3.8 kyr in core MD99-2286 reflects strengthening of the Jutland Current towards the present day sedimentation system in the Skagerrak–Kattegat. These changes are correlated to previously reported hydrographic shifts at 5.5 14C years BP in the Skagerrak and at 4.0 14C years BP in the Kattegat. It is suggested that these shifts were separate features of a transitional period related to strengthening of the current system. The resulting changes are differently manifested in different parts of the Skagerrak–Kattegat, due to the complex circulation system.

    The last 800 years are characterised by poorly sorted sediments with a relatively high and variable proportion of coarse material, reflecting a circulation system significantly modified by regional climatic conditions, especially the general wind directions and storm frequency over the southern North Sea.

  • 15.
    Gyllencreutz, Richard
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Freire, Francis
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mayer, Larry
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Glacial landforms in a hard bedrock terrain, Melville Bay off nortwestern GreenlandManuscript (preprint) (Other academic)
  • 16.
    Gyllencreutz, Richard
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Kissel, K
    Late Glacial and Holocene sediment sources and transport patterns in the Skagerrak interpreted from mineral magnetic properties and grain size data2006In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 25, no 11-12, p. 1247-1263Article in journal (Refereed)
    Abstract [en]

    Lateglacial and Holocene changes in circulation, sedimentation and provenance in north-eastern Skagerrak were studied using high-resolution mineral magnetic and grain size data from the 32-m-long IMAGES core MD99-2286. Ages are given in calibrated thousand years BP (‘cal. kyr’). Between 12 and 11.3 cal. kyr, a calving ice front occupied the Oslo Fjord, and sedimentation was strongly influenced by meltwater carrying re-deposited glacial sediments from southern Norway and western Sweden. Between 11.3 and 10.3 cal. kyr, sedimentation was dominated by re-deposited glacial sediments transported by meltwater outflow across south-central Sweden. After the Otteid-Stenselva outlet was closed at 10.3 cal. kyr, glacial marine sedimentation changed to normal marine sedimentation. At 8.5 cal. kyr, a hydrographic shift, marking the onset of modern circulation in the Skagerrak–Kattegat, occurred as a result of increased Atlantic inflow, transgression of former land areas, and opening of the English Channel and the Danish Straits. After 8.5 cal. kyr, sedimentation was governed by input from the Atlantic Ocean and the North Sea, with varying contributions from the South Jutland Current, Baltic Current, and currents along the coasts of western Sweden and southern Norway. From 0.9 cal. kyr until present, the sedimentation was totally dominated by southern North Sea and Atlantic Ocean sources.

  • 17.
    Gyllencreutz, Richard
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mahiques, M. M.
    Alves, D. V. P.
    Wainer, I. K. C.
    Mid- to late-Holocene paleoceanographic changes on the southeastern Brazilian shelf based on grain size records2010In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 20, no 6, p. 863-875Article in journal (Refereed)
    Abstract [en]

    ; High-resolution grain size analyses of three AMS C-14-dated cores from the Southeastern Brazilian shelf provide a detailed record of mid- to late-Holocene environmental changes in the Southwestern Atlantic Margin. The cores exhibit millennial variability that we associate with the previously described southward shift of the Inter Tropical Convergence Zone (ITCZ) average latitudinal position over the South American continent during the Holocene climatic maximum. This generated changes in the wind-driven current system of the SW Atlantic margin and modified the grain size characteristics of the sediments deposited there. Centennial variations in the grain size are associated with a previously described late-Holocene enhancement of the El Nino-Southern Oscillation (ENSO) amplitude, which led to stronger NNE trade winds off eastern Brazil, favouring SW transport of sediments from the Paraiba do Sul River. This is recorded in a core from off Cabo Frio as a coarsening trend from 3000 cal. BP onwards. The ENSO enhancement also caused changes in precipitation and wind pattern in southern Brazil, allowing high discharge events and northward extensions of the low-saline water plume from Rio de la Plata. We propose that this resulted in a net increase in northward alongshore transport of fine sediments, seen as a prominent fine-shift at 2000 cal. BP in a core from similar to 24 degrees S on the Brazilian shelf. Wavelet-and spectral analysis of the sortable silt records show a significant similar to 1000-yr periodicity, which we attribute to solar forcing. If correct, this is one of the first indications of solar forcing of this timescale on the Southwestern Atlantic margin.

  • 18. Haflidason, Haflidi
    et al.
    Zweidorff, Julie L.
    Baumer, Marlene
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Svendsen, John Inge
    Gladysh, Vyacheslav
    Logvina, Elizaveta
    The Lastglacial and Holocene seismostratigraphy and sediment distribution of Lake Bolshoye Shchuchye, Polar Ural Mountains, Arctic Russia2019In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 48, no 2, p. 452-469Article in journal (Refereed)
    Abstract [en]

    Seismostratigraphical studies of the 11.8-km(2)-large and similar to 140-m-deep Lake Bolshoye Shchuchye, Polar Ural Mountains, reveal up to 160-m-thick acoustically laminated sediments in the lake basin. Using a dense grid of seismic lines, the spatial and temporal distributions of the sedimentary history have been reconstructed. Three regional seismic horizons have been identified and correlated with the well-dated 24-m-long sediment core retrieved from the lake. Isopach maps constructed from the seismic data show four phases of sedimentation. A contour map of the deepest regional seismic reflector represents the earliest hemipelagic sedimentation in the lake. Three contour maps represent time intervals covering the last 23cal. ka based on the well-dated core stratigraphy from the lake. The detailed time constraints on the upper stratigraphical units in the lake allow calculation of the lake's development in terms of sediment fluxes and the denudation rates from the Last Glacial Maximum (LGM) to the present. The sedimentation in Lake Bolshoye Shchuchye has been dominated by hemipelagic processes during at least the last 24cal. ka BP only locally interrupted by delta progradation and slope processes. A major shift in the sediment accumulation at c.18.7cal. ka BP is interpreted to mark the end of the local glacial maximum, greatly reduced denudation and the onset of the deglaciation period; this also demonstrates how fast the glaciers melted and possibly disappeared at the end of the LGM. The denudation rate during the Holocene is only a fifth of the LGM rate. The age of the oldest stratified sediments in Lake Bolshoye Shchuchye is not well constrained, but estimated as c. 50-60 ka.

  • 19. Hebbeln, Dierk
    et al.
    Knudsen, Karen-Luise
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Kristensen, Peter
    Klitgaard-Kristensen, Dorthe
    Backman, Jan
    Scheurle, Carolyn
    Jiang, Hui
    Gil, Isabelle
    Smelror, Morten
    Jones, Phil
    Sejrup, Hans-Petter
    Late Holocene coastal hydrographic and climate changes in the eastern North Sea2006In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 16, no 7, p. 987-1001Article in journal (Refereed)
    Abstract [en]

    We present a high-resolution palaeoenvironmental reconstruction covering the late Holocene from the Skagerrak and other sites in the North Sea area. The data, which are based on the analyses of marine sediment cores, reveal a marked environmental shift that took place between AD 700 and AD 1100, with the most pronounced changes occurring at AD 900. Both surface and bottom waters in the Skagerrak were subject to major circulation and productivity changes at this time due to an enhanced advection of Atlantic waters to the North Sea marking the beginning of the 'Mediaeval Warm Period' (MWP). The observed increase in bottom current strength is especially remarkable as there is hardly any comparable signal in the older part of the record going back to 1000 BC. At the transition to the 'Little Ice Age' (LIA) the bottom current strength remains at a high level, now probably forced by atmospheric circulation. Thus, despite opposite temperature forcing, these two consecutive climate scenarios are apparently able to generate distinctly stronger bottom currents in the Skagerrak than observed in the preceding 2000 years, and demonstrate the significance of climatic forcing in shaping the marine environment. Indeed, both the MWP and the LIA are reported as strong climatic signals in northwest Europe, being the warmest (except the late twentieth century) and coldest periods, respectively, during at least the last 2000 years.

  • 20. Hughes, Anna L. C.
    et al.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lohne, Øystein S.
    Mangerud, Jan
    Svendsen, John Inge
    The last Eurasian ice sheets - a chronological database and time-slice reconstruction, DATED-12016In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 45, no 1, p. 1-+Article in journal (Refereed)
    Abstract [en]

    We present a new time-slice reconstruction of the Eurasian ice sheets (British-Irish, Svalbard-Barents-Kara Seas and Scandinavian) documenting the spatial evolution of these interconnected ice sheets every 1000 years from 25 to 10 ka, and at four selected time periods back to 40 ka. The time-slice maps of ice-sheet extent are based on a new Geographical Information System (GIS) database, where we have collected published numerical dates constraining the timing of ice-sheet advance and retreat, and additionally geomorphological and geological evidence contained within the existing literature. We integrate all uncertainty estimates into three ice-margin lines for each time-slice; a most-credible line, derived from our assessment of all available evidence, with bounding maximum and minimum limits allowed by existing data. This approach was motivated by the demands of glaciological, isostatic and climate modelling and to clearly display limitations in knowledge. The timing of advance and retreat were both remarkably spatially variable across the ice-sheet area. According to our compilation the westernmost limit along the British-Irish and Norwegian continental shelf was reached up to 7000 years earlier (at c. 2726 ka) than the eastern limit on the Russian Plain (at c. 20-19 ka). The Eurasian ice sheet complex as a whole attained its maximum extent (5.5 Mkm(2)) and volume (similar to 24 m Sea Level Equivalent) at c. 21 ka. Our continental-scale approach highlights instances of conflicting evidence and gaps in the ice-sheet chronology where uncertainties remain large and should be a focus for future research. Largest uncertainties coincide with locations presently below sea level and where contradicting evidence exists. This first version of the database and time-slices (DATED-1) has a census date of 1 January 2013 and both are available to download via the Bjerknes Climate Data Centre and PANGAEA (www.bcdc.no; http://doi.pangaea.de/10.1594/PANGAEA.848117).

  • 21.
    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.

  • 22.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Anderson, John B.
    Nitsche, Frank O.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kirshner, Alexandra E.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    O'Regan, Matthew
    Mohammad, Rezwan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Eriksson, Bjorn
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ice sheet retreat dynamics inferred from glacial morphology of the central Pine Island Bay Trough, West Antarctica2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 38, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Pine Island Glacier drains portions of the West Antarctic Ice Sheet into the Amundsen Sea. During the Last Glacial Maximum the glacier extended nearly 500 km from its present location onto the outer continental shelf. Unusually restricted sea-ice cover during the austral summer of 2010 allowed for a systematic multibeam swath-bathymetric and chirp sonar survey of the mid-shelf section of Pine Island Trough. The mapped glacial landforms reveal new information about the paleo-Pine Island Ice Stream's dynamic retreat from the mid-shelf area and confirm previous suggestion of a retreat in distinct steps. The periods of grounding line stability during the overall retreat phase are marked by sediment accumulations, i.e. grounding zone wedges. These wedges are here mapped in sufficient detail to characterize spatial dimensions and estimate the volume of deposited sediment. Considering a range of sediment flux rates from the paleo-Pine Island Ice Stream we estimate that the largest and most clearly defined grounding zone wedge, located at about 73 degrees S in the surveyed area, took between 600 and 2000 years to form. The ice stream retreated landward of this wedge before 12.3 cal ka BP. The swath-bathymetric imagery of landforms in Pine Island Trough includes glacial features that suggest that retreat between periods of grounding line stability may be associated with episodes of ice shelf break-up. The depths of grounding line wedges decrease in a landward direction, from 740 to 670 m, and record elevation of the grounding line as it stepped landward. In all, the grounding line elevation varied by only similar to 80 m over a distance of just over 100 km, implying a low ice sheet profile during retreat. Finally, we revisited seismic reflection profile NB9902, acquired along Pine Island Trough in 1999, in combination with the newly acquired swath-bathymetric imagery from 2010. Together these data show that the ice stream paused during its retreat to form grounding zone wedges at an area in central Pine Island Trough where a high in dipping bedrock strata exists and the glacial trough is narrow, forming a bathymetric bottle neck.

  • 23.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Weidner, Elizabeth
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of New Hampshire, USA.
    Hansson, Jim
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Elfwing, Tina
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Norkko, Alf
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. University of Helsinki, Finland.
    Norkko, Joanna
    Nilsson, Björn
    Sjöstrom, Arne
    Potential links between Baltic Sea submarine terraces and groundwater seeping2020In: Earth Surface Dynamics, ISSN 2196-6311, Vol. 8, no 1, p. 1-15Article in journal (Refereed)
    Abstract [en]

    Submarine groundwater discharge (SGD) influences ocean chemistry, circulation, and the spreading of nutrients and pollutants; it also shapes sea floor morphology. In the Baltic Sea, SGD was linked to the development of terraces and semicircular depressions mapped in an area of the southern Stockholm archipelago, Sweden, in the 1990s. We mapped additional parts of the Stockholm archipelago, areas in Blekinge, southern Sweden, and southern Finland using high-resolution multibeam sonars and sub-bottom profilers to investigate if the sea floor morphological features discovered in the 1990s are widespread and to further address the hypothesis linking their formation to SGD. Sediment coring and sea floor photography conducted with a remotely operated vehicle (ROV) and divers add additional information to the geophysical mapping results. We find that terraces, with general bathymetric expressions of about 1 m and lateral extents of sometimes > 100 m, are widespread in the surveyed areas of the Baltic Sea and are consistently formed in glacial clay. Semicircular depressions, however, are only found in a limited part of a surveyed area east of the island of Asko, southern Stockholm archipelago. While submarine terraces can be produced by several processes, we interpret our results to be in support of the basic hypothesis of terrace formation initially proposed in the 1990s; i.e. groundwater flows through siltier, more permeable layers in glacial clay to discharge at the sea floor, leading to the formation of a sharp terrace when the clay layers above seepage zones are undermined enough to collapse. By linking the terraces to a specific geologic setting, our study further refines the formation hypothesis and thereby forms the foundation for a future assessment of SGD in the Baltic Sea that may use marine geological mapping as a starting point. We propose that SGD through the submarine sea floor terraces is plausible and could be intermittent and linked to periods of higher groundwater levels, implying that to quantify the contribution of freshwater to the Baltic Sea through this potential mechanism, more complex hydrogeological studies are required.

  • 24. Kaboth-Bahr, Stefanie
    et al.
    Denis, Vianney
    Su, Chih-Chieh
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Löwemark, Ludvig
    Deciphering similar to 45.000 years of Arctic Ocean lithostratigraphic variability through multivariate statistical analysis2019In: Quaternary International, ISSN 1040-6182, E-ISSN 1873-4553, Vol. 514, p. 141-151Article in journal (Refereed)
    Abstract [en]

    Our understanding of past climate conditions in the Arctic Ocean has been hampered by poor age control caused in part by low sedimentation rates (< 1 cm/kyr), hiatuses during glacial intervals as well as the scarcity and poor preservation of calcareous nanno-and microfossils in the sediments. Although recent advances using variations in single element (e.g. Mn) content or physical sediment properties (e.g. bulk density, grain size, colour) of the recovered sediments have aided Arctic core-to-core correlations, unique depositional events and post-depositional changes can complicate stratigraphic interpretations based on individual or even multiple, physical or chemical parameters. Furthermore, clear correlations between cores using physical and chemical parameters are not always possible to establish. To tackle this issue, we developed an algorithm that combines clustering and multivariate ordination to test the interrelation of multiple input parameters (e.g. an array of individual XRF elemental contents), and subsequently identifies statistically significant stratigraphic units on centimetre to decimetre scales. Our preliminary results show that a distinct sedimentological pattern during the past 45,000 years characterizes cores from the region of the Morris Jesup Rise and the Greenland side of the Lomonosov Ridge. Stratigraphic patterns of the Siberian Side of the Lomonosov Ridge yield distinct differences, thus allowing for novel insights into sedimentary processes shaping the different regions within the Arctic Ocean. We also argue that our approach can compensate for some of the weakness of single element or proxy applications, and hence aid the construction of a robust stratigraphic framework for a wide geographical range of Arctic Ocean sediments.

  • 25.
    Kirchner, N.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hutter, Kolumban
    Swiss Federal Institute of Technology.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Capabilities and limitations of numerical ice sheet models: a discussion for Earth-scientists and modelers2011In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, no 25-26, p. 3691-3704Article in journal (Refereed)
    Abstract [en]

    The simulation of dynamically coupled ice sheet, ice stream, and ice shelf-systems poses a challenge to most numerical ice sheet models. Here we review present ice sheet model limitations targeting a broader audience within Earth Sciences, also those with no specific background in numerical modeling, in order to facilitate cross-disciplinary communication between especially paleoglaciologists, marine and terrestrial geologists, and numerical modelers. The ‘zero order’(Shallow Ice Approximation, SIA)-,‘higher order’-, and‘full Stokes’ice sheet models are described conceptually and complemented by an outline of their derivations. We demonstrate that higher order models are required to simulate coupled ice sheetice shelf and ice sheet-ice stream systems, in particular if the results are aimed to complement spatial ice flow reconstructions based on higher resolution geological and geophysical data. The zero order SIA model limitations in capturing ice stream behavior are here illustrated by conceptual simulations of a glaciation on Svalbard. The limitations are obvious from the equations comprising a zero order model. However, under certain circumstances, simulation results may falsely give the impression that ice streams indeed are simulated with a zero order SIA model.

  • 26.
    Kylander, Malin E.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Martínez-Cortizas, Antonio
    Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI). Universidade de Santiago de Compostela, Spain.
    Sjöström, Jenny K.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Gåling, Jenny
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Bindler, Richard
    Alexanderson, Helena
    Schenk, Frederik
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Reinardy, Benedict T. I.
    Chandler, Benjamin M. P.
    Gallagher, Kerry
    Storm chasing: Tracking Holocene storminess in southern Sweden using mineral proxies from inland and coastal peat bogs2023In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 299, article id 107854Article in journal (Refereed)
    Abstract [en]

    Severe extratropical winter storms are a recurrent feature of the European climate and cause widespread socioeconomic losses. Due to insufficient long-term data, it remains unclear whether storminess has shown a notable response to changes in external forcing over the past millennia, which impacts our ability to project future storminess in a changing climate. Reconstructing past storm variability is essential to improving our understanding of storms on these longer, missing timescales. Peat sequences from coastal ombrotrophic bogs are increasingly used for this purpose, where greater quantities of coarser grained beach sand are deposited by strong winds during storm events. Moving inland however, storm intensity decreases, as does sand availability, muting potential paleostorm signals in bogs. We circumvent these issues by taking the innovative approach of using mid-infrared (MIR) spectral data, supported by elemental information, from the inorganic fraction of Store Mosse Dune South (SMDS), a 5000-year-old sequence from a large peatland located in southern Sweden. We infer past changes in mineral composition and thereby, the grain size of the deposited material. The record is dominated by quartz, whose coarse nature was confirmed through analyses of potential local source sediments. This was supported by further mineralogical and elemental proxies of atmospheric input. Comparison of SMDS with within-bog and regionally relevant records showed that there is a difference in proxy and site response to what should be similar timing in shifts in storminess over the ∼100 km transect considered. We suggest the construction of regional storm stacks, built here by applying changepoint modelling to four transect sites jointly. This modelling approach has the effect of reinforcing signals in common while reducing the influence of random noise. The resulting Southern Sweden-Storm Stack dates stormier periods to 4495–4290, 3880–3790, 2885–2855, 2300–2005, 1175–1065 and 715-425 cal yr BP. By comparing with a newly constructed Western Scotland-Storm Stack and proximal dune records, we argue that regional storm stacks allow us to better compare past storminess over wider areas, gauge storm track movements and by extension, increase our understanding of the drivers of storminess on centennial to millennial timescales.

  • 27.
    Kylander, Malin E.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Söderlindh, Jenny
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Schenk, Frederik
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Rydberg, Johan
    Bindler, Richard
    Martínez Cortizas, Antonio
    Skelton, Alasdair
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    It's in your glass: a history of sea level and storminess from the Laphroaig bog, Islay (southwestern Scotland)2020In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 49, no 1, p. 152-167Article in journal (Refereed)
    Abstract [en]

    Severe winter windstorms have become an increasingly common occurrence over recent decades in northwestern Europe. Although there exists considerable uncertainty, storminess is projected to increase in the future. On centennial to millennial time scales in particular, the mechanisms forcing storminess remain unsettled. We contribute to available palaeostorm records by reconstructing changes over the last 6670 years using a coastal peat sequence retrieved from the ombrotrophic Laphroaig bog on Islay, southwestern Scotland. We use a combination of ash content, grain size and elemental chemistry to identify periods of greater storminess, which are dated to 6605, 6290-6225, 5315-5085, 4505, 3900-3635, 3310-3130, 2920-2380, 2275-2190, 2005-1860, 1305-1090, 805-435 and 275 cal. a BP. Storm signals in the first half of the record up to similar to 3000 cal. a BP are mainly apparent in the grain-size changes. Samples from this time period also have a different elemental signature than those later in the record. We speculate that this is due to receding sea levels and the consequent establishment of a new sand source in the form of dunes, which are still present today. The most significant events and strongest winds are found during the Iron Ages Cold Epoch (2645 cal. a BP), the transition into, and in the middle of, the Roman Ages Warm Period (2235 and 1965 cal. a BP) and early in the Little Ice Age (545 cal. a BP). The Laphroaig record generally agrees with regionally relevant peat palaeostorm records from Wales and the Outer Hebrides, although the relative importance of the different storm periods is not the same. In general, stormier periods are coeval with cold periods in the region as evidenced by parallels with increased ice-rafted debris in the North Atlantic, highlighting that sea-ice conditions could impact future storminess and storm track position.

  • 28. 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, review/survey (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.

  • 29. Löwemark, Ludvig
    et al.
    Chao, Weng-Si
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hanebuth, Till J. J.
    Chiu, Pin-Yao
    Yang, Tien-Nan
    Su, Chih-Chieh
    Chuang, Chih-Kai
    Leon Dominguez, Dora Carolina
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Variations in glacial and interglacial marine conditions over the last two glacial cycles off northern Greenland2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 147, no SI, p. 164-177Article in journal (Refereed)
    Abstract [en]

    Five sediment cores from the Lomonosov Ridge and the Morris Jesup Rise north of Greenland show the history of sea-ice coverage and primary productivity over the last two glacial cycles. Variations in Manganese content, benthic and planktonic foraminifera, bioturbation, and trace fossil diversity are interpreted to reflect differences in sea-ice cover and sediment depositional conditions between the identified interglacials. Marine Isotope Stage (MIS) 1 and MIS 2 are represented by thin (<< 5 cm) sediment units while the preceding interglacial MIS 5 and glacial MIS 6 are characterized by thick (10 -20 cm) deposits. Foraminiferal abundances and bioturbation suggest that MIS 1 was generally characterized by severe sea-ice conditions north of Greenland while MISS appears to have been considerably warmer with more open water, higher primary productivity, and higher sedimentation rates. Strengthened flow of Atlantic water along the northern continental shelf of Greenland rather than development of local polynyas is here suggested as a likely cause for the relatively warmer marine conditions during MIS 5 compared to MIS 1. The cores also suggest distinct differences between the glacial intervals MIS 2 and MIS 6. While MIS 6 is distinguished by a relatively thick sediment unit poor in foraminifera and with low Mn values, MIS 2 is practically missing. We speculate that this could be the effect from a paleocrystic sea-ice cover north of Greenland during MIS 2 that prevented sediment delivery from sea ice and icebergs. In contrast, the thick sequence deposited during MIS 6 indicates a longer glacial period with dynamic intervals characterized by huge drifting icebergs delivering ice rafted debris (IRD). A drastic shift from thinner sedimentary cycles where interglacial sediment parameters indicate more severe sea-ice conditions gave way to larger amplitude cycles with more open water indicators was observed around the boundary between MIS 7/8. This shift is in agreement with a sedimentary regime shift previously identified in the Eurasian Basin and may be an indicator for the growth of larger ice sheets on the Eurasian landmass during the penultimate glacial period.

  • 30.
    O'Regan, Matt
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cronin, Thomas M.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kaboth, Stefanie
    Lowemark, Ludvig
    Wiers, Steffen
    West, Gabriel
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stratigraphic Occurrences of Sub-Polar Planktic Foraminifera in Pleistocene Sediments on the Lomonosov Ridge, Arctic Ocean2019In: Frontiers in Earth Science, E-ISSN 2296-6463, Vol. 7, article id 71Article in journal (Refereed)
    Abstract [en]

    Turborotalita quinqueloba is a species of planktic foraminifera commonly found in the sub-polar North Atlantic along the pathway of Atlantic waters in the Nordic seas and sometimes even in the Arctic Ocean, although its occurrence there remains poorly understood. Existing data show that T. quinqueloba is scarce in Holocene sediments from the central Arctic but abundance levels increase in sediments from the last interglacial period [Marine isotope stage (MIS) 5, 71-120 ka] in cores off the northern coast of Greenland and the southern Mendeleev Ridge. Turborotalita also occurs in earlier Pleistocene interglacials in these regions, with a unique and widespread occurrence of the less known Turborotalita egelida morphotype, proposed as a biostratigraphic marker for MIS 11 (474-374 ka). Here we present results from six new sediment cores, extending from the central to western Lomonosov Ridge, that show a consistent Pleistocene stratigraphy over 575 km. Preliminary semi-quantitative assessments of planktic foraminifer abundance and assemblage composition in two of these records (LOMROG12-7PC and AO16-5PC) reveal two distinct stratigraphic horizons containing Turborotalita in MIS 5. Earlier occurrences in Pleistocene interglacials are recognized, but contain significantly fewer specimens and do not appear to be stratigraphically coeval in the studied sequences. In all instances, the Turborotalita specimens resemble the typical T. quinqueloba morphotype but are smaller (63-125 mu m), smooth-walled and lack the final thickened calcite layer common to adults of the species. These results extend the geographical range for T. quinqueloba in MIS 5 sediments of the Arctic Ocean and provide compelling evidence for recurrent invasions during Pleistocene interglacials.

  • 31.
    Regnéll, Carl
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Alexanderson, Helena
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Öhrling, Christian
    The Lund Moraine - the geomorphic limit of the last Young Baltic ice advance in the Öresund region2023In: GFF, ISSN 1103-5897, E-ISSN 2000-0863Article in journal (Refereed)
    Abstract [en]

    Here we present geomorphological evidence of a previously unrecognised ∼50 km long, ice-marginal moraine complex in southwestern Skåne, southernmost Sweden, which we name the “Lund Moraine”. This lobate moraine marks a sharp boundary between heavily streamlined and gently undulating landscapes, and closely outlines the extent of the “Lund till/diamicton”. We interpret that the moraine was formed by a northward readvance, corresponding to a last Young Baltic readvance of the Scandinavian Ice Sheet into Öresund. Consequently, we infer that the “Lund till/diamicton” was formed subglacially, in contrast to earlier interpretations of it being a waterlain diamicton. Based on previously published dates, stratigraphically below “Lund till/diamicton”, we infer that this readvance occurred sometime after c. 16 cal. ka BP. This readvance could offer an explanation to the apparent discrepancy of observations of the postglacial marine limit from outside and inside the Lund Moraine. Our observations will hopefully settle the ∼50 years long controversy concerning the extent or even existence of such a readvance into Öresund. We expect that our findings will guide further work towards disentangling the complex deglacial history of Skåne and the wider Öresund region.

  • 32.
    Regnéll, Carl
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Becher, Gustaf Peterson
    Ohrling, Christian
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Blomdin, Robin
    Brendryen, Jo
    Goodfellow, Bradley W.
    Mikko, Henrik
    Ransed, Gunnel
    Smith, Colby
    Ice-dammed lakes and deglaciation history of the Scandinavian Ice Sheet in central Jämtland, Sweden2023In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 314, article id 108219Article in journal (Refereed)
    Abstract [en]

    Extensive glacial lakes dammed in the Scandinavian Mountains during the retreat of the last Scandinavian Ice Sheet were first hypothesised over a century ago. Here, using high-resolution LiDAR, we report >4500 relict shorelines, deltas and palaeo-channels related to ice-dammed lakes over a -30 000 km2 area of central Jämtland, west-central Sweden. Shorelines occur as flights on the valley sides, a consequence of sequential lowering of palaeo-lake levels during ice margin retreat and lower threshold outlets becoming ice-free. Based on the extent and elevation of shorelines, we identify requisite lake-damming ice-margin positions and lake drainage outlets, and we reconstruct the coupled evolution of ice-dammed lakes and the retreating ice margin. Beginning as a series of smaller ice-dammed lakes along the Swedish-Norwegian border, draining westward across the present-day water divide and into the Atlantic Ocean, the lakes successively coalesced during eastward ice margin retreat to form water bodies covering 1000s of km2 with 10s of km-long calving margins. Ultimately, the lake system coalesced into a single lake: the Central Jämtland Ice Lake, which exceeded 3500 km2 in area and 360 km3 in volume. Eventually, the damming ice-margin split in two, resulting in a large (-200 km2) catastrophic glacial lake outburst flood (GLOF) that reversed the drainage of the entire lake system from the west to an eastern outlet draining to the Baltic basin. We present new radiocarbon ages for one lake drainage event prior to the eastward outburst flood and, together with previously published deglacial ages and local varve records, we suggest that the region was possibly deglaciated within just 350 years, sometime between 10.5 and 9.2 cal ka BP. We tentatively correlate the penultimate drainage of the Central Jämtland Ice Lake to the zero-varve of the Swedish Time Scale, a drainage varve at Döviken, eastern Jämtland, raising the tantalising prospect of using the evolution of the ice-dammed lake system to tie the varve-based Swedish Time Scale to the radiocarbon timescale with a new programme of radiocarbon dating in central Jämtland. 

  • 33. Seaman, Paul
    et al.
    Sturkell, Erik
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stockmann, Gabrielle J.
    Geirsson, Halldór
    New multibeam mapping of the unique Ikaite columns in Ikka Fjord, SW Greenland2022In: Marine Geology, ISSN 0025-3227, E-ISSN 1872-6151, Vol. 444, article id 106710Article in journal (Refereed)
    Abstract [en]

    Ikka Fjord in SW Greenland is world famous for its submarine, cold-water craving ikaite (CaCO3·6H2O) tufa columns. Due to the uniqueness of the columns, Ikka Fjord is declared a protected area by the Greenlandic authorities. In the summers of 2018–19, multibeam sonar bathymetry and aerial drone photogrammetric surveys were made in Ikka Fjord mapping and counting the columns and comparing the results to data from geophysical surveys of the fjord in 1995–96. The new surveys provide highly detailed maps of the fjord bathymetry and its columns, their height and position, and several hitherto unknown pockmarks in the seabed. A total of 938 individual columns and structures ranging 0.5–20 m in height from the sea floor were identified: a number surpassing the 678 taller columns (> 1 m) known from previous mapping. Our results support previous observations that the columns are restricted to the spatial extents of the Grønnedal-Íka igneous complex. The new survey data show that column distribution exhibits lineations and variable density over the fjord floor, notably that the innermost central deep part is free of columns. The tallest columns are observed to grow up to the halocline at approximately 2–4 m water depth. The majority of columns have reached only 15–50% of their growth potential. The ~60 columns of maximum growth stand in clusters, interpreted as representing exceptionally favourable growth settings. New seawater data collected in 2019 shows a worrying increase in temperature since the previous measurements in 1995 and 2007–2009, which could potentially affect the stability of the delicate columns of Ikka Fjord.

  • 34. Stockmann, Gabrielle. J. J.
    et al.
    Seaman, Paul
    Balic-Zunic, Tonci
    Peternell, Mark
    Sturkell, Erik
    Liljebladh, Bengt
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mineral Changes to the Tufa Columns of Ikka Fjord, SW Greenland2022In: Minerals, E-ISSN 2075-163X, Vol. 12, no 11, article id 1430Article in journal (Refereed)
    Abstract [en]

    The submarine tufa columns of Ikka Fjord in Southwest Greenland have been studied during multiple field campaigns since 1995. The fjord contains close to thousand columns previously shown to consist of the metastable carbonate mineral ikaite (CaCO3·6H2O), which requires near-freezing conditions to remain stable over longer periods of time. During a field campaign to Ikka Fjord in the summer of 2019, seawater temperatures of 6–9 °C and visual physical changes to the columns were observed. These are the highest recorded seawater temperatures measured in Ikka Fjord in over three decades of research. In response, three selected columns at three different locations were sampled at their bases, middle, and top sections for mineralogical analysis. These samples were supplemented by a four further column samples and an extensive hydrographical campaign during fieldwork in the summer 2021. Here, we report the results of the mineralogical analyses performed by X-ray diffraction and µ-Raman Spectroscopy on these column samples. The results show that the columns analysed now consist of the less hydrated carbonate minerals, monohydrocalcite (CaCO3·H2O), aragonite, and calcite (CaCO3). One of the columns has completely altered into monohydrocalcite, whereas the other columns have crusts of ikaite and cores of monohydrocalcite ± aragonite and calcite. This change is interpreted as a dehydration reaction and mineral alteration from ikaite to monohydrocalcite continuing to aragonite ± calcite in response to being bathed in warming seawater. Hydrographic profilers and static dataloggers recorded seawater temperatures of 4–8 °C in the column-containing fjord areas during June–August 2021. The upper parts of the columns are particularly exposed to temperatures > 6 °C, considered to be the long-term stability threshold of ikaite in Ikka Fjord. The mineral dehydration reactions are irreversible. It is therefore predicted in a warming Arctic, ikaite will only appear as new growth on the columns for a short period, and that with time, the columns of Ikka Fjord will change mineralogy into mainly monohydrocalcite.

  • 35. Stokes, Chris R.
    et al.
    Tarasov, Lev
    Blomdin, Robin
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Cronin, Thomas M.
    Fisher, Timothy G.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hindmarsh, Richard C. A.
    Hughes, Anna L. C.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Livingstone, Stephen J.
    Margold, Martin
    Stockholm University, Faculty of Science, Department of Physical Geography. Durham University, UK.
    Murton, Julian B.
    Noormets, Riko
    Peltier, W. Richard
    Peteet, Dorothy M.
    Piper, David J. W.
    Preusser, Frank
    Renssen, Hans
    Roberts, David H.
    Roche, Didier M.
    Saint-Ange, Francky
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Teller, James T.
    On the reconstruction of palaeo-ice sheets: Recent advances and future challenges2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 125, p. 15-49Article, review/survey (Refereed)
    Abstract [en]

    Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding mechanisms of global climate change and associated sea-level fluctuations in the past, present and future. The significance of palaeo-ice sheets is further underlined by the broad range of disciplines concerned with reconstructing their behaviour, many of which have undergone a rapid expansion since the 1980s. In particular, there has been a major increase in the size and qualitative diversity of empirical data used to reconstruct and date ice sheets, and major improvements in our ability to simulate their dynamics in numerical ice sheet models. These developments have made it increasingly necessary to forge interdisciplinary links between sub-disciplines and to link numerical modelling with observations and dating of proxy records. The aim of this paper is to evaluate recent developments in the methods used to reconstruct ice sheets and outline some key challenges that remain, with an emphasis on how future work might integrate terrestrial and marine evidence together with numerical modelling. Our focus is on pan-ice sheet reconstructions of the last deglaciation, but regional case studies are used to illustrate methodological achievements, challenges and opportunities. Whilst various disciplines have made important progress in our understanding of ice-sheet dynamics, it is clear that data-model integration remains under-used, and that uncertainties remain poorly quantified in both empirically-based and numerical ice-Sheet reconstructions. The representation of past climate will continue to be the largest source of uncertainty for numerical modelling. As such, palaeo-observations are critical to constrain and validate modelling. State-of-the-art numerical models will continue to improve both in model resolution and in the breadth of inclusion of relevant processes, thereby enabling more accurate and more direct comparison with the increasing range of palaeo-observations. Thus, the capability is developing to use all relevant palaeo-records to more strongly constrain deglacial (and to a lesser extent pre-LGM) ice sheet evolution. In working towards that goal, the accurate representation of uncertainties is required for both constraint data and model outputs. Close cooperation between modelling and data-gathering communities is essential to ensure this capability is realised and continues to progress.

  • 36. Sundblad, Krister
    et al.
    Salin, Evgenia
    Claesson, Stefan
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Billström, Kjell
    The Precambrian of Gotland, a key for understanding the Proterozoic evolution in southern Fennoscandia2021In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 363, article id 106321Article in journal (Refereed)
    Abstract [en]

    Gotland is an island in the central part of the Baltic Sea, with up to 800 m Palaeozoic sedimentary rocks on top of a Precambrian basement belonging to the East European Craton. In this contribution, two major ductile deformation zones (Lickershamn - Östergarn and Lilla Karlsö-Ronehamn) are recognized and connected with the Vingåker-Nyköping and Linköping-Loftahammar Deformation Zones in the adjacent Fennoscandian Shield. These deformation zones constitute the borders between three main Precambrian segments that are correlated with crustal units within the Fennoscandian Shield and concealed parts of the East European Craton east of the Baltic Sea.

    The Fårö-Northern Gotland segment is dominated by continental Jotnian sandstones and Svecofennian metasedimentary rocks, separated from each other by a fault and an associated dolerite dyke. The metasediments show a specific provenance pattern with 3.29 Ga, 2.95–2.63 Ga and 2.11–1.96 Ga sources, devoid of < 1.90 Ga detrital zircons. The Alby granite truncates the metasedimentary rocks of the Fårö-Northern Gotland segment and is part of the 1.58 Ga Riga rapakivi batholith. The Central Gotland segment is dominated by metabasalts and 1.90–1.88 Ga granitoids and is correlated with the Tiveden and Valdemarsvik areas in the Fennoscandian Shield. The amphibolites in the Southern Gotland segment are correlated with 1.87–1.86 Ga metabasalts, intercalated with the Västervik quartzites in the Fennoscandian Shield. They were intruded by TIB 0 granitoids, recognized at Frigsarve and correlated with the Askersund-Loftahammar granitoids in the Fennoscandian Shield. The TIB 0 granitoids on Gotland can also be followed to the east, first to the E6-1 offshore drill hole, 30 km west of the Latvian coast and further east into southwestern Latvia and western Lithuania as a major component in the Mid-Lithuanian Domain. The Kvarne granitoid on southernmost Gotland is correlated with the TIB 1a generation in the Fennoscandian Shield and with granitoids within the Mid-Lithuanian Domain.

    1.48 Ga small stitching plutons on southern Gotland penetrate the TIB 0 and 1a granitoids and are correlated with the Götemar and Karlshamn plutons in the Fennoscandian Shield and several plutons in western and southern Lithuania.

  • 37. Svendsen, John Inge
    et al.
    Færseth, Lars Martin B.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Haflidason, Haflidi
    Henriksen, Mona
    Hovland, Morten N.
    Lohne, Øystein S.
    Mangerud, Jan
    Nazarov, Dmitry
    Regnéll, Carl
    Schaefer, Joerg M.
    Glacial and environmental changes over the last 60000years in the Polar Ural Mountains, Arctic Russia, inferred from a high-resolution lake record and other observations from adjacent areas2019In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 48, no 2, p. 407-431Article in journal (Refereed)
    Abstract [en]

    Our knowledge about the glaciation history in the Russian Arctic has to a large extent been based on geomorphological mapping supplemented by studies of short stratigraphical sequences found in exposed sections. Here we present new geochronological data from the Polar Ural Mountains along with a high-resolution sediment record from Bolshoye Shchuchye, the largest and deepest lake in the mountain range. Seismic profiles show that the lake contains a 160-m-thick sequence of unconsolidated lacustrine sediments. A well-dated 24-m-long core from the southern end of the lake spans the last 24cal. ka. From downward extrapolation of sedimentation rates we estimate that sedimentation started about 50-60 ka ago, most likely just after a large glacier had eroded older sediments from the basin. Terrestrial cosmogenic nuclide (TCN) exposure dating (Be-10) of boulders and Optically Stimulated Luminescence (OSL) dating of sediments indicate that this part of the Ural Mountains was last covered by a coherent ice-field complex during Marine Isotope Stage (MIS) 4. A regrowth of the glaciers took place during a late stage of MIS 3, but the central valleys remained ice free until the present. The presence of small- and medium-sized glaciers during MIS 2 is reflected by a sequence of glacial varves and a high sedimentation rate in the lake basin and likewise from Be-10 dating of glacial boulders. The maximum extent of the mountain glaciers during MIS 2 was attained prior to 24cal. ka BP. Some small present-day glaciers, which are now disappearing completely due to climate warming, were only slightly larger during the Last Glacial Maximum (LGM) as compared to AD 1953. A marked decrease in sedimentation rate around 18-17cal. ka BP indicates that the glaciers then became smaller and probably disappeared altogether around 15-14cal. ka BP.

  • 38.
    Åkesson, Henning
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of Bergen, Norway; Bjerknes Centre for Climate Research, Norway.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mangerud, Jan
    Svendsen, John Inge
    Nick, Faezeh M.
    Nisancioglu, Kerim H.
    Rapid retreat of a Scandinavian marine outlet glacier in response to warming at the last glacial termination2020In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 250, article id 106645Article in journal (Refereed)
    Abstract [en]

    Marine outlet glaciers on Greenland are retreating, yet it is unclear if the recent fast retreat will persist, and how atmosphere and ocean warming will impact future retreat. We show how a marine outlet glacier in Hardangerfjorden retreated rapidly in response to the abrupt warming following the Younger Dryas cold period (approximately 11,600 years before present). This almost 1000 m deep fjord, with several sills at 300-500 m depth, hosted a 175 km long outlet glacier at the western rim of the Scandinavian Ice Sheet. We use a dynamic ice-flow model constrained by well-dated terminal and lateral moraines to simulate the reconstructed 500-year retreat of Hardangerfjorden glacier. The model includes an idealized oceanic and atmospheric forcing based on reconstructions, but excludes the surface mass balance-elevation feedback. Our simulations show a highly episodic retreat driven by surface melt and warming fjord waters, paced by the fjord bathymetry. Warming air and ocean temperatures by 4-5 degrees C during the period of retreat result in a 125-km retreat of Hardangerfjorden glacier in 500 years. Retreat rates throughout the deglaciation vary by an order of magnitude from 50 to 2500 m a(-1), generally close to 200 m a(-1), punctuated by brief events of swift retreat exceeding 500 m a(-1), each event lasting a few decades. We show that the fastest retreat rates occur in regions of the bed with the largest retrograde slopes; ice shelf length and fjord water depth is less important. Our results have implications for modern glacial fjord settings similar to Hardangerfjorden, where high retreat rates have been observed. Our findings imply that increasing air temperatures and warming subsurface waters in Greenland fjords will continue to drive extensive retreat of marine outlet glaciers. However, the recent high retreat rates are not expected to be sustained for longer than a few decades due to constraints by the fjord bathymetry.

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