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  • 1. Aze, Tracy
    et al.
    Ezard, Thomas H. G.
    Purvis, Andy
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stewart, Duncan R. M.
    Wade, Bridget S.
    Pearson, Paul N.
    Identifying anagenesis cladogenesis in the fossil record2013In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 110, no 32, p. E2946-E2946Article in journal (Other academic)
  • 2.
    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)
  • 3.
    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)
  • 4.
    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)
  • 5.
    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.

  • 6. Berndt, Christian
    et al.
    Planke, Sverre
    Teagle, Damon
    Huismans, Ritske
    Torsvik, Trond
    Frieling, Joost
    Jones, Morgan T.
    Jerram, Dougal A.
    Tegner, Christian
    Faleide, Jan Inge
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hong, Wei-Li
    Northeast Atlantic breakup volcanism and consequences for Paleogene climate change - MagellanPlus Workshop report2019In: Scientific Drilling, ISSN 1816-8957, E-ISSN 1816-3459, Vol. 26, p. 69-85Article in journal (Refereed)
    Abstract [en]

    The northeast Atlantic encompasses archetypal examples of volcanic rifted margins. Twenty-five years after the last ODP (Ocean Drilling Program) leg on these volcanic margins, the reasons for excess melting are still disputed with at least three competing hypotheses being discussed. We are proposing a new drilling campaign that will constrain the timing, rates of volcanism, and vertical movements of rifted margins. This will allow us to parameterise geodynamic models that can distinguish between the hypotheses. Furthermore, the drilling-derived data will help us to understand the role of breakup magmatism as a potential driver for the Palaeocene-Eocene thermal maximum (PETM) and its influence on the oceanographic circulation in the earliest phase of the northeast Atlantic Ocean formation. Tackling these questions with a new drilling campaign in the northeast Atlantic region will advance our understanding of the long-term interactions between tectonics, volcanism, oceanography, and climate and the functioning of subpolar northern ecosystems and climate during intervals of extreme warmth.

  • 7. Birch, Heather
    et al.
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearson, Paul N.
    Kroon, Dick
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Planktonic foraminifera stable isotopes and water column structure: Disentangling ecological signals2013In: Marine Micropaleontology, ISSN 0377-8398, E-ISSN 1872-6186, Vol. 101, p. 127-145Article in journal (Refereed)
    Abstract [en]

    Differential carbon and oxygen stable isotope (delta C-13 and delta O-18) fractionation between planktonic foraminifera test calcite and sea water related to ecology and life stage confound the potential for reconstructing palaeo-water column temperature and carbon gradients. Multi-species analysis and strict selection of test sizes are useful methods for identifying these fractionation processes, also known as 'vital effects', in fossil taxa. However, there are a limited number of species with adequate size-controlled data sets, needed for ground truthing the approach in the modern. Here we report delta C-13 and delta O-18 measurements made on twelve species of modern planktonic foraminifera across a range of fourteen tightly constrained size windows from a tropical Indian Ocean core top sample. This data set includes more test size windows per species, especially from the smallest (identifiable) test size-classes, and a wider range of species than previously attempted. We use the size controlled delta O-18 calcite trajectories to infer depth habitats and calculate species-specific calcification temperatures. The temperatures are then used to constrain species-specific calcification depths along the modern vertical temperature profile in the western tropical Indian Ocean. By overlaying the per species delta C-13 calcite trajectories on local water column delta C-13(DIC) profiles, we estimate if and when (i.e. at which test sizes) the planktonic foraminifera species investigated approach ambient delta C-13(DIC) values. The profiling shows significant size-controlled delta C-13 deviation from seawater values in all species at some life/growth stage, which we attribute to (i) metabolic fractionation in tests <150-300 mu m (juveniles of all species and small adults), and; (ii) photosymbiont fractionation, affecting large tests (>similar to 300 mu m) of mixed layer photosymbiotic taxa. For most species there is a size-window where these effects appear to be at a minimum, and/or in balance. Exceptions are Globigerinita glutinata, a small (<200 mu m) surface living species, Globigerina bulloides, which is highly opportunistic, and deep living Globorotalia tumida and Globorotaloides hexagonus, the latter two species being affected by various unexplained delta C-13 vital effects. Use of our refined guidelines for test-size selection should improve the potential for making realistic reconstructions of water column delta C-13(DIC) in a modern tropical stratified setting and potentially in the distant geological past when there are no living analogues present.

  • 8.
    Birch, Heather
    et al.
    School of Earth and Ocean Science, Cardiff University.
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Pearson, Paul
    School of Ocean and Earth Sciences, Cardiff University.
    Schmidt, Daniela
    Earth Sciences, University of Bristol.
    Return to the light: Evolution of photosymbiosis after the end-Cretaceous mass extinction2009In: 6., 2009, p. 16-Conference paper (Other academic)
    Abstract [en]

    The Cretaceous/Paleogene (K/Pg) mass extinction seriously affected the marine pelagic ecosystem causing >90% loss of planktonic foraminifera species. Surface to deep-ocean foraminiferal d13C gradients and carbonate accumulation show that the extinctions coincided with a crash in organic matter flux to the sea floor that disrupted carbon cycling and took 3Myr to recover. Establishing the evolutionary and ecological response of the plankton through this recovery is important for understanding the role of the pelagic ecosystem in marine carbon cycling. Here we present new multispecies foraminiferal stable isotope data and planktic shell size distributions from a new, well-dated and continuous Atlantic deep sea core. The data document the evolution and diversification of photosymbiosis (thought to be an adaptation to low nutrient pelagic environments) in Paleocene planktonic species 3 million years after the K/Pg extinction when the pelagic carbon system recovered to a pre-K/Pg state and Oligotropic conditions returned. The data show that the geochemical signature of photosymbiosis evolved in an initially thermocline dwelling species, Preamurica pseudoinconstans, that started migrating to the shallower photic levels during later life stages. Initially appearing less than 1 myr after the K/ Pg extinction, symbiosis as an ecological strategy did not become important for a further 2 million years when the genus Morozevlla underwent major diversification, probably in response to an expanding ecologic opportunity that in turn resulted from final recovery of the marine carbon cycle.

  • 9. Birch, Heather S.
    et al.
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pearson, Paul N.
    Kroon, Dick
    Schmidt, Daniela N.
    Partial collapse of the marine carbon pump after the Cretaceous-Paleogene boundary2016In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 44, no 4, p. 287-290Article in journal (Refereed)
    Abstract [en]

    The impact of an asteroid at the end of the Cretaceous caused mass extinctions in the oceans. A rapid collapse in surface to deep-ocean carbon isotope gradients suggests that transfer of organic matter to the deep sea via the biological pump was severely perturbed. However, this view has been challenged by the survival of deep-sea benthic organisms dependent on surface-derived food and uncertainties regarding isotopic fractionation in planktic foraminifera used as tracers. Here we present new stable carbon (delta C-13) and oxygen (delta O-18) isotope data measured on carefully selected planktic and benthic foraminifera from an orbitally dated deep-sea sequence in the southeast Atlantic. Our approach uniquely combines delta O-18 evidence for habitat depth of foraminiferal tracer species with species-specific delta C-13 eco-adjustments, and compares isotopic patterns with corresponding benthic assemblage data. Our results show that changes in ocean circulation and foraminiferal vital effects contribute to but cannot explain all of the observed collapse in surface to deep-ocean foraminiferal delta C-13 gradient. We conclude that the biological pump was weakened as a consequence of marine extinctions, but less severely and for a shorter duration (maximum of 1.77 m.y.) than has previously been suggested.

  • 10.
    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.

  • 11.
    Coxall, Helen K.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wilson, Paul A.
    Early Oligocene glaciation and productivity in the eastern equatorial Pacific: Insights into global carbon cycling2011In: Paleoceanography, ISSN 0883-8305, E-ISSN 1944-9186, Vol. 26, p. PA2221-Article in journal (Refereed)
    Abstract [en]

    The onset of sustained Antarctic glaciation across the Eocene-Oligocene transition (EOT) marks a pivotal change in Earth's climate, but our understanding of this event, particularly the role of the carbon cycle, is limited. To help address this gap we present the following paleoceanographic proxy records from Ocean Drilling Program Site 1218 in the eastern equatorial Pacific (EEP): (1) stable isotope (delta(18)O and delta(13)C) records generated in epifaunal benthic foraminifera (Cibicidoides spp.) to improve (double the resolution) the previously published records; (2) delta(18)O and delta(13)C records measured on Oridorsalis umbonatus, a shallow infaunal species; and (3) a record of benthic foraminifera accumulation rate (BFAR). Our new isotope data sets confirm the existence at Site 1218 of a two-step delta(18)O increase. They also lend support to the hypothesized existence of a late Eocene transient delta(18)O increase and early Oligocene Oi-1a and Oi-1b glacial maxima. Our record of BFAR indicates a transient (similar to 500 kyr) twofold to threefold peak relative to baseline Oligocene values associated with the onset of Antarctic glaciation that we attribute to enhanced biological export production in the EEP. This takes the same general form as the history of opal accumulation in the Southern Ocean, suggesting strong high-to-low-latitude oceanic coupling. These findings appear to lend support to the idea that the EOT delta(13)C excursion is traceable to increased organic carbon (C(org)) burial. Paradoxically, early Oligocene sediments in the EEP are extremely C(org)-poor, and proxy records of atmospheric pCO(2) indicate a transient increase associated with the EOT.

  • 12. Cronin, Thomas M.
    et al.
    Keller, Katherine J.
    Farmer, Jesse R.
    Schaller, Morgan F.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Poirier, Robert
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Dwyer, Gary S.
    Bauch, Henning
    Kindstedt, Ingalise G.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Marzen, Rachel
    Santin, Emiliano
    Interglacial Paleoclimate in the Arctic2019In: Paleoceanography and paleoclimatology, ISSN 2572-4517, Vol. 34, no 12, p. 1959-1979Article in journal (Refereed)
    Abstract [en]

    Marine Isotope Stage 11 from similar to 424 to 374 ka experienced peak interglacial warmth and highest global sea level similar to 410-400 ka. MIS 11 has received extensive study on the causes of its long duration and warmer than Holocene climate, which is anomalous in the last half million years. However, a major geographic gap in MIS 11 proxy records exists in the Arctic Ocean where fragmentary evidence exists for a seasonally sea ice-free summers and high sea-surface temperatures (SST; similar to 8-10 degrees C near the Mendeleev Ridge). We investigated MIS 11 in the western and central Arctic Ocean using 12 piston cores and several shorter cores using proxies for surface productivity (microfossil density), bottom water temperature (magnesium/calcium ratios), the proportion of Arctic Ocean Deep Water versus Arctic Intermediate Water (key ostracode species), sea ice (epipelagic sea ice dwelling ostracode abundance), and SST (planktic foraminifers). We produced a new benthic foraminiferal delta O-18 curve, which signifies changes in global ice volume, Arctic Ocean bottom temperature, and perhaps local oceanographic changes. Results indicate that peak warmth occurred in the Amerasian Basin during the middle of MIS 11 roughly from 410 to 400 ka. SST were as high as 8-10 degrees C for peak interglacial warmth, and sea ice was absent in summers. Evidence also exists for abrupt suborbital events punctuating the MIS 12-MIS 11-MIS 10 interval. These fluctuations in productivity, bottom water temperature, and deep and intermediate water masses (Arctic Ocean Deep Water and Arctic Intermediate Water) may represent Heinrich-like events possibly involving extensive ice shelves extending off Laurentide and Fennoscandian Ice Sheets bordering the Arctic.

  • 13. Ferreira, David
    et al.
    Cessi, Paola
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    de Boer, Agatha
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Dijkstra, Henk A.
    Drijfhout, Sybren S.
    Eldevik, Tor
    Harnik, Nili
    McManus, Jerry F.
    Marshall, David P.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Roquet, Fabien
    Stockholm University, Faculty of Science, Department of Meteorology .
    Schneider, Tapio
    Wills, Robert C.
    Atlantic-Pacific Asymmetry in Deep Water Formation2018In: Annual Review of Earth and Planetary Science, ISSN 0084-6597, E-ISSN 1545-4495, Vol. 46, p. 327-352Article, review/survey (Refereed)
    Abstract [en]

    While the Atlantic Ocean is ventilated by high-latitude deep water formation and exhibits a pole-to-pole overturning circulation, the Pacific Ocean does not. This asymmetric global overturning pattern has persisted for the past 2-3 million years, with evidence for different ventilation modes in the deeper past. In the current climate, the Atlantic-Pacific asymmetry occurs because the Atlantic is more saline, enabling deep convection. To what extent the salinity contrast between the two basins is dominated by atmospheric processes (larger net evaporation over the Atlantic) or oceanic processes (salinity transport into the Atlantic) remains an outstanding question. Numerical simulations have provided support for both mechanisms; observations of the present climate support a strong role for atmospheric processes as well as some modulation by oceanic processes. A major avenue for future work is the quantification of the various processes at play to identify which mechanisms are primary in different climate states.

  • 14.
    Firth, J. V.
    et al.
    Integrated Ocean Drilling Program.
    Eldrett, J. S.
    Shell Exploration and Production Inc.
    Harding, I. C.
    University of Southampton, National Oceanography Centre.
    Coxall, H. K.
    Cardiff University.
    Wade, B. S.
    Integrated biomagnetochronology for the palaeogene of ODP hole 647A: Implications for correlating palaeoceanographic events from high to low latitudes2013In: Geological Society Special Publication, ISSN 0305-8719, E-ISSN 2041-4927, Vol. - 373, no - 1, p. 29-78Article in journal (Refereed)
    Abstract [en]

    Lower Eocene to Oligocene microfossil-rich hemipelagic sediments in ODP Hole 647A, southern Labrador Sea, provide a strategic section for resolving the early history of high North Atlantic climates and ocean circulation, and for correlating with carbonate-poor lower Cenozoic sediments in the Arctic and Nordic seas. Our new, integrated palaeomagneto- and multigroup biostratigraphy (63 dinoflagellate cyst, calcareous nannofossil, planktonic foraminifer and diatom datums) significantly improves Site 647 chronostratigraphy and provides a framework for future studies. This new age model, coupled with provisional δ18O analyses, provides greater confidence in the location of significant ocean-climate events at this site, including the Eocene–Oligocene transition and the Middle Eocene Climatic Optimum. Early Eocene hyperthermals may also be present near the base of the section. Palaeomagnetic age control is significantly improved in the Eocene, but not in the Oligocene. Revised estimates of sedimentation and biogenic flux indicate changes in supply and preservation that may be climatically controlled. A Lower to Middle Eocene hiatus is more precisely constrained, with a c. 4 million year duration. Age and depth errors quantify the age uncertainties throughout the section. Our revised age model will play an important role in stratigraphic correlation between very high latitude and lower latitude sites

  • 15. 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.

  • 16.
    Hutchinson, David K.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    de Boer, Agatha M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Arctic closure as a trigger for Atlantic overturning at the Eocene-Oligocene Transition2019In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 3797Article in journal (Refereed)
    Abstract [en]

    The Eocene-Oligocene Transition (EOT), approximately 34 Ma ago, marks a period of major global cooling and inception of the Antarctic ice sheet. Proxies of deep circulation suggest a contemporaneous onset or strengthening of the Atlantic meridional overturning circulation (AMOC). Proxy evidence of gradual salinification of the North Atlantic and tectonically driven isolation of the Arctic suggest that closing the Arctic-Atlantic gateway could have triggered the AMOC at the EOT. We demonstrate this trigger of the AMOC using a new paleoclimate model with late Eocene boundary conditions. The control simulation reproduces Eocene observations of low Arctic salinities. Subsequent closure of the Arctic-Atlantic gateway triggers the AMOC by blocking freshwater inflow from the Arctic. Salt advection feedbacks then lead to cessation of overturning in the North Pacific. These circulation changes imply major warming of the North Atlantic Ocean, and simultaneous cooling of the North Pacific, but no interhemispheric change in temperatures.

  • 17.
    Hutchinson, David K.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    de Boer, Agatha M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Baatsen, Michiel
    Climate sensitivity and meridional overturning circulation in the late Eocene using GFDL CM2.12018In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 14, no 6, p. 789-810Article in journal (Refereed)
    Abstract [en]

    The Eocene-Oligocene transition (EOT), which took place approximately 34 Ma ago, is an interval of great interest in Earth's climate history, due to the inception of the Antarctic ice sheet and major global cooling. Climate simulations of the transition are needed to help interpret proxy data, test mechanistic hypotheses for the transition and determine the climate sensitivity at the time. However, model studies of the EOT thus far typically employ control states designed for a different time period, or ocean resolution on the order of 3 degrees. Here we developed a new higher resolution palaeoclimate model configuration based on the GFDL CM2.1 climate model adapted to a late Eocene (38 Ma) palaeogeography reconstruction. The ocean and atmosphere horizontal resolutions are 1 degrees similar to 1.5 degrees and 3 degrees 3.75 ffi respectively. This represents a significant step forward in resolving the ocean geography, gateways and circulation in a coupled climate model of this period. We run the model under three different levels of atmospheric CO2: 400, 800 and 1600 ppm. The model exhibits relatively high sensitivity to CO2 compared with other recent model studies, and thus can capture the expected Eocene high latitude warmth within observed estimates of atmospheric CO2. However, the model does not capture the low meridional temperature gradient seen in proxies. Equatorial sea surface temperatures are too high in the model (3037 degrees C) compared with observations (max 32 degrees C), although observations are lacking in the warmest regions of the western Pacific. The model exhibits bipolar sinking in the North Pacific and Southern Ocean, which persists under all levels of CO2. North Atlantic surface salinities are too fresh to permit sinking (25-30 psu), due to surface transport from the very fresh Arctic (similar to 20 psu), where surface salinities approximately agree with Eocene proxy estimates. North Atlantic salinity increases by 1-2 psu when CO2 is halved, and similarly freshens when CO2 is doubled, due to changes in the hydrological cycle.

  • 18.
    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.

  • 19.
    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.

  • 20. Jimenez Berrocoso, Alvaro
    et al.
    Huber, Brian T.
    MacLeod, Kenneth G.
    Petrizzo, Maria Rose
    Lees, Jacqueline A.
    Wendler, Ines
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences. Cardiff University, UK.
    Mweneinda, Amina K.
    Falzoni, Francesca
    Birch, Heather
    Haynes, Shannon J.
    Bown, Paul R.
    Robinson, Stuart A.
    Singano, Joyce M.
    The Lindi Formation (upper Albian-Coniacian) and Tanzania Drilling Project Sites 36-40 (Lower Cretaceous to Paleogene): Lithostratigraphy, biostratigraphy and chemostratigraphy2015In: Journal of African earth sciences, ISSN 1464-343X, Vol. 101, p. 282-308Article in journal (Refereed)
    Abstract [en]

    The 2009 Tanzania Drilling Project (TDP) expedition to southeastern Tanzania cored a total of 572.3 m of sediments at six new mid-Cretaceous to mid-Paleocene boreholes (TDP Sites 36, 37, 38, 39, 40A, 40B). Added to the sites drilled in 2007 and 2008, the new boreholes confirm the common excellent preservation of planktonic and benthic foraminifera and calcareous nannofossils from core samples that will be used for biostratigraphy, evolutionary studies, paleoceanography and climatic reconstructions from the Tanzanian margin, with implications elsewhere. The new sites verify the presence of a relatively expanded Upper Cretaceous succession in the region that has allowed a new stratigraphic unit, named here as the Lindi Formation (Fm), to be formally defined. The Lindi Fm (upper Albian to Coniacian), extending similar to 120 km between Kilwa and Lindi, comprises a 335-m-thick, outer-shelf to upper-slope unit, consisting of dark gray claystone and siltstone interbeds, common finely-laminated intervals, minor cm-thick sandstones and up to 2.6% organic carbon in the Turonian. A subsurface, composite stratotype section is proposed for the Lindi Fm, with a gradational top boundary with the overlying Nangurukuru Fm (Santonian to Maastrichtian) and a sharp bottom contact with underlying upper Albian sandstones. The section cored at TDP Sites 36 and 38 belongs to the Lindi Fm and are of lower to middle Turonian age (planktonic foraminifera Whiteinella archaeocretacea to Helvetoglobotruncana helvetica Zones and nannofossils subzones UC6b +/- UC7). The lower portion of TDP Site 39 (uppermost part of the Lindi Fm) is assigned to the lower to upper Coniacian (planktonic foraminifera Dicarinella concavata Zone and nannofossils zone UC 10), while the remaining part of this site is attributed to the Coniacian-Santonian transition and younger Santonian (planktonic foraminifera D. asymetrica Zone and upper part of nannofossils zone UC10). TDP Site 37 recovered relatively expanded (150 m thick), monotonous calcareous claystones from the lower to upper Maastrichtian (planktonic foraminifera Pseudoguembelina palpebra to Abathomphalus mayaroensis Zones and nannofossils zones UC19 to UC20a(TP)) that were separated by a hiatus and/or a faulted contact from overlying brecciated carbonates of the Selandian (middle Paleocene: PF Zone P3 and nannofossil zone NP5). The lower portion of TDP Sites 40A and 40B recovered sandstones and conglomerates barren of microfossils. Their overlying parts were assigned to incomplete sections of the nannofossil zones NC6A to NC8 (uppermost Barremian to lower Albian). Benthic foraminiferal assemblages allowed the Barremian to lower Aptian to be identified in TDP Sites 40A and 40B, while the upper Aptian to middle Albian (Hedbergella trocoidea to Ticinella primula Zones) were assigned using planktonic foraminifera. Cores recovered at TDP 39 (Coniacian-Santonian) and at TDP Sites 40A and 40B (Barremian-middle Albian) represent the first time that these two intervals have been continuously cored and publicly documented in Tanzania. Bulk sediment isotope records generated for the new sites show lower delta O-18(carb) values in the Turonian and Santonian (similar to-3.5 parts per thousand to -5 parts per thousand) than in the Maastrichtian (similar to-3 parts per thousand), a situation consistent with extreme global warmth in the older intervals and cooling toward the end of the Cretaceous. Also, similar to Turonian sites from previous TDP expeditions, a negative delta C-13(org) excursion was detected across the W. archaeocretacea-H. helvetica boundary of TDP Site 36 (close to, but above, the Cenomanian-Turonian boundary). This excursion probably responded to local processes in the region, but it is unknown whether they were related to the recovery phase from Ocean Anoxic Event 2.

  • 21. John, E. H.
    et al.
    Pearson, P. N.
    Coxall, H.elen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Birch, H.
    Wade, B.S.
    Foster, G. L.
    Warm ocean processes and carbon cycling in the Eocene2013In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 371, no 2001, p. 1-21Article in journal (Refereed)
    Abstract [en]

    Sea surface and subsurface temperatures over large parts of the ocean during the Eocene epoch (55.5-33.7 Ma) exceeded modern values by several degrees, which must have affected a number of oceanic processes. Here, we focus on the effect of elevated water column temperatures on the efficiency of the biological pump, particularly in relation to carbon and nutrient cycling. We use stable isotope values from exceptionally well-preserved planktonic foraminiferal calcite from Tanzania and Mexico to reconstruct vertical carbon isotope gradients in the upper water column, exploiting the fact that individual species lived and calcified at different depths. The oxygen isotope ratios of different species' tests are used to estimate the temperature of calcification, which we converted to absolute depths using Eocene temperature profiles generated by general circulation models. This approach, along with potential pitfalls, is illustrated using data from modern core-top assemblages from the same area. Our results indicate that, during the Early and Middle Eocene, carbon isotope gradients were steeper (and larger) through the upper thermocline than in the modern ocean. This is consistent with a shallower average depth of organic matter remineralization and supports previously proposed hypotheses that invoke high metabolic rates in a warm Eocene ocean, leading to more efficient recycling of organic matter and reduced burial rates of organic carbon.

  • 22. Kiel, Steffen
    et al.
    Altamirano, Ali J.
    Birgel, Daniel
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hybertsen, Frida
    Peckmann, Jörn
    Fossiliferous methane-seep deposits from the Cenozoic Talara Basin in northern Peru2019In: Lethaia: an international journal of palaeontology and stratigraphy, ISSN 0024-1164, E-ISSN 1502-3931Article in journal (Refereed)
    Abstract [en]

    Thirteen fossiliferous limestone deposits from Cenozoic strata in the Talara Basin in northern Peru are identified as ancient methane-seep deposits. Planktonic foraminifera and the existing stratigraphical framework of the Talara Basin indicate an early Oligocene, or possibly late Eocene, age of these deposits. They are found in three distinct areas - Belen, Cerro La Salina and Cerros El Pelado - and differ in their petrography, stable isotope signatures, and lipid biomarker and macrofaunal contents. At Belen, the carbon stable isotope signature of the carbonate and the abundance of n-alkanes indicates the possibility of oil seepage in addition to methane seepage; for Belen and Cerro La Salina the high abundance of the biomarker crocetane indicates a dominance of anaerobic methane-oxidizing archaea of the ANME-2 group, whereas the rather small combined crocetane/phytane peak of a Cerros El Pelado limestone agrees with mixed ANME-1/ANME-2 input. The macrofauna consists mainly of molluscs; the Cerro La Salina sites include mostly infaunal thyasirid and lucinid bivalves and only few vesicomyid bivalves; gastropods include Provanna antiqua, the limpet Pyropelta and several vetigastropods. The Belen site is dominated by the elongate vesicomyid bivalve Pleurophopsis lithophagoides. The most common bivalve at the Cerros El Pelado sites is an undetermined, possible vesicomyid, and a smooth provannid gastropod. Biogeographically the faunas are most similar to those of the northwestern United States, as indicated by two joint species; similarities on the genus level (Conchocele, Lucinoma, Pleurophopsis, Provanna, Colus) exist also with Japan and the Caribbean region.

  • 23. Lear, Caroline H.
    et al.
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Foster, Gavin L.
    Lunt, Daniel J.
    Mawbey, Elaine M.
    Rosenthal, Yair
    Sosdian, Sindia M.
    Thomas, Ellen
    Wilson, Paul A.
    Neogene ice volume and ocean temperatures: Insights from infaunal foraminiferal Mg/Ca paleothermometry2015In: Paleoceanography, ISSN 0883-8305, E-ISSN 1944-9186, Vol. 30, no 11, p. 1437-1454Article in journal (Refereed)
    Abstract [en]

    Antarctic continental-scale glaciation is generally assumed to have initiated at the Eocene-Oligocene Transition, yet its subsequent evolution is poorly constrained. We reconstruct changes in bottom water temperature and global ice volume from 0 to 17 Ma using delta O-18 in conjunction with Mg/Ca records of the infaunal benthic foraminifer, O. umbonatus from Ocean Drilling Program (ODP) Site 806 (equatorial Pacific; similar to 2500m). Considering uncertainties in core top calibrations and sensitivity to seawater Mg/Ca (Mg/Ca)(sw), we produce a range of Mg/Ca-temperature-Mg/Ca-sw calibrations. Our favored exponential temperature calibration is Mg/Ca = 0.66 +/- 0.08 x Mg/Ca-sw(0.27 +/- 0.06) x e((0.114 +/- 0.02 x BWT)) and our favored linear temperature calibration is Mg/Ca = (1.21 +/- 0.04 + 0.12 +/- 0.004 x BWT (bottom water temperature)) x (Mg/Ca-sw -0.003 +/- 0.02) (stated errors are 2 s.e.). The equations are obtained by comparing O. umbonatus Mg/Ca for a Paleocene-Eocene section from Ocean Drilling Program (ODP) Site 690 (Weddell Sea) to delta O-18 temperatures, calculated assuming ice-free conditions during this peak warmth period of the Cenozoic. This procedure suggests negligible effect of Mg/Ca-sw on the Mg distribution coefficient (D-Mg). Application of the new equations to the Site 806 record leads to the suggestion that global ice volume was greater than today after the Middle Miocene Climate Transition (similar to 14Ma). ODP Site 806 bottom waters cooled and freshened as the Pacific zonal sea surface temperature gradient increased, and climate cooled through the Pliocene, prior to the Plio-Pleistocene glaciation of the Northern Hemisphere. The records indicate a decoupling of deep water temperatures and global ice volume, demonstrating the importance of thresholds in the evolution of the Antarctic ice sheet.

  • 24. Moore, T. C., Jr.
    et al.
    Wade, Bridget S.
    Westerhold, Thomas
    Erhardt, Andrea M.
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Baldauf, Jack
    Wagner, Meghan
    Equatorial Pacific productivity changes near the Eocene-Oligocene boundary2014In: Paleoceanography, ISSN 0883-8305, E-ISSN 1944-9186, Vol. 29, no 9, p. 825-844Article in journal (Refereed)
    Abstract [en]

    There is general agreement that productivity in high latitudes increased in the late Eocene and remained high in the early Oligocene. Evidence for both increased and decreased productivity across the Eocene-Oligocene transition (EOT) in the tropics has been presented, usually based on only one paleoproductivity proxy and often in sites with incomplete recovery of the EOT itself. A complete record of the Eocene-Oligocene transition was obtained at three drill sites in the eastern equatorial Pacific Ocean (ODP Site 1218 and IODP Sites U1333 and U1334). Four paleoproductivity proxies that have been examined at these sites, together with carbon and oxygen isotope measurements on early Oligocene planktonic foraminifera, give evidence of ecologic and oceanographic change across this climatically important boundary. Export productivity dropped sharply in the basal Oligocene (similar to 33.7Ma) and only recovered several hundred thousand years later; however, overall paleoproductivity in the early Oligocene never reached the average levels found in the late Eocene and in more modern times. Changes in the isotopic gradients between deep- and shallow-living planktonic foraminifera suggest a gradual shoaling of the thermocline through the early Oligocene that, on average, affected accumulation rates of barite, benthic foraminifera, and opal, as well as diatom abundance near 33.5Ma. An interval with abundant large diatoms beginning at 33.3Ma suggests an intermediate thermocline depth, which was followed by further shoaling, a dominance of smaller diatoms, and an increase in average primary productivity as estimated from accumulation rates of benthic foraminifera.

  • 25.
    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.

  • 26.
    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, 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.

  • 27.
    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)
  • 28. Pearson, Paul N.
    et al.
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Cardiff University, UK.
    Origin of the Eocene planktonic foraminifer Hantkenina by gradual evolution: 2014In: Palaeontology, ISSN 0031-0239, E-ISSN 1475-4983, Vol. 57, no 2, p. 243-267Article in journal (Refereed)
    Abstract [en]

    Hantkenina is a distinctive planktonic foraminiferal genus characterized by the presence of tubulospines (robust hollow projections) on each adult chamber, from Middle and Upper Eocene marine sediments worldwide. Here we illustrate its evolutionary origin using c. 150 specimens from 30 stratigraphic intervals in two sediment cores from Tanzania. The specimens, which span an estimated time interval of 300 ka, show four intermediate steps in the evolution of the tubulospines that amount to a complete intergradation from Clavigerinella caucasica, which does not possess them, to Hantkenina mexicana, which does. Stable isotope analyses indicate that the transitional forms evolved in a deep planktonic habitat not occupied at that time by other species of planktonic foraminifera. We discuss the morphogenetic constraints involved in the evolutionary transition and propose an ecological/adaptive model for the selective pressures that resulted in the evolution of tubulospines. We compare our record with similar, recently described assemblages from Austria and Italy, and we update the biostratigraphy and systematic taxonomy of the key morphospecies involved in the transition.

  • 29.
    Reghellin, Daniele
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Dickens, Gerald
    Stockholm University, Faculty of Science, Department of Geological Sciences. Rice University, USA.
    Comparison of stable isotope records across the Eastern Equatorial Pacific, from the Biogenic Bloom to Present-dayManuscript (preprint) (Other academic)
    Abstract [en]

    The oceanographic evolution of the eastern equatorial Pacific Ocean (EEP) since the late Neogene is still under debate. One school of thought proposes weaker than modern equatorial upwelling and sustained warm sea surface temperatures (SSTs) during the late Miocene to early Pliocene, while another suggests stronger than modern upwelling and cool SSTs over this period. These opposing theories appear to be proxy dependent and new perspectives are needed. Bulk carbonate stable isotopes signals have shown potential to carry information on EEP mixed layer water properties including temperature but the relative contribution of different biogenic carbonate components, and thus the origin of these signals, remains uncertain. Here we measured δ13C and δ18O of bulk carbonate, and several finer fractions that concentrate coccoliths, from ODP Site 851 sediments over the last 7 Ma. These data are compared to a series of new and published planktic and benthic foraminifera and foraminifera fragment δ13C and δ18O records to help disentangle coccolith ecological and ocean signals, and refine the use of bulk carbonate d13C and d18O as palaeoceanographic proxies. Our results imply that, once coccolith vital effects are accounted for, bulk δ13C and δ18O records mixed layer signals shallower than the depth of the planktonic foraminifera Globigerinoides sacculifer. Higher bulk carbonate δ13C, δ18O, sedimentation rate and opal content, combined with lower CaCO3 and >63 µm content during the late Miocene and until 4.6 Ma imply enhanced upwelling and cool SSTs along the EEP at this time, supporting the biogenic bloom hypothesis.

  • 30.
    Reghellin, Daniele
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Dickens, Gerald R.
    Stockholm University, Faculty of Science, Department of Geological Sciences. Rice University, USA.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Carbon and oxygen isotopes of bulk carbonate in sediment deposited beneath the eastern equatorial Pacific over the last 8 million years2015In: Paleoceanography, ISSN 0883-8305, E-ISSN 1944-9186, Vol. 30, no 10, p. 1261-1286Article in journal (Refereed)
    Abstract [en]

    To improve the understanding and utility of bulk carbonate stable carbon and oxygen isotope measurements, we examine sediment from cores in the eastern equatorial Pacific that span the last 8Ma. We measured C-13 and O-18 in 791 samples from Integrated Ocean Drilling Program Site U1338 and Deep Sea Drilling Project Site 573, both located close to the Pacific equator. In 100 samples, we measured C-13 and O-18 on isolated <63 mu m and <38 mu m fractions, which concentrates calcareous nannofossil carbonate and progressively excludes foraminiferal carbonate. Bulk carbonate C-13 and O-18 records are similar to published records from other sites drilled near the equator and seem to reflect mixed layer conditions, albeit with some important caveats involving the precipitation of calcite by coccolithophores. The comparatively lower C-13 and O-18 of the <63 mu m and <38 mu m fractions in sediments younger than 4.4Ma is attributed to an increase in deep-dwelling planktic foraminifera material in bulk carbonate, shifting the bulk isotopic signals toward higher values. Bulk carbonate C-13 is similar over 2500km along the Pacific equator, suggesting covarying concentrations and C-13 of dissolved inorganic carbon within surface waters since 8Ma. Greater bulk sediment C-13 and O-18, higher sedimentation rates, and low content of coarse material suggest intensified wind-driven upwelling and enhanced primary productivity along the Pacific equator between 8.0 and 4.4Ma, although a full understanding of bulk carbonate records will require extensive future work.

  • 31. Schiebel, Ralf
    et al.
    Smart, Sandi M.
    Jentzen, Anna
    Jonkers, Lukas
    Morard, Raphaël
    Meilland, Julie
    Michel, Elisabeth
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hull, Pincelli M.
    de Garidel-Thoron, Thibault
    Aze, Tracy
    Quillévéré, Frédéric
    Ren, Haojia
    Sigman, Daniel M.
    Vonhof, Hubert B.
    Martinez-García, Alfredo
    Kučera, Michal
    Bijma, Jelle
    Spero, Howard J.
    Haug, Gerald H.
    Advances in planktonic foraminifer research: New perspectives for paleoceanography2018In: Revue de Micropaleontologie, ISSN 0035-1598, E-ISSN 1873-4413, Vol. 61, no 3-4, p. 113-138Article, review/survey (Refereed)
    Abstract [en]

    Planktonic foraminifer tests are major archives of environmental change and provide a multitude of proxies in paleoceanography and paleoclimatology. The application of such proxies is contingent upon a collaborative effort to better understand how the living organisms record the properties of their environment and how the resulting signals are recorded in marine sediments. In this contribution, we provide a review of the rapidly developing sub-fields of research, where new advances have been made possibleby technological developments, and by cross-disciplinary work of the scientific community. Following brief historical overviews of the sub-fields, we discuss the latest advances in planktonic foraminifer research and highlight the resulting new perspectives in ocean and climate research. Natural classification based on consistent species concepts forms the basis for analysis of any foraminifer-derived proxy. New approaches in taxonomy and phylogeny of Cenozoic planktonic foraminifers (Section 2) are presented, highlighting new perspectives on sensitivity and response of planktonic foraminifers to the changing climate and environment (Section 4). Calibration of foraminifer-specific data and environmental parameters is improving along with the technical development of probes and the access to samples from the natural environment (Section 3), enhancing our understanding of the ever-changing climate and ocean system. Comprehension of sedimentation and flux dynamics facilitates maximum gain of information from fossil assemblages (Section 5). Subtle changes in the physical (e.g., temperature), chemical (e.g., pH), and biological (e.g., food) conditions of ambient seawater affect the abundance of species and composition of assemblages as well as the chemical composition of the foraminifer shell and provide increasingly-detailed proxy data on paleoenvironments (Section 6).

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