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  • 1
    Electronic Resource
    Electronic Resource
    No extreme bipolar glaciation during the main Eocene calcite compensation shift (2007)
    [s.l.] : Nature Publishing Group
    Nature 448 (2007), S. 908-911 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Major ice sheets were permanently established on Antarctica approximately 34 million years ago, close to the Eocene/Oligocene boundary, at the same time as a permanent deepening of the calcite compensation depth in the world’s oceans. Until recently, it was thought that Northern ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature06053
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Insensitivity of alkenone carbon isotopes to atmospheric CO2 at low to moderate CO2 levels (2019)
    copernicus publications
    In:  EPIC3Climate of the Past, copernicus publications, 15(2), pp. 539-554, ISSN: 1814-9332
    Details
    Publication Date: 2019-03-28
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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    PAPER (OA)
  • 3
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    Insensitivity of alkenone carbon isotopes to atmospheric CO2 at low to moderate CO2 levels (2019)
    European Geosciences Union
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Badger, M. P. S., Chalk, T. B., Foster, G. L., Bown, P. R., Gibbs, S. J., Sexton, P. F., Schmidt, D. N., Paelike, H., Mackensen, A., & Pancost, R. D.. Insensitivity of alkenone carbon isotopes to atmospheric CO2 at low to moderate CO2 levels. Climate of the Past, 15(2), (2019):539-554 doi:10.5194/cp-15-539-2019.
    Description: Atmospheric pCO2 is a critical component of the global carbon system and is considered to be the major control of Earth's past, present, and future climate. Accurate and precise reconstructions of its concentration through geological time are therefore crucial to our understanding of the Earth system. Ice core records document pCO2 for the past 800 kyr, but at no point during this interval were CO2 levels higher than today. Interpretation of older pCO2 has been hampered by discrepancies during some time intervals between two of the main ocean-based proxy methods used to reconstruct pCO2: the carbon isotope fractionation that occurs during photosynthesis as recorded by haptophyte biomarkers (alkenones) and the boron isotope composition (δ11B) of foraminifer shells. Here, we present alkenone and δ11B-based pCO2 reconstructions generated from the same samples from the Pliocene and across a Pleistocene glacial–interglacial cycle at Ocean Drilling Program (ODP) Site 999. We find a muted response to pCO2 in the alkenone record compared to contemporaneous ice core and δ11B records, suggesting caution in the interpretation of alkenone-based records at low pCO2 levels. This is possibly caused by the physiology of CO2 uptake in the haptophytes. Our new understanding resolves some of the inconsistencies between the proxies and highlights that caution may be required when interpreting alkenone-based reconstructions of pCO2.
    Description: This study used samples provided by the International Ocean Discovery Program (IODP). We thank Alex Hull and Gemma Bowler for laboratory work, Lisa Schönborn and Günter Meyer for technical assistance, Alison Kuhl and Ian Bull for research support, and Andy Milton at the University of Southampton for maintaining some of the mass spectrometers used in this study. This study was funded by NERC grant NE/H006273/1 to Richard D. Pancost, Daniela N. Schmidt and Gavin L. Foster (which supported Marcus P. S. Badger). We also acknowledge the ERC Award T-GRES and a Royal Society Wolfson Research Merit Award to Richard D. Pancost. Gavin L. Foster is also supported by a Royal Society Wolfson Research Merit Award. We thank Kirsty Edgar for comments on an early draft of the manuscript, the two anonymous reviewers of this submission, and reviewers through various rounds of review whose comments greatly improved the manuscript. We are grateful to Thomas Bauska for encouraging us to do better at referencing the ice core data, and John Jasper for discussion of the early days of the alkenone palaeobarometer.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    Causes of ice age intensification across the Mid-Pleistocene Transition (2017)
    National Academy of Sciences
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 114 (2017): 13114-13119, doi: 10.1073/pnas.1702143114.
    Description: During the Mid-Pleistocene Transition (MPT; 1,200–800 kya), Earth’s orbitally paced ice age cycles intensified, lengthened from ∼40,000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO2 data to show that the glacial to interglacial CO2 difference increased from ∼43 to ∼75 μatm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO2-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets.
    Description: Research was supported by National Environmental Research Council (NERC) Studentship NE/I528626/1 (to T.B.C.); NERC Grant NE/P011381/1 (to T.B.C., M.P.H., G.L.F., E.J.R., and P.A.W.); NERC Fellowships NE/K00901X/1 (to M.P.H.), NE/I006346/1 (to G.L.F. and R.D.P), and NE/H006273/1 (to R.D.P.); Royal Society Wolfson Awards (to G.L.F. and P.A.W.); Australian Research Council Laureate Fellowship FL1201000050 (to E.J.R.); Swiss National Science Foundation Grant PP00P2-144811 (to S.L.J.); ETH Research Grant ETH-04 11-1 (to S.L.J.); European Research Council Consolidator Grant (ERC CoG) Grant 617462 (to H.P.); and NERC UK IODP Grant NE/F00141X/1 (to P.A.W.).
    Keywords: Boron isotopes ; MPT ; Geochemistry ; Carbon dioxide ; Paleoclimate
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    Calcification and growth processes in planktonic foraminifera complicate the use of B/Ca and U/Ca as carbonate chemistry proxies (2016)
    Elsevier
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Earth and Planetary Science Letters 449 (2016): 372-381, doi:10.1016/j.epsl.2016.05.016.
    Description: Although boron and uranium to calcium ratios (B/Ca, U/Ca) in planktonic foraminifera have recently received much attention as potential proxies for ocean carbonate chemistry, the extent of a carbonate chemistry control on these ratios remains contentious. Here, we use bi-weekly sediment trap samples collected from the subtropical North Atlantic in combination with measured oceanographic data from the same location to evaluate the dominant oceanographic controls on B/Ca and U/Ca in three depth-stratified species of planktonic foraminifera. We also test the control of biological, growth-related, processes on planktonic foraminiferal B and U incorporation by using foraminifer test area density (μg/μm2)(μg/μm2) (a monitor of test thickness) and test size from the same samples. B/Ca and U/Ca show little or no significant correlation with carbonate system parameters both within this study and in comparison with other published works. We provide the first evidence for a strong positive relationship between area density (test thickness) and B/Ca, and reveal that this is consistent in all species studied, suggesting a likely role for calcification in controlling boron partitioning into foraminiferal calcite. This finding is consistent with previous observations of less efficient discrimination against trace element ‘impurities’ (such as B), at higher calcification rates. We observe little or no dependency of B/Ca on test size. In marked contrast, we find that U/Ca displays a strong species-specific dependency on test size in all species, but no relationship with test thickness, implicating some other biological control (possibly related to growth), rather than a calcification control, on U incorporation into foraminiferal calcite. Our results caution against the use of B/Ca and U/Ca in planktonic foraminifera as reliable proxies for the ocean carbonate system and recommend that future work should concentrate on improving the mechanistic understanding of how planktonic foraminifer calcification and growth rates regulate boron and uranium incorporation into the test.
    Description: This research was funded through the U.K. Ocean Acidification Research Program by Natural Environment Research Council grant to P. Anand and P. Sexton (grant NE/I019891/1). K.S. thanks the Cushman Foundation for their financial support through the Johanna Resig Foraminifera Fellowship. We acknowledge the National Science Foundation for its support of the Oceanic Flux Program time-series (most recently by grant OCE-1234292) and the Bermuda Atlantic Time Series (most recently by grant OCE-0801991).
    Keywords: Planktonic foraminifera ; Boron ; Uranium ; Proxy ; Sediment trap
    Repository Name: Woods Hole Open Access Server
    Type: Article
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    PAPER (OA)
  • 6
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    Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum (2017)
    Nature Research
    In:  Nature, 548 (7669). pp. 573-577.
    Details
    Publication Date: 2020-06-18
    Description: The Palaeocene-Eocene Thermal Maximum(1,2) (PETM) was a global warming event that occurred about 56 million years ago, and is commonly thought to have been driven primarily by the destabilization of carbon from surface sedimentary reservoirs such as methane hydrates(3). However, it remains controversial whether such reservoirs were indeed the source of the carbon that drove the warming(1,3-5). Resolving this issue is key to understanding the proximal cause of the warming, and to quantifying the roles of triggers versus feedbacks. Here we present boron isotope data-a proxy for seawater pH-that show that the ocean surface pH was persistently low during the PETM. We combine our pH data with a paired carbon isotope record in an Earth system model in order to reconstruct the unfolding carbon-cycle dynamics during the event(6,7). We find strong evidence for a much larger (more than 10,000 petagrams)-and, on average, isotopically heavier-carbon source than considered previously(8,9). This leads us to identify volcanism associated with the North Atlantic Igneous Province(10,11), rather than carbon from a surface reservoir, as the main driver of the PETM. This finding implies that climate-driven amplification of organic carbon feedbacks probably played only a minor part in driving the event. However, we find that enhanced burial of organic matter seems to have been important in eventually sequestering the released carbon and accelerating the recovery of the Earth system(12).
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/nature23646
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Onset of North Atlantic Deep Water production coincident with inception of the Cenozoic global cooling trend (2012)
    Geological Society of America (GSA)
    Details
    Publication Date: 2012-03-01
    Description: Here we show that the onset of deep water overflow from the Norwegian-Greenland Sea into the North Atlantic, interpreted to represent the onset of a modern-style North Atlantic Deep Water mass, commenced close to the early to middle Eocene boundary. This finding is based on the identification of a large, elongate contourite sediment drift, the “Judd Falls Drift,” in the Faeroe-Shetland Basin, through detailed mapping of high-resolution two-dimensional and three-dimensional seismic data. This sediment drift covers an area of ~9000 km2 in one of the critical present-day deep water gateways into the North Atlantic Ocean. Interpretation of the body as a contourite drift is based on standard seismic-stratigraphic diagnostic criteria including tridirectional onlap, lensoid sediment geometry, upslope progradational configurations of stacked onlap units, and an erosional base cut in a deepwater setting. The internal reflection configuration indicates that the drift was deposited under a southwest-flowing current regime, which we propose represents the onset of North Atlantic Deep Water production, with continual deep water flow until at least the latest Eocene (ca. 35 million years ago [Ma]). Onset of drift deposition is dated by several key boreholes as occurring at ca. 50–49 Ma, across the early to middle Eocene boundary, and is coincident with independent geochemical evidence for major changes in the configuration of deep-sea circulation patterns, global biological production, and the onset of Cenozoic climatic cooling. These temporal concurrences suggest a strong link between the initiation of North Atlantic Deep Water production and Cenozoic global climate evolution.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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    PAPER CURRENT
  • 8
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    Supplementary material of IODP Site 342-U1410 and COSMOS model (2018)
    PANGAEA
    In:  Supplement to: Vahlenkamp, Maximilian; Niezgodzki, Igor; De Vleeschouwer, David; Bickert, Torsten; Harper, Dustin T; Kirtland Turner, Sandra; Lohmann, Gerrit; Sexton, Philip F; Zachos, James C; Pälike, Heiko (2018): Astronomically paced changes in deep-water circulation in the western North Atlantic during the middle Eocene. Earth and Planetary Science Letters, 484, 329-340, https://doi.org/10.1016/j.epsl.2017.12.016
    Details
    Publication Date: 2023-03-03
    Description: North Atlantic Deep Water (NADW) currently redistributes heat and salt between Earth's ocean basins, and plays a vital role in the ocean-atmosphere CO2 exchange. Despite its crucial role in today's climate system, vigorous debate remains as to when deep-water formation in the North Atlantic started. Here, we present datasets from carbonate-rich middle Eocene sediments from the Newfoundland Ridge, revealing a unique archive of paleoceanographic change from the progressively cooling climate of the middle Eocene. Well-defined lithologic alternations between calcareous ooze and clay-rich intervals occur at the ~41-kyr beat of axial obliquity. Hence, we identify obliquity as the driver of middle Eocene (43.5-46 Ma) Northern Component Water (NCW, the predecessor of modern NADW) variability. High-resolution benthic foraminiferal d18O and d13C suggest that obliquity minima correspond to cold, nutrient-depleted, western North Atlantic deep waters. We thus link stronger NCW formation with obliquity minima. In contrast, during obliquity maxima, Deep Western Boundary Currents were weaker and warmer, while abyssal nutrients were more abundant. These aspects reflect a more sluggish NCW formation. This obliquity-paced paleoceanographic regime is in excellent agreement with results from an Earth system model, in which obliquity minima configurations enhance NCW formation.
    Keywords: Center for Marine Environmental Sciences; Integrated Ocean Drilling Program / International Ocean Discovery Program; IODP; MARUM
    Type: Dataset
    Format: application/zip, 7 datasets
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    DATA PANGAEA
  • 9
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    Splice tie points form IODP Site 342-U1410 (2018)
    PANGAEA
    Details
    Publication Date: 2023-03-03
    Keywords: 342-U1410; Center for Marine Environmental Sciences; Depth, composite revised; DEPTH, sediment/rock; DRILL; Drilling/drill rig; DSDP/ODP/IODP sample designation; Exp342; Integrated Ocean Drilling Program / International Ocean Discovery Program; IODP; Joides Resolution; MARUM; Method comment; Paleogene Newfoundland Sediment Drifts; Sample code/label; Tie point
    Type: Dataset
    Format: text/tab-separated-values, 284 data points
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    DATA PANGAEA
  • 10
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    COSMOS model middle Eocene sensitivity tests with different obliquity values and Greenland-Scotland Ridge depths (2018)
    PANGAEA
    Details
    Publication Date: 2023-03-03
    Keywords: Center for Marine Environmental Sciences; File format; File name; File size; Integrated Ocean Drilling Program / International Ocean Discovery Program; IODP; MARUM; Uniform resource locator/link to file
    Type: Dataset
    Format: text/tab-separated-values, 12 data points
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    DATA PANGAEA
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