1
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Kirtland Turner S, Ridgwell A, Keller AL, Vahlenkamp M, Aleksinski AK, Sexton PF, Penman DE, Hull PM, Norris RD. Sensitivity of ocean circulation to warming during the Early Eocene greenhouse. Proc Natl Acad Sci U S A 2024; 121:e2311980121. [PMID: 38830092 PMCID: PMC11181020 DOI: 10.1073/pnas.2311980121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Accepted: 04/19/2024] [Indexed: 06/05/2024] Open
Abstract
Multiple abrupt warming events ("hyperthermals") punctuated the Early Eocene and were associated with deep-sea temperature increases of 2 to 4 °C, seafloor carbonate dissolution, and negative carbon isotope (δ13C) excursions. Whether hyperthermals were associated with changes in the global ocean overturning circulation is important for understanding their driving mechanisms and feedbacks and for gaining insight into the circulation's sensitivity to climatic warming. Here, we present high-resolution benthic foraminiferal stable isotope records (δ13C and δ18O) throughout the Early Eocene Climate Optimum (~53.26 to 49.14 Ma) from the deep equatorial and North Atlantic. Combined with existing records from the South Atlantic and Pacific, these indicate consistently amplified δ13C excursion sizes during hyperthermals in the deep equatorial Atlantic. We compare these observations with results from an intermediate complexity Earth system model to demonstrate that this spatial pattern of δ13C excursion size is a predictable consequence of global warming-induced changes in ocean overturning circulation. In our model, transient warming drives the weakening of Southern Ocean-sourced overturning circulation, strengthens Atlantic meridional water mass aging gradients, and amplifies the magnitude of negative δ13C excursions in the equatorial to North Atlantic. Based on model-data consistency, we conclude that Eocene hyperthermals coincided with repeated weakening of the global overturning circulation. Not accounting for ocean circulation impacts on δ13C excursions will lead to incorrect estimates of the magnitude of carbon release driving hyperthermals. Our finding of weakening overturning in response to past transient climatic warming is consistent with predictions of declining Atlantic Ocean overturning strength in our warm future.
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Affiliation(s)
- Sandra Kirtland Turner
- Department of Earth and Planetary Sciences, University of California, Riverside, CA92521
| | - Andy Ridgwell
- Department of Earth and Planetary Sciences, University of California, Riverside, CA92521
| | - Allison L. Keller
- Department of Earth and Planetary Sciences, University of California, Riverside, CA92521
| | - Maximilian Vahlenkamp
- Center for Marine Environmental Sciences (MARUM), University of Bremen, Bremen28359, Germany
| | - Adam K. Aleksinski
- Department of Earth and Planetary Sciences, University of California, Riverside, CA92521
- Department of Earth, Atmospheric and Planetary Sciences, Purdue University, West Lafayette, IN47906
| | - Philip F. Sexton
- School of Environment, Earth and Ecosystem Sciences, The Open University, Milton KeynesMK7 6AA, United Kingdom
| | - Donald E. Penman
- Department of Geosciences, Utah State University, Logan, UT84322
| | - Pincelli M. Hull
- Department of Earth and Planetary Sciences, Yale University, New Haven, CT06511
| | - Richard D. Norris
- Center for Marine Biodiversity and Conservation, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA92093
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2
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Wang Y, Costa KM, Lu W, Hines SKV, Nielsen SG. Global oceanic oxygenation controlled by the Southern Ocean through the last deglaciation. SCIENCE ADVANCES 2024; 10:eadk2506. [PMID: 38241365 PMCID: PMC10798564 DOI: 10.1126/sciadv.adk2506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Accepted: 12/19/2023] [Indexed: 01/21/2024]
Abstract
Ocean dissolved oxygen (DO) can provide insights on how the marine carbon cycle affects global climate change. However, the net global DO change and the controlling mechanisms remain uncertain through the last deglaciation. Here, we present a globally integrated DO reconstruction using thallium isotopes, corroborating lower global DO during the Last Glacial Maximum [19 to 23 thousand years before the present (ka B.P.)] relative to the Holocene. During the deglaciation, we reveal reoxygenation in the Heinrich Stadial 1 (~14.7 to 18 ka B.P.) and the Younger Dryas (11.7 to 12.9 ka B.P.), with deoxygenation during the Bølling-Allerød (12.9 to 14.7 ka B.P.). The deglacial DO changes were decoupled from North Atlantic Deep Water formation rates and imply that Southern Ocean ventilation controlled ocean oxygen. The coherence between global DO and atmospheric CO2 on millennial timescales highlights the Southern Ocean's role in deglacial atmospheric CO2 rise.
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Affiliation(s)
- Yi Wang
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
- NIRVANA Laboratories, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
- Department of Earth and Environmental Sciences, Tulane University, New Orleans, LA 70118, USA
| | - Kassandra M. Costa
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
| | - Wanyi Lu
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
| | - Sophia K. V. Hines
- Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
| | - Sune G. Nielsen
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
- NIRVANA Laboratories, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
- Centre de Recherches Pétrographiques et Géochimiques, CNRS, Université de Lorraine, 15 rue Notre Dame des Pauvres, 54501 Vandoeuvre lès Nancy, France
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3
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Chang L, Hoogakker BAA, Heslop D, Zhao X, Roberts AP, De Deckker P, Xue P, Pei Z, Zeng F, Huang R, Huang B, Wang S, Berndt TA, Leng M, Stuut JBW, Harrison RJ. Indian Ocean glacial deoxygenation and respired carbon accumulation during mid-late Quaternary ice ages. Nat Commun 2023; 14:4841. [PMID: 37563128 PMCID: PMC10415292 DOI: 10.1038/s41467-023-40452-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Accepted: 07/28/2023] [Indexed: 08/12/2023] Open
Abstract
Reconstructions of ocean oxygenation are critical for understanding the role of respired carbon storage in regulating atmospheric CO2. Independent sediment redox proxies are essential to assess such reconstructions. Here, we present a long magnetofossil record from the eastern Indian Ocean in which we observe coeval magnetic hardening and enrichment of larger, more elongated, and less oxidized magnetofossils during glacials compared to interglacials over the last ~900 ka. Our multi-proxy records of redox-sensitive magnetofossils, trace element concentrations, and benthic foraminiferal Δδ13C consistently suggest a recurrence of lower O2 in the glacial Indian Ocean over the last 21 marine isotope stages, as has been reported for the Atlantic and Pacific across the last glaciation. Consistent multi-proxy documentation of this repeated oxygen decline strongly supports the hypothesis that increased Indian Ocean glacial carbon storage played a significant role in atmospheric CO2 cycling and climate change over recent glacial/interglacial timescales.
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Affiliation(s)
- Liao Chang
- Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, 100871, Beijing, China.
- Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, 266071, Qingdao, China.
| | | | - David Heslop
- Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia
| | - Xiang Zhao
- Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia
| | - Andrew P Roberts
- Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia
| | - Patrick De Deckker
- Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia
| | - Pengfei Xue
- Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, 100871, Beijing, China
| | - Zhaowen Pei
- Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, 100871, Beijing, China
| | - Fan Zeng
- Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, 100871, Beijing, China
| | - Rong Huang
- Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, 100871, Beijing, China
| | - Baoqi Huang
- Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, 100871, Beijing, China
| | - Shishun Wang
- Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, 100871, Beijing, China
| | - Thomas A Berndt
- Department of Geophysics, School of Earth and Space Sciences, Peking University, 100871, Beijing, China
| | - Melanie Leng
- National Environmental Isotope Facility, British Geological Survey, Keyworth, NG12 5GG, UK
- School of Biosciences, University of Nottingham, Sutton Bonington, LE12 5RD, UK
| | - Jan-Berend W Stuut
- NIOZ-Royal Netherlands Institute for Sea Research and Utrecht University, Texel, The Netherlands
| | - Richard J Harrison
- Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, UK
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4
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Yi L, Medina-Elizalde M, Tan L, Kemp DB, Li Y, Kletetschka G, Xie Q, Yao H, He H, Deng C, Ogg JG. Plio-Pleistocene deep-sea ventilation in the eastern Pacific and potential linkages with Northern Hemisphere glaciation. SCIENCE ADVANCES 2023; 9:eadd1467. [PMID: 36827375 PMCID: PMC9956117 DOI: 10.1126/sciadv.add1467] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Accepted: 01/25/2023] [Indexed: 06/18/2023]
Abstract
Antarctic bottom water (AABW) production is a key factor governing global ocean circulation, and the present disintegration of the Antarctic Ice Sheet slows it. However, its long-term variability has not been well documented. On the basis of high-resolution chemical scanning of a well-dated marine ferromanganese nodule from the eastern Pacific, we derive a record of abyssal ventilation spanning the past 4.7 million years and evaluate its linkage to AABW formation over this period. We find that abyssal ventilation was relatively weak in the early Pliocene and persistently intensified from 3.4 million years ago onward. Seven episodes of markedly reduced ocean ventilation indicative of AABW formation collapse are identified since the late Pliocene, which were accompanied by key stages of Northern Hemisphere glaciation. We suggest that the interpolar climate synchronization within these inferred seven collapse events may have intensified global glaciation by inducing poleward moisture transport in the Northern Hemisphere.
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Affiliation(s)
- Liang Yi
- State Key Laboratory of Marine Geology, Tongji University, Shanghai, China
| | | | - Liangcheng Tan
- State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, China
- Institute of Global Environmental Change, Xi’an Jiaotong University, Xi’an, China
| | - David B. Kemp
- State Key Laboratory for Biogeology and Environmental Geology and Hubei Key Laboratory of Critical Zone Evolution, School of Earth Sciences, China University of Geosciences (Wuhan), Wuhan, China
| | - Yanzhen Li
- State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, China
- State Key Laboratory for Biogeology and Environmental Geology and Hubei Key Laboratory of Critical Zone Evolution, School of Earth Sciences, China University of Geosciences (Wuhan), Wuhan, China
| | - Gunther Kletetschka
- Institute of Hydrogeology, Engineering Geology, and Applied Geophysics, Faculty of Science, Charles University, Prague, Czech Republic
- Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA
| | - Qiang Xie
- Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya, China
| | - Huiqiang Yao
- Key Laboratory of Marine Mineral Resources, Ministry of Natural Resources, Guangzhou Marine Geological Survey, China Geological Survey, Guangzhou, China
- Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, China
| | - Huaiyu He
- State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Chenglong Deng
- State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - James G. Ogg
- Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA
- State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, China
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5
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Rafter PA, Gray WR, Hines SK, Burke A, Costa KM, Gottschalk J, Hain MP, Rae JW, Southon JR, Walczak MH, Yu J, Adkins JF, DeVries T. Global reorganization of deep-sea circulation and carbon storage after the last ice age. SCIENCE ADVANCES 2022; 8:eabq5434. [PMID: 36383653 PMCID: PMC9668286 DOI: 10.1126/sciadv.abq5434] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Accepted: 09/27/2022] [Indexed: 06/16/2023]
Abstract
Using new and published marine fossil radiocarbon (14C/C) measurements, a tracer uniquely sensitive to circulation and air-sea gas exchange, we establish several benchmarks for Atlantic, Southern, and Pacific deep-sea circulation and ventilation since the last ice age. We find the most 14C-depleted water in glacial Pacific bottom depths, rather than the mid-depths as they are today, which is best explained by a slowdown in glacial deep-sea overturning in addition to a "flipped" glacial Pacific overturning configuration. These observations cannot be produced by changes in air-sea gas exchange alone, and they underscore the major role for changes in the overturning circulation for glacial deep-sea carbon storage in the vast Pacific abyss and the concomitant drawdown of atmospheric CO2.
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Affiliation(s)
| | - William R. Gray
- Laboratoire des Science du Climat et de l’Environnement (LSCE/IPSL), Université-Paris-Saclay, Gif-sur-Yvette, France
| | | | - Andrea Burke
- University of St. Andrews, St. Andrews, Scotland, UK
| | | | | | - Mathis P. Hain
- University of California, Santa Cruz, Santa Cruz, CA, USA
| | | | | | | | - Jimin Yu
- Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266237, China
- Australia National University, Canberra, Australia
| | | | - Timothy DeVries
- Department of Geography and Earth Research Institute, University of California, Santa Barbara, CA, USA
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6
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Multiple carbon cycle mechanisms associated with the glaciation of Marine Isotope Stage 4. Nat Commun 2022; 13:5443. [PMID: 36114188 PMCID: PMC9481522 DOI: 10.1038/s41467-022-33166-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Accepted: 09/02/2022] [Indexed: 12/01/2022] Open
Abstract
Here we use high-precision carbon isotope data (δ13C-CO2) to show atmospheric CO2 during Marine Isotope Stage 4 (MIS 4, ~70.5-59 ka) was controlled by a succession of millennial-scale processes. Enriched δ13C-CO2 during peak glaciation suggests increased ocean carbon storage. Variations in δ13C-CO2 in early MIS 4 suggest multiple processes were active during CO2 drawdown, potentially including decreased land carbon and decreased Southern Ocean air-sea gas exchange superposed on increased ocean carbon storage. CO2 remained low during MIS 4 while δ13C-CO2 fluctuations suggest changes in Southern Ocean and North Atlantic air-sea gas exchange. A 7 ppm increase in CO2 at the onset of Dansgaard-Oeschger event 19 (72.1 ka) and 27 ppm increase in CO2 during late MIS 4 (Heinrich Stadial 6, ~63.5-60 ka) involved additions of isotopically light carbon to the atmosphere. The terrestrial biosphere and Southern Ocean air-sea gas exchange are possible sources, with the latter event also involving decreased ocean carbon storage. Summary for general audience: We used carbon stable isotope data from an Antarctic ice core to evaluate which mechanisms caused changes in atmospheric carbon dioxide 74-59 thousand years ago, including a ~40 ppm decrease at the beginning of the last ice age.
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7
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Auderset A, Moretti S, Taphorn B, Ebner PR, Kast E, Wang XT, Schiebel R, Sigman DM, Haug GH, Martínez-García A. Enhanced ocean oxygenation during Cenozoic warm periods. Nature 2022; 609:77-82. [PMID: 36045236 PMCID: PMC9433325 DOI: 10.1038/s41586-022-05017-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Accepted: 06/09/2022] [Indexed: 11/09/2022]
Abstract
Dissolved oxygen (O2) is essential for most ocean ecosystems, fuelling organisms’ respiration and facilitating the cycling of carbon and nutrients. Oxygen measurements have been interpreted to indicate that the ocean’s oxygen-deficient zones (ODZs) are expanding under global warming1,2. However, models provide an unclear picture of future ODZ change in both the near term and the long term3–6. The paleoclimate record can help explore the possible range of ODZ changes in warmer-than-modern periods. Here we use foraminifera-bound nitrogen (N) isotopes to show that water-column denitrification in the eastern tropical North Pacific was greatly reduced during the Middle Miocene Climatic Optimum (MMCO) and the Early Eocene Climatic Optimum (EECO). Because denitrification is restricted to oxygen-poor waters, our results indicate that, in these two Cenozoic periods of sustained warmth, ODZs were contracted, not expanded. ODZ contraction may have arisen from a decrease in upwelling-fuelled biological productivity in the tropical Pacific, which would have reduced oxygen demand in the subsurface. Alternatively, invigoration of deep-water ventilation by the Southern Ocean may have weakened the ocean’s ‘biological carbon pump’, which would have increased deep-ocean oxygen. The mechanism at play would have determined whether the ODZ contractions occurred in step with the warming or took centuries or millennia to develop. Thus, although our results from the Cenozoic do not necessarily apply to the near-term future, they might imply that global warming may eventually cause ODZ contraction. By using foraminifera-bound nitrogen isotopes, it is shown that, during two warm periods of the Cenozoic, oxygen-deficient zones contracted rather than expanded, suggesting that global warming may not necessarily lead to increased oceanic anoxia.
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Affiliation(s)
- Alexandra Auderset
- Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany. .,Department of Earth Sciences, ETH Zurich, Zurich, Switzerland.
| | - Simone Moretti
- Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany.,Department of Earth Sciences, ETH Zurich, Zurich, Switzerland
| | - Björn Taphorn
- Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
| | - Pia-Rebecca Ebner
- Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
| | - Emma Kast
- Department of Geosciences, Princeton University, Princeton, NJ, USA.,Department of Earth Sciences, University of Cambridge, Cambridge, UK
| | - Xingchen T Wang
- Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, MA, USA
| | - Ralf Schiebel
- Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
| | - Daniel M Sigman
- Department of Geosciences, Princeton University, Princeton, NJ, USA
| | - Gerald H Haug
- Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz, Germany.,Department of Earth Sciences, ETH Zurich, Zurich, Switzerland
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8
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Thomas NC, Bradbury HJ, Hodell DA. Changes in North Atlantic deep-water oxygenation across the Middle Pleistocene Transition. Science 2022; 377:654-659. [PMID: 35926027 DOI: 10.1126/science.abj7761] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The oxygen concentrations of oceanic deep-water and atmospheric carbon dioxide (pCO2) are intrinsically linked through organic carbon remineralization and storage as dissolved inorganic carbon in the deep sea. We present a high-resolution reconstruction of relative changes in oxygen concentration in the deep North Atlantic for the past 1.5 million years using the carbon isotope gradient between epifaunal and infaunal benthic foraminifera species as a proxy for paleo-oxygen. We report a significant (>40 micromole per kilogram) reduction in glacial Atlantic deep-water oxygenation at ~960 thousand to 900 thousand years ago that coincided with increased continental ice volume and a major change in ocean thermohaline circulation. Paleo-oxygen results support a scenario of decreasing deep-water oxygen concentrations, increased respired carbon storage, and a reduction in glacial pCO2 across the Middle Pleistocene Transition.
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Affiliation(s)
- Nicola C Thomas
- Department of Earth Science, University of Cambridge, Cambridge, UK
| | | | - David A Hodell
- Department of Earth Science, University of Cambridge, Cambridge, UK
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9
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Zheng J, Chen T, Ng HC, Robinson LF, Zheng XY, Shi X, Huang M. Determination of Picogram-per-Gram Concentrations of 231Pa and 230Th in Sediments by Melt Quenching and Laser Ablation Mass Spectrometry. Anal Chem 2022; 94:7576-7583. [PMID: 35576450 DOI: 10.1021/acs.analchem.2c00438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Uranium, thorium, and protactinium radionuclides in marine sediments are important proxies for understanding the earth's environmental evolution. Conventional solution-based methods, which typically involve isotope spike preparation, concentrated acid sample digestion, column chemistry, and mass spectrometry, allow precise but time-consuming and costly measurements of these nuclide concentrations (i.e., 230Th and 231Pa). In this work, we have established an efficient method for 230Th and 231Pa measurement of marine sediments down to the picogram-per-gram level without purification and enrichment. Our method first transforms a small amount of thermally decomposed sediments (∼0.1-0.2 g) to homogeneous silicate glass using a melt quenching technique and then analyzes the glass with laser ablation multicollector inductively coupled plasma-mass spectrometry. Standard sample bracketing with isotope-spike-calibrated glass standards prepared in this study was used to correct for instrumental fractionation during measurement. It is demonstrated that our method can accurately determine the U-Th-Pa concentrations of typical marine sediments in the late Pleistocene with precision of a few percent. Compared with the conventional solution-based methods, the turnover time of sample preparation and measurement with our established protocol is greatly reduced, facilitating future application of U-series radionuclides in reconstructing oceanic processes at high temporal and spatial resolution.
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Affiliation(s)
- Jianfan Zheng
- State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering and Frontiers Science Center for Critical Earth Material Cycling, Nanjing University, Nanjing 210046, China
| | - Tianyu Chen
- State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering and Frontiers Science Center for Critical Earth Material Cycling, Nanjing University, Nanjing 210046, China.,Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China
| | - Hong Chin Ng
- School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, U.K
| | - Laura F Robinson
- School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, U.K
| | - Xin-Yuan Zheng
- Department of Earth and Environmental Sciences, University of Minnesota─Twin Cities, Minneapolis, Minnesota 55455, United States
| | - Xuefa Shi
- Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China.,Key Laboratory of Marine Geology and Metallogeny, First Institute of Oceanography, Ministry of Natural Resources (MNR), Qingdao 266061, China
| | - Mu Huang
- Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China.,Key Laboratory of Marine Geology and Metallogeny, First Institute of Oceanography, Ministry of Natural Resources (MNR), Qingdao 266061, China
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10
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Persistent deep water anoxia in the eastern South Atlantic during the last ice age. Proc Natl Acad Sci U S A 2021; 118:2107034118. [PMID: 34873057 DOI: 10.1073/pnas.2107034118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/26/2021] [Indexed: 11/18/2022] Open
Abstract
During the last glacial interval, marine sediments recorded reduced current ventilation within the ocean interior below water depths of approximately >1,500 m [B. A. Hoogakker et al., Nat. Geosci. 8, 40-43 (2015)]. The degree of the associated oxygen depletion in the different ocean basins, however, is still poorly constrained. Here, we present sedimentary records of redox-sensitive metals from the southwest African margin. These records show evidence of continuous bottom water anoxia in the eastern South Atlantic during the last glaciation that led to enhanced carbon burial over a prolonged period of time. Our geochemical data indicate that upwelling-related productivity and the associated oxygen minimum zone in the eastern South Atlantic shifted far seaward during the last glacial period and only slowly retreated during deglaciation times. While increased productivity during the last ice age may have contributed to oxygen depletion in bottom waters, especially on the upper slope, slow-down of the Late Quaternary deep water circulation pattern [Rutberg et al., Nature 405, 935-938 (2000)] appears to be the ultimate driver of anoxic conditions in deep waters.
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11
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Woods HA, Moran AL. Reconsidering the Oxygen-Temperature Hypothesis of Polar Gigantism: Successes, Failures, and Nuance. Integr Comp Biol 2021; 60:1438-1453. [PMID: 32573680 DOI: 10.1093/icb/icaa088] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
"Polar gigantism" describes a biogeographic pattern in which many ectotherms in polar seas are larger than their warmer-water relatives. Although many mechanisms have been proposed, one idea-the oxygen-temperature hypothesis-has received significant attention because it emerges from basic biophysical principles and is appealingly straightforward and testable. Low temperatures depress metabolic demand for oxygen more than supply of oxygen from the environment to the organism. This creates a greater ratio of oxygen supply to demand, releasing polar organisms from oxygen-based constraints on body size. Here we review evidence for and against the oxygen-temperature hypothesis. Some data suggest that larger-bodied taxa live closer to an oxygen limit, or that rising temperatures can challenge oxygen delivery systems; other data provide no evidence for interactions between body size, temperature, and oxygen sufficiency. We propose that these findings can be partially reconciled by recognizing that the oxygen-temperature hypothesis focuses primarily on passive movement of oxygen, implicitly ignoring other important processes including ventilation of respiratory surfaces or internal transport of oxygen by distribution systems. Thus, the hypothesis may apply most meaningfully to organisms with poorly developed physiological systems (eggs, embryos, egg masses, juveniles, or adults without mechanisms for ventilating internal or external surfaces). Finally, most tests of the oxygen-temperature hypothesis have involved short-term experiments. Many organisms can mount effective responses to physiological challenges over short time periods; however, the energetic cost of doing so may have impacts that appear only in the longer term. We therefore advocate a renewed focus on long-term studies of oxygen-temperature interactions.
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Affiliation(s)
- H Arthur Woods
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Amy L Moran
- School of Life Sciences, University of Hawai'i at Mānoa, Honolulu, HI 96822, USA
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12
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Deglacial patterns of South Pacific overturning inferred from 231Pa and 230Th. Sci Rep 2021; 11:20473. [PMID: 34650117 PMCID: PMC8517020 DOI: 10.1038/s41598-021-00111-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Accepted: 10/06/2021] [Indexed: 11/25/2022] Open
Abstract
The millennial-scale variability of the Atlantic Meridional Overturning Circulation (AMOC) is well documented for the last glacial termination and beyond. Despite its importance for the climate system, the evolution of the South Pacific overturning circulation (SPOC) is by far less well understood. A recently published study highlights the potential applicability of the 231Pa/230Th-proxy in the Pacific. Here, we present five sedimentary down-core profiles of 231Pa/230Th-ratios measured on a depth transect from the Pacific sector of the Southern Ocean to test this hypothesis using downcore records. Our data are consistent with an increase in SPOC as early as 20 ka that peaked during Heinrich Stadial 1. The timing indicates that the SPOC did not simply react to AMOC changes via the bipolar seesaw but were triggered via Southern Hemisphere processes.
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13
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Kobayashi H, Oka A, Yamamoto A, Abe-Ouchi A. Glacial carbon cycle changes by Southern Ocean processes with sedimentary amplification. SCIENCE ADVANCES 2021; 7:7/35/eabg7723. [PMID: 34433564 PMCID: PMC8386940 DOI: 10.1126/sciadv.abg7723] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Accepted: 07/06/2021] [Indexed: 06/13/2023]
Abstract
Recent paleo reconstructions suggest that increased carbon storage in the Southern Ocean during glacial periods contributed to low glacial atmospheric carbon dioxide concentration (pCO2). However, quantifying its contribution in three-dimensional ocean general circulation models (OGCMs) has proven challenging. Here, we show that OGCM simulation with sedimentary process considering enhanced Southern Ocean salinity stratification and iron fertilization from glaciogenic dust during glacial periods improves model-data agreement of glacial deep water with isotopically light carbon, low oxygen, and old radiocarbon ages. The glacial simulation shows a 77-ppm reduction of atmospheric pCO2, which closely matches the paleo record. The Southern Ocean salinity stratification and the iron fertilization from glaciogenic dust amplified the carbonate sedimentary feedback, which caused most of the increased carbon storage in the deep ocean and played an important role in pCO2 reduction. The model-data agreement of Southern Ocean properties is crucial for simulating glacial changes in the ocean carbon cycle.
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Affiliation(s)
- Hidetaka Kobayashi
- Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan.
| | - Akira Oka
- Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan
| | - Akitomo Yamamoto
- Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
| | - Ayako Abe-Ouchi
- Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan
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14
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Meridional changes in the South Atlantic Subtropical Gyre during Heinrich Stadials. Sci Rep 2021; 11:9419. [PMID: 33941820 PMCID: PMC8093259 DOI: 10.1038/s41598-021-88817-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2020] [Accepted: 04/14/2021] [Indexed: 02/02/2023] Open
Abstract
Subtropical ocean gyres play a key role in modulating the global climate system redistributing energy between low and high latitudes. A poleward displacement of the subtropical gyres has been observed over the last decades, but the lack of long-term monitoring data hinders an in-depth understanding of their dynamics. Paleoceanographic records offer the opportunity to identify meridional changes in the subtropical gyres and investigate their consequences to the climate system. Here we use the abundance of planktonic foraminiferal species Globorotalia truncatulinodes from a sediment core collected at the northernmost boundary of the South Atlantic Subtropical Gyre (SASG) together with a previously published record of the same species from the southernmost boundary of the SASG to reconstruct meridional fluctuations of the SASG over last ca. 70 kyr. Our findings indicate southward displacements of the SASG during Heinrich Stadials (HS) 6-4 and HS1, and a contraction of the SASG during HS3 and HS2. During HS6-4 and HS1, the SASG southward displacements likely boosted the transfer of heat to the Southern Ocean, ultimately strengthening deep-water upwelling and CO2 release to the atmosphere. We hypothesize that the ongoing SASG poleward displacement may further increase oceanic CO2 release.
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15
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Geochronology and Geochemical Properties of Mid-Pleistocene Sediments on the Caiwei Guyot in the Northwest Pacific Imply a Surface-to-Deep Linkage. JOURNAL OF MARINE SCIENCE AND ENGINEERING 2021. [DOI: 10.3390/jmse9030253] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Seamounts are ubiquitous topographic units in the global ocean, and their effects on local circulation have attracted great research attention in physical oceanography; however, fewer relevant efforts were made on geological timescales in previous studies. The Caiwei (Pako) Guyot in the Magellan Seamounts of the western Pacific is a typical seamount and oceanographic characteristics have been well documented. In this study, we investigate a sediment core by geochronological and geochemical studies to reveal a topography-induce surface-to-bottom linkage. The principal results are as follows: (1) Two magnetozones are recognized in core MABC–11, which can be correlated to the Brunhes and Matuyama chrons; (2) Elements Ca, Si, Cl, K, Mn, Ti, and Fe are seven elements with high intensities by geochemical scanning; (3) Ca intensity can be tuned to global ice volume to refine the age model on glacial-interglacial timescales; (4) The averaged sediment accumulation rate is ~0.73 mm/kyr, agreeing with the estimate of the excess 230Th data in the upper part. Based on these results, a proxy of element Mn is derived, whose variability can be correlated with changes in global ice volume and deep-water masses on glacial-interglacial timescales. This record is also characterized by an evident 23-kyr cycle, highlighting a direct influence of solar insolation on deep-sea sedimentary processes. Overall, sedimentary archives of the Caiwei Guyot not only record an intensified abyssal ventilation during interglaciations in the western Pacific, but also provide a unique window for investigating the topography-induced linkage between the upper and bottom ocean on orbital timescales.
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16
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Li T, Robinson LF, Chen T, Wang XT, Burke A, Rae JWB, Pegrum-Haram A, Knowles TDJ, Li G, Chen J, Ng HC, Prokopenko M, Rowland GH, Samperiz A, Stewart JA, Southon J, Spooner PT. Rapid shifts in circulation and biogeochemistry of the Southern Ocean during deglacial carbon cycle events. SCIENCE ADVANCES 2020; 6:6/42/eabb3807. [PMID: 33067227 PMCID: PMC7567589 DOI: 10.1126/sciadv.abb3807] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Accepted: 08/25/2020] [Indexed: 06/11/2023]
Abstract
The Southern Ocean plays a crucial role in regulating atmospheric CO2 on centennial to millennial time scales. However, observations of sufficient resolution to explore this have been lacking. Here, we report high-resolution, multiproxy records based on precisely dated deep-sea corals from the Southern Ocean. Paired deep (∆14C and δ11B) and surface (δ15N) proxy data point to enhanced upwelling coupled with reduced efficiency of the biological pump at 14.6 and 11.7 thousand years (ka) ago, which would have facilitated rapid carbon release to the atmosphere. Transient periods of unusually well-ventilated waters in the deep Southern Ocean occurred at 16.3 and 12.8 ka ago. Contemporaneous atmospheric carbon records indicate that these Southern Ocean ventilation events are also important in releasing respired carbon from the deep ocean to the atmosphere. Our results thus highlight two distinct modes of Southern Ocean circulation and biogeochemistry associated with centennial-scale atmospheric CO2 jumps during the last deglaciation.
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Affiliation(s)
- Tao Li
- MOE Key Laboratory of Surficial Geochemistry, Department of Earth and Planetary Sciences, Nanjing University, Nanjing, China.
- School of Earth Sciences, University of Bristol, Bristol, UK
| | | | - Tianyu Chen
- MOE Key Laboratory of Surficial Geochemistry, Department of Earth and Planetary Sciences, Nanjing University, Nanjing, China
- School of Earth Sciences, University of Bristol, Bristol, UK
| | - Xingchen T Wang
- Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, MA, USA
| | - Andrea Burke
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
| | - James W B Rae
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
| | - Albertine Pegrum-Haram
- School of Earth Sciences, University of Bristol, Bristol, UK
- School of Earth Science and Engineering, Imperial College London, London, UK
| | - Timothy D J Knowles
- Bristol Radiocarbon Accelerator Mass Spectrometry Facility, School of Chemistry and School of Arts, University of Bristol, Bristol, UK
| | - Gaojun Li
- MOE Key Laboratory of Surficial Geochemistry, Department of Earth and Planetary Sciences, Nanjing University, Nanjing, China
| | - Jun Chen
- MOE Key Laboratory of Surficial Geochemistry, Department of Earth and Planetary Sciences, Nanjing University, Nanjing, China
| | - Hong Chin Ng
- School of Earth Sciences, University of Bristol, Bristol, UK
| | | | | | - Ana Samperiz
- School of Earth Sciences, University of Bristol, Bristol, UK
| | | | - John Southon
- School of Physical Sciences, University of California, Irvine, Irvine, CA, USA
| | - Peter T Spooner
- School of Earth Sciences, University of Bristol, Bristol, UK
- Department of Geography, University College London, London, UK
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17
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Nehrbass-Ahles C, Shin J, Schmitt J, Bereiter B, Joos F, Schilt A, Schmidely L, Silva L, Teste G, Grilli R, Chappellaz J, Hodell D, Fischer H, Stocker TF. Abrupt CO 2 release to the atmosphere under glacial and early interglacial climate conditions. Science 2020; 369:1000-1005. [PMID: 32820127 DOI: 10.1126/science.aay8178] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Accepted: 07/09/2020] [Indexed: 11/02/2022]
Abstract
Pulse-like carbon dioxide release to the atmosphere on centennial time scales has only been identified for the most recent glacial and deglacial periods and is thought to be absent during warmer climate conditions. Here, we present a high-resolution carbon dioxide record from 330,000 to 450,000 years before present, revealing pronounced carbon dioxide jumps (CDJ) under cold and warm climate conditions. CDJ come in two varieties that we attribute to invigoration or weakening of the Atlantic meridional overturning circulation (AMOC) and associated northward and southward shifts of the intertropical convergence zone, respectively. We find that CDJ are pervasive features of the carbon cycle that can occur during interglacial climate conditions if land ice masses are sufficiently extended to be able to disturb the AMOC by freshwater input.
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Affiliation(s)
- C Nehrbass-Ahles
- Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland. .,Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland.,Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge, UK
| | - J Shin
- Institute of Environmental Geosciences (IGE), Grenoble INP, IRD, CNRS, Université Grenoble Alpes, Grenoble, France
| | - J Schmitt
- Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland.,Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
| | - B Bereiter
- Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland.,Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland.,Laboratory for Air Pollution/Environmental Technology, Empa-Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland
| | - F Joos
- Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland.,Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
| | - A Schilt
- Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland.,Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
| | - L Schmidely
- Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland.,Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
| | - L Silva
- Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland.,Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
| | - G Teste
- Institute of Environmental Geosciences (IGE), Grenoble INP, IRD, CNRS, Université Grenoble Alpes, Grenoble, France
| | - R Grilli
- Institute of Environmental Geosciences (IGE), Grenoble INP, IRD, CNRS, Université Grenoble Alpes, Grenoble, France
| | - J Chappellaz
- Institute of Environmental Geosciences (IGE), Grenoble INP, IRD, CNRS, Université Grenoble Alpes, Grenoble, France
| | - D Hodell
- Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge, UK
| | - H Fischer
- Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland.,Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
| | - T F Stocker
- Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland.,Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
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18
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Deep Equatorial Pacific Ocean Oxygenation and Atmospheric CO 2 Over The Last Ice Age. Sci Rep 2020; 10:6606. [PMID: 32313063 PMCID: PMC7171191 DOI: 10.1038/s41598-020-63628-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Accepted: 04/03/2020] [Indexed: 11/08/2022] Open
Abstract
Ventilation of carbon stored in the deep ocean is thought to play an important role in atmospheric CO2 increases associated with Pleistocene deglaciations. The presence of this respired carbon has been recorded by an array of paleoceanographic proxies from various locations across the global ocean. Here we present a new sediment core from the Eastern Equatorial Pacific (EEP) Ocean spanning the last 180,000 years and reconstruct high-resolution 230Th-derived fluxes of 232Th and excess barium, along with redox-sensitive uranium concentrations to examine past variations in dust delivery, export productivity, and bottom-water oxygenation, respectively. Our bottom-water oxygenation record is compared to other similar high-resolution records from across the Pacific and in the Southern Ocean. We suggest that the deep Pacific is a site of respired carbon storage associated with periods of decreased global atmospheric CO2 concentration during the LGM, confirming the conclusions from a wealth of previous studies. However, our study is the first to show a similar relationship beyond the last glacial, extending to at least 70,000 years.
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19
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20
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Huang H, Gutjahr M, Eisenhauer A, Kuhn G. No detectable Weddell Sea Antarctic Bottom Water export during the Last and Penultimate Glacial Maximum. Nat Commun 2020; 11:424. [PMID: 31969564 PMCID: PMC6976697 DOI: 10.1038/s41467-020-14302-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Accepted: 12/18/2019] [Indexed: 11/30/2022] Open
Abstract
Weddell Sea-derived Antarctic Bottom Water (AABW) is one of the most important deep water masses in the Southern Hemisphere occupying large portions of the deep Southern Ocean (SO) today. While substantial changes in SO-overturning circulation were previously suggested, the state of Weddell Sea AABW export during glacial climates remains poorly understood. Here we report seawater-derived Nd and Pb isotope records that provide evidence for the absence of Weddell Sea-derived AABW in the Atlantic sector of the SO during the last two glacial maxima. Increasing delivery of Antarctic Pb to regions outside the Weddell Sea traced SO frontal displacements during both glacial terminations. The export of Weddell Sea-derived AABW resumed late during glacial terminations, coinciding with the last major atmospheric CO2 rise in the transition to the Holocene and the Eemian. Our new records lend strong support for a previously inferred AABW overturning stagnation event during the peak Eemian interglacial. The Southern Ocean plays a key role in glacial-interglacial transitions and today, Weddell Sea derived Antarctic Bottom Water is one of the most important deep water masses. New records show that in contrast to today, no Weddell Sea water was exported during the last two glacial maxima, providing new insights towards the condition of Antarctic Bottom Water formation in extreme climate states.
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Affiliation(s)
- Huang Huang
- GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstraße 1-3, 24148, Kiel, Germany.
| | - Marcus Gutjahr
- GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstraße 1-3, 24148, Kiel, Germany
| | - Anton Eisenhauer
- GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstraße 1-3, 24148, Kiel, Germany
| | - Gerhard Kuhn
- Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Am Alten Hafen 26, 27568, Bremerhaven, Germany
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21
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Kubota K, Yokoyama Y, Ishikawa T, Sagawa T, Ikehara M, Yamazaki T. Equatorial Pacific seawater pCO 2 variability since the last glacial period. Sci Rep 2019; 9:13814. [PMID: 31554821 PMCID: PMC6761199 DOI: 10.1038/s41598-019-49739-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Accepted: 08/30/2019] [Indexed: 11/24/2022] Open
Abstract
The ocean may have played a central role in the atmospheric pCO2 rise during the last deglaciation. However, evidence on where carbon was exchanged between the ocean and the atmosphere in this period is still lacking, hampering our understanding of global carbon cycle on glacial-interglacial timescales. Here we report a new surface seawater pCO2 reconstruction for the western equatorial Pacific Ocean based on boron isotope analysis-a seawater pCO2 proxy-using two species of near-surface dwelling foraminifera from the same marine sediment core. The results indicate that the region remained a modest CO2 sink throughout the last deglaciation.
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Affiliation(s)
- Kaoru Kubota
- Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku, Japan.
| | - Yusuke Yokoyama
- Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan
| | - Tsuyoshi Ishikawa
- Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku, Japan
| | - Takuya Sagawa
- Institute of Science and Engineering, Kanazawa University, Kanazawa, Japan
| | - Minoru Ikehara
- Center for Advanced Marine Core Research, Kochi University, Nankoku, Japan
| | - Toshitsugu Yamazaki
- Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan
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22
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MacGilchrist GA, Naveira Garabato AC, Brown PJ, Jullion L, Bacon S, Bakker DCE, Hoppema M, Meredith MP, Torres-Valdés S. Reframing the carbon cycle of the subpolar Southern Ocean. SCIENCE ADVANCES 2019; 5:eaav6410. [PMID: 31489364 PMCID: PMC6713492 DOI: 10.1126/sciadv.aav6410] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Accepted: 07/18/2019] [Indexed: 05/24/2023]
Abstract
Global climate is critically sensitive to physical and biogeochemical dynamics in the subpolar Southern Ocean, since it is here that deep, carbon-rich layers of the world ocean outcrop and exchange carbon with the atmosphere. Here, we present evidence that the conventional framework for the subpolar Southern Ocean carbon cycle, which attributes a dominant role to the vertical overturning circulation and shelf-sea processes, fundamentally misrepresents the drivers of regional carbon uptake. Observations in the Weddell Gyre-a key representative region of the subpolar Southern Ocean-show that the rate of carbon uptake is set by an interplay between the Gyre's horizontal circulation and the remineralization at mid-depths of organic carbon sourced from biological production in the central gyre. These results demonstrate that reframing the carbon cycle of the subpolar Southern Ocean is an essential step to better define its role in past and future climate change.
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Affiliation(s)
| | | | | | - Loïc Jullion
- Aix-Marseille Univ, Université de Toulon, CNRS, IRD, MIO, UM 110, Marseille, France
| | - Sheldon Bacon
- National Oceanography Centre, Southampton SO14 3ZH, UK
| | - Dorothee C. E. Bakker
- Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK
| | - Mario Hoppema
- Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
| | | | - Sinhué Torres-Valdés
- Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
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23
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More efficient North Atlantic carbon pump during the Last Glacial Maximum. Nat Commun 2019; 10:2170. [PMID: 31092826 PMCID: PMC6520411 DOI: 10.1038/s41467-019-10028-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2018] [Accepted: 04/12/2019] [Indexed: 11/13/2022] Open
Abstract
During the Last Glacial Maximum (LGM; ~20,000 years ago), the global ocean sequestered a large amount of carbon lost from the atmosphere and terrestrial biosphere. Suppressed CO2 outgassing from the Southern Ocean is the prevailing explanation for this carbon sequestration. By contrast, the North Atlantic Ocean—a major conduit for atmospheric CO2 transport to the ocean interior via the overturning circulation—has received much less attention. Here we demonstrate that North Atlantic carbon pump efficiency during the LGM was almost doubled relative to the Holocene. This is based on a novel proxy approach to estimate air–sea CO2 exchange signals using combined carbonate ion and nutrient reconstructions for multiple sediment cores from the North Atlantic. Our data indicate that in tandem with Southern Ocean processes, enhanced North Atlantic CO2 absorption contributed to lowering ice-age atmospheric CO2. Atmospheric CO2 is governed by CO2 gains (e.g., via Southern Ocean outgassing) and losses (e.g., via North Atlantic absorption). Using a novel method to estimate air–sea CO2 exchange signals, the authors show that North Atlantic CO2 absorption became more efficient and contributed to lowering atmospheric CO2 during ice ages.
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24
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Hu R, Piotrowski AM. Neodymium isotope evidence for glacial-interglacial variability of deepwater transit time in the Pacific Ocean. Nat Commun 2018; 9:4709. [PMID: 30413704 PMCID: PMC6226442 DOI: 10.1038/s41467-018-07079-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2018] [Accepted: 10/10/2018] [Indexed: 11/25/2022] Open
Abstract
There is evidence for greater carbon storage in the glacial deep Pacific, but it is uncertain whether it was caused by changes in ventilation, circulation, and biological productivity. The spatial εNd evolution in the deep Pacific provides information on the deepwater transit time. Seven new foraminiferal εNd records are presented to systematically constrain glacial to interglacial changes in deep Pacific overturning and two different εNd evolution regimes occur spatially in the Pacific with reduced meridional εNd gradients in glacials, suggesting a faster deep Pacific overturning circulation. This implies that greater glacial carbon storage due to sluggish circulation, that is believed to have occurred in the deep Atlantic, did not operate in a similar manner in the Pacific Ocean. Other mechanisms such as increased biological pump efficiency and poor high latitude air-sea exchange could be responsible for increased carbon storage in the glacial Pacific. The response of deep Pacific overturning to glacial-interglacial climate change is still debated. Here the authors show a generally faster deep Pacific overturning operated in recent glacial periods based on a novel application of Nd isotopes recorded in foraminifera.
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Affiliation(s)
- Rong Hu
- School of Geography and Ocean Science, Nanjing University, 210023, Nanjing, China. .,Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, UK.
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25
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Rae JWB, Burke A, Robinson LF, Adkins JF, Chen T, Cole C, Greenop R, Li T, Littley EFM, Nita DC, Stewart JA, Taylor BJ. CO 2 storage and release in the deep Southern Ocean on millennial to centennial timescales. Nature 2018; 562:569-573. [PMID: 30356182 DOI: 10.1038/s41586-018-0614-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Accepted: 08/29/2018] [Indexed: 11/09/2022]
Abstract
The cause of changes in atmospheric carbon dioxide (CO2) during the recent ice ages is yet to be fully explained. Most mechanisms for glacial-interglacial CO2 change have centred on carbon exchange with the deep ocean, owing to its large size and relatively rapid exchange with the atmosphere1. The Southern Ocean is thought to have a key role in this exchange, as much of the deep ocean is ventilated to the atmosphere in this region2. However, it is difficult to reconstruct changes in deep Southern Ocean carbon storage, so few direct tests of this hypothesis have been carried out. Here we present deep-sea coral boron isotope data that track the pH-and thus the CO2 chemistry-of the deep Southern Ocean over the past forty thousand years. At sites closest to the Antarctic continental margin, and most influenced by the deep southern waters that form the ocean's lower overturning cell, we find a close relationship between ocean pH and atmospheric CO2: during intervals of low CO2, ocean pH is low, reflecting enhanced ocean carbon storage; and during intervals of rising CO2, ocean pH rises, reflecting loss of carbon from the ocean to the atmosphere. Correspondingly, at shallower sites we find rapid (millennial- to centennial-scale) decreases in pH during abrupt increases in CO2, reflecting the rapid transfer of carbon from the deep ocean to the upper ocean and atmosphere. Our findings confirm the importance of the deep Southern Ocean in ice-age CO2 change, and show that deep-ocean CO2 release can occur as a dynamic feedback to rapid climate change on centennial timescales.
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Affiliation(s)
- J W B Rae
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK.
| | - A Burke
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
| | - L F Robinson
- School of Earth Sciences, University of Bristol, Bristol, UK
| | - J F Adkins
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
| | - T Chen
- School of Earth Sciences, University of Bristol, Bristol, UK.,School of Earth Sciences and Engineering, Nanjing University, Nanjing, China
| | - C Cole
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
| | - R Greenop
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
| | - T Li
- School of Earth Sciences, University of Bristol, Bristol, UK.,School of Earth Sciences and Engineering, Nanjing University, Nanjing, China
| | - E F M Littley
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
| | - D C Nita
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK.,Faculty of Environmental Science and Engineering, Babes-Bolyai University, Cluj-Napoca, Romania
| | - J A Stewart
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK.,School of Earth Sciences, University of Bristol, Bristol, UK
| | - B J Taylor
- School of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
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26
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Enhanced ocean-atmosphere carbon partitioning via the carbonate counter pump during the last deglacial. Nat Commun 2018; 9:2396. [PMID: 29921874 PMCID: PMC6008475 DOI: 10.1038/s41467-018-04625-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Accepted: 05/08/2018] [Indexed: 11/18/2022] Open
Abstract
Several synergistic mechanisms were likely involved in the last deglacial atmospheric pCO2 rise. Leading hypotheses invoke a release of deep-ocean carbon through enhanced convection in the Southern Ocean (SO) and concomitant decreased efficiency of the global soft-tissue pump (STP). However, the temporal evolution of both the STP and the carbonate counter pump (CCP) remains unclear, thus preventing the evaluation of their contributions to the pCO2 rise. Here we present sedimentary coccolith records combined with export production reconstructions from the Subantarctic Pacific to document the leverage the SO biological carbon pump (BCP) has imposed on deglacial pCO2. Our data suggest a weakening of BCP during the phases of carbon outgassing, due in part to an increased CCP along with higher surface ocean fertility and elevated [CO2aq]. We propose that reduced BCP efficiency combined with enhanced SO ventilation played a major role in propelling the Earth out of the last ice age. The contribution of the carbonate counter pump (CCP) to the last deglacial atmospheric CO2 rise has yet been largely ignored. Here, the authors show that an increased CCP in the Subantarctic Pacific along with high surface ocean fertility and [CO2aq], contributed in propelling the Earth out of the last ice age.
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27
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Jacobel AW, McManus JF, Anderson RF, Winckler G. Repeated storage of respired carbon in the equatorial Pacific Ocean over the last three glacial cycles. Nat Commun 2017; 8:1727. [PMID: 29167433 PMCID: PMC5700088 DOI: 10.1038/s41467-017-01938-x] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Accepted: 10/26/2017] [Indexed: 12/02/2022] Open
Abstract
As the largest reservoir of carbon exchanging with the atmosphere on glacial–interglacial timescales, the deep ocean has been implicated as the likely location of carbon sequestration during Pleistocene glaciations. Despite strong theoretical underpinning for this expectation, radiocarbon data on watermass ventilation ages conflict, and proxy interpretations disagree about the depth, origin and even existence of the respired carbon pool. Because any change in the storage of respiratory carbon is accompanied by corresponding changes in dissolved oxygen concentrations, proxy data reflecting oxygenation are valuable in addressing these apparent inconsistencies. Here, we present a record of redox-sensitive uranium from the central equatorial Pacific Ocean to identify intervals associated with respiratory carbon storage over the past 350 kyr, providing evidence for repeated carbon storage over the last three glacial cycles. We also synthesise our data with previous work and propose an internally consistent picture of glacial carbon storage and equatorial Pacific Ocean watermass structure. During glacial periods the oceans stored carbon removed from the atmosphere, yet identifying precisely where that storage occurred remains challenging. Here, the authors show that the deep equatorial Pacific Ocean was a reservoir for respired carbon during glacial periods for at least the last 350 kyr.
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Affiliation(s)
- A W Jacobel
- Department of Earth and Environmental Sciences, Columbia University, New York, 10027, NY, USA. .,Lamont-Doherty Earth Observatory, Palisades, 10964, NY, USA.
| | - J F McManus
- Department of Earth and Environmental Sciences, Columbia University, New York, 10027, NY, USA.,Lamont-Doherty Earth Observatory, Palisades, 10964, NY, USA
| | - R F Anderson
- Department of Earth and Environmental Sciences, Columbia University, New York, 10027, NY, USA.,Lamont-Doherty Earth Observatory, Palisades, 10964, NY, USA
| | - G Winckler
- Department of Earth and Environmental Sciences, Columbia University, New York, 10027, NY, USA.,Lamont-Doherty Earth Observatory, Palisades, 10964, NY, USA
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28
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Tagliabue A, Bowie AR, Boyd PW, Buck KN, Johnson KS, Saito MA. The integral role of iron in ocean biogeochemistry. Nature 2017; 543:51-59. [PMID: 28252066 DOI: 10.1038/nature21058] [Citation(s) in RCA: 147] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Accepted: 12/06/2016] [Indexed: 11/09/2022]
Abstract
The micronutrient iron is now recognized to be important in regulating the magnitude and dynamics of ocean primary productivity, making it an integral component of the ocean's biogeochemical cycles. In this Review, we discuss how a recent increase in observational data for this trace metal has challenged the prevailing view of the ocean iron cycle. Instead of focusing on dust as the major iron source and emphasizing iron's tight biogeochemical coupling to major nutrients, a more complex and diverse picture of the sources of iron, its cycling processes and intricate linkages with the ocean carbon and nitrogen cycles has emerged.
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Affiliation(s)
- Alessandro Tagliabue
- Department of Earth Ocean and Ecological Sciences, School of Environmental Sciences, University of Liverpool, Liverpool, UK
| | - Andrew R Bowie
- Institute for Marine and Antarctic Studies and Antarctic Climate and Ecosystems Co-operative Research Centre, University of Tasmania, Hobart, Australia
| | - Philip W Boyd
- Institute for Marine and Antarctic Studies and Antarctic Climate and Ecosystems Co-operative Research Centre, University of Tasmania, Hobart, Australia
| | | | | | - Mak A Saito
- Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
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29
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Frisia S, Weyrich LS, Hellstrom J, Borsato A, Golledge NR, Anesio AM, Bajo P, Drysdale RN, Augustinus PC, Rivard C, Cooper A. The influence of Antarctic subglacial volcanism on the global iron cycle during the Last Glacial Maximum. Nat Commun 2017; 8:15425. [PMID: 28598412 PMCID: PMC5472753 DOI: 10.1038/ncomms15425] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2016] [Accepted: 03/27/2017] [Indexed: 11/09/2022] Open
Abstract
Marine sediment records suggest that episodes of major atmospheric CO2 drawdown during the last glacial period were linked to iron (Fe) fertilization of subantarctic surface waters. The principal source of this Fe is thought to be dust transported from southern mid-latitude deserts. However, uncertainty exists over contributions to CO2 sequestration from complementary Fe sources, such as the Antarctic ice sheet, due to the difficulty of locating and interrogating suitable archives that have the potential to preserve such information. Here we present petrographic, geochemical and microbial DNA evidence preserved in precisely dated subglacial calcites from close to the East Antarctic Ice-Sheet margin, which together suggest that volcanically-induced drainage of Fe-rich waters during the Last Glacial Maximum could have reached the Southern Ocean. Our results support a significant contribution of Antarctic volcanism to subglacial transport and delivery of nutrients with implications on ocean productivity at peak glacial conditions.
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Affiliation(s)
- Silvia Frisia
- School of Environmental and Life Sciences, The University of Newcastle, Callaghan, New South Wales 2308, Australia
| | - Laura S. Weyrich
- Australian Centre for Ancient DNA (ACAD), The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - John Hellstrom
- School of Earth Sciences, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Andrea Borsato
- School of Environmental and Life Sciences, The University of Newcastle, Callaghan, New South Wales 2308, Australia
| | - Nicholas R. Golledge
- Antarctic Research Centre, Victoria University of Wellington, Wellington 6140, New Zealand
- GNS Science, Avalon, Lower Hut 5011, New Zealand
| | - Alexandre M. Anesio
- Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UK
| | - Petra Bajo
- School of Geography, The University of Melbourne, Parkville, Victoria 3010, Australia
| | - Russell N. Drysdale
- School of Geography, The University of Melbourne, Parkville, Victoria 3010, Australia
- Environnements, Dynamiques et Territoires de la Montagne, UMR CNRS, Université de Savoie-Mont Blanc, 73376 Le Bourget du Lac, France
| | - Paul C. Augustinus
- School of Environment, The University of Auckland, Private Bag, Auckland 92019, New Zealand
| | - Camille Rivard
- European Synchrotron Radiation Facility, 38000 Grenoble, France
| | - Alan Cooper
- Australian Centre for Ancient DNA (ACAD), The University of Adelaide, Adelaide, South Australia 5005, Australia
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30
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Punctuated Shutdown of Atlantic Meridional Overturning Circulation during Greenland Stadial 1. Sci Rep 2016; 6:25902. [PMID: 27194601 PMCID: PMC4872135 DOI: 10.1038/srep25902] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2015] [Accepted: 04/21/2016] [Indexed: 11/08/2022] Open
Abstract
The Greenland Stadial 1 (GS-1; ~12.9 to 11.65 kyr cal BP) was a period of North Atlantic cooling, thought to have been initiated by North America fresh water runoff that caused a sustained reduction of North Atlantic Meridional Overturning Circulation (AMOC), resulting in an antiphase temperature response between the hemispheres (the 'bipolar seesaw'). Here we exploit sub-fossil New Zealand kauri trees to report the first securely dated, decadally-resolved atmospheric radiocarbon ((14)C) record spanning GS-1. By precisely aligning Southern and Northern Hemisphere tree-ring (14)C records with marine (14)C sequences we document two relatively short periods of AMOC collapse during the stadial, at ~12,920-12,640 cal BP and 12,050-11,900 cal BP. In addition, our data show that the interhemispheric atmospheric (14)C offset was close to zero prior to GS-1, before reaching 'near-modern' values at ~12,660 cal BP, consistent with synchronous recovery of overturning in both hemispheres and increased Southern Ocean ventilation. Hence, sustained North Atlantic cooling across GS-1 was not driven by a prolonged AMOC reduction but probably due to an equatorward migration of the Polar Front, reducing the advection of southwesterly air masses to high latitudes. Our findings suggest opposing hemispheric temperature trends were driven by atmospheric teleconnections, rather than AMOC changes.
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31
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Gottschalk J, Skinner LC, Lippold J, Vogel H, Frank N, Jaccard SL, Waelbroeck C. Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes. Nat Commun 2016; 7:11539. [PMID: 27187527 PMCID: PMC4873644 DOI: 10.1038/ncomms11539] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2015] [Accepted: 04/06/2016] [Indexed: 11/09/2022] Open
Abstract
Millennial-scale climate changes during the last glacial period and deglaciation were accompanied by rapid changes in atmospheric CO2 that remain unexplained. While the role of the Southern Ocean as a 'control valve' on ocean-atmosphere CO2 exchange has been emphasized, the exact nature of this role, in particular the relative contributions of physical (for example, ocean dynamics and air-sea gas exchange) versus biological processes (for example, export productivity), remains poorly constrained. Here we combine reconstructions of bottom-water [O2], export production and (14)C ventilation ages in the sub-Antarctic Atlantic, and show that atmospheric CO2 pulses during the last glacial- and deglacial periods were consistently accompanied by decreases in the biological export of carbon and increases in deep-ocean ventilation via southern-sourced water masses. These findings demonstrate how the Southern Ocean's 'organic carbon pump' has exerted a tight control on atmospheric CO2, and thus global climate, specifically via a synergy of both physical and biological processes.
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Affiliation(s)
- Julia Gottschalk
- Godwin Laboratory for Palaeoclimate Research, Earth Sciences Department, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
| | - Luke C Skinner
- Godwin Laboratory for Palaeoclimate Research, Earth Sciences Department, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
| | - Jörg Lippold
- Institute of Geological Sciences and Oeschger Center for Climate Change Research, University of Bern, Baltzerstr. 1-3, Bern 3012, Switzerland
| | - Hendrik Vogel
- Institute of Geological Sciences and Oeschger Center for Climate Change Research, University of Bern, Baltzerstr. 1-3, Bern 3012, Switzerland
| | - Norbert Frank
- Institute of Environmental Physics, University of Heidelberg, Im Neuenheimer Feld 229, Heidelberg 69120, Germany
| | - Samuel L Jaccard
- Institute of Geological Sciences and Oeschger Center for Climate Change Research, University of Bern, Baltzerstr. 1-3, Bern 3012, Switzerland
| | - Claire Waelbroeck
- Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CNRS-CEA-UVSQ, Université de Paris-Saclay, Domaine du CNRS, bât. 12, Gif-sur-Yvette 91198, France
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32
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Lu Z, Hoogakker BAA, Hillenbrand CD, Zhou X, Thomas E, Gutchess KM, Lu W, Jones L, Rickaby REM. Oxygen depletion recorded in upper waters of the glacial Southern Ocean. Nat Commun 2016; 7:11146. [PMID: 27029225 PMCID: PMC4821880 DOI: 10.1038/ncomms11146] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2015] [Accepted: 02/24/2016] [Indexed: 11/08/2022] Open
Abstract
Oxygen depletion in the upper ocean is commonly associated with poor ventilation and storage of respired carbon, potentially linked to atmospheric CO2 levels. Iodine to calcium ratios (I/Ca) in recent planktonic foraminifera suggest that values less than ∼2.5 μmol mol(-1) indicate the presence of O2-depleted water. Here we apply this proxy to estimate past dissolved oxygen concentrations in the near surface waters of the currently well-oxygenated Southern Ocean, which played a critical role in carbon sequestration during glacial times. A down-core planktonic I/Ca record from south of the Antarctic Polar Front (APF) suggests that minimum O2 concentrations in the upper ocean fell below 70 μmol kg(-1) during the last two glacial periods, indicating persistent glacial O2 depletion at the heart of the carbon engine of the Earth's climate system. These new estimates of past ocean oxygenation variability may assist in resolving mechanisms responsible for the much-debated ice-age atmospheric CO2 decline.
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Affiliation(s)
- Zunli Lu
- Department of Earth Sciences, Syracuse University, Syracuse, New York 13244, USA
| | | | | | - Xiaoli Zhou
- Department of Earth Sciences, Syracuse University, Syracuse, New York 13244, USA
| | - Ellen Thomas
- Department of Geology and Geophysics, Yale University, New Haven, Connecticut, USA
| | - Kristina M. Gutchess
- Department of Earth Sciences, Syracuse University, Syracuse, New York 13244, USA
| | - Wanyi Lu
- Department of Earth Sciences, Syracuse University, Syracuse, New York 13244, USA
| | - Luke Jones
- Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, UK
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