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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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2
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Muglia J, Mulitza S, Repschläger J, Schmittner A, Lembke-Jene L, Lisiecki L, Mix A, Saraswat R, Sikes E, Waelbroeck C, Gottschalk J, Lippold J, Lund D, Martinez-Mendez G, Michel E, Muschitiello F, Naik S, Okazaki Y, Stott L, Voelker A, Zhao N. A global synthesis of high-resolution stable isotope data from benthic foraminifera of the last deglaciation. Sci Data 2023; 10:131. [PMID: 36899009 PMCID: PMC10006181 DOI: 10.1038/s41597-023-02024-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Accepted: 02/14/2023] [Indexed: 03/12/2023] Open
Abstract
We present the first version of the Ocean Circulation and Carbon Cycling (OC3) working group database, of oxygen and carbon stable isotope ratios from benthic foraminifera in deep ocean sediment cores from the Last Glacial Maximum (LGM, 23-19 ky) to the Holocene (<10 ky) with a particular focus on the early last deglaciation (19-15 ky BP). It includes 287 globally distributed coring sites, with metadata, isotopic and chronostratigraphic information, and age models. A quality check was performed for all data and age models, and sites with at least millennial resolution were preferred. Deep water mass structure as well as differences between the early deglaciation and LGM are captured by the data, even though its coverage is still sparse in many regions. We find high correlations among time series calculated with different age models at sites that allow such analysis. The database provides a useful dynamical approach to map physical and biogeochemical changes of the ocean throughout the last deglaciation.
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Affiliation(s)
- Juan Muglia
- Centro para el Estudio de los Sistemas Marinos, CONICET, 2915 Boulevard Brown, U9120ACD, Puerto Madryn, Argentina.
| | - Stefan Mulitza
- MARUM - Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
| | - Janne Repschläger
- Department of Climate Geochemistry, Max Planck Institute for Chemistry, Hahn-Meitner Weg 1, 55128, Mainz, Germany
| | - Andreas Schmittner
- College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA
| | - Lester Lembke-Jene
- Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
| | - Lorraine Lisiecki
- Department of Earth Science, University of California, Santa Barbara, CA, 93106, USA
| | - Alan Mix
- College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA
| | - Rajeev Saraswat
- Micropaleontology Laboratory, Geological Oceanography Division, National Institute of Oceanography, Goa, India
| | - Elizabeth Sikes
- Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA
| | - Claire Waelbroeck
- LOCEAN/IPSL, Sorbonne Université-CNRS-IRD-MNHN, UMR7159, Paris, France
| | | | - Jörg Lippold
- Institute of Earth Sciences, Heidelberg University, Heidelberg, Germany
| | - David Lund
- Department of Marine Sciences, University of Connecticut - Avery Point, Groton, CT, 06340, USA
| | - Gema Martinez-Mendez
- Helmholtz Institute for Functional Marine Biodiversity at the University of Oldenburg (HIFMB), Ammerländer Heerstrasse 231, D-26129, Oldenburg, Germany
| | - Elisabeth Michel
- LSCE-IPSL (CEA-CNRS-UVSQ), Paris-Saclay University, 91190, Gif-sur Yvette, France
| | - Francesco Muschitiello
- Department of Geography, University of Cambridge, Cambridge, CB2 3EQ, UK
- Centre for Climate Repair at Cambridge, Downing College, Cambridge, CB2 1DQ, UK
| | - Sushant Naik
- CSIR-National Institute of Oceanography, Dona Paula, Goa, India
| | - Yusuke Okazaki
- Graduate School of Science, Kyushu University, Nishi-ku, Fukuoka, 819-0395, Japan
| | - Lowell Stott
- Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA
| | - Antje Voelker
- Instituto Portuguēs do Mar e da Atmosfera, Divisâo de Geologia e Georecursos Marinhos, Av. Doutor Alfredo Magalhâes Ramalho 6, 1495-165, Alges, Portugal
- Centre of Marine Sciences, Universidade do Algarve, Faro, Portugal
| | - Ning Zhao
- State Key Laboratory of Estuarine and Coastal Research & School of Marine Science, East China Normal University, Dongchuan Rd 500, 200241, Shanghai, China
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3
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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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4
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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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5
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Planktonic foraminifera organic carbon isotopes as archives of upper ocean carbon cycling. Nat Commun 2022; 13:4841. [PMID: 35977937 PMCID: PMC9386020 DOI: 10.1038/s41467-022-32480-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Accepted: 08/01/2022] [Indexed: 11/25/2022] Open
Abstract
The carbon cycle is a key regulator of Earth’s climate. On geological time-scales, our understanding of particulate organic matter (POM), an important upper ocean carbon pool that fuels ecosystems and an integrated part of the carbon cycle, is limited. Here we investigate the relationship of planktonic foraminifera-bound organic carbon isotopes (δ13Corg-pforam) with δ13Corg of POM (δ13Corg-POM). We compare δ13Corg-pforam of several planktonic foraminifera species from plankton nets and recent sediment cores with δ13Corg-POM on a N-S Atlantic Ocean transect. Our results indicate that δ13Corg-pforam of planktonic foraminifera are remarkably similar to δ13Corg-POM. Application of our method on a glacial sample furthermore provided a δ13Corg-pforam value similar to glacial δ13Corg-POM predictions. We thus show that δ13Corg-pforam is a promising proxy to reconstruct environmental conditions in the upper ocean, providing a route to isolate past variations in δ13Corg-POM and better understanding of the evolution of the carbon cycle over geological time-scales. Our understanding of ancient organic carbon cycling in marine environments is limited. Here the authors developed a method to reconstruct upper ocean organic carbon chemistry in the geological past, which when applied, can help to create a better understanding of the evolution of the carbon cycle.
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6
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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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7
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Woehle C, Roy AS, Glock N, Michels J, Wein T, Weissenbach J, Romero D, Hiebenthal C, Gorb SN, Schönfeld J, Dagan T. Denitrification in foraminifera has an ancient origin and is complemented by associated bacteria. Proc Natl Acad Sci U S A 2022; 119:e2200198119. [PMID: 35704763 PMCID: PMC9231491 DOI: 10.1073/pnas.2200198119] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2022] [Accepted: 05/05/2022] [Indexed: 11/18/2022] Open
Abstract
Benthic foraminifera are unicellular eukaryotes that inhabit sediments of aquatic environments. Several foraminifera of the order Rotaliida are known to store and use nitrate for denitrification, a unique energy metabolism among eukaryotes. The rotaliid Globobulimina spp. has been shown to encode an incomplete denitrification pathway of bacterial origin. However, the prevalence of denitrification genes in foraminifera remains unknown, and the missing denitrification pathway components are elusive. Analyzing transcriptomes and metagenomes of 10 foraminiferal species from the Peruvian oxygen minimum zone, we show that denitrification genes are highly conserved in foraminifera. We infer the last common ancestor of denitrifying foraminifera, which enables us to predict the ability to denitrify for additional foraminiferal species. Additionally, an examination of the foraminiferal microbiota reveals evidence for a stable interaction with Desulfobacteraceae, which harbor genes that complement the foraminiferal denitrification pathway. Our results provide evidence that foraminiferal denitrification is complemented by the foraminifera-associated microbiome. The interaction of foraminifera with their resident bacteria is at the basis of foraminiferal adaptation to anaerobic environments that manifested in ecological success in oxygen depleted habitats.
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Affiliation(s)
- Christian Woehle
- Institute of General Microbiology, Kiel University, Kiel 24118, Germany
| | | | - Nicolaas Glock
- GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel 24148, Germany
| | - Jan Michels
- Zoological Institute, Kiel University, Kiel 24118, Germany
| | - Tanita Wein
- Institute of General Microbiology, Kiel University, Kiel 24118, Germany
| | - Julia Weissenbach
- Institute of General Microbiology, Kiel University, Kiel 24118, Germany
| | - Dennis Romero
- Dirección General de Investigaciones Oceanográficas y Cambio Climático, Instituto del Mar del Perú, Callao 01, Peru 17
| | - Claas Hiebenthal
- GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel 24148, Germany
| | | | - Joachim Schönfeld
- GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel 24148, Germany
| | - Tal Dagan
- Institute of General Microbiology, Kiel University, Kiel 24118, Germany
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8
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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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9
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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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10
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Galbraith ED, Skinner LC. The Biological Pump During the Last Glacial Maximum. ANNUAL REVIEW OF MARINE SCIENCE 2020; 12:559-586. [PMID: 31899673 DOI: 10.1146/annurev-marine-010419-010906] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Much of the global cooling during ice ages arose from changes in ocean carbon storage that lowered atmospheric CO2. A slew of mechanisms, both physical and biological, have been proposed as key drivers of these changes. Here we discuss the current understanding of these mechanisms with a focus on how they altered the theoretically defined soft-tissue and biological disequilibrium carbon storage at the peak of the last ice age. Observations and models indicate a role for Antarctic sea ice through its influence on ocean circulation patterns, but other mechanisms, including changes in biological processes, must have been important as well, and may have been coordinated through links with global air temperature. Further research is required to better quantify the contributions of the various mechanisms, and there remains great potential to use the Last Glacial Maximum and the ensuing global warming as natural experiments from which to learn about climate-driven changes in the marine ecosystem.
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Affiliation(s)
- Eric D Galbraith
- Department of Earth and Planetary Sciences, McGill University, Montreal H3A 0E8, Canada;
- Institut de Ciència i Tecnologia Ambientals (ICTA-UAB), Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain
| | - Luke C Skinner
- Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, United Kingdom;
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11
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Marine nitrogen fixers mediate a low latitude pathway for atmospheric CO 2 drawdown. Nat Commun 2019; 10:4611. [PMID: 31601810 PMCID: PMC6787065 DOI: 10.1038/s41467-019-12549-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Accepted: 09/16/2019] [Indexed: 02/02/2023] Open
Abstract
Roughly a third (~30 ppm) of the carbon dioxide (CO2) that entered the ocean during ice ages is attributed to biological mechanisms. A leading hypothesis for the biological drawdown of CO2 is iron (Fe) fertilisation of the high latitudes, but modelling efforts attribute at most 10 ppm to this mechanism, leaving ~20 ppm unexplained. We show that an Fe-induced stimulation of dinitrogen (N2) fixation can induce a low latitude drawdown of 7–16 ppm CO2. This mechanism involves a closer coupling between N2 fixers and denitrifiers that alleviates widespread nitrate limitation. Consequently, phosphate utilisation and carbon export increase near upwelling zones, causing deoxygenation and deeper carbon injection. Furthermore, this low latitude mechanism reproduces the regional patterns of organic δ15N deposited in glacial sediments. The positive response of marine N2 fixation to dusty ice age conditions, first proposed twenty years ago, therefore compliments high latitude changes to amplify CO2 drawdown. Iron fertilisation of the high latitude oceans is a well-established biological mechanism to explain the ice age drawdown of atmospheric CO2, yet modelling has so far struggled to account for a sufficient drawdown via this mechanism. Here, the authors propose that N2 fixers, which inhabit the lower latitude ocean, made a significant contribution to CO2 drawdown and so amplified the global response to iron fertilisation during ice ages.
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