1
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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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2
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Robinson RS, Smart SM, Cybulski JD, McMahon KW, Marcks B, Nowakowski C. Insights from Fossil-Bound Nitrogen Isotopes in Diatoms, Foraminifera, and Corals. ANNUAL REVIEW OF MARINE SCIENCE 2023; 15:407-430. [PMID: 35977410 DOI: 10.1146/annurev-marine-032122-104001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Nitrogen is a major limiting element for biological productivity, and thus understanding past variations in nitrogen cycling is central to understanding past and future ocean biogeochemical cycling, global climate cycles, and biodiversity. Organic nitrogen encapsulated in fossil biominerals is generally protected from alteration, making it an important archive of the marine nitrogen cycle on seasonal to million-year timescales. The isotopic composition of fossil-bound nitrogen reflects variations in the large-scale nitrogen inventory, local sources and processing, and ecological and physiological traits of organisms. The ability to measure trace amounts of fossil-bound nitrogen has expanded with recent method developments. In this article, we review the foundations and ground truthing for three important fossil-bound proxy types: diatoms, foraminifera, and corals. We highlight their utility with examples of high-resolution evidence for anthropogenic inputs of nitrogen to the oceans, glacial-interglacial-scale assessments of nitrogen inventory change, and evidence for enhanced CO2 drawdown in the high-latitude ocean. Future directions include expanded method development, characterization of ecological and physiological variation, and exploration of extended timescales to push reconstructions further back in Earth's history.
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Affiliation(s)
- Rebecca S Robinson
- Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA; , , , ,
| | - Sandi M Smart
- Department of Geological Sciences, University of Alabama, Tuscaloosa, Alabama, USA;
| | - Jonathan D Cybulski
- Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA; , , , ,
- Smithsonian Tropical Research Institute, Balboa, Republic of Panama
| | - Kelton W McMahon
- Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA; , , , ,
| | - Basia Marcks
- Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA; , , , ,
| | - Catherine Nowakowski
- Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA; , , , ,
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3
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Lüdecke T, Leichliter JN, Aldeias V, Bamford MK, Biro D, Braun DR, Capelli C, Cybulski JD, Duprey NN, Ferreira da Silva MJ, Foreman AD, Habermann JM, Haug GH, Martínez FI, Mathe J, Mulch A, Sigman DM, Vonhof H, Bobe R, Carvalho S, Martínez-García A. Carbon, nitrogen, and oxygen stable isotopes in modern tooth enamel: A case study from Gorongosa National Park, central Mozambique. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.958032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
The analyses of the stable isotope ratios of carbon (δ13C), nitrogen (δ15N), and oxygen (δ18O) in animal tissues are powerful tools for reconstructing the feeding behavior of individual animals and characterizing trophic interactions in food webs. Of these biomaterials, tooth enamel is the hardest, most mineralized vertebrate tissue and therefore least likely to be affected by chemical alteration (i.e., its isotopic composition can be preserved over millions of years), making it an important and widely available archive for biologists and paleontologists. Here, we present the first combined measurements of δ13C, δ15N, and δ18O in enamel from the teeth of modern fauna (herbivores, carnivores, and omnivores) from the well-studied ecosystem of Gorongosa National Park (GNP) in central Mozambique. We use two novel methods to produce high-precision stable isotope enamel data: (i) the “oxidation-denitrification method,” which permits the measurement of mineral-bound organic nitrogen in tooth enamel (δ15Nenamel), which until now, has not been possible due to enamel’s low organic content, and (ii) the “cold trap method,” which greatly reduces the sample size required for traditional measurements of inorganic δ13Cenamel and δ18Oenamel (from ≥0.5 to ≤0.1 mg), permitting analysis of small or valuable teeth and high-resolution serial sampling of enamel. The stable isotope results for GNP fauna reveal important ecological information about the trophic level, dietary niche, and resource consumption. δ15Nenamel values clearly differentiate trophic level (i.e., carnivore δ15Nenamel values are 4.0‰ higher, on average, than herbivores), δ13Cenamel values distinguish C3 and/or C4 biomass consumption, and δ18Oenamel values reflect local meteoric water (δ18Owater) in the park. Analysis of combined carbon, nitrogen, and oxygen stable isotope data permits geochemical separation of grazers, browsers, omnivores, and carnivores according to their isotopic niche, while mixed-feeding herbivores cannot be clearly distinguished from other dietary groups. These results confirm that combined C, N, and O isotope analyses of a single aliquot of tooth enamel can be used to reconstruct diet and trophic niches. Given its resistance to chemical alteration, the analysis of these three isotopes in tooth enamel has a high potential to open new avenues of research in (paleo)ecology and paleontology.
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4
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Wang XT, Wang Y, Auderset A, Sigman DM, Ren H, Martínez-García A, Haug GH, Su Z, Zhang YG, Rasmussen B, Sessions AL, Fischer WW. Oceanic nutrient rise and the late Miocene inception of Pacific oxygen-deficient zones. Proc Natl Acad Sci U S A 2022; 119:e2204986119. [PMID: 36322766 PMCID: PMC9659387 DOI: 10.1073/pnas.2204986119] [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: 03/22/2022] [Accepted: 10/01/2022] [Indexed: 05/14/2024] Open
Abstract
The modern Pacific Ocean hosts the largest oxygen-deficient zones (ODZs), where oxygen concentrations are so low that nitrate is used to respire organic matter. The history of the ODZs may offer key insights into ocean deoxygenation under future global warming. In a 12-My record from the southeastern Pacific, we observe a >10‰ increase in foraminifera-bound nitrogen isotopes (15N/14N) since the late Miocene (8 to 9 Mya), indicating large ODZs expansion. Coinciding with this change, we find a major increase in the nutrient content of the ocean, reconstructed from phosphorus and iron measurements of hydrothermal sediments at the same site. Whereas global warming studies cast seawater oxygen concentrations as mainly dependent on climate and ocean circulation, our findings indicate that modern ODZs are underpinned by historically high concentrations of seawater phosphate.
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Affiliation(s)
- Xingchen Tony Wang
- Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, MA 02467
| | - Yuwei Wang
- Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, MA 02467
| | - Alexandra Auderset
- Department of Climate Geochemistry, Max Planck Institute for Chemistry, 55128 Mainz, Germany
- Department of Geosciences, Princeton University, Princeton, NJ 08544
| | - Daniel M. Sigman
- Department of Geosciences, Princeton University, Princeton, NJ 08544
| | - Haojia Ren
- Department of Geosciences, National Taiwan University, Taipei 106, Taiwan
| | - Alfredo Martínez-García
- Department of Climate Geochemistry, Max Planck Institute for Chemistry, 55128 Mainz, Germany
| | - Gerald H. Haug
- Department of Climate Geochemistry, Max Planck Institute for Chemistry, 55128 Mainz, Germany
- Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland
| | - Zhan Su
- Department of Physics, University of Toronto, Toronto, ON M5S 1A7, Canada
| | - Yi Ge Zhang
- Department of Oceanography, Texas A&M University, College Station, TX 77843
| | - Birger Rasmussen
- School of Earth Sciences, The University of Western Australia, Crawley, WA 6009, Australia
| | - Alex L. Sessions
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91101
| | - Woodward W. Fischer
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91101
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5
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Deglacial Subantarctic CO 2 outgassing driven by a weakened solubility pump. Nat Commun 2022; 13:5193. [PMID: 36057689 PMCID: PMC9440897 DOI: 10.1038/s41467-022-32895-9] [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: 07/09/2022] [Accepted: 08/23/2022] [Indexed: 11/09/2022] Open
Abstract
The Subantarctic Southern Ocean has long been thought to be an important contributor to increases in atmospheric carbon dioxide partial pressure (pCO2) during glacial-interglacial transitions. Extensive studies suggest that a weakened biological pump, a process associated with nutrient utilization efficiency, drove up surface-water pCO2 in this region during deglaciations. By contrast, regional influences of the solubility pump, a process mainly linked to temperature variations, have been largely overlooked. Here, we evaluate relative roles of the biological and solubility pumps in determining surface-water pCO2 variabilities in the Subantarctic Southern Ocean during the last deglaciation, based on paired reconstructions of surface-water pCO2, temperature, and nutrient utilization efficiency. We show that compared to the biological pump, the solubility pump imposed a strong impact on deglacial Subantarctic surface-water pCO2 variabilities. Our findings therefore reveal a previously underappreciated role of the solubility pump in modulating deglacial Subantarctic CO2 release and possibly past atmospheric pCO2 fluctuations. Using paired reconstructions of seawater pCO2, temperature, and nutrient utilization, Dai et al. show underappreciated influences of the solubility pump on deglacial Subantarctic surface-water pCO2 variabilities compared to the biological pump.
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6
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Ai XE, Studer AS, Sigman DM, Martínez-García A, Fripiat F, Thöle LM, Michel E, Gottschalk J, Arnold L, Moretti S, Schmitt M, Oleynik S, Jaccard SL, Haug GH. Southern Ocean upwelling, Earth's obliquity, and glacial-interglacial atmospheric CO 2 change. Science 2020; 370:1348-1352. [PMID: 33303618 DOI: 10.1126/science.abd2115] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Accepted: 10/30/2020] [Indexed: 11/02/2022]
Abstract
Previous studies have suggested that during the late Pleistocene ice ages, surface-deep exchange was somehow weakened in the Southern Ocean's Antarctic Zone, which reduced the leakage of deeply sequestered carbon dioxide and thus contributed to the lower atmospheric carbon dioxide levels of the ice ages. Here, high-resolution diatom-bound nitrogen isotope measurements from the Indian sector of the Antarctic Zone reveal three modes of change in Southern Westerly Wind-driven upwelling, each affecting atmospheric carbon dioxide. Two modes, related to global climate and the bipolar seesaw, have been proposed previously. The third mode-which arises from the meridional temperature gradient as affected by Earth's obliquity (axial tilt)-can explain the lag of atmospheric carbon dioxide behind climate during glacial inception and deglaciation. This obliquity-induced lag, in turn, makes carbon dioxide a delayed climate amplifier in the late Pleistocene glacial cycles.
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Affiliation(s)
- Xuyuan E Ai
- Department of Geosciences, Princeton University, Princeton, NJ 08544, USA. .,Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany
| | - Anja S Studer
- Department of Environmental Sciences, University of Basel, Basel, Switzerland
| | - Daniel M Sigman
- Department of Geosciences, Princeton University, Princeton, NJ 08544, USA
| | | | - François Fripiat
- Department of Geosciences, Environment and Society, Université Libre de Bruxelles, Brussels, Belgium
| | - Lena M Thöle
- Institute of Geological Sciences and Oeschger Center for Climate Change Research, University of Bern, Bern, Switzerland.,Department of Earth Sciences, Utrecht University, Utrecht, Netherlands
| | - Elisabeth Michel
- Laboratoire des Sciences du Climat et de l'Environnement (LSCE), Laboratoire CNRS-CEA-UVSQ, Gif-sur-Yvette, France
| | | | - Laura Arnold
- Department of Earth Sciences, ETH Zürich, Zürich, Switzerland
| | - Simone Moretti
- Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany.,Department of Earth Sciences, ETH Zürich, Zürich, Switzerland
| | - Mareike Schmitt
- Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany
| | - Sergey Oleynik
- Department of Geosciences, Princeton University, Princeton, NJ 08544, USA
| | - Samuel L Jaccard
- Institute of Geological Sciences and Oeschger Center for Climate Change Research, University of Bern, Bern, Switzerland
| | - Gerald H Haug
- Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany.,Department of Earth Sciences, ETH Zürich, Zürich, Switzerland
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7
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Struve T, Pahnke K, Lamy F, Wengler M, Böning P, Winckler G. A circumpolar dust conveyor in the glacial Southern Ocean. Nat Commun 2020; 11:5655. [PMID: 33168803 PMCID: PMC7652835 DOI: 10.1038/s41467-020-18858-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2020] [Accepted: 09/14/2020] [Indexed: 11/22/2022] Open
Abstract
The increased flux of soluble iron (Fe) to the Fe-deficient Southern Ocean by atmospheric dust is considered to have stimulated the net primary production and carbon export, thus promoting atmospheric CO2 drawdown during glacial periods. Yet, little is known about the sources and transport pathways of Southern Hemisphere dust during the Last Glacial Maximum (LGM). Here we show that Central South America (~24‒32°S) contributed up to ~80% of the dust deposition in the South Pacific Subantarctic Zone via efficient circum-Antarctic dust transport during the LGM, whereas the Antarctic Zone was dominated by dust from Australia. This pattern is in contrast to the modern/Holocene pattern, when South Pacific dust fluxes are thought to be primarily supported by Australian sources. Our findings reveal that in the glacial Southern Ocean, Fe fertilization critically relies on the dynamic interaction of changes in dust-Fe sources in Central South America with the circumpolar westerly wind system. Dust deposition brings iron that fuels ocean productivity, a connection impacting climate over geological time. Here the authors use sediment cores to show that in contrast to dynamics today, during the last glacial maximum westerly winds shuttled dust from Australia and South America around Antarctica and into the South Pacific.
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Affiliation(s)
- Torben Struve
- Marine Isotope Geochemistry, Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, 26129, Oldenburg, Germany.
| | - Katharina Pahnke
- Marine Isotope Geochemistry, Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, 26129, Oldenburg, Germany
| | - Frank Lamy
- Alfred Wegener Institute for Polar and Marine Research, 27568, Bremerhaven, Germany
| | - Marc Wengler
- Alfred Wegener Institute for Polar and Marine Research, 27568, Bremerhaven, Germany
| | - Philipp Böning
- Marine Isotope Geochemistry, Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, 26129, Oldenburg, Germany
| | - Gisela Winckler
- Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, 10964, USA.,Department of Earth and Environmental Sciences, Columbia University, New York, New York, 10027, USA
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8
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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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9
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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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10
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Hasenfratz AP, Jaccard SL, Martínez-García A, Sigman DM, Hodell DA, Vance D, Bernasconi SM, Kleiven HKF, Haumann FA, Haug GH. The residence time of Southern Ocean surface waters and the 100,000-year ice age cycle. Science 2019; 363:1080-1084. [PMID: 30846597 DOI: 10.1126/science.aat7067] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Accepted: 01/23/2019] [Indexed: 11/02/2022]
Abstract
From 1.25 million to 700,000 years ago, the ice age cycle deepened and lengthened from 41,000- to 100,000-year periodicity, a transition that remains unexplained. Using surface- and bottom-dwelling foraminifera from the Antarctic Zone of the Southern Ocean to reconstruct the deep-to-surface supply of water during the ice ages of the past 1.5 million years, we found that a reduction in deep water supply and a concomitant freshening of the surface ocean coincided with the emergence of the high-amplitude 100,000-year glacial cycle. We propose that this slowing of deep-to-surface circulation (i.e., a longer residence time for Antarctic surface waters) prolonged ice ages by allowing the Antarctic halocline to strengthen, which increased the resistance of the Antarctic upper water column to orbitally paced drivers of carbon dioxide release.
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Affiliation(s)
- Adam P Hasenfratz
- Geological Institute, Department of Earth Sciences, ETH Zürich, Zürich, Switzerland. .,Institute of Geological Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
| | - Samuel L Jaccard
- Institute of Geological Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland.
| | | | - Daniel M Sigman
- Department of Geosciences, Guyot Hall, Princeton University, Princeton, NJ, USA
| | - David A Hodell
- Department of Earth Sciences, University of Cambridge, Cambridge, UK
| | - Derek Vance
- Institute of Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland
| | - Stefano M Bernasconi
- Geological Institute, Department of Earth Sciences, ETH Zürich, Zürich, Switzerland
| | - Helga Kikki F Kleiven
- Department of Earth Science, University of Bergen and Bjerknes Centre for Climate Research, Bergen, Norway
| | - F Alexander Haumann
- British Antarctic Survey, Cambridge, UK.,Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ, USA
| | - Gerald H Haug
- Geological Institute, Department of Earth Sciences, ETH Zürich, Zürich, Switzerland.,Max Planck Institute for Chemistry, Mainz, Germany
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11
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Khatiwala S, Schmittner A, Muglia J. Air-sea disequilibrium enhances ocean carbon storage during glacial periods. SCIENCE ADVANCES 2019; 5:eaaw4981. [PMID: 31206024 PMCID: PMC6561735 DOI: 10.1126/sciadv.aaw4981] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/27/2018] [Accepted: 05/09/2019] [Indexed: 06/09/2023]
Abstract
The prevailing hypothesis for lower atmospheric carbon dioxide (CO2) concentrations during glacial periods is an increased efficiency of the ocean's biological pump. However, tests of this and other hypotheses have been hampered by the difficulty to accurately quantify ocean carbon components. Here, we use an observationally constrained earth system model to precisely quantify these components and the role that different processes play in simulated glacial-interglacial CO2 variations. We find that air-sea disequilibrium greatly amplifies the effects of cooler temperatures and iron fertilization on glacial ocean carbon storage even as the efficiency of the soft-tissue biological pump decreases. These two processes, which have previously been regarded as minor, explain most of our simulated glacial CO2 drawdown, while ocean circulation and sea ice extent, hitherto considered dominant, emerge as relatively small contributors.
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Affiliation(s)
- S. Khatiwala
- Department of Earth Sciences, University of Oxford, Oxford, UK
| | - A. Schmittner
- College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA
| | - J. Muglia
- College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA
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12
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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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13
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Natural forcing of the North Atlantic nitrogen cycle in the Anthropocene. Proc Natl Acad Sci U S A 2018; 115:10606-10611. [PMID: 30275314 DOI: 10.1073/pnas.1801049115] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Human alteration of the global nitrogen cycle intensified over the 1900s. Model simulations suggest that large swaths of the open ocean, including the North Atlantic and the western Pacific, have already been affected by anthropogenic nitrogen through atmospheric transport and deposition. Here we report an ∼130-year-long record of the 15N/14N of skeleton-bound organic matter in a coral from the outer reef of Bermuda, which provides a test of the hypothesis that anthropogenic atmospheric nitrogen has significantly augmented the nitrogen supply to the open North Atlantic surface ocean. The Bermuda 15N/14N record does not show a long-term decline in the Anthropocene of the amplitude predicted by model simulations or observed in a western Pacific coral 15N/14N record. Rather, the decadal variations in the Bermuda 15N/14N record appear to be driven by the North Atlantic Oscillation, most likely through changes in the formation rate of Subtropical Mode Water. Given that anthropogenic nitrogen emissions have been decreasing in North America since the 1990s, this study suggests that in the coming decades, the open North Atlantic will remain minimally affected by anthropogenic nitrogen deposition.
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14
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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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