1
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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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2
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Higher sea surface temperature in the Indian Ocean during the Last Interglacial weakened the South Asian monsoon. Proc Natl Acad Sci U S A 2022; 119:e2107720119. [PMID: 35238640 PMCID: PMC8915836 DOI: 10.1073/pnas.2107720119] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Understanding the drivers of South Asian monsoon intensity is pivotal for improving climate forecasting under global warming scenarios. Solar insolation is assumed to be the dominant driver of monsoon variability in warm climate regimes, but this has not been verified by proxy data. We report a South Asian monsoon rainfall record spanning the last ∼130 kyr in the Ganges–Brahmaputra–Meghna river catchment. Our multiproxy data reveal that the South Asian monsoon was weaker during the Last Interglacial (130 to 115 ka)—despite higher insolation—than during the Holocene (11.6 ka to present), thus questioning the widely accepted model assumption. Our work implies that Indian Ocean warming may increase the occurrence of severe monsoon failures in South Asia. Addressing and anticipating future South Asian monsoon changes under continuing global warming is of critical importance for the food security and socioeconomic well-being of one-quarter of the world’s population. However, climate model projections show discrepancies in future monsoon variability in South Asian monsoon domains, largely due to our still limited understanding of the monsoon response to warm climate change scenarios. Particularly, climate models are largely based on the assumption that higher solar insolation causes higher rainfall during similar warm climatic regimes, but this has not been verified by proxy data for different interglacial periods. Here, we compare Indian summer monsoon (ISM) variability during the Last Interglacial and Holocene using a sedimentary leaf wax δD and δ13C record from the northern Bay of Bengal, representing the Ganges–Brahmaputra–Meghna (G-B-M) river catchment. In combination with a seawater salinity record, our results show that ISM intensity broadly follows summer insolation on orbital scales, but ISM intensity during the Last Interglacial was lower than during the Holocene despite higher summer insolation and greenhouse gas concentrations. We argue that sustained warmer sea surface temperature in the equatorial and tropical Indian Ocean during the Last Interglacial increased convective rainfall above the ocean but dampened ISM intensity on land. Our study demonstrates that besides solar insolation, internal climatic feedbacks also play an important role for South Asian monsoon variability during warm climate states. This work can help to improve future climate model projections and highlights the importance of understanding controls of monsoonal rainfall under interglacial boundary conditions.
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3
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Barker S, Knorr G. Millennial scale feedbacks determine the shape and rapidity of glacial termination. Nat Commun 2021; 12:2273. [PMID: 33859188 PMCID: PMC8050095 DOI: 10.1038/s41467-021-22388-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 03/11/2021] [Indexed: 11/08/2022] Open
Abstract
Within the Late Pleistocene, terminations describe the major transitions marking the end of glacial cycles. While it is established that abrupt shifts in the ocean/atmosphere system are a ubiquitous component of deglaciation, significant uncertainties remain concerning their specific role and the likelihood that terminations may be interrupted by large-amplitude abrupt oscillations. In this perspective we address these uncertainties in the light of recent developments in the understanding of glacial terminations as the ultimate interaction between millennial and orbital timescale variability. Innovations in numerical climate simulation and new geologic records allow us to highlight new avenues of research and identify key remaining uncertainties such as sea-level variability.
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Affiliation(s)
- Stephen Barker
- School of Earth and Environmental Sciences, Cardiff University, Cardiff, UK.
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4
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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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5
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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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6
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Antarctic and global climate history viewed from ice cores. Nature 2018; 558:200-208. [DOI: 10.1038/s41586-018-0172-5] [Citation(s) in RCA: 74] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Accepted: 03/19/2018] [Indexed: 11/08/2022]
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7
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Mean global ocean temperatures during the last glacial transition. Nature 2018; 553:39-44. [PMID: 29300008 DOI: 10.1038/nature25152] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 11/17/2017] [Indexed: 11/08/2022]
Abstract
Little is known about the ocean temperature's long-term response to climate perturbations owing to limited observations and a lack of robust reconstructions. Although most of the anthropogenic heat added to the climate system has been taken up by the ocean up until now, its role in a century and beyond is uncertain. Here, using noble gases trapped in ice cores, we show that the mean global ocean temperature increased by 2.57 ± 0.24 degrees Celsius over the last glacial transition (20,000 to 10,000 years ago). Our reconstruction provides unprecedented precision and temporal resolution for the integrated global ocean, in contrast to the depth-, region-, organism- and season-specific estimates provided by other methods. We find that the mean global ocean temperature is closely correlated with Antarctic temperature and has no lead or lag with atmospheric CO2, thereby confirming the important role of Southern Hemisphere climate in global climate trends. We also reveal an enigmatic 700-year warming during the early Younger Dryas period (about 12,000 years ago) that surpasses estimates of modern ocean heat uptake.
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8
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Hare VJ, Loftus E, Jeffrey A, Ramsey CB. Atmospheric CO 2 effect on stable carbon isotope composition of terrestrial fossil archives. Nat Commun 2018; 9:252. [PMID: 29343713 PMCID: PMC5772509 DOI: 10.1038/s41467-017-02691-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Accepted: 12/19/2017] [Indexed: 11/21/2022] Open
Abstract
The 13C/12C ratio of C3 plant matter is thought to be controlled by the isotopic composition of atmospheric CO2 and stomatal response to environmental conditions, particularly mean annual precipitation (MAP). The effect of CO2 concentration on 13C/12C ratios is currently debated, yet crucial to reconstructing ancient environments and quantifying the carbon cycle. Here we compare high-resolution ice core measurements of atmospheric CO2 with fossil plant and faunal isotope records. We show the effect of pCO2 during the last deglaciation is stronger for gymnosperms (-1.4 ± 1.2‰) than angiosperms/fauna (-0.5 ± 1.5‰), while the contributions from changing MAP are -0.3 ± 0.6‰ and -0.4 ± 0.4‰, respectively. Previous studies have assumed that plant 13C/12C ratios are mostly determined by MAP, an assumption which is sometimes incorrect in geological time. Atmospheric effects must be taken into account when interpreting terrestrial stable carbon isotopes, with important implications for past environments and climates, and understanding plant responses to climate change.
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Affiliation(s)
- Vincent J Hare
- Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, 1 South Parks Road, Oxford, OX1 3TG, UK.
- Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, 14627, USA.
| | - Emma Loftus
- Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, 1 South Parks Road, Oxford, OX1 3TG, UK
- Merton College, University of Oxford, Merton Street, Oxford, OX1 4JD, UK
| | - Amy Jeffrey
- Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, 1 South Parks Road, Oxford, OX1 3TG, UK
| | - Christopher Bronk Ramsey
- Research Laboratory for Archaeology and the History of Art, School of Archaeology, University of Oxford, 1 South Parks Road, Oxford, OX1 3TG, UK
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9
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Sea level fall during glaciation stabilized atmospheric CO 2 by enhanced volcanic degassing. Nat Commun 2017; 8:15867. [PMID: 28681844 PMCID: PMC5504290 DOI: 10.1038/ncomms15867] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Accepted: 05/09/2017] [Indexed: 11/08/2022] Open
Abstract
Paleo-climate records and geodynamic modelling indicate the existence of complex interactions between glacial sea level changes, volcanic degassing and atmospheric CO2, which may have modulated the climate system's descent into the last ice age. Between ∼85 and 70 kyr ago, during an interval of decreasing axial tilt, the orbital component in global temperature records gradually declined, while atmospheric CO2, instead of continuing its long-term correlation with Antarctic temperature, remained relatively stable. Here, based on novel global geodynamic models and the joint interpretation of paleo-proxy data as well as biogeochemical simulations, we show that a sea level fall in this interval caused enhanced pressure-release melting in the uppermost mantle, which may have induced a surge in magma and CO2 fluxes from mid-ocean ridges and oceanic hotspot volcanoes. Our results reveal a hitherto unrecognized negative feedback between glaciation and atmospheric CO2 predominantly controlled by marine volcanism on multi-millennial timescales of ∼5,000-15,000 years.
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10
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Episodic release of CO 2 from the high-latitude North Atlantic Ocean during the last 135 kyr. Nat Commun 2017; 8:14498. [PMID: 28224985 PMCID: PMC5322501 DOI: 10.1038/ncomms14498] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2016] [Accepted: 01/06/2017] [Indexed: 11/21/2022] Open
Abstract
Antarctic ice cores document glacial-interglacial and millennial-scale variability in atmospheric pCO2 over the past 800 kyr. The ocean, as the largest active carbon reservoir on this timescale, is thought to have played a dominant role in these pCO2 fluctuations, but it remains unclear how and where in the ocean CO2 was stored during glaciations and released during (de)glacial millennial-scale climate events. The evolution of surface ocean pCO2 in key locations can therefore provide important clues for understanding the ocean's role in Pleistocene carbon cycling. Here we present a 135-kyr record of shallow subsurface pCO2 and nutrient levels from the Norwegian Sea, an area of intense CO2 uptake from the atmosphere today. Our results suggest that the Norwegian Sea probably acted as a CO2 source towards the end of Heinrich stadials HS1, HS4 and HS11, and may have contributed to the increase in atmospheric pCO2 at these times. Glacial-interglacial variations in atmospheric pCO2 remain unexplained. Here, the authors show that the Norwegian Sea, an modern area of intense CO2 uptake, acted as a CO2 source during the terminations of Heinrich stadials 1, 4 and 11, sometimes characterized by rapid increases in atmospheric pCO2.
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11
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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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12
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Covariation of deep Southern Ocean oxygenation and atmospheric CO2 through the last ice age. Nature 2016; 530:207-10. [DOI: 10.1038/nature16514] [Citation(s) in RCA: 144] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2015] [Accepted: 11/27/2015] [Indexed: 11/09/2022]
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13
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Siple Dome ice reveals two modes of millennial CO2 change during the last ice age. Nat Commun 2014; 5:3723. [PMID: 24781344 PMCID: PMC4015316 DOI: 10.1038/ncomms4723] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2013] [Accepted: 03/26/2014] [Indexed: 11/08/2022] Open
Abstract
Reconstruction of atmospheric CO2 during times of past abrupt climate change may help us better understand climate-carbon cycle feedbacks. Previous ice core studies reveal simultaneous increases in atmospheric CO2 and Antarctic temperature during times when Greenland and the northern hemisphere experienced very long, cold stadial conditions during the last ice age. Whether this relationship extends to all of the numerous stadial events in the Greenland ice core record has not been clear. Here we present a high-resolution record of atmospheric CO2 from the Siple Dome ice core, Antarctica for part of the last ice age. We find that CO2 does not significantly change during the short Greenlandic stadial events, implying that the climate system perturbation that produced the short stadials was not strong enough to substantially alter the carbon cycle. Whether all rapid climate events during the last ice age impacted the global carbon cycle is not clearly understood. Ahn and Brook present a high-resolution record of atmospheric CO2 from Antarctica and suggest that only Greenland stadials associated with massive iceberg discharge influenced atmospheric CO2.
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14
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Martínez-García A, Sigman DM, Ren H, Anderson RF, Straub M, Hodell DA, Jaccard SL, Eglinton TI, Haug GH. Iron fertilization of the Subantarctic ocean during the last ice age. Science 2014; 343:1347-50. [PMID: 24653031 DOI: 10.1126/science.1246848] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
John H. Martin, who discovered widespread iron limitation of ocean productivity, proposed that dust-borne iron fertilization of Southern Ocean phytoplankton caused the ice age reduction in atmospheric carbon dioxide (CO2). In a sediment core from the Subantarctic Atlantic, we measured foraminifera-bound nitrogen isotopes to reconstruct ice age nitrate consumption, burial fluxes of iron, and proxies for productivity. Peak glacial times and millennial cold events are characterized by increases in dust flux, productivity, and the degree of nitrate consumption; this combination is uniquely consistent with Subantarctic iron fertilization. The associated strengthening of the Southern Ocean's biological pump can explain the lowering of CO2 at the transition from mid-climate states to full ice age conditions as well as the millennial-scale CO2 oscillations.
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15
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Hiscock WT, Fischer H, Bigler M, Gfeller G, Leuenberger D, Mini O. Continuous flow analysis of labile iron in ice-cores. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 47:4416-4425. [PMID: 23594184 DOI: 10.1021/es3047087] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The important active and passive role of mineral dust aerosol in the climate and the global carbon cycle over the last glacial/interglacial cycles has been recognized. However, little data on the most important aeolian dust-derived biological micronutrient, iron (Fe), has so far been available from ice-cores from Greenland or Antarctica. Furthermore, Fe deposition reconstructions derived from the palaeoproxies particulate dust and calcium differ significantly from the Fe flux data available. The ability to measure high temporal resolution Fe data in polar ice-cores is crucial for the study of the timing and magnitude of relationships between geochemical events and biological responses in the open ocean. This work adapts an existing flow injection analysis (FIA) methodology for low-level trace Fe determinations with an existing glaciochemical analysis system, continuous flow analysis (CFA) of ice-cores. Fe-induced oxidation of N,N'-dimethyl-p-pheylenediamine (DPD) is used to quantify the biologically more important and easily leachable Fe fraction released in a controlled digestion step at pH ~1.0. The developed method was successfully applied to the determination of labile Fe in ice-core samples collected from the Antarctic Byrd ice-core and the Greenland Ice-Core Project (GRIP) ice-core.
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Affiliation(s)
- William T Hiscock
- Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland.
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16
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Jaccard SL, Hayes CT, Martínez-García A, Hodell DA, Anderson RF, Sigman DM, Haug GH. Two modes of change in Southern Ocean productivity over the past million years. Science 2013; 339:1419-23. [PMID: 23520109 DOI: 10.1126/science.1227545] [Citation(s) in RCA: 169] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Export of organic carbon from surface waters of the Antarctic Zone of the Southern Ocean decreased during the last ice age, coinciding with declining atmospheric carbon dioxide (CO(2)) concentrations, signaling reduced exchange of CO(2) between the ocean interior and the atmosphere. In contrast, in the Subantarctic Zone, export production increased into ice ages coinciding with rising dust fluxes, thus suggesting iron fertilization of subantarctic phytoplankton. Here, a new high-resolution productivity record from the Antarctic Zone is compiled with parallel subantarctic data over the past million years. Together, they fit the view that the combination of these two modes of Southern Ocean change determines the temporal structure of the glacial-interglacial atmospheric CO(2) record, including during the interval of "lukewarm" interglacials between 450 and 800 thousand years ago.
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Affiliation(s)
- S L Jaccard
- Geological Institute, Department of Earth Sciences, ETH Zurich, Zurich, Switzerland.
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