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Meredith MP, Povl Abrahamsen E, Alexander Haumann F, Leng MJ, Arrowsmith C, Barham M, Firing YL, King BA, Brown P, Alexander Brearley J, Meijers AJS, Sallée JB, Akhoudas C, Tarling GA. Tracing the impacts of recent rapid sea ice changes and the A68 megaberg on the surface freshwater balance of the Weddell and Scotia Seas. Philos Trans A Math Phys Eng Sci 2023; 381:20220162. [PMID: 37150196 PMCID: PMC10164467 DOI: 10.1098/rsta.2022.0162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The Southern Ocean upper-layer freshwater balance exerts a global climatic influence by modulating density stratification and biological productivity, and hence the exchange of heat and carbon between the atmosphere and the ocean interior. It is thus important to understand and quantify the time-varying freshwater inputs, which is challenging from measurements of salinity alone. Here we use seawater oxygen isotopes from samples collected between 2016 and 2021 along a transect spanning the Scotia and northern Weddell Seas to separate the freshwater contributions from sea ice and meteoric sources. The unprecedented retreat of sea ice in 2016 is evidenced as a strong increase in sea ice melt across the northern Weddell Sea, with surface values increasing approximately two percentage points between 2016 and 2018 and column inventories increasing approximately 1 to 2 m. Surface meteoric water concentrations exceeded 4% in early 2021 close to South Georgia due to meltwater from the A68 megaberg; smaller icebergs may influence meteoric water at other times also. Both these inputs highlight the importance of a changing cryosphere for upper-ocean freshening; potential future sea ice retreats and increases in iceberg calving would enhance the impacts of these freshwater sources on the ocean and climate. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.
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Affiliation(s)
- Michael P Meredith
- British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
| | - E Povl Abrahamsen
- British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
| | - F Alexander Haumann
- British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
- Atmospheric and Oceanic Sciences Program, Princeton University, NJ 08544, USA
| | - Melanie J Leng
- National Environmental Isotope Facility, British Geological Survey, NG12 5GG, UK
- School of Biosciences, University of Nottingham, Loughborough, LE12 5RD, UK
| | - Carol Arrowsmith
- National Environmental Isotope Facility, British Geological Survey, NG12 5GG, UK
| | - Mark Barham
- British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
| | - Yvonne L Firing
- National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
| | - Brian A King
- National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
| | - Peter Brown
- National Oceanography Centre, European Way, Southampton SO14 3ZH, UK
| | | | - Andrew J S Meijers
- British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
| | - Jean-Baptiste Sallée
- Sorbonne Université, CNRS/IRD/MNHN, Laboratoire d'Océanographie et du Climat Expérimentations et, Approches Numériques (LOCEAN), Paris, 75005, France
| | - Camille Akhoudas
- Sorbonne Université, CNRS/IRD/MNHN, Laboratoire d'Océanographie et du Climat Expérimentations et, Approches Numériques (LOCEAN), Paris, 75005, France
| | - Geraint A Tarling
- British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
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Akhoudas CH, Sallée JB, Reverdin G, Haumann FA, Pauthenet E, Chapman CC, Margirier F, Lo Monaco C, Metzl N, Meilland J, Stranne C. Isotopic evidence for an intensified hydrological cycle in the Indian sector of the Southern Ocean. Nat Commun 2023; 14:2763. [PMID: 37179409 PMCID: PMC10183002 DOI: 10.1038/s41467-023-38425-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Accepted: 05/02/2023] [Indexed: 05/15/2023] Open
Abstract
The hydrological cycle is expected to intensify in a warming climate. However, observational evidence of such changes in the Southern Ocean is difficult to obtain due to sparse measurements and a complex superposition of changes in precipitation, sea ice, and glacial meltwater. Here we disentangle these signals using a dataset of salinity and seawater oxygen isotope observations collected in the Indian sector of the Southern Ocean. Our results show that the atmospheric water cycle has intensified in this region between 1993 and 2021, increasing the salinity in subtropical surface waters by 0.06 ± 0.07 g kg-1 per decade, and decreasing the salinity in subpolar surface waters by -0.02 ± 0.01 g kg-1 per decade. The oxygen isotope data allow to discriminate the different freshwater processes showing that in the subpolar region, the freshening is largely driven by the increase in net precipitation (by a factor two) while the decrease in sea ice melt is largely balanced by the contribution of glacial meltwater at these latitudes. These changes extend the growing evidence for an acceleration of the hydrological cycle and a melting cryosphere that can be expected from global warming.
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Affiliation(s)
- Camille Hayatte Akhoudas
- Department of Geological Sciences, Stockholm University, Stockholm, Sweden.
- Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.
| | | | | | - F Alexander Haumann
- Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
- Ludwig-Maximilians-University Munich, Munich, Germany
- Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, NJ, USA
| | - Etienne Pauthenet
- LOPS, CNRS/IFREMER/IRD/UBO, Institut Universitaire Européen de la Mer, Plouzané, France
| | | | - Félix Margirier
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
| | | | - Nicolas Metzl
- CNRS/IRD/MNHN, LOCEAN, Sorbonne Université, Paris, France
| | | | - Christian Stranne
- Department of Geological Sciences, Stockholm University, Stockholm, Sweden
- Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
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Chen H, Haumann FA, Talley LD, Johnson KS, Sarmiento JL. The Deep Ocean's Carbon Exhaust. Global Biogeochem Cycles 2022; 36:e2021GB007156. [PMID: 36248262 PMCID: PMC9540790 DOI: 10.1029/2021gb007156] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 06/23/2022] [Accepted: 07/01/2022] [Indexed: 05/24/2023]
Abstract
The deep ocean releases large amounts of old, pre-industrial carbon dioxide (CO2) to the atmosphere through upwelling in the Southern Ocean, which counters the marine carbon uptake occurring elsewhere. This Southern Ocean CO2 release is relevant to the global climate because its changes could alter atmospheric CO2 levels on long time scales, and also affects the present-day potential of the Southern Ocean to take up anthropogenic CO2. Here, year-round profiling float measurements show that this CO2 release arises from a zonal band of upwelling waters between the Subantarctic Front and wintertime sea-ice edge. This band of high CO2 subsurface water coincides with the outcropping of the 27.8 kg m-3 isoneutral density surface that characterizes Indo-Pacific Deep Water (IPDW). It has a potential partial pressure of CO2 exceeding current atmospheric CO2 levels (∆PCO2) by 175 ± 32 μatm. Ship-based measurements reveal that IPDW exhibits a distinct ∆PCO2 maximum in the ocean, which is set by remineralization of organic carbon and originates from the northern Pacific and Indian Ocean basins. Below this IPDW layer, the carbon content increases downwards, whereas ∆PCO2 decreases. Most of this vertical ∆PCO2 decline results from decreasing temperatures and increasing alkalinity due to an increased fraction of calcium carbonate dissolution. These two factors limit the CO2 outgassing from the high-carbon content deep waters on more southerly surface outcrops. Our results imply that the response of Southern Ocean CO2 fluxes to possible future changes in upwelling are sensitive to the subsurface carbon chemistry set by the vertical remineralization and dissolution profiles.
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Affiliation(s)
- Haidi Chen
- Atmospheric and Oceanic Sciences ProgramPrinceton UniversityPrincetonNJUSA
| | | | - Lynne D. Talley
- Scripps Institution of OceanographyUniversity of California, San DiegoLa JollaCaliforniaUSA
| | | | - Jorge L. Sarmiento
- Atmospheric and Oceanic Sciences ProgramPrinceton UniversityPrincetonNJUSA
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Akhoudas CH, Sallée JB, Haumann FA, Meredith MP, Garabato AN, Reverdin G, Jullion L, Aloisi G, Benetti M, Leng MJ, Arrowsmith C. Publisher Correction: Ventilation of the abyss in the Atlantic sector of the Southern Ocean. Sci Rep 2021; 11:16733. [PMID: 34385553 PMCID: PMC8361090 DOI: 10.1038/s41598-021-95949-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Affiliation(s)
- Camille Hayatte Akhoudas
- CNRS/IRD/MNHN Laboratoire d'Océanographie et du Climat-Expérimentations et Approches Numériques, Sorbonne Université, Paris, France.
| | - Jean-Baptiste Sallée
- CNRS/IRD/MNHN Laboratoire d'Océanographie et du Climat-Expérimentations et Approches Numériques, Sorbonne Université, Paris, France
| | - F Alexander Haumann
- Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, USA.,British Antarctic Survey, Cambridge, UK
| | | | - Alberto Naveira Garabato
- School of Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, UK
| | - Gilles Reverdin
- CNRS/IRD/MNHN Laboratoire d'Océanographie et du Climat-Expérimentations et Approches Numériques, Sorbonne Université, Paris, France
| | - Loïc Jullion
- School of Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, UK
| | - Giovanni Aloisi
- Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, UMR 7154 CNRS, Paris, France
| | - Marion Benetti
- Institute of Earth Sciences, University of Iceland, Reykjavik, Iceland
| | - Melanie J Leng
- NERC Isotope Geosciences Laboratory, British Geological Survey, Nottingham, UK.,Centre for Environmental Geochemistry, University of Nottingham, Nottingham, UK
| | - Carol Arrowsmith
- NERC Isotope Geosciences Laboratory, British Geological Survey, Nottingham, UK
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Akhoudas CH, Sallée JB, Haumann FA, Meredith MP, Garabato AN, Reverdin G, Jullion L, Aloisi G, Benetti M, Leng MJ, Arrowsmith C. Ventilation of the abyss in the Atlantic sector of the Southern Ocean. Sci Rep 2021; 11:6760. [PMID: 33762612 PMCID: PMC7991437 DOI: 10.1038/s41598-021-86043-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 03/09/2021] [Indexed: 11/09/2022] Open
Abstract
The Atlantic sector of the Southern Ocean is the world's main production site of Antarctic Bottom Water, a water-mass that is ventilated at the ocean surface before sinking and entraining older water-masses-ultimately replenishing the abyssal global ocean. In recent decades, numerous attempts at estimating the rates of ventilation and overturning of Antarctic Bottom Water in this region have led to a strikingly broad range of results, with water transport-based calculations (8.4-9.7 Sv) yielding larger rates than tracer-based estimates (3.7-4.9 Sv). Here, we reconcile these conflicting views by integrating transport- and tracer-based estimates within a common analytical framework, in which bottom water formation processes are explicitly quantified. We show that the layer of Antarctic Bottom Water denser than 28.36 kg m[Formula: see text] [Formula: see text] is exported northward at a rate of 8.4 ± 0.7 Sv, composed of 4.5 ± 0.3 Sv of well-ventilated Dense Shelf Water, and 3.9 ± 0.5 Sv of old Circumpolar Deep Water entrained into cascading plumes. The majority, but not all, of the Dense Shelf Water (3.4 ± 0.6 Sv) is generated on the continental shelves of the Weddell Sea. Only 55% of AABW exported from the region is well ventilated and thus draws down heat and carbon into the deep ocean. Our findings unify traditionally contrasting views of Antarctic Bottom Water production in the Atlantic sector, and define a baseline, process-discerning target for its realistic representation in climate models.
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Affiliation(s)
- Camille Hayatte Akhoudas
- CNRS/IRD/MNHN Laboratoire d'Océanographie et du Climat-Expérimentations et Approches Numériques, Sorbonne Université, Paris, France.
| | - Jean-Baptiste Sallée
- CNRS/IRD/MNHN Laboratoire d'Océanographie et du Climat-Expérimentations et Approches Numériques, Sorbonne Université, Paris, France
| | - F Alexander Haumann
- Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, USA.,British Antarctic Survey, Cambridge, UK
| | | | - Alberto Naveira Garabato
- School of Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, UK
| | - Gilles Reverdin
- CNRS/IRD/MNHN Laboratoire d'Océanographie et du Climat-Expérimentations et Approches Numériques, Sorbonne Université, Paris, France
| | - Loïc Jullion
- School of Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, UK
| | - Giovanni Aloisi
- Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, UMR 7154 CNRS, Paris, France
| | - Marion Benetti
- Institute of Earth Sciences, University of Iceland, Reykjavik, Iceland
| | - Melanie J Leng
- NERC Isotope Geosciences Laboratory, British Geological Survey, Nottingham, UK.,Centre for Environmental Geochemistry, University of Nottingham, Nottingham, UK
| | - Carol Arrowsmith
- NERC Isotope Geosciences Laboratory, British Geological Survey, Nottingham, UK
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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Haumann FA, Gruber N, Münnich M, Frenger I, Kern S. Sea-ice transport driving Southern Ocean salinity and its recent trends. Nature 2016; 537:89-92. [DOI: 10.1038/nature19101] [Citation(s) in RCA: 138] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Accepted: 07/08/2016] [Indexed: 11/10/2022]
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Landschützer P, Gruber N, Haumann FA, Rödenbeck C, Bakker DCE, van Heuven S, Hoppema M, Metzl N, Sweeney C, Takahashi T, Tilbrook B, Wanninkhof R. The reinvigoration of the Southern Ocean carbon sink. Science 2015; 349:1221-4. [DOI: 10.1126/science.aab2620] [Citation(s) in RCA: 258] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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