Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling
Recent geochemical models invoke ocean alkalinity changes, particularly in the surface Southern Ocean, to explain glacial age pCO2 reduction. In such models, alkalinity increases in glacial periods are driven by reductions in North Atlantic Deep Water (NADW) supply, which lead to increases in deepwa...
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American Geophysical Union
1994
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Online Access: | https://doi.org/10.1029/93PA03524 http://ecite.utas.edu.au/35726 |
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ftunivtasecite:oai:ecite.utas.edu.au:35726 2023-05-15T17:13:51+02:00 Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling Howard, W Prell, WL 1994 https://doi.org/10.1029/93PA03524 http://ecite.utas.edu.au/35726 en eng American Geophysical Union http://dx.doi.org/10.1029/93PA03524 Howard, W and Prell, WL, Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling, Paleoceanography, 9, (3) pp. 453-482. ISSN 0883-8305 (1994) [Refereed Article] http://ecite.utas.edu.au/35726 Earth Sciences Geology Geology not elsewhere classified Refereed Article PeerReviewed 1994 ftunivtasecite https://doi.org/10.1029/93PA03524 2019-12-13T21:14:09Z Recent geochemical models invoke ocean alkalinity changes, particularly in the surface Southern Ocean, to explain glacial age pCO2 reduction. In such models, alkalinity increases in glacial periods are driven by reductions in North Atlantic Deep Water (NADW) supply, which lead to increases in deepwater nutrients and dissolution of carbonate sediments, and to increased alkalinity of Circumpolar Deep Water upwelling in the surface Southern Ocean. We use cores from the Southeast Indian Ridge and from the deep Cape Basin in the South Atlantic to show that carbonate dissolution was enhanced during glacial stages in areas now bathed by Circumpolar Deep Water. This suggests that deep Southern Ocean carbonate ion concentrations were lower in glacial stages than in interglacials, rather than higher as suggested by the polar alkalinity model [Broecker and Peng, 1989]. Our observations show that changes in Southern Ocean CaCO3 preservation are coherent with changes in the relative flux of NADW, suggesting that Southern Ocean carbonate chemistry is closely linked to changes in deepwater circulation. The pattern of enhanced dissolution in glacials is consistent with a reduction in the supply of nutrientdepleted water (NADW) to the Southern Ocean and with an increase of nutrients in deep water masses. Carbonate mass accumulation rates on the Southeast Indian Ridge (32003800 m), and in relatively shallow cores (<3000 m) from the Kerguelen Plateau and the South Pacific were significantly reduced during glacial stages, by about 50%. The reduced carbonate mass accumulation rates and enhanced dissolution during glacials may be partly due to decreases in CaCO3:Corg flux ratios, acting as another mechanism which would raise the alkalinity of Southern Ocean surface waters. The polar alkalinity model assumes that the ratio of organic carbon to carbonate production on surface alkalinity is constant. Even if overall productivity in the Southern Ocean were held constant, a decrease in the CaCO3:Corg ratio would result in increased alkalinity and reduced pCO2 in Southern Ocean surface waters during glacials. This ecologically driven surface alkalinity change may enhance deepwatermediated changes in alkalinity, and amplify rapid changes in pCO2. Copyright 1994 by the American Geophysical Union. Article in Journal/Newspaper NADW North Atlantic Deep Water North Atlantic Southern Ocean eCite UTAS (University of Tasmania) Southern Ocean Kerguelen Pacific Indian Southeast Indian Ridge ENVELOPE(110.000,110.000,-50.000,-50.000) Paleoceanography 9 3 453 482 |
institution |
Open Polar |
collection |
eCite UTAS (University of Tasmania) |
op_collection_id |
ftunivtasecite |
language |
English |
topic |
Earth Sciences Geology Geology not elsewhere classified |
spellingShingle |
Earth Sciences Geology Geology not elsewhere classified Howard, W Prell, WL Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling |
topic_facet |
Earth Sciences Geology Geology not elsewhere classified |
description |
Recent geochemical models invoke ocean alkalinity changes, particularly in the surface Southern Ocean, to explain glacial age pCO2 reduction. In such models, alkalinity increases in glacial periods are driven by reductions in North Atlantic Deep Water (NADW) supply, which lead to increases in deepwater nutrients and dissolution of carbonate sediments, and to increased alkalinity of Circumpolar Deep Water upwelling in the surface Southern Ocean. We use cores from the Southeast Indian Ridge and from the deep Cape Basin in the South Atlantic to show that carbonate dissolution was enhanced during glacial stages in areas now bathed by Circumpolar Deep Water. This suggests that deep Southern Ocean carbonate ion concentrations were lower in glacial stages than in interglacials, rather than higher as suggested by the polar alkalinity model [Broecker and Peng, 1989]. Our observations show that changes in Southern Ocean CaCO3 preservation are coherent with changes in the relative flux of NADW, suggesting that Southern Ocean carbonate chemistry is closely linked to changes in deepwater circulation. The pattern of enhanced dissolution in glacials is consistent with a reduction in the supply of nutrientdepleted water (NADW) to the Southern Ocean and with an increase of nutrients in deep water masses. Carbonate mass accumulation rates on the Southeast Indian Ridge (32003800 m), and in relatively shallow cores (<3000 m) from the Kerguelen Plateau and the South Pacific were significantly reduced during glacial stages, by about 50%. The reduced carbonate mass accumulation rates and enhanced dissolution during glacials may be partly due to decreases in CaCO3:Corg flux ratios, acting as another mechanism which would raise the alkalinity of Southern Ocean surface waters. The polar alkalinity model assumes that the ratio of organic carbon to carbonate production on surface alkalinity is constant. Even if overall productivity in the Southern Ocean were held constant, a decrease in the CaCO3:Corg ratio would result in increased alkalinity and reduced pCO2 in Southern Ocean surface waters during glacials. This ecologically driven surface alkalinity change may enhance deepwatermediated changes in alkalinity, and amplify rapid changes in pCO2. Copyright 1994 by the American Geophysical Union. |
format |
Article in Journal/Newspaper |
author |
Howard, W Prell, WL |
author_facet |
Howard, W Prell, WL |
author_sort |
Howard, W |
title |
Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling |
title_short |
Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling |
title_full |
Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling |
title_fullStr |
Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling |
title_full_unstemmed |
Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling |
title_sort |
late quaternary caco3 production and preservation in the southern ocean: implications for oceanic and atmospheric carbon cycling |
publisher |
American Geophysical Union |
publishDate |
1994 |
url |
https://doi.org/10.1029/93PA03524 http://ecite.utas.edu.au/35726 |
long_lat |
ENVELOPE(110.000,110.000,-50.000,-50.000) |
geographic |
Southern Ocean Kerguelen Pacific Indian Southeast Indian Ridge |
geographic_facet |
Southern Ocean Kerguelen Pacific Indian Southeast Indian Ridge |
genre |
NADW North Atlantic Deep Water North Atlantic Southern Ocean |
genre_facet |
NADW North Atlantic Deep Water North Atlantic Southern Ocean |
op_relation |
http://dx.doi.org/10.1029/93PA03524 Howard, W and Prell, WL, Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling, Paleoceanography, 9, (3) pp. 453-482. ISSN 0883-8305 (1994) [Refereed Article] http://ecite.utas.edu.au/35726 |
op_doi |
https://doi.org/10.1029/93PA03524 |
container_title |
Paleoceanography |
container_volume |
9 |
container_issue |
3 |
container_start_page |
453 |
op_container_end_page |
482 |
_version_ |
1766071046245449728 |