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Late Quaternary CaCO3 production and preservation in the Southern Ocean: Implications for oceanic and atmospheric carbon cycling

Citation

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]

DOI: doi:10.1029/93PA03524

Abstract

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 deep‐water 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 nutrient‐depleted 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 (3200"3800 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 deepwater‐mediated changes in alkalinity, and amplify rapid changes in pCO2. Copyright 1994 by the American Geophysical Union.

Item Details

Item Type:Refereed Article
Research Division:Earth Sciences
Research Group:Geology
Research Field:Geology not elsewhere classified
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Earth Sciences
Author:Howard, W (Associate Professor William Howard)
ID Code:35726
Year Published:1994
Web of Science® Times Cited:123
Deposited By:CRC-Antarctic Climate & Ecosystems
Deposited On:2005-08-26
Last Modified:2011-08-26
Downloads:0

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