Deep Pacific CaCO sub(3) compensation and glacial-interglacial atmospheric CO sub(2)

• Published in: Earth and planetary science letters Vol. 231; no. 3-4; pp. 317 - 336
• Main Authors: Marchitto, T M, Lynch-Stieglitz, J, Hemming, SR
• Format: Journal Article
• Language: English
• Published: 01.03.2005
• Subjects: Marine
• ISSN: 0012-821X
• DOI: 10.1016/j.epsl.2004.12.024

Benthic foraminiferal delta super(13)C suggests that there was a net shift of isotopically light metabolic CO sub(2) from the upper ocean into the deep ocean during the last glacial period. According to the 'CaCO sub(3) compensation' hypothesis, this should have caused a transient drop in deep ocean CO sub(3) super(2-) that was eventually reversed by seafloor dissolution of CaCO sub(3). The resulting increase in whole-ocean pH may have had a significant impact on atmospheric CO sub(2), compounding any decrease that was due to the initial vertical CO sub(2) shift. The opposite hypothetically occurred during deglaciation, when CO sub(2) was returned to the upper ocean (and atmosphere) and deep ocean CO sub(3) super(2-) temporarily increased, followed by excess burial of CaCO sub(3) and a drop in whole-ocean pH. The deep sea record of CaCO sub(3) preservation appears to reflect these processes, with the largest excursion during deglaciation (as expected), but various factors make quantification of deep sea paleo-CO sub(3) super(2-) difficult. Here we reconstruct deep equatorial Pacific CO sub(3) super(2-) over the last glacial-interglacial cycle using benthic foraminiferal Zn/Ca, which is strongly affected by saturation state during calcite precipitation. Our data are in agreement with the CaCO sub(3) compensation theory, including glacial CO sub(3) super(2-) concentrations similar to (or slightly lower than) today, and a Termination I CO sub(3) super(2-) peak of similar to 25-30 mu mol kg super(-1). The deglacial CO sub(3) super(2-) rise precedes ice sheet melting, consistent with the timing of the atmospheric CO sub(2) rise. A later portion of the peak could reflect removal of CO sub(2) from the atmosphere-ocean system due to boreal forest regrowth. CaCO sub(3) compensation alone may explain more than one third of the atmospheric CO sub(2) lowering during glacial times.