Global variations of surface ocean productivity in low and mid latitudes: influence on C0$_2$ reservoirs of the deep
Résumé
Based on detailed reconstructions of global distribution patterns, both paleoproductivity and the benthic δ13C record of CO$_2$, which is dissolved in the deep ocean, strongly differed between the Last Glacial Maximum and the Holocene. With the onset of Termination I about 15,000 years ago, the new (export) production of low- and mid-latitude upwelling cells started to decline by more than 2-4 Gt carbon/year. This reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric CO$_2$ as recorded in ice cores and, with a slight delay of more than 1000 years, to a large-scale gradual CO$_2$ depletion of the deep ocean by about 650 Gt C. This estimate is based on an average increase in benthic δ13C by 0.4–0.5‰. The decrease in new production also matches a clear 13C depletion of organic matter, possibly recording an end of extreme nutrient utilization in upwelling cells. As shown by Sarnthein et al., [1987], the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades, which in turn was linked via a shrinking extent of sea ice to a massive increase in high-latitude insolation, i.e., to orbital forcing as primary cause.
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Paleoceanography - June 1988 - Sarnthein - Global variations of surface ocean productivity in low and mid latitudes .pdf (2.23 Mo)
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