Global variations of surface ocean productivity in low and mid latitudes: Influence on CO₂ reservoirs of the deep ocean and atmosphere during the last 21,000 years

Abstract

Based on detailed reconstructions of global distribution patterns, both paleoproductivity and the benthic δ 13 C 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 δ 13 C by 0.4–0.5‰. The decrease in new production also matches a clear 13 C 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.