Glacial northeast Atlantic surface water PCO2: Productivity and deep-water formation

Abstract

The carbon isotopic composition of bound organic material within the crystal lattice of planktonic foraminiferal calcite is a valuable proxy for the isotopic composition of primary photosynthate in surface waters. This proxy can be used to estimate p co 2 in the surface waters of the northeast Atlantic during the last glacial period, if combined with data on the carbon isotopic composition of foraminiferal calcite. Our first estimates of surface water p co 2 at the location of Biogeochemical Ocean Flux Studies Core 5K (50 °41.3′N, 21 °51.9′W) indicate that this region was probably a more important sink for CO 2 during the glacial than during the Holocene. This increased sink could not have been caused by local high primary productivity, because glacial primary productivity as estimated from benthic foraminiferal data was extremely low at 5K. We thus conclude that the enhanced sink at these latitudes resulted from increased convection of surface water to intermediate or greater depths, i.e. from the southward shift of an important centre of deep-intermediate water formation, as confirmed by computer simulation.