The Role of the Eastern Equatorial Pacific in Carbon Sequestration and Ventilation over the Last Glacial-Interglacial Transition

Abstract:

The last glacial-interglacial transition is punctuated by brief periods of rapid return to glacial-like conditions followed by abrupt warmings. Ice core records reveal episodes of rapid increases in CO₂ and synchronous decreases in Δ¹⁴C that co-occur with these abrupt warmings (Hughen et al., 2000; Fairbanks et al., 2005). As the largest mobile carbon reservoir, the deep oceans have been implicated as the most likely source of this ¹⁴C-deplete CO₂. Records of benthic radiocarbon offsets from the atmosphere provide evidence of intermediate depth ventilation of a ¹⁴C-deplete reservoir during deglaciation. However, modeling studies focusing on ocean circulation changes alone are unable to replicate the full-observed glacial-interglacial CO₂ change. Changes in the biological pump could provide an additional mechanism contributing to the glacial drawdown and deglacial release of CO_2.  The Eastern Equatorial Pacific (EEP) is currently responsible for ~10% of global ocean primary productivity and is strongly connected to the Southern Ocean (Pennington et al., 2006) making it ideally suited for studying past changes in the biological pump. This study uses a multi-proxy approach to investigate the role of carbonate compensation and export productivity over the last 26,000yrs. Intermediate to deep-water transects of B/Ca, Cd/Ca, and U/Ca for the benthic foraminifera Cibicidoides wuelerstorfi were developed from 7 EEP cores (1620-3200m water-depth) extending from 8.2°N to 2.3°S in the Panama Basin. The fraction of calcite dissolved was estimated for high-resolution core TR163-23 (2,730m; 0.41°N, 92.16°W) using the G. menardii fractionation index (MFI) (Mekik et al., 2002). A record of benthic foraminiferal radiocarbon offsets from the atmosphere was also developed for TR163-23 providing a larger picture of the relative role of both ventilation and the biological pump in changing atmospheric CO₂ concentrations over the last glacial-interglacial transition.