Quantifying LGM carbon drawdown due to changes in the biological pump efficiency through the reconstruction of deep-water oxygen, preformed phosphate, and preformed δ13C

Abstract:

Upwelling deep waters in the Southern Ocean release biologically sequestered carbon into the atmosphere, contributing to the relatively high atmospheric CO₂ levels during interglacial climate periods. Paleoceanographic evidence suggests this ‘CO₂ leak’ was lessened during the Last Glacial Maximum (LGM), potentially due to increased stratification, weaker and equatorward-shifted winds, and/or enhanced biological carbon export. The collective influences of these mechanisms on the ocean’s biological pump efficiency and atmospheric CO₂ can be quantified by determining preformed phosphate or preformed δ¹³C of deep waters. We have updated the Hoogakker et al. 2014 Δδ¹³C – O₂ calibration to over 25 core locations located through the Pacific, Atlantic, and Indian oceans from depths of 200 m to 4000 m. Preliminary results show a similar calibration to the findings from Hoogakker et al. 2014. Using this updated calibration, we independently quantify preformed PO₄ and preformed δ¹³C in LGM bottom waters using a compilation of published paleo-temperature, nutrient and oxygen estimates from benthic foraminifera. Note, our reconstructions of preformed PO₄ and performed δ¹³C are determined using apparent oxygen utilization (AOU). Thus, changes in our reconstructed preformed phosphate include changes in the biological pump efficiency, as well as changes in air-sea disequilibrium. Our results show that preformed phosphate of the Pacific and Indian deep ocean was reduced by about -0.6±0.2 µM and suggest that much of the Glacial-Interglacial CO₂ drawdown resulted from changes in the ocean’s biological pump efficiency. Preformed δ¹³C shows similar results.