More efficient North Atlantic carbon pump during the Last Glacial Maximum

J Yu,E J Rohling,P J Chen,Z D Jin,F He,L Menviel,H Ren,I N Mccave,G L Foster,F Zhang,A P Roberts,D J R Thornalley,J F Mcmanus,Y Dai

doi:10.1038/s41467-019-10028-z

Abstract

During the Last Glacial Maximum (LGM; ~20,000 years ago), the global ocean sequestered a large amount of carbon lost from the atmosphere and terrestrial biosphere. Suppressed CO2 outgassing from the Southern Ocean is the prevailing explanation for this carbon sequestration. By contrast, the North Atlantic Ocean—a major conduit for atmospheric CO2 transport to the ocean interior via the overturning circulation—has received much less attention. Here we demonstrate that North Atlantic carbon pump efficiency during the LGM was almost doubled relative to the Holocene. This is based on a novel proxy approach to estimate air–sea CO2 exchange signals using combined carbonate ion and nutrient reconstructions for multiple sediment cores from the North Atlantic. Our data indicate that in tandem with Southern Ocean processes, enhanced North Atlantic CO2 absorption contributed to lowering ice-age atmospheric CO2.

Highlights

During the Last Glacial Maximum (LGM; ~20,000 years ago), the global ocean sequestered a large amount of carbon lost from the atmosphere and terrestrial biosphere
We find that the last glacial North Atlantic carbon absorption became more efficient, highlighting a critical role of the North Atlantic Ocean in regulating glacial–interglacial atmospheric CO2 changes
Any effect of ocean processes on atmospheric pressure of CO2 (pCO2) must occur via air–sea CO2 exchange

Summary

Introduction

During the Last Glacial Maximum (LGM; ~20,000 years ago), the global ocean sequestered a large amount of carbon lost from the atmosphere and terrestrial biosphere. We demonstrate that North Atlantic carbon pump efficiency during the LGM was almost doubled relative to the Holocene. Large-scale oceanic carbon sequestration occurred during Plio-Pleistocene glaciations[5,6,7]. This is commonly attributed to reduced glacial Southern Ocean CO2 outgassing[6,8,9], while even the sign of past North Atlantic CO2 uptake efficiency changes remains unconstrained. We present a novel proxy approach to trace atmospheric CO2 invasion in the North Atlantic and thereby evaluate its role in carbon sequestration in ice-age oceans. We find that the last glacial North Atlantic carbon absorption became more efficient, highlighting a critical role of the North Atlantic Ocean in regulating glacial–interglacial atmospheric CO2 changes

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