More efficient North Atlantic carbon pump during the Last Glacial Maximum

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 CO ₂ outgassing from the Southern Ocean is the prevailing explanation for this carbon sequestration. By contrast, the North Atlantic Ocean—a major conduit for atmospheric CO ₂ 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 CO ₂ 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 CO ₂ absorption contributed to lowering ice-age atmospheric CO ₂.

Abstract

Atmospheric CO ₂ is governed by CO ₂ gains (e.g., via Southern Ocean outgassing) and losses (e.g., via North Atlantic absorption). Using a novel method to estimate air–sea CO ₂ exchange signals, the authors show that North Atlantic CO ₂ absorption became more efficient and contributed to lowering atmospheric CO ₂ during ice ages.