Glacial Atlantic Carbon Storage Enhanced by a Shallow AMOC and Marine Aggregates Sinking

Abstract

Abstract Representing glacial‐interglacial changes in ocean carbon sequestration remains a major challenge for Earth System Models (ESMs). Uncertainties in ocean circulation and biological carbon export are essential causes for model‐data mismatch. We quantify the impact of these factors by calibrating the Max Planck Institute‐ESM. A shallower and weaker glacial Atlantic Meridional Overturning Circulation (AMOC) than the present day, achieved by decreasing background vertical diffusivity, enables capturing the main features in observed δ13C, 14C and CO32−. A prognostic sinking scheme responding to changing dust deposition and biological production enhances glacial ocean organic matter export efficiency in high latitudes. Together, the shallower AMOC and a comprehensive sinking scheme substantially improve model‐data comparison and carbon storage in the glacial Atlantic but not in the Pacific and Indian oceans, mainly due to reduced primary production. Our results yield that representing glacial‐interglacial ocean carbon storage in ESMs requires both constraining ocean circulation and improved biogeochemical processes.

Keywords

• ocean biogeochemistry
• last glacial maximum
• model‐data comparison
• ocean circulation
• marine aggregate sinking
• Earth system model