Is There Robust Evidence for Freshwater-Driven AMOC Changes? A Synthesis of Data, Models, and Mechanisms

The Atlantic Meridional Overturning Circulation (AMOC) transports heat to high latitudes and carbon to the deep ocean. Paleoceanographic observations have led to the widely held view that the strength of the AMOC was significantly reduced at two intervals during the most recent glacial-to-interglacial transition, with global climate impacts. Climate models predict that the AMOC may decline in the future due to anthropogenic forcing, but the time periods for modern observations are too short to detect recent trends with high confidence. To understand the likelihood of future changes in the AMOC, it is important to understand the mechanisms that drove past changes in AMOC strength. In this paper we review (1) the paleoceanographic proxy data that have led to the widespread view that the AMOC sharply decreased for periods of several thousand years during the last deglaciation, (2) climate model simulations of the last deglaciation, with particular attention to their use of fresh water to alter the AMOC, (3) the physical mechanisms that could have driven past changes in the AMOC, and (4) how insights from past ocean change can inform our understanding of what may happen in the future.