Links between subpolar Northwest Atlantic surface to deep ocean variability and Atlantic Meridional Overturning Circulation since the Last Glacial Maximum
Final Report Abstract
The SAINT project focused on the reconstruction of (sub)surface ocean conditions and foraminiferal stable oxygen and carbon isotope ratios of the subpolar Atlantic to assess mechanism underlying rapid climate events and climate transitions since the LGM. The main tools used for paleoenvironmental reconstructions were the stable oxygen/carbon isotope and Mg/Ca composition as well as radiocarbon dating of benthic and planktic foraminifera. Important results include (1) the successful reconstruction of temporal and spatial changes in water mass distribution in the subpolar Northwest Atlantic since the LGM, (2) the description of the response of surface-to-subsurface ocean conditions during AMOC slowdowns (3) the key observation that rapid changes of subsurface temperatures in the subpolar western North Atlantic are pivotal to understand rapid ocean – ice sheet interactions during rapid ice-sheet instabilities associated with Heinrich Events. Our records verify and expand results from theoretical model experiments, further proposing subsurface ocean warming of the western subpolar North Atlantic as a natural feedback mechanism to slowdowns of the AMOC over the last 27,000 years. Moreover, our results are in close agreement with ice-sheet modeling studies suggesting that subsurface ocean warming in the western subpolar North Atlantic triggered rapid ice-sheet instabilities during Heinrich Events. The most recent report of the Intergovernmental Panel on Climate Change projects a future decline of the AMOC due to anthropogenic warming in the 21st century (IPCC, 2021). New empirical data suggest the AMOC has been evolved to a point close to a critical transition to its weak circulation mode. The achieved results during SAINT provide robust evidence for past critical transitions to a weak AMOC mode are accompanied by the massive build-up of ocean heat in the western subpolar North Atlantic that triggers ice-sheet instabilities during Heinrich Events. The expected weakening of the AMOC in the 21st century may result in an amplified increase in the North Atlantic heat content that could be critical for the stability of modern, marine-terminating Arctic glaciers and the freshwater budget of the North Atlantic. The project results are paramount in the sense of refining future climate model simulations to better project ocean-ice sheet interactions under warming climate.
Publications
- (2020). Northern-sourced water dominated the Atlantic Ocean during the Last Glacial Maximum. Geology, 48(8), 826– 829
Pöppelmeier, F., Blaser, P., Gutjahr, M., Jaccard, S. L., Frank, M., Max, L., & Lippold, J.
(See online at https://doi.org/10.1130/g47628.1)
