Ice sheet decline and rising atmospheric CO2 control AMOC sensitivity to deglacial meltwater discharge

• Published in: Global and Planetary Change
• Main Authors: Sun, Yuchen, Knorr, Gregor, Zhang, Xu, Tarasov, Lev, Barker, Stephen, Werner, Martin, Lohmann, Gerrit
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2022
• Subjects: Ice Sheet; North Atlantic Deep Water; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/55514/; https://oceanrep.geomar.de/id/eprint/55514/1/1_s2_0_S0921818122000224_main.pdf; https://doi.org/10.1016/j.gloplacha.2022.103755

Highlights: • Climate model sensitivity experiments are performed using state-of-the-art ice sheet and freshwater reconstructions • Declining Northern Hemisphere ice sheets increase the sensitivity of the AMOC to North Atlantic meltwater discharge • Deglacial rise in atmospheric CO2 concentration decreases the sensitivity of the AMOC to North Atlantic meltwater discharge • Both effects provide a complementary perspective to existing explanations for abrupt AMOC transitions Abstract: The last deglaciation was characterized by a sequence of abrupt climate events thought to be linked to rapid changes in Atlantic meridional overturning circulation (AMOC). The sequence includes a weakening of the AMOC after the Last Glacial Maximum (LGM) during Heinrich Stadial 1 (HS1), which ends with an abrupt AMOC amplification at the transition to the Bølling/Allerød (B/A). This transition occurs despite persistent deglacial meltwater fluxes that counteract vigorous North Atlantic deep-water formation. Using the Earth system model COSMOS with a range of deglacial boundary conditions and reconstructed deglacial meltwater fluxes, we show that deglacial CO2 rise and ice sheet decline modulate the sensitivity of the AMOC to these fluxes. While declining ice sheets increase the sensitivity, increasing atmospheric CO2 levels tend to counteract this effect. Therefore, the occurrence of a weaker HS1 AMOC and an abrupt AMOC increase in the presence of meltwater, might be explained by these effects, as an alternative to or in combination with changes in the magnitude or routing of meltwater discharge.