Statistical precursor signals for Dansgaard-Oeschger cooling transitions

Abstract

Given the likely bistability of the Atlantic Meridional Overturning Circulation (AMOC) and its recently inferred weakening, it is important to investigate the capability of identifying robust precursor signals for a possible future AMOC collapse. Dansgaard-Oeschger (DO) events, manifested most clearly as abrupt Northern-Atlantic temperature jumps during glacial conditions, likely reflect past switches between strong and weak AMOC modes. Previous studies find statistical precursor signals for the DO warming transitions associated with a strengthening AMOC. Statistical precursor signals for the abrupt DO cooling transitions, presumably associated with AMOC transitions from the strong to the weak mode, have not been identified although these would be practically much more relevant given the concern of a future AMOC collapse. Here we identify robust and statistically significant precursor signals for several DO cooling transitions from Greenland ice core records, using the concept of critical slowing down. The main source of predictability stems from so-called rebound event, humps in the temperature observed at the end of interstadial, some decades to centuries prior to the transition. Based on conceptual models, we propose several dynamical mechanisms producing such rebound events.