The role of sea ice in AMOC recovery in TraCE-21KII simulation

Freshwater forcing (FWF) is recognized as a primary driver of abrupt Atlantic Meridional Overturning Circulation (AMOC) changes during significant paleoclimate variations. Numerous hosing experiments have been conducted to examine the sensitivity of AMOC to FWF; however, most of research effort was on the AMOC shutdown with few examining its recovery. Therefore, the processes underlying AMOC recovery remain uncertain.

This study employs version II of the TraCE-21K simulation (TraCE-21K-II) using the Community Climate System Model version 3 (CCSM3) to investigate key factors and mechanisms behind the two-phase AMOC recovery, shown in the TraCE-21K-II simulation, following the sudden cessation of FWF input at the end of the Younger Dryas (YD). Our findings reveal a strong correlation between AMOC strength and sea surface salinity (SSS) patterns in the North Atlantic, influenced differently by FWF and sea ice cover during various paleoclimate periods. Before the initial AMOC recovery, SSS is dominated by FWF input, with sea ice mostly covering high-latitude regions throughout the YD. As the FWF ceases, the interaction of warm, salty subtropical water with cold, fresh northern water induces AMOC strength oscillations. Eventually, persistent northward flow of warm, salty water leads to sea ice collapse, resulting in a sharp SSS increase and triggering the second recovery phase. These results highlight the critical role of SSS-related processes in AMOC variation and argue that the AMOC recovery may not be solely influenced by the cessation of FWF. Investigating these mechanisms further could prompt a reassessment of our current knowledge of AMOC dynamics and their implications for future climate projections.