WHOI PO
Alexey Fedorov, Yale - Millennial Variability, Regime Shifts, and Equilibrium States of Global Ocean Meridional Overturning Circulation in Long Climate Simulations
| Date |
Time |
Location |
| August 12th, 2025 |
3:05pm-4:05pm |
Clark 507 |
Title: Millennial Variability, Regime Shifts, and Equilibrium States of Global Ocean Meridional Overturning Circulation in Long Climate Simulations
Abstract: The long-term response of meridional overturning circulation (MOC) to radiative forcing is critical in regulating Earth’s climate. To investigate this problem, we perform ultra-long climate simulations, with both high and low atmospheric CO2 concentrations ranging from 0.35 to 16 times the preindustrial level. The experiments use one of the CESM1 configurations and last up to 11,000 years. In the global warming experiments, a rapid collapse of the AMOC occurs, attributed to a strengthening upper-ocean stratification whichinhibits deep-water formation in the subpolar North Atlantic, aided by the positive salinity advection feedback. The AMOC recovers in the 2xCO2 and 4xCO2 experiments, but not in the 8xCO2 and 16xCO2 experiments. In the abrupt 4xCO2 experiment, with the AMOC in a state of weak overturning, a spontaneous activation of the Pacific MOC (PMOC) occurs some 2,500 years after the start of the experiment, attributed to destabilization of the North Pacific water column by slowly increasing ocean heat content below the halocline, and increasing salinity above, but not below the halocline. Then, at 3,500 years the PMOC collapses concomitantly with an AMOC recovery in the experiment, highlighting the Atlantic-Pacific seesaw as a critical part of the system’s transition toward equilibrium. Several global cooling experiments exhibit spontaneous millennial oscillations, closely resembling the Dansgaard-Oeschger events of the late Pleistocene Epoch. The interaction between ocean salinity stratification and overturning circulation drives this oscillation. In the warm 2xCO2 experiment we also observe millennial variability, but linked to the global ocean abyssal overturning cell. Thus, our experiments reveal a very rich dynamics of the global MOC, which however emerges only at sufficiently long, multi-millennial timescales.