1306 / 2024-09-20 23:59:59

Dynamics of Mixed Layer Temperature Responses to the Southern Annular Mode in the Subantarctic

SAM,Mixed Layer Temperature,CMIP6

Through changing atmosphere pressure and wind fields and heat budget in the mixed layer, at different time scales, the influence of positive Southern Annular Mode (SAM) affecting the variation of Southern Ocean mixed layer temperatures (MLTs) are different. This work investigated how MLTs at latitudes 55°S to 70°S respond to the SAM on multiple timescales. Consistency was observed across 23 future scenario models included in the Climate Modeling Intercomparison Project phase 6 (CMIP6), displaying an initial negative trend that shifts to positive. Using the heat budget balance, we identified varying influencing factors over different time periods. Notably, different components of the heat budget have a significant impact on the warming rate of MLTs. For the instantaneous response (0 year), the heat budget terms influenced by horizontal flows in local sea areas show a significant positive correlation, indicating that the meridional flow-induced increase in heat flux contributes to an accelerated warming rate of MLTs. For the 1-7 year period, aside from the warm water masses of Circumpolar Deep Water (CDW), the net surface heat flux also significantly affects MLTs. Over 8-20 years, both the zonal velocity and vertical temperature gradient show a significant positive correlation with MLT changes, with anomalies in northward flow and enhanced CDW warm water masses jointly accelerating the MLT warming rate.