The Roles of Wind and Sea Ice in Driving the Deglacial Change in the Southern Ocean Upwelling: A Modeling Study

Abstract

The Southern Ocean (SO) played a fundamental role in the deglacial climate system by exchanging carbon-rich deep ocean water with the surface. The contribution of the SO’s physical mechanisms toward improving our understanding of SO upwelling’s dynamical changes is developing. Here, we investigated the simulated transient SO atmosphere, ocean, and sea ice evolution during the last deglaciation in a fully coupled Earth system model. Our results showed that decreases in SO upwelling followed the weakening of the Southern Hemisphere surface westerlies, wind stress forcing, and Antarctic sea ice coverage from the Last Glacial Maximum to the Heinrich Stadial 1 and the Younger Dryas. Our results support the idea that the SO upwelling is primarily driven by wind stress forcing. However, during the onset of the Holocene, SO upwelling increased while the strength of the wind stress decreased. The Antarctic sea ice change controlled the salt and freshwater fluxes, ocean density, and buoyancy flux, thereby influencing the SO’s dynamics. Our study highlighted the dynamic linkage of the Southern Hemisphere westerlies, ocean, and sea ice in the SO’s latitudes. Furthermore, it emphasized that zonal wind stress forcing and buoyancy forcing control by sea ice together regulate the change in the SO upwelling.

The Roles of Orbital and Meltwater Climate Forcings on the Southern Ocean Dynamics during the Last Deglaciation

“…For example, the TraCE-21ka model replicated the Asian-African monsoon [88], El Niño [89], the highlatitude seasonal temperature [90], the AMOC transport, and the SH regional sea surface temperature [5]. In addition, the model reasonably simulated the present-day atmospheric circulation and sea surface temperature in the SO [49,91].…”

The Influence of Antarctic Sea Ice Distribution on the Southern Ocean Overturning Circulation for the Past 20,000 Years

“…Previous studies have shown that the melting of Antarctic sea ice releases freshwater, which increases the buoyancy of Southern Ocean upwelled water (Iudicone et al, 2008) and strengthened the upper limb of the ocean meridional overturning circulation (Abernathey et al, 2016;Saenko et al, 2002). Furthermore, numerical simulations have confirmed the importance of freshwater fluxes in determining changes in Southern Ocean upwelling during the last deglacial period (Mandal et al, 2021;Mandal et al, 2022;Morrison et al, 2011).…”

“…The paleoclimatology community recognizes that the Southern Ocean overturning circulation is primarily driven by wind (Anderson et al, 2009;Menviel et al, 2018). Several studies, however, have found that changes in buoyancy flux caused by freshwater discharge (Abernathey et al, 2016;Liu et al, 2021), ocean eddies (Lauderdale et al, 2017), topography (Liu et al, 2021), and Antarctic sea ice feedback (Ferrari et al, 2014;Jansen & Nadeau, 2016;Mandal et al, 2021;Mandal et al, 2022;Marzocchi & Jansen, 2017;Stein et al, 2020) contribute to the Southern Ocean dynamical changes during the most recent deglacial period. As a result, it is critical to comprehend the role of Antarctic sea ice in surface buoyancy flux, which influences the Southern Ocean overturning circulation.…”

Deglacial Carbon Escape From the Northern Rim of the Southern Ocean

“…However, relatively stable LGM atmospheric CO 2 levels suggest that this was likely not a significant source of CO 2 to the atmosphere at this time. Model simulations have projected that reduced deep ocean ventilation was linked to expanded sea ice along with equatorward shifted Westerlies and Southern Ocean fronts in the LGM (Chen & Wang, 2021; Ferrari et al., 2014; Mandal et al., 2021; Menviel et al., 2015; Russell et al., 2006; Toggweiler et al., 2006). These new data are the first to clarify that the individual fronts did not move in sync or in parallel and identifies that the narrowing of the SAZ in the Indian Ocean was a significant process sequestering CO 2 .…”