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

Abstract

The last deglacial climate evolution, from 19 to 9 thousand years before the present, represents the vital role of feedback in the Earth’s climate system. The Southern Ocean played a fundamental role by exchanging nutrients and carbon-rich deep ocean water with the surface during the last deglaciation. This study employs a fully coupled Earth system model to investigate the evolution of Southern Ocean dynamics and the roles of changes in orbital and meltwater forcings during the last deglaciation. The simulation supports that the Southern Ocean upwelling was primarily driven by windstress. The results show that the melting and formation of Antarctic sea ice feedback influenced Southern Ocean surface buoyancy flux. The increase in Antarctic sea ice melt-induced freshwater flux resulted in a steepened north-south surface salinity gradient in the Southern Ocean, which enhanced the upwelling. The single-forcing experiments indicate that the deglacial changes in orbital insolation influenced the Southern Ocean upwelling. The experiments also highlight the dominant role of Northern Hemisphere meltwater discharge in the upper and lower branch of the Meridional Overturning Circulation. Furthermore, orbital forcing shows lesser deglacial Antarctic sea ice retreat than the Northern Hemisphere meltwater forcing, which follows the bipolar seesaw mechanism.

Unraveling the Influence of the Atlantic Subpolar Gyre on the Thermohaline Circulation in the Past 20,000 Years

“…We found that the average and maximum mixed layer depth vary coherently with a Pearson correlation coefficient of 0.89 (p = 0) (Figure 1e,f). The mixed layer depth decreased during the HS1 and YD periods, which indicates reduced deep convection and a weakened AMOC strength (Figure 1g), which is in agreement with previous studies [10][11][12][13]. The reduction in the AMOC strength weakened the upper meridional overturning cell, inducing a bipolar seesaw response [11], and it reduced the northward meridional heat transport.…”

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.…”

The Association of Antarctic Sea Ice with the Subantarctic Mode and Antarctic Intermediate Waters during the Last Deglaciation

“…Recent publications employing the TraCE-21ka experiment model simulations have highlighted the relationship between Antarctic sea ice and SO processes [7,9,10]. The SO upwelling was made stronger by an increase in freshwater discharge brought on by Antarctic sea ice melting [6,10].…”

“…Paleoclimate scientists acknowledge the SO overturning circulation to be predominantly wind-driven [4,5]. However, numerous studies have demonstrated that variations in buoyant flux caused by freshwater outflow [6,7], ocean eddies [8], topography [7], and Antarctic sea ice feedback [9][10][11][12][13][14] contribute to the SO dynamical changes during the last deglacial time. Therefore, understanding how the distribution of Antarctic sea ice affects the surface distribution and transport of AAIW and SAMW movement is crucial.…”