Du Plessis, MDSwart, SBiddle, LCGiddy, ISMonteiro, Pedro MReason, CJCThompson, AFNicholson, Sarah-Anne2023-04-062023-04-062022-04Du Plessis, M., Swart, S., Biddle, L., Giddy, I., Monteiro, P.M., Reason, C., Thompson, A. & Nicholson, S. et al. 2022. The daily-resolved Southern Ocean mixed layer: Regional contrasts assessed using glider observations. <i>Journal of Geophysical Research: Oceans, 127(4).</i> http://hdl.handle.net/10204/127282169-92752169-9291https://doi.org/10.1029/2021JC017760http://hdl.handle.net/10204/12728Water mass transformation in the Southern Ocean is vital for driving the large-scale overturning circulation, which transports heat from the surface to the ocean interior. Using profiling gliders, this study investigates the role of summertime buoyancy forcing and wind-driven processes on the intraseasonal (1–10 days) mixed layer thermohaline variability in three Southern Ocean regions southwest of Africa important for water mass transformation—the Subantarctic Zone (SAZ), Polar Frontal Zone (PFZ), and Marginal Ice Zone (MIZ). At intraseasonal time scales, heat flux was shown as the main driver of buoyancy gain in all regions. In the SAZ and MIZ, shallow mixed layers and strong stratification enhanced mixed layer buoyancy gain by trapping incoming heat, while buoyancy loss resulted primarily from the entrainment of cold, salty water from below. In the PFZ, rapid mixing linked to Southern Ocean storms set persistently deep mixed layers and suppressed mixed layer intraseasonal thermohaline variability. In the polar regions, lateral stirring of meltwater from seasonal sea-ice melt dominated daily mixed layer salinity variability. We propose that these meltwater fronts are advected to the PFZ during late summer, indicating the potential for seasonal sea-ice freshwater to impact a region where the upwelling limb of overturning circulation reaches the surface. This study reveals a regional dependence of how the mixed layer thermohaline properties respond to small spatiotemporal processes, emphasizing the importance of surface forcing occurring between 1 and 10 days on the mixed layer water mass transformation in the Southern Ocean.FulltextenBuoyancyMarginal Ice ZonePolar Frontal ZoneRegional glider missionsSea-ice impacted Southern OceanStorms suppressesSubantarcticArticleDu Plessis, M., Swart, S., Biddle, L., Giddy, I., Monteiro, P. M., Reason, C., ... Nicholson, S. (2022). The daily-resolved Southern Ocean mixed layer: Regional contrasts assessed using glider observations. <i>Journal of Geophysical Research: Oceans, 127(4)</i>, http://hdl.handle.net/10204/12728Du Plessis, MD, S Swart, LC Biddle, IS Giddy, Pedro M Monteiro, CJC Reason, AF Thompson, and Sarah-Anne Nicholson "The daily-resolved Southern Ocean mixed layer: Regional contrasts assessed using glider observations." <i>Journal of Geophysical Research: Oceans, 127(4)</i> (2022) http://hdl.handle.net/10204/12728Du Plessis M, Swart S, Biddle L, Giddy I, Monteiro PM, Reason C, et al. The daily-resolved Southern Ocean mixed layer: Regional contrasts assessed using glider observations. Journal of Geophysical Research: Oceans, 127(4). 2022; http://hdl.handle.net/10204/12728.TY - Article AU - Du Plessis, MD AU - Swart, S AU - Biddle, LC AU - Giddy, IS AU - Monteiro, Pedro M AU - Reason, CJC AU - Thompson, AF AU - Nicholson, Sarah-Anne AB - Water mass transformation in the Southern Ocean is vital for driving the large-scale overturning circulation, which transports heat from the surface to the ocean interior. Using profiling gliders, this study investigates the role of summertime buoyancy forcing and wind-driven processes on the intraseasonal (1–10 days) mixed layer thermohaline variability in three Southern Ocean regions southwest of Africa important for water mass transformation—the Subantarctic Zone (SAZ), Polar Frontal Zone (PFZ), and Marginal Ice Zone (MIZ). At intraseasonal time scales, heat flux was shown as the main driver of buoyancy gain in all regions. In the SAZ and MIZ, shallow mixed layers and strong stratification enhanced mixed layer buoyancy gain by trapping incoming heat, while buoyancy loss resulted primarily from the entrainment of cold, salty water from below. In the PFZ, rapid mixing linked to Southern Ocean storms set persistently deep mixed layers and suppressed mixed layer intraseasonal thermohaline variability. In the polar regions, lateral stirring of meltwater from seasonal sea-ice melt dominated daily mixed layer salinity variability. We propose that these meltwater fronts are advected to the PFZ during late summer, indicating the potential for seasonal sea-ice freshwater to impact a region where the upwelling limb of overturning circulation reaches the surface. This study reveals a regional dependence of how the mixed layer thermohaline properties respond to small spatiotemporal processes, emphasizing the importance of surface forcing occurring between 1 and 10 days on the mixed layer water mass transformation in the Southern Ocean. DA - 2022-04 DB - ResearchSpace DP - CSIR J1 - Journal of Geophysical Research: Oceans, 127(4) KW - Buoyancy KW - Marginal Ice Zone KW - Polar Frontal Zone KW - Regional glider missions KW - Sea-ice impacted Southern Ocean KW - Storms suppresses KW - Subantarctic LK - https://researchspace.csir.co.za PY - 2022 SM - 2169-9275 SM - 2169-9291 T1 - The daily-resolved Southern Ocean mixed layer: Regional contrasts assessed using glider observations TI - The daily-resolved Southern Ocean mixed layer: Regional contrasts assessed using glider observations UR - http://hdl.handle.net/10204/12728 ER -26535