Preconditioning of Polynya Formation by Ocean Mixing at Maud Rise, Antarctica

Antarctic open-ocean polynyas trigger vigorous wintertime convection, influencing ocean circulation and atmospheric processes. In the Weddell Sea, interaction between the Weddell Gyre and the Maud Rise seamount generates a Taylor column that favors polynya formation. However, owing to limited observations, the dynamics of such polynya formation remain partially understood, particularly the long-term preconditioning that sets the stage for polynya occurrence. We use glider observations from late austral summer 2022 to investigate the role of mixing in preconditioning, focusing on the interior layer below the pycnocline, which stores heat that melts sea ice and regulates deep convection. We show that multiple mixing processes contribute to the preconditioning. Widespread interleaving structures along the northwestern flank of Maud Rise are identified, indicating that warm, salty water intrudes into the Taylor column along isopycnals. This intrusion is likely driven by lateral shear and eddies, both arising from the flank's anticyclonic circulation. Moreover, eddy shedding, cabbeling, and diffusive convection jointly enhance lateral homogenization and destratification of the Taylor column interior below the pycnocline. Using the large eddy method and a triple decomposition of the tracer variance equation, we calculate snapshot-based along-isopycnal heat and salt transports from the Rise flanks into the Taylor column as ∼0.18 TW and ∼4.7 ×1⁢03 ⁢g ⁡k⁢g−1 ⁡m3 s−1, respectively. At these rates, idealized estimates suggest that polynya-favorable conditions could develop within 2–6 years of the observations. Our results highlight the role of mixing in polynya formation and the need to realistically represent these processes in climate-scale ocean models.