Controls on Wintertime Ventilation in Southern Drake Passage

Abstract

Drake Passage is a key region for transport between the surface and interior ocean, but a mechanistic understanding of this exchange remains immature. Here, we present wintertime, submesoscale‐resolving hydrographic transects spanning the southern boundary of the Antarctic Circumpolar Current and the Polar Front (PF). Despite the strong surface wind and buoyancy forcing, a freshwater lens suppresses surface‐interior exchange south of the PF; ventilation is instead localized to the PF. Multiple lines of the analysis suggest submesoscale processes contribute to ventilation at the PF, including small‐scale, O(10 km), frontal structure in water mass properties below the mixed layer and modulation of a surface eddy diffusivity at sub‐50 km scales. These results show that ventilation is sensitive to both submesoscale properties near fronts and non‐local processes, for example, sea‐ice melt, that set stratification and mixed layer properties. This highlights the need for adaptive observing strategies to constrain Southern Ocean heat and carbon budgets.

Sub‐Mesoscale Wind‐Front Interactions: The Combined Impact of Thermal and Current Feedback

“…We select this region because it is aligned with the westerly wind stress maximum (Figure 1b), and the Southern Ocean is a key site of air-sea exchange and ventilation (Dove et al, 2021;Gruber et al, 2019;Marshall & Speer, 2012), both of which may be impacted by vertical velocities linked to small-scale wind-front interactions (Gaube et al, 2015;Renault et al, 2023). Furthermore, the two 5° × 5° subdomains compare a quiescent, low eddy kinetic energy (EKE) regime, and a turbulent frontal region with higher background energy levels, the latter of which have been shown to localize and enhance ventilation (Dove et al, 2022(Dove et al, , 2023. The surface Ro distribution (Figures 1c and 1d) for quiescent and energetic regions both favor cyclonic eddies and respectively have skewness values of 0.4 and 0.9, suggesting more sub-mesoscale fronts (Barkan et al, 2019;Buckingham et al, 2016) and frontal slumping (Hoskins & Brertherton, 1972) in the energetic region; Ro also has a larger magnitude in the energetic region.…”

Tracer Stirring and Variability in the Antarctic Circumpolar Current Near the Southwest Indian Ridge

“…Sections of tracers show intricate structure at many scales, in addition to the largest tracer anomalies (Figure 2; Figure S3 in Supporting Information S1), which also emerge as coherent clusters in T-S plots (see Figure 5 in Dove et al (2021) or Figure S4 in Supporting Information S1, also (Dove et al, 2023)). These anomalies, spanning across large depth ranges and isopycnals, are likely formed due to lateral stirring by the barotropic flow, and evidence of the baroclinic vertical shear impacting tracer structures can be seen in the layered structures of the anomalies.…”