Presenter: Yue Bai (California Institute of Technology)

Description:
Enhanced vertical velocities due to submesoscale dynamics impact near-surface exchanges of carbon and heat. These processes are particularly relevant to the Southern Ocean, where surface-derived waters are subducted and deep waters outcrop into the surface mixed layer. The interaction between the surface wind stress and oceanic fronts occurs through thermal and current feedbacks, which influence the ocean surface vertical velocity and therefore could substantially modify surface-interior exchange. These dynamics have been explored at mesoscales, yet the importance of submesoscale wind-front interactions on large-scale property distributions remains largely unconstrained. Here, we investigate submesoscale wind-front interactions in both energetic, e.g. Drake Passage, and quiescent regions of the Southern Ocean using a realistic global coupled simulation of GEOS atmosphere and MITgcm ocean (2-4 km grid). Consistent with previous mesoscale studies, extreme values of wind stress curl and divergence arise from thermal and current feedbacks. However, the magnitude of these anomalies, O(100) N/m²/10,000km, are at least O(10) times larger than those reported at mesoscale, suggesting more vigorous submesoscale wind-front coupling. The simulation also reveals that both feedbacks may jointly produce and reinforce wind stress curl anomalies. Thus, analyzing either feedback in isolation misrepresents their impact. Spatial variations in background energy levels partition the relative strength of each feedback: the thermal feedback is severely diminished in quiescent regions whereas the current feedback is more spatially homogeneous. Overall, energetic regimes host stronger wind-front coupling and may make a leading order contribution to upper-ocean vertical transport. This new appreciation of submesoscale wind-front interactions might shed light on model-observation discrepancies on the Southern Ocean’s carbon uptake and the region’s long-term ability to mediate climate change.