Deep convection and ocean overturning

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• Bishakh Gayen, University of Melbourne
• Friday 04 April 2025, 13:00-14:00
• BAS Seminar Room 1.

If you have a question about this talk, please contact Dr Birgit Rogalla.

The ocean’s circulation plays a pivotal role in Earth’s climate system, with its changes during climate transitions being of critical importance. This study, grounded in the principle of dynamical similarity, employs Direct Numerical Simulation (DNS) in an idealized setup to dissect the complexities of ocean circulation, with a particular focus on the North Atlantic and the role of buoyancy and wind in shaping the hydrological cycle.

We begin with a simple system—a non-rotating ocean forced by a single scalar—then gradually introduce complexity by adding constant/variable rotation, wind forcing, and a second scalar. Surprisingly, our results show the spontaneous formation of gyres and a western boundary current, along with full-depth overturning, even without the introduction of wind. Wind forcing further localizes upwelling near the western boundary current and primarily strengthens the gyres while having less influence on overturning circulation. With the introduction of a second scalar (salinity), our results become more representative of the real ocean, reproducing key features such as mode water formation, mid-latitude deeper thermocline structures, and polar haloclines, both with and without wind forcing. Our DNS framework is well-suited for resolving convection processes, including diffusive convection near the poles and salt fingering in mid-latitudes, both of which are crucial for establishing mixed layers and pycnoclines in these regions.

A key highlight of our study is capturing ocean circulation across multiple scales—from basin-scale overturning and gyres to mesoscale eddies, submesoscale dynamics, and millimeter-scale convection. These multiscale interactions regulate heat, salt, and tracer transport. Our highresolution approach explicitly resolves the interplay between large-scale circulation and small-scale turbulent mixing, offering deeper insights into ocean stratification, ventilation, and buoyancy-driven flows, providing critical insights for forecasting the evolving dynamics of the North Atlantic.

This talk is part of the British Antarctic Survey - Polar Oceans seminar series series.

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