Submesoscale flows described during the Southern Ocean winter for the first time

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Dr Louise Biddle is a researcher at the University of Gothenburg, Sweden. She is interested in the interactions between ice and ocean around Antarctica, with research focusing on both glacial meltwater and sea ice-ocean dynamics to understand how these processes affect the upper ocean. Using the MEOP database, she and co-author Dr Sebastiaan Swart described the variability in submesoscale processes under sea ice during the Southern Ocean winter for the first time, highlighting a significant submesoscale flux during the winter months of August and September (Biddle and Swart, 2020).

Submesoscale processes occur on small (1-10 km) and short (< day) scales, but can have a significant impact on vertical oceanic fluxes. Due to their submesoscale resolution, until recently they have been hard to observe – particularly so in the Southern Ocean. The oceanic uptake of heat and carbon in this region is of global significance and understanding any processes that can contribute to their vertical transport is of critical importance. However, with very few observations during the winter months, especially in the sea ice covered ocean, there was no knowledge of how the magnitude and impact of submesoscale processes may vary seasonally. To combat this challenge, we used the MEOP database, targeting Southern Elephant seals that like to transit through the sea ice zone during winter months. 

By focusing on a dataset tagged on Bouvet Island in 2008, we showed that the seal dives are able to resolve submesoscale features. To provide some statistical confidence in our results, we combined all 14 seals that dived under the sea ice to measure seasonal changes in mixed layer depth and horizontal buoyancy gradients (amongst other parameters), in order to estimate two submesoscale processes; Ekman Buoyancy Flux and Mixed Layer Eddy flux. Whilst Ekman Buoyancy Flux, which is a function of surface wind or ice stress, was moderated by the presence of sea ice, the deeper mixed layers formed during winter months in combination with increases in the horizontal buoyancy gradient resulted in a mid-winter maximum in Mixed Layer Eddy flux. This flux can result in stratification and shoaling of the mixed layer when it is greater than opposing wind or buoyancy fluxes, signifying a possible important driver in Southern Ocean vertical transport. 

We hope to extend this analysis to the circumpolar MEOP dataset, and make use of the new MEOP-SMS data to understand any regional differences in submesoscale processes – and any future high resolution observations under the sea ice can only enhance our current knowledge!


Reference: Biddle, L. C., & Swart, S. ( 2020). The observed seasonal cycle of submesoscale processes in the Antarctic marginal ice zone. Journal of Geophysical Research: Oceans, 125, e2019JC015587. https://doi.org/10.1029/2019JC015587

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