Heat is going up in the Kerguelen fronts, following elephant seals

Image of the Month - January 2020

Absolute dynamic topography (top left) and filaments (FSLE, top right) with buoyancy mapped along an elephant seal's track. Bottom, buoyancy and buoyancy gradient along the elephant seal track, and vertical heat transport deduced from the different measurements (Adapted from Siegelman et al. [2019, Nat. Geosci.])
Absolute dynamic topography (top left) and filaments (FSLE, top right) with buoyancy mapped along an elephant seal's track. Bottom, buoyancy and buoyancy gradient along the elephant seal track, and vertical heat transport deduced from the different measurements (Adapted from Siegelman et al. [2019, Nat. Geosci.])


Kerguelen Island area is a oceanographically dynamic area, part of the Antarctic Circumpolar Current system, and a very sensitive biological hotspot. It has been the focus of several oceanographic campaigns, with ocean color, eddies and currents measurements. A number of marine animals around the archipelago have also been tracked, turning around eddies, or reaching fronts as pinpointed by altimetry-extracted filament data (FSLE). However, the elephant seals are also diving when foraging. The Argos beacons used to track their positions at the surface is also recording information on those dives: temperature, salinity (conductivity), depth (pressure). Much like an Argo float, but with much shorter and numerous measurement cycles. Thus they enable to measure sections along their paths in the ocean depths. 

From those measurements, density (or its reverse, buoyancy) can be deduced. With this information, and the Absolute Dynamic Topography from altimetry (providing surface pressure), plus the filaments the fronts, an analysis of the in-depth structure of the ocean in the area has been done. It appears that in addition with warm water getting down in large scale fronts, the vertical heat transport in the deep-reaching fronts at submesoscale around Kerguelen is "warm water upwards". This can be important for the atmosphere cooling effect of the ocean, and lead to more studies in other places, ideally at submesocale. Swot should provide with this level of ocean feature at the surface in the future. In-depth data will still be needed, from living auxiliaries such as elephant seals, or from automated floats.

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Reference:

  •  Lia Siegelman, Patrice Klein, Pascal Rivière, Andrew F. Thompson, Hector S. Torres, Mar Flexas, Dimitris Menemenlis, 2019: Enhanced upward heat transport at deep
    submesoscale ocean fronts, Nature Geoscience, https://doi.org/10.1038/s41561-019-0489-1