Oceanic submesoscales from satellite and in situ observations
SWOT satellite © NASA/JPL-Caltech

Submesoscale fronts are difficult to observe in the ocean because of their small size and short lifetime (hours to days). Here we develop a methodology to study them at depth from satellite observations of sea level height and in situ CTD data. We provide observational evidence that submesoscale motions extend below the surface mixed layer and generate intense upward heat transport from the ocean interior back to the surface.
Submesoscale features refers to fronts and currents that are ~1-100 km in size. They are known to be associated with intense vertical velocities acting as a conduit between the atmosphere and ocean through which heat, carbon and other climatologicaly important gases enter the deep ocean.

Deep-reaching submesoscales in a high-resolution numerical model

Surface currents from LLC4320 in the Kergueln region, Indian sector of the Southern Ocean
Here we use the high-resolution numerical simulation  MITgcm LLC4320 to confirm the observational results regarding deep-reaching submesoscales and study their underlying dynamics.

We show that, contrary to the classical paradigm, energetic submesoscales extend below the mixed-layer depth in the Antarctic Circumpolar Current in late spring/early summer. These deep-reaching submesoscale fronts are characterized by large Rossby and low Richardson numbers and vigorous frontogenesis. They are an efficient pathway for the transport of heat from the ocean interior to the surface, suggesting the presence of an intensified oceanic restratification at depth.
Bio-physics interactions

Read more about it on the NASA and MEOP webpages
It has been hypothezised that submesoscale features affect oceanic biological productivity and higher trophic levels. Here, we show that submesoscale ocean fronts located within a standing meander of the Antarctic Circumpolar Current enhance the foraging activity of southern elephant seals using high-resolution profiles from seal-borne CTD (conductivity-temperature-depth) tags.

Post-processing calibration of animal-borne CTD tags

Read more about it here
Hydrographic data collected by marine mammals equipped with conductivity–temperature–depth (CTD) tags represent a consequent source of information, especially in the undersampled polar oceans where observations are notoriously hard to acquire. However, to be fitted on marine mammals, the tags are considerably smaller than a traditional CTD and often contain residual noise related to the miniaturized sensors capabilities. Here, we develop a processing method to calibrate the CTD data, which is implemented in the MEOP (Marine Mammals Exploring the Oceans Pole to Pole) database.

Siegelman, L., Klein, P., Thompson, A. F., Torres, H. S., & Menemenlis, D. (2020). Altimetry-based diagnosis of deep-reaching sub-mesoscale ocean fronts. Fluids, 5(3), 145. [doi, pdf]

Siegelman, L., Klein, P., Rivière, P., Thompson, A. F., Torres, H. S., Flexas, M., & Menemenlis, D. (2020). Enhanced upward heat transport at deep submesoscale ocean fronts. Nature Geoscience, 13(1), 50-55. [doi, pdf]

Siegelman, L. (2020). Energetic submesoscale dynamics in the ocean interior. Journal of Physical Oceanography, 50(3), 727-749. [doi, pdf]

Siegelman, L. (2019). Ageostrophic dynamics in the ocean interior (Doctoral dissertation, Université de Bretagne Occidentale). [doi, pdf]

Siegelman, L., O’toole, M., Flexas, M., Rivière, P., & Klein, P. (2019). Submesoscale ocean fronts act as biological hotspot for southern elephant seal. Scientific reports, 9(1), 1-13. [doi, pdf]

Rivière, P., Jaud, T., Siegelman, L., Klein, P., Cotté, C., Le Sommer, J., Dencausse, G., & Guinet, C. (2019). Sub‐mesoscale fronts modify elephant seals foraging behavior. Limnology and Oceanography Letters, 4(6), 193-204. [doi,

Siegelman, L., Roquet, F., Mensah, V., Rivière, P., Pauthenet, E., Picard, B., & Guinet, C. (2019). Correction and accuracy of high-and low-resolution CTD data from animal-borne instruments. Journal of Atmospheric and Oceanic Technology, 36(5), 745-760. [doi, pdf]

Mensah, V., Roquet, F., Siegelman, L., Picard, B., Pauthenet, E., & Guinet, C. (2018). A Correction for the thermal mass–induced errors of CTD tags mounted on marine mammals. Journal of atmospheric and oceanic technology, 35(6), 1237-1252. [doi, pdf]

© 2021 Lia Siegelman | Image Credits