Altimetry-Based Diagnosis of Deep-Reaching Sub-Mesoscale Ocean Fronts

In this study, Siegelman et al., demonstrate that the FSLEs distributed by AVISO+ allow the reconstruction of sub-mesoscale dynamics down to 500 m in the ocean interior. More precisely, they highlight a relation between FSLE at the surface and lateral buoyancy gradients at depth. This work proposes an innovative methodology to recover the correct orientation and strength of sub-mesocale fonts that should be useful to the physical oceanographic community to analyze their sub-mesoscale-resolving datasets and plan future oceanographic field campaigns.

FSLE at (a) 39 m, (b) 209 m and |∇ b| at (c) 39 m, (d) 209 m. Randomly selected snapshot taken on 27 October 2011 from a numerical simulation. See Siegelman et al. Fluids (2020)

Reference:

Siegelman, L.; Klein, P.; Thompson, A.F.; Torres, H.S.; Menemenlis, D. Altimetry-Based Diagnosis of Deep-Reaching Sub-Mesoscale Ocean Fronts. Fluids 2020, 5, 145. https://doi.org/10.3390/fluids5030145

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

In their Antarctic Circumpolar Current vertical heat transport study, Siegelman et al demonstrated that submesoscale fronts are shown to drive vertical upward heat transport from the ocean interior back to the surface that is larger than other contributions to vertical heat transport. They showed that the FSLE estimations and buoyancy gradients at 300m estimated from data collected by a female elephant seal are in good agreement as well as the relationship linking the two (see figures).
This study suggests that the submesoscale ocean dynamics play a crucial role in the earth heat budget of the climate system.
Also in the image of the month, January 2020.

Oil spills and red tides

Lagrangian Coherent Structures (LCSs) identified using techniques similar to the FSLE, the so-called geodesic theory of LCS by Haller and Beron-Vera (2012), have been also used to monitor dispersion patterns of red tides, and oil spills. In Olascoaga et al. (2006), LCSs extracted from simulated currents suggested the presence of a resilient barrier to transport across the West Florida Shelf which provides a large degree of isolation that favors red tide development. The dispersion of the nutrients released by rivers in the Gulf of Mexico that could trigger a red tide event was analyzed in Olascoaga et al., 2008 and Olascoaga, 2010.
Persistently attracting cores of simulated geodesic LCSs were found to predict with a few days of anticipation fingering instabilities in the oil slick produced by the Deepwater Horizon spill (Olascoaga and Haller, 2012). More recently, and relying on currents from the Aviso product, Olascoaga et al. (2013) predicted similar fingering patterns in drifting buoys from the Grand Lagrangian Deployment (GLAD) carried out in the northern Gulf of Mexico to gain insight into its circulation in connection to the transport of hydrocarbons.

Identifying eddies with the risk of contamination by Fukushima-derived radionuclides

The cruise of R/V “Professor Gagarinskiy” was conducted in the Northwest Pacific from 12 June to 10 July 2012 with the aim to measure artificial radionuclides after the accident at the Fukushima Nuclear Power Plant on 11 March 2011. FTLE and other Lagrangian maps computed on the velocity AVISO products and outputs of numerical models of circulation, are actively used in analyzing mixing and transport in the ocean ( Prants et al., 2011 DES, Prants et al., 2014 PNG, Prants 2013 PhScr, Prants, 2014 EPJST).

Those maps have been sent electronically each day to the board. They helped to correct the cruise track in order to cross prominent eddies in the area (Budyansky et al., 2015 DSR). Simulated distribution of radionuclides concentration to the end of June 2012 with measured concentrations of ¹³⁴Cs and ¹³⁷Cs are shown in figure below (left). The Lyapunov map in the right show anticyclonic eddies A, B, C, D, E, F and G which have been sampled at the surface and in depth. The results of observations are consistent with the simulated results. The highest concentrations of ¹³⁴Cs and ¹³⁷Cs have been found to exceed ten times the background levels before the accident. Maximal content of radiocesium was observed inside the mesoscale anticyclonic eddies. Among the sampled eddies, the eddy B and the Kuroshio warm-core ring G presented the highest concentration of cesium.