Erosion of the Subsurface Salinity Maximum of the Loop Current Eddies From Glider Observations and a Numerical Model

Sosa‐Gutierrez, Rosmery; Pallàs‐Sanz, Enric; Jouanno, Julien; Chaigneau, Alexis; Candela, Julio; Tenreiro, M.

doi:10.1029/2019jc015397

Cited by 16 publications

(20 citation statements)

References 46 publications

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“…By taking advantage of the synopticity of along-track altimetry data, this method allows to relocate gliders dives in a synoptic frame of reference. The method shares some similarity with the commonly used composite method [42][43][44], which consists of detecting a number of eddies using altimetry and to use all available in situ data, relocated in non-dimensional radial coordinate, to build climatological means of eddies vertical structure. However, rather than reconstructing smooth vertical sections averaged over tens or hundreds of eddies, here, we use one single along-track SSH profile acquired simultaneously with the glider survey, to relocate precisely each glider's dive.…”

Section: The Relocation Methodsmentioning

confidence: 99%

The Dynamical Structure of a Warm Core Ring as Inferred from Glider Observations and Along-Track Altimetry

et al. 2021

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This study investigates the vertical structure of the dynamical properties of a warm-core ring in the Gulf of Mexico (Loop Current ring) using glider observations. We introduce a new method to correct the glider’s along-track coordinate, which is, in general, biased by the unsteady relative movements of the glider and the eddy, yielding large errors on horizontal derivatives. Here, we take advantage of the synopticity of satellite along-track altimetry to apply corrections on the glider’s position by matching in situ steric height with satellite-measured sea surface height. This relocation method allows recovering the eddy’s azimuthal symmetry, precisely estimating the rotation axis position, and computing reliable horizontal derivatives. It is shown to be particularly appropriate to compute the eddy’s cyclo-geostrophic velocity, relative vorticity, and shear strain, which are otherwise out of reach when using the glider’s raw traveled distance as a horizontal coordinate. The Ertel potential vorticity (PV) structure of the warm core ring is studied in details, and we show that the PV anomaly is entirely controlled by vortex stretching. Sign reversal of the PV gradient across the water column suggests that the ring might be baroclinically unstable. The PV gradient is also largely controlled by gradients of the vortex stretching term. We also show that the ring’s total energy partition is strongly skewed, with available potential energy being 3 times larger than kinetic energy. The possible impact of this energy partition on the Loop Current rings longevity is also discussed.

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Section: The Relocation Methodsmentioning

confidence: 99%

The Dynamical Structure of a Warm Core Ring as Inferred from Glider Observations and Along-Track Altimetry

et al. 2021

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“…The green contours indicate the periphery of the Loop Current Eddy (LCE) Poseidon, for the dates shown in panels, computed using the algorithm implemented in Sosa‐Gutiérrez et al. (2020). The yellow lines refer to glider tracks during each mission and the yellow dot is the glider position for each date (plus and cross markers indicate the beginning and ending locations of each glider mission).…”

Section: Datamentioning

confidence: 99%

“…Daily ADT helps the pilots to fly the gliders following a trajectory as much perpendicular to geostrophic velocity as possible. ADT is also used to detect the centroid and periphery of the LCE following Chaigneau et al (2008) and modified in Sosa-Gutiérrez et al (2020). The glider location relative to the center of the eddy or nondimensional radial coordinate is computed as 𝐴𝐴 𝐴𝐴𝑛𝑛 = 𝑑𝑑∕ , where d is the distance between glider location and eddy center and 𝐴𝐴  is the eddy radius.…”

Section: Altimetrymentioning

confidence: 99%

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Overturning Instabilities Across a Warm Core Ring From Glider Observations

et al. 2022

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This work presents new evidence for conducive conditions for the existence of overturning instabilities in the mixed layer across a mesoscale anticyclonic Loop Current Eddy (LCE) and surrounding cyclonic eddies in the Gulf of Mexico (GoM). The LCE was intensively sampled using four gliders during 12 months. The LCE is characterized by a strong anomaly of fresh and warm water in the center and strong strain at the periphery. Mixed layers prone to overturning instabilities are diagnosed from the gradients of buoyancy. In the GoM, the reduction of potential vorticity (PV) in the mixed layer is driven by surface cooling by year‐round persistent negative turbulent heat fluxes, eventually reaching −700 W m−2 during extreme winter wind events. Lateral buoyancy gradients associated with submesoscale filaments and fronts at the periphery of the LCE enhance the frictional torque supplied by the wind stress when aligned with the geostrophic jet current. Negative PV in the mixed layer occurs simultaneously with negative turbulent heat fluxes and events of Ekman buoyancy fluxes that reduce the stratification. These regions are susceptible to mixed‐layer gravitational‐symmetric instability preferentially in winter. Extreme Ekman equivalent heat flux (≤−10,000 W m−2) associated with wind stress of 1.2 N m−2 coincides with the development of inertial‐symmetric instability across anticyclonic vorticity. These observations might have several implications for the restratification processes, kinetic energy budget, and biogeochemical cycles inside LCEs and can contribute to the formation of low‐PV waters that could feed mode water formation inside the GoM.

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“…[Chl] is widely used as a proxy for photosynthetic biomass (Strickland, 1965;Cullen, 1982). However, in addition to depending on phytoplankton concentration, it is also affected by several other factors mainly produced by intracellular physiological mechanisms (Geider, 1987).…”

Section: Appendix A: [Chl] / C-biomass Ratio and Ecosystem Structurementioning

confidence: 99%

Do Loop Current eddies stimulate productivity in the Gulf of Mexico?

et al. 2021

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Abstract. Surface chlorophyll concentrations inferred from satellite images suggest a strong influence of the mesoscale activity on biogeochemical variability within the oligotrophic regions of the Gulf of Mexico (GoM). More specifically, long-living anticyclonic Loop Current eddies (LCEs) are shed episodically from the Loop Current and propagate westward. This study addresses the biogeochemical response of the LCEs to seasonal forcing and show their role in driving phytoplankton biomass distribution in the GoM. Using an eddy resolving (1/12∘) interannual regional simulation, it is shown that the LCEs foster a large biomass increase in winter in the upper ocean. It is based on the coupled physical–biogeochemical model NEMO-PISCES (Nucleus for European Modeling of the Ocean and Pelagic Interaction Scheme for Carbon and Ecosystem Studies) that yields a realistic representation of the surface chlorophyll distribution. The primary production in the LCEs is larger than the average rate in the surrounding open waters of the GoM. This behavior cannot be directly identified from surface chlorophyll distribution alone since LCEs are associated with a negative surface chlorophyll anomaly all year long. This anomalous biomass increase in the LCEs is explained by the mixed-layer response to winter convective mixing that reaches deeper and nutrient-richer waters.

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Erosion of the Subsurface Salinity Maximum of the Loop Current Eddies From Glider Observations and a Numerical Model

Cited by 16 publications

References 46 publications

The Dynamical Structure of a Warm Core Ring as Inferred from Glider Observations and Along-Track Altimetry

The Dynamical Structure of a Warm Core Ring as Inferred from Glider Observations and Along-Track Altimetry

Overturning Instabilities Across a Warm Core Ring From Glider Observations

Do Loop Current eddies stimulate productivity in the Gulf of Mexico?

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