-New insights into the circulation in the Western Gulf of Mexico from Eulerian, Lagrangian and Autonomous observing
platforms (CICESE).
Miguel Tenreiro

Three ocean observing groups at CICESE (CANEK, GMOG and GIOLA), working together, have been using moorings, gliders and drifters to investigate the dynamics of one of the key features that drives the circulation in the Gulf of Mexico, i.e., the Loop Current Eddies (LCEs) that aperiodically detach from the Loop Current (LC) and translate always with a westward component. The water source of these coherent structures is warm and salty Caribbean waters, and they are thought to play an important role in transporting distinct properties and matter into the western part of the basin.

Figure 1.- CANEK mooring positions and GMOG glider & GIOLA drifter trajectories from different projects between 2007-18.

-2018: Hydrography of the Central and Western Gulf of Mexico
Portela, E., M. Tenreiro, E. Pallàs-Sanz, T. Meunier, A. Ruíz-Angulo, R. Sosa-Gutiérrez, and S. Cusí.

This study describes in detail the water masses of the Gulf of Mexico (GoM) west of 88°W based on their thermohaline properties and dissolved oxygen concentration. The existent historical information is complemented with new data from 14 cruises, Argo floats, and over one year of continuous glider monitoring. The results describe the general hydrography of the central and western GoM with focus on the difference between the water properties inside and outside Loop Current Eddies (LCEs). Caribbean Surface Water, Subtropical Underwater, and 18 °C Sargasso Sea Water (18SSW) are exclusive of the LCEs, and they are found along the LCEs preferred path between 23°N and 27°N. Outside the LCEs, the prominent characteristics of these water masses erode, and the Gulf Common Water is ubiquitous in the subsurface. It is shown that the water masses in the GoM need to be described in the frame of the dominant mesoscale features that take place there and that the dissolved oxygen is a key variable to identify some water masses of Caribbean origin as the Tropical Atlantic Central Water and the 18SSW. The previous potential temperature and salinity limits of the water masses within the GoM were revised and redefined in terms of absolute salinity and conservative temperature in the frame of the Thermodynamic Equation of Seawater, 2010 (TEOS-10). While temperature values after conversion have little variation compared to the previous ones, the absolute salinity is in average 0.2 units greater than the former practical salinity.

Fig1.- a) Grupo de Monitoreo Oceanográfico con Gliders (GMOG?s) gliders tracks. b) diagram and dissolved oxygen (DO, mL L-1, color-coded) from the glider data displayed in (a) with the whole database diagram as the background grey dots. Dashed lines are the proposed new limits of the water masses in the GoM west of 88˚W; blue dashed box represents the outer limit of influence of the Tropical Atlantic Central Water (TACW) and the black dashed box inside represents its nucleus defined by DO lower than 2.2 mL L-1. The black and red solid, thick lines are the averaged relationship for LCEs Water and Gulf Water respectively.

-2018: Intra-Thermocline Eddies Embedded within an Anticyclonic Vortex Ring
Meunier, T., M. Tenreiro, E. Pallàs-Sanz, J., Ochoa, A. Ruíz-Angulo, E. Portela, S. Cusí, P. Damien, and X. Carton.

High-resolution hydrographic measurements reveal the presence of three Intra-Thermocline Eddies (ITEs) embedded within a Loop Current Eddy (LCE). ITEs are lenticular bodies of nearly homogeneous water which contrasts with the well stratified surrounding water. Their radii and thickness ranged between [19-32] km and [150-250] m. Negative relative vorticity within their cores (down to -0.85 times the Coriolis frequency), along with a large negative stratification anomaly, result in low Ertel Potential Vorticity (PV) and intense negative Ertel Potential Vorticity Anomalies (PVA). Vortex stretching and relative vorticity have comparable contributions to PVA, resulting in Burger numbers of order unity. The similarity of thermohaline properties within the ITE?s cores and the surrounding LCE water, suggests that these ITEs likely form by intense mixing events followed by Rossby adjustment.

Fig2.- (b)Vertical section of squared Brunt Väisälä (N2) across LCE Poseidon. ITEs centers are marked with a red vertical line. They are obvious as bubbles of weak stratification embedded within the LCE's well stratified lower pycnocline below the eddy core.

-2018: The Vertical Structure of a Loop Current Eddy.
Meunier, T., E., Pallàs-Sanz, M., Tenreiro, E,. Portela, J., Ochoa, A. Ruíz-Angulo, and S. Cusí

The vertical structure of a recently detached Loop Current Eddy (LCE) is studied using in-situ data collected with an underwater glider from August to November 2016. Altimetry and Argo data are analyzed to discuss the context of the eddy shedding and evolution as well as the origin and transformation of its thermohaline properties. The LCE appeared as a large body of nearly homogeneous water between 50 and 250 m confined between the seasonal and main thermoclines. A temperature anomaly relative to surrounding Gulf's water of up to 9.7 ºC was observed within the eddy core. The salinity structure had a double core pattern. The subsurface fresh core had a negative anomaly of 0.27 psu while the deeper saline core's positive anomaly reached 1.22 psu. Both temperature and salinity maxima were stronger than previously reported. The saline core, of Caribbean origin, was well conserved during its journey from the Yucatan Basin to the Loop Current and at least 7 months after eddy detachment. The fresher homogeneous core resulted from surface diabatic transformations including surface heat fluxes and mixing within the top 200 m during the winter preceding eddy detachment. Heat and salt excess carried by the LCE were large and require important negative heat fluxes and positive fresh water input to be balanced. The geostrophic velocity structure had the form of a subsurface intensified vortex ring.

Fig3.- Hydrographic properties along a cross-section of Loop Current Eddie (LCE) Poseidon. The bottom x-axis is the distance from the start of the transect while the top x-axis is the latitude. Vertical sections of (a) Temperature (ºC), (b) Temperature anomaly (ºC), (c) Salinity (psu), and (d) Salinity anomaly (psu).

-Assessing Vertical Structure of the Anticyclonic Loop Current Eddies with Autonomous Underwater Gliders.

Fig4.- Estructura vertical de temperatura del remolino de la corriente del lazo Poseidon muestreado en la misión 0003 de GMOG (Fig. realizada por Meunier, T.).

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