We construct a Markov-chain representation of the surface-ocean Lagrangian dynamics in a region occupied by the Gulf of Mexico (GoM) and adjacent portions of the Caribbean Sea and North Atlantic using satellite-tracked drifter trajectory data, the largest collection so far considered. From the analysis of the eigenvectors of the transition matrix associated with the chain, we identify almost-invariant attracting sets and their basins of attraction. With this information we decompose the GoM’s geography into weakly dynamically interacting provinces, which constrain the connectivity between distant locations within the GoM. Offshore oil exploration, oil spill contingency planning, and fish larval connectivity assessment are among the many activities that can benefit from the dynamical information carried in the geography constructed here.

Four years (September 2012 to August 2016) of simultaneous current observations across the Yucatan Channel (~21.5°N) and the Straits of Florida (~81°W) have permitted us to investigate the characteristics of the flow through the Gulf of Mexico. The average transport in both channels is 27.6 Sv (1 Sv = 106 m3 s−1), in accordance with previous estimates. At the Straits of Florida section, the transport related to the astronomical tide explains 55% of the observed variance with a mixed semidiurnal/diurnal character, while in the Yucatan Channel tides contribute 82% of the total variance and present a dominant diurnal character. At periods longer than a week the transports in the Yucatan and Florida sections have a correlation of 0.83 without any appreciable lag. The yearly running means of the transport time series in both channels are well correlated (0.98) and present a 3-Sv range variation in the 4 years analyzed. This long-term variability is well related to the convergence of the Sverdrup transport in the North Atlantic between 14.25° and 18.75°N. Using 2 years (July 2014–July 2016) of simultaneous currents observations in the Florida section, the Florida Cable section (~26.7°N), and a section across the Old Bahama Channel (~78.4°W), a mean northward transport of 28.4, 31.1, and 1.6 Sv, respectively, is obtained, implying that only 1.1 Sv is contributed by the Northwest Providence Channel to the mean transport observed at the Cable section during this 2-yr period.

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[1] The circulation over the continental shelf break of the western and southwestern Gulf of Mexico is inferred from the analysis of drifter trajectories and 12-19 months of continuous current measurements at seven different locations. The interpretation of the data is backed up by satellite altimetry, coastal sea level from tide gauges and wind model outputs. In accordance with previous numerical results, subinertial surface currents are driven by the wind along the shelves of the states of Tamaulipas and Veracruz. Northern wind regimes would force southward currents, whereas southern wind regimes would force northward currents at the surface but southward near the bottom, through a process involving Ekman drift and geostrophic balance. Our results show, however, that alongshore current variations are not correlated with the wind over the Western Campeche Bank. In addition, we identify other sources of current forcing. The transient eddies that collapse along the continental shelf can force strong alongshore currents and overwhelm the influence of established wind regimes. Their erratic occurrence is likely to be a major factor of interannual variability of the alongshore currents. Also, we point out the existence of coastally trapped waves generated by the wind in the northern shelf of Tamaulipas and propagating down to the Western Campeche Bank. The period of these waves ranges between 6 and 10 days, with phase speeds in the 4 m/s range.Citation: Dubranna, J., P. Pérez-Brunius, M. López, and J. Candela (2011), Circulation over the continental shelf of the western and southwestern Gulf of Mexico,

The large-scale circulation of the bottom layer of the Gulf of Mexico is analyzed, with special attention to the historically least studied western basin. The analysis is based on 4 years of data collected by 158 subsurface floats parked at 1500 and 2500 m and is complemented with data collected by current meter moorings in the western basin during the same period. Three main circulation patterns stand out: a cyclonic boundary current, a cyclonic gyre in the abyssal plain, and the very high eddy kinetic energy observed in the eastern Gulf. The boundary current and the cyclonic gyre appear as distinct features, which interact in the western tip of the Yucatan shelf. The persistence and continuity of the boundary current is addressed. Although high variability is observed, the boundary flow serves as a pathway for water to travel around the western basin in approximately 2 years. An interesting discovery is the separation of the boundary current over the northwestern slope of the Yucatan shelf. The separation and retroflection of the along-slope current appears to be a persistent feature and is associated with anticyclonic eddies whose genesis mechanism remains to be understood. As the boundary flow separates, it feeds into the westward flow of the deep cyclonic gyre. The location of this gyre-named the Sigsbee Abyssal Gyre-coincides with closed geostrophic contours, so eddy-topography interaction via bottom form stresses may drive this mean flow. The contribution to the cyclonic vorticity of the gyre by modons traveling under Loop Current eddies is discussed.