Submesoscale Instability in the Straits of Florida

The Florida Current (FC) flows in the Straits of Florida (SoF) and connects the Loop Current in the Gulf of Mexico to the Gulf Stream (GS) in the Western Atlantic Ocean. Its journey through the SoF is at time characterized by the formation and presence of mesoscale but mostly submesoscale frontal eddies on the cyclonic side of the current. The formation of those frontal eddies was investigated in a very high resolution two-way nested simulation using the Regional Oceanic Modeling System (ROMS). Frontal eddies were either locally formed or originated from outside the SoF. The northern front of the incoming eddies was susceptible to superinertial shear instability over the shelf slope when the eddies were pushed up against the slope by the FC. Otherwise, incoming eddies could be advected relatively unaffected by the current, when in the southern part of the straits. In absence of incoming eddies, submesoscale eddies were locally formed by the roll-up of superinertial barotropically unstable vorticity filaments when the FC was pushed up against the shelf slope. The vorticity filaments were intensified by the friction-induced bottom layer vorticity flux as previously demonstrated by Gula et al. (2015b) in the GS. When the FC retreated further south, negative vorticity West Florida Shelf waters overflowed into the SOF and led to the formation of submesocale eddies by baroclinic instability. The instability regimes, hence, the submesoscale frontal eddies formation appear to be controlled by the lateral ‘sloshing’ of the FC in the SoF.

The Role of Mesoscale Dynamics over Northwestern Cuba in the Loop Current Evolution in 2010, during the Deepwater Horizon Incident

The Loop Current (LC) system controls the connectivity between the northern Gulf of Mexico (GoM) region and the Straits of Florida. The evolution of the LC and the shedding sequence of the LC anticyclonic ring (Eddy Franklin) were crucial for the fate of the hydrocarbons released during the Deepwater Horizon (DwH) oil spill in 2010. In a previous study, we identified LC-related anticyclonic eddies in the southern GoM, named “Cuba anticyclones” (“CubANs”). Here, we investigate the relation between these eddies and LC evolution in 2010, focusing on the DwH period. We use high-resolution model results in tandem with observational data to describe the connection between the LC system evolution within the GoM (LC extensions, Eddy Franklin and LC Frontal Eddies—LCFEs) and the mesoscale dynamics within the Straits of Florida where CubANs propagate. Five periods of CubAN eddy activity were identified during the oil spill period, featuring different formation processes under a combination of local and regional conditions. Most of these cases are related to the retracted LC phases, when the major LC anticyclone (Eddy Franklin in 2010) is detached from the main body and CubAN eddy activity is most likely. However, two cases of CubAN eddy presence during elongated LC were detected, which led to the attenuation of the eastward flows of warm waters through the Straits (Florida Current; outflow), allowing the stronger supply of Caribbean waters through the Yucatan Channel into the Gulf (inflow), which contributed to short-term LC northward extensions. Oceanographic (LCFEs) and meteorological (wind-induced upwelling) conditions contributed to the release of CubANs from the main LC body, which, in tandem with other processes, contributed to the LC evolution during the DwH oil spill incident.

Some like it hot, hungry tunas do not! Implications of temperature and plankton food web dynamics on growth and diet of tropical tuna larvae

Restricted to low-productivity environments near their thermal maxima, larval tunas may be threatened by warming global temperatures, yet our understanding of how they are constrained is limited. We examined blackfin tuna (Thunnus atlanticus, presumptive) diet and growth in the context of their prey and predators in the Straits of Florida in 2 years with contrasting summer conditions: low temperature (26.7–28.3°C)–high prey and high temperature (28.4–29.0°C)–low prey. In the cooler, high-prey conditions, larvae had 30% faster growth (0.45 mm d−1), fuller guts from predominantly feeding on calanoid copepods, and were 10× more abundant, dominating the larval fish assemblage. In contrast, in warm, low-prey conditions fewer, younger, and slower-growing (0.35 mm d−1) T. atlanticus fed predominantly on nauplii and had less full guts. Modelling individual growth across years revealed that growth peaked at an optimum of 28.5°C (5°C below known thermal maxima in the field) and high densities of predators selectively consumed slower-growing larvae. Low-prey availability may reduce the thermal optima of larvae, as growth and survival are diminished when low prey and high temperature coincide. Our results illustrate the importance of considering food web dynamics with temperature when predicting the response of organisms to ecosystem variability, particularly ongoing climate change.

Pathways of Oil Spills from Potential Cuban Offshore Exploration: Influence of Ocean Circulation

The DeepWater Horizon oil spill in the Gulf of Mexico (GoM) in 2010 raised the public awareness on potential spills from offshore exploration activities. It became apparent that knowledge of potential oil pathways in the case of a spill is important for preparedness and response. This study focuses on such scenarios from potential oil spills in the Cuban Exclusive Economic Zone (EEZ), a vast area in the GoM and the Straits of Florida that has not received much attention in oil spill studies, even though this region has been under evaluation for oil exploration. The Cuban EEZ is also in the crossroads of heavy tanker traffic, from the areas of intense oil exploration in the Northern GoM to the adjacent Caribbean Sea and Atlantic Ocean. The study also evaluates how the oil transport and fate are influenced by the main circulation patterns of the GoM, such as the Loop Current (LC) system and the mesoscale dynamics inside the Straits of Florida, such as the Florida Current (FC) and the accompanying cyclonic (along the northern Straits) and anticyclonic (along the Cuban coasts) eddies. We used oil spill numerical simulations, in tandem with high resolution data-assimilative ocean simulations, to test the fate of potential oil spills originating from different release sites within the Cuban EEZ during a six-year period (2011–2016) to exhibit certain aspects of interannual variability of ocean dynamics. The LC extended and retracted phases in the GoM interior revealed different impacts on the oil fate depending on the release site. The meandering of the FC, which is strongly related to the mesoscale eddies that evolve inside the Straits of Florida, controlled oil pathways either towards the northern Straits or along the Cuban coast. The most likely scenario for oil stranding at southern Florida is from oil released at the deep central Straits of Florida. Oil release near the Yucatan Strait and in the deep Gulf interior showed the highest risk of overall oil beaching at the Gulf beaches. The regional (e.g., LC) and local (e.g., eddies in the Straits) dynamics are proven to be significant indicators to predict the oil fate and stranding along the Gulf coasts, which should lead to improving planning and preparedness in the case of a spill in the Cuban EEZ.

The Flow through the Gulf of Mexico

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.