Description: Since 2010, an intense effort in the collection of in situ observations has been carried out in the northwestern Mediterranean Sea thanks to gliders, profiling floats, regular cruises, and mooring lines. This integrated observing system enabled a year-to-year monitoring of the deep waters formation that occurred in the Gulf of Lions area during four consecutive winters (2010–2013). Vortical structures remnant of wintertime deep vertical mixing events were regularly sampled by the different observing platforms. These are Submesoscale Coherent Vortices (SCVs) characterized by a small radius (∼5–8 km), strong depth-intensified orbital velocities (∼10–20 cm s−1) with often a weak surface signature, high Rossby (∼0.5) and Burger numbers O(0.5–1). Anticyclones transport convected waters resulting from intermediate (∼300 m) to deep (∼2000 m) vertical mixing. Cyclones are characterized by a 500–1000 m thick layer of weakly stratified deep waters (or bottom waters that cascaded from the shelf of the Gulf of Lions in 2012) extending down to the bottom of the ocean at ∼2500 m. The formation of cyclonic eddies seems to be favored by bottom-reaching convection occurring during the study period or cascading events reaching the abyssal plain. We confirm the prominent role of anticyclonic SCVs and shed light on the important role of cyclonic SCVs in the spreading of a significant amount (∼30%) of the newly formed deep waters away from the winter mixing areas. Since they can survive until the following winter, they can potentially have a great impact on the mixed layer deepening through a local preconditioning effect.

Description: Ocean color satellite measurements in the Gulf of Mexico open waters evidenced a clear seasonal variability in the surface chlorophyll concentration. Recent investigations in subtropical oligotrophic regions suggested that the surface chlorophyll increase may not be systematically associated to a real biomass increase but may result from physiological mechanisms. This finding may be relevant in the Gulf of Mexico as suggested by bio-optical measurements recently acquired by APEX profiling floats. Despite the increasing amount of observations in the Gulf of Mexico open waters, data are still lacking to regionalize the seasonal and interannual variability of the chlorophyll vertical structure or to investigate how the energetic mesoscale dynamics within the Gulf of Mexico modulate the chlorophyll distribution. To overcome these limitations, we set up an eddy resolving (1/12deg) coupled bio-physical model (NEMO-PISCES) of the Gulf of Mexico. The use of recent sets of observations allowed for a careful evaluation of the vertical distribution of the nutrient and chlorophyll concentrations throughout the different seasons. The analysis of the seasonal variability of the integrated chlorophyll content revealed a much more contrasted and complex behavior than the basin scale homogeneous pattern of variability inferred from modeled and observed surface chlorophyll concentration. We show that the variability of the mixed-layer depth strongly shape the seasonal distribution of the chlorophyll concentration but also its year to year variability. Finally, we investigate some of the physical-biogeochemical coupling processes specific to GoM sub-regions and mesoscale dynamics (in particular the Loop Current and Loop Current eddies).

Description: Throughout the Gulf of Mexico open waters, satellite measurements evidenced a clear seasonal variability in the surface chlorophyll concentration. The most important factor controlling this annual cycle is the depth of the mixed layer. Recent studies carried on in subtropical oligotrophic regions suggested that the surface chlorophyll increase may not be systematically associated to a real biomass increase but may results from physiological mechanisms. This finding may be echoed in the Gulf of Mexico as the integrated biomass derived from fluorescence data acquired by the first deployment of profiling floats presents low variability. Despite the increasing amount of observations in the Gulf of Mexico open waters, data is still lacking to infer the seasonal and interannual variability of the chlorophyll vertical structure at a sub-basin scale, as well as the mesoscale variability. Moreover, a strong limitation of observational-based studies remains in the difficulty to provide a synoptic view of all the factors that influence the water column biogeochemical state. In that sense, coupled physical-biological models have been found to be complementary and indispensable tools, especially for understanding the mechanisms controlling the close relationship between physical and biogeochemical processes. In the framework of Cigom consorcium, the biogeochemical model PISCES was coupled to a 1/12 degrees resolution simulation of the Gulf of Mexico circulation. We review the capability of the coupled model to reproduce the main biogeochemical patterns and variability in the basin. The model reveals a more contrasted situation than an unique basin scale chlorophyll pattern. This variability appears to be dependent of sub-regions of the Gulf of Mexico and is strongly affected by the mesoscale dynamic (in particular by Loop Current eddies). We investigate some of the physical-biogeochemical coupling processes associated with the GoM sub-regions and with Loop Current eddies.

Description: We perform a systematic analysis of the risk for a given region of the coast of the Gulf of Mexico to experience a contamination by oil or pollutant in the case of a spill occurring offshore in deep (deeper than 1000 m) waters. The main objective of our study is to determine whether some coastal regions are more exposed to pollution than others, which is of major importance to implement Marine Protected Areas. A special focus of this study is given to the role of the oceanic eddies and the Loop Current, as they largely impact the circulation of the GoM and therefore the dispersion of contaminants. We use the NEMO model framework and implemented a total of 370 “passive tracers” covering the whole region of the GoM. Tracers are released either at surface or at depth (1000 m). For each of the release, we consider three behavior of the tracers, mimicking oil or contaminant properties : - the contaminant is passively transported in the ocean without decay, - the contaminant decays - the contaminant accumulates once it lands at the coast. Each experiment is integrated over 50 years under climatological forcings in order to assess the role of the internal and the eddy variability

Description: The Gulf of Mexico is a very productive basin presenting an important seasonality in surface chlorophyll concentrations. This variability is, in first order, driven by meteorological conditions that impact the stratification of the water column. Rivers discharges and the basin circulation , dominated by the energetic Loop Current and the Loop Current Eddies, are also known to play a crucial role in the distribution and variability of biogeochemical properties Recent studies showed the important submesoscale activity in the upper ocean of the Gulf that impact both horizontal and vertical transports and may be an important feature in the characterization of the biogeochemical processes. Understand the physical-biogeochemical coupling processes and estimate the biogeochemical parameters budgets in the Gulf of Mexico remain important tasks to be done. In the framework of SENER group, the biogeochemical model PISCES was coupled to a 1/12 degrees resolution simulation of the Gulf of Mexico circulation. The first objective was to review the capabilities of the coupled model to reproduce the main biogeochemical patterns and variability in the basin. To do so, comparisons were performed with the available data set and sensitivity test to key processes were carried on. Then, the coupled model, associated to a vortex tracking algorithm, were used to shed light on the physical-biogeochemical coupling processes associated with the Loop Current Eddies and the integral impact of these typical structures in the advection of biogeochemical parameters.

Description: The seasonal and interannual variability of chlorophyll in the Gulf of Mexico open waters is studied using a three‐dimensional coupled physical‐biogeochemical model. A 5 years hindcast driven by realistic open‐boundary conditions, atmospheric forcings, and freshwater discharges from rivers is performed. The use of recent in situ observations allowed an in‐depth evaluation of the model nutrient and chlorophyll seasonal distributions, including the chlorophyll vertical structure. We find that different chlorophyll patterns of temporal variability coexist in the deep basin which thereby cannot be considered as a homogeneous region with respect to chlorophyll dynamics. A partitioning of the Gulf of Mexico open waters based on the winter chlorophyll concentration increase is then proposed. This partition is basically explained by the amount of nutrients injected into the euphotic layer which is highly constrained by the dynamic of the winter mixed layer. The seasonal and interannual variability appears to be affected by the variability of atmospheric fluxes and mesoscale dynamics (Loop Current eddies in particular). Finally, estimates of primary production in the deep basin are provided.

Description: The Gulf of Mexico (GoM) is heavily exploited by the oil industry. Incidental oil releases, such as the 2010 blowout of the Deepwater Horizon platform, lead to a large scale dispersion of pollutants by ocean currents, contaminating the coastline and damaging the ecosystems. In order to determine whether the ocean dynamics hampers or conversely fosters the landing of material in the coastal regions, we simulate more than 29000 individual tracer releases in the offshore waters of the GoM. We assume that the tracers are not decaying and transported passively by the ocean currents. In a first part of our study we focus on the mean dispersion pattern of 80 releases occurring at the location of the Deepwater Horizon. In a second part, we generalize the metrics that we defined to the whole GoM. Our study shows that releases occurring in specific regions, i.e the bay of Campeche, off the Mississipi-Alabama-Florida and the West Florida shelfs are associated with higher environmental costs as the ocean currents steer the released material toward the productive coastal ecosystems and foster landings. Conversely, the tracers released off the Louisiana-Texas-shelfs and the center of the Gulf of Mexico are less threatening for coastal regions as the material recirculates offshore. We show that the coastline of the southwest part of the Bay of Campeche, the Mississipi's mouth and the Island of Cuba are particularly exposed as 70 % of the landings occur in these 3 regions.

Description: 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 Yucatan Chanel 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 based on the coupled physical-biogeochemical model NEMO-PISCES that yields a realistic representation of the surface chlorophyll distribution, it is shown that the LCEs foster a large biomass increase in winter in the upper ocean. 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.