Gulf of Mexico


The Gulf of Mexico is a semi-enclosed basin connected, to the south, to the Caribbean Sea, and to the North Atlantic Ocean to the east. The main dynamical feature of the Gulf of Mexico is the Loop Current, which is a portion, upstream of the Gulf Stream, of the North Atlantic western boundary current that carries ocean waters from the Tropics towards the high latitudes. The Loop Current indeed carries warm waters from the Caribbean Sea into the colder Gulf of Mexico, and then into the North Atlantic Ocean. The Loop Current is a fascinating ocean current, which changes extension with time: from a retracted, direct pathway between the Yucatan Channel at the southern entrance of the Gulf and its exit at the Straits of Florida, it slowly grows inside the eastern Gulf of Mexico, until its extension almost reaches the Mississippi Delta and forms a large loop (hence its name) before exiting the Gulf. When the Loop Current is extended, it eventually sheds a large eddy, or Ring, which then drifts westward, whereas the Loop Current retracts to the south.

The Loop Current and associated eddies are routinely monitored via satellite products. In particular, the Loop Current is associated with high sea surface height, measured by altimetry. It is also usually associated with warm waters visible in Sea Surface Temperature. The Loop Current system is a determining factor for the presence of bluefin tuna larvae. NOAA/AOML developed an index based on satellite data, that maps where the conditions are favorable for the presence of bluefin tuna larvae.

The Loop Current and the associated eddies at its edge played a critical role in the spreading of oil at the surface of the Gulf during the Deepwater Horizon oil spill in 2010. AOML/PhOD has been at the frontline during that event to monitor and analyze ocean observations at the time.


Loop Current visible on Sea Surface Temperature observed by satellite (source: NOAA/AOML OceanViewer).


Another fascinating feature of the Gulf of Mexico is the signature of the Mississippi River, one of the largest rivers in the world, which discharges gigantic amounts of fresh water and nutrients into the Gulf. This inflow affects the local dynamics and ecosystems of the northern Gulf of Mexico and beyond, as the brackish waters from the Mississippi River can sometimes be transported by the Loop Current as far as the Atlantic Ocean.

The signature of the Mississippi River is visible in satellite ocean color products.


Surface Chlorophyll-a concentration (mg/m3) measured by MODIS satellite on August 7, 2015. The large Chlorophyll-a values in red are associated with brackish waters from river origins.


Finally, the Gulf of Mexico is also part of the North Atlantic warm pool that forms in summer. Every summer, the whole Gulf of Mexico is marked with high sea surface temperatures, which support the formation and presence of tropical storms and hurricanes. This process is strengthened by the local ocean circulation inside the Gulf of Mexico, as the Loop Current and associated Rings are marked by a surface layer of warm waters that is thicker than in the rest of the Gulf. For example, a Loop Current Ring was involved in the intensification of Hurricane Opal in 1995, and of Hurricane Katrina in 2005. Currently, NOAA/AOML operates ocean gliders in the Atlantic hurricane region to detect the presence of warm waters that can influence hurricane evolution.


Track of Hurricane Katrina (2005) overlaid on Tropical Cyclone Heat Potential (TCHP) conditions in the Gulf of Mexico on August 20, 2005. TCHP represents the quantity of heat available in the ocean’s upper layer.


Projects:

  • Evaluation of Gulf of Mexico oceanographic observation networks, impact assessment on ecosystem management and recommendations (NOAA RESTORE Act Science Program, 09/01/2015-08/31/2019, M. Le Hénaff Lead PI)
In this project, we study the impact of oceanic processes and their observations on local ecosystems in the Gulf, with the specific goal of supporting ecosystem management. We used satellite observations to characterize episodes of transport of coastal and river waters from the Mississippi Delta and the Campeche Bank (north of Yucatan in Mexico) toward the Straits of Florida, which host the Florida Keys National Marine Sanctuary (Otis et al., 2019). In parallel, we were contacted by the managers of the Flower Garden Banks National Marine Sanctuary to help them understand an episode of sudden coral mortality that affected their sanctuary in July 2016. We used satellite observations, as well as a high-resolution configuration (2 km) of the HYbrid Coordinate Ocean Model (HYCOM) of the Gulf of Mexico (Le Hénaff and Kourafalou, 2016), to investigate this study case. We found that the presence of brackish waters, in excess along the coasts of Texas due to intense precipitation and flooding, was a determining factor for that event (Le Hénaff et al., 2019). That analysis led us to develop, in partnership with the Marine Biodiversity Observation Network project supported by NOAA, a web tool to monitor the ocean conditions in and around the Flower Garden Banks National Marine Sanctuary, in particular the presence of brackish waters and unusual temperature conditions, based on satellite and in-situ observations. The tool is available here. A similar tool was then developed to monitor the ocean conditions in the Florida Keys National Marine Sanctuary, in particular the presence of turbid waters, the presence of algae, as well as unusual temperature conditions. That second tool is available here.


Surface Chlorophyll-a concentration (mg/m3) measured by MODIS satellite on July 22, 2016. The white dots mark the locations of both Flower Garden Banks National Marine Sanctuary sites. The large Chlorophyll-a values in red are associated with brackish waters from river origins, which reached the Sanctuary sites in July 2016, preceding an episode of intense coral mortality.


  • Influence of river induced fronts on hydrocarbon transport (01/01/2016-12/31/2019, Gulf of Mexico Research Initiative – GoMRI)
In this project, we investigate the role played by river induced fronts on the transport of oil at the sea surface. Indeed, it was observed during the Deepwater Horizon oil spill in 2010 that the Mississippi River plume influenced the spread of the oil. As part of that project, we characterized, with satellite data and surface drifter observations, how the Mississippi River plume can influence the transport of oil at the Taylor Energy site, where oil was observed at the sea surface after the destruction of an oil platform by Hurricane Ivan in 2004. We found that the Mississippi plume can transport surface material to the west, under common easterly winds, to the east when the winds reverse, and southward under the influence of eddies typical of the deep Gulf of Mexico (Androulidakis et al., 2018). That project also supported efforts in the characterization of surface oil spills from observations, using satellite (Sun et al., 2018) as well as on-site remote sensing and surface drifters (Garcia-Pineda et al., 2019). Finally, we used the high-resolution GoM-HYCOM simulation of the Gulf of Mexico (Le Hénaff and Kourafalou, 2016) to study the evolution of the vertical structure of the Mississippi River plume in the summer of 2015, during which it extended far offshore down to the Straits of Florida. We found that the river plume extended to 30 m depth near the Mississippi Delta, to 10-20 m depth in the eastern Gulf, and to 5-10 m depth in the Straits of Florida, with variations due to the presence of eddies (Androulidakis et al., 2019).


(top) Surface Chlorophyll-a concentration (mg/m3) measured by MODIS satellite on April 20, 2017, showing the river plume (high Chlorophyll-a content) spreading around the Mississippi Delta. (bottom) Images of two fronts separating different types of waters, from heavily brackish to clear blue waters, observed on April 20, 2017.


  • Southeastern Gulf of Mexico processes affecting basin-wide connectivity and hydrocarbon transport: the role of mesoscale eddies and upwelling near Cuba (01/01/2018-12/31/2019, GoMRI, M. Le Hénaff Co-PI)
In this project, we investigate the local oceanic processes taking place along the Cuban coasts inside the Gulf of Mexico, their impact on the regional circulation, and their potential impact on oil transport in case of an oil spill, as this is a region of oil exploration. Recent results have indeed identified the presence of mesoscale anticyclonic eddies evolving along the coast of Cuba, which were never reported before (Kourafalou et al., 2017). These eddies appear to be strongly connected to the situation of the Loop Current inside the Gulf and inside the Straits of Florida (where it is called the Florida Current). These eddies also appear to be connected to coastal upwelling taking place along the coasts of Cuba, and the associated formation of small cyclonic eddies. As part of that project, we analyzed ocean observations collected in Cuban waters inside the Gulf of Mexico, mostly during NOAA Fisheries cruises, which provide details on the structure and evolution of these typical ocean processes taking place along the Cuban coasts, i.e. anticyclonic eddies, upwelling and cyclonic eddies (Le Hénaff et al., 2019). In addition, we used the high-resolution GoM-HYCOM simulation of the Gulf of Mexico (Le Hénaff and Kourafalou, 2016) to further characterize these processes, their connection with the regional circulation, and their impact on the transport of oil in case of an oil spill.


(left) Surface Chlorophyll-a (colors, mg/m3) observed from MODIS Aqua on May 21, 2015. In red is the track of the NOAA ship Nancy Foster. Superimposed are the contours of the Mapped Absolute Dynamic Topography obtained from satellite altimetry, showing the contours of the Loop Current. The black arrows are the velocity vectors measured by the on-board current-meter from May 21 to 26, 2015. (right) Zoom over the area marked by the dashed white rectangle on left panel, showing how the veering of the incoming current along the Cuban coast entrains waters with high Chlorophyll content offshore to the Loop Current.


The high-resolution GoM-HYCOM configuration used in these various projects also provides 7-day forecast of the Gulf of Mexico conditions once a week, available here.

Reference list:

  • Androulidakis Y., V. Kourafalou, T. Özgökmen, O. Garcia–Pineda, B. Lund, M. Le Hénaff, C. Hu, B.K. Haus, G. Novelli, C. Guigand, and H. Kang (2018). Influence of River-Induced Fronts on Hydrocarbon Transport: A Multiplatform Observational Study. Journal of Geophysical Research - Oceans, 123, 3259-3285.
  • Androulidakis, Y., V.H. Kourafalou, M. Le Hénaff, H.-S. Kang, T. Sutton, S. Chen, C. Hu, and N. Ntaganou (2019). Offshore spreading of Mississippi waters: pathways and vertical structure under eddy influence. Journal of Geophysical Research: Oceans., In Press.
  • Garcia-Pineda, O., Y. Androulidakis, M. Le Hénaff, V. Kourafalou, L. R. Hole, H.-S Kang, G. Staples, E. Ramirez, L. DiPinto (2019). Measuring oil residence time with GPS-drifters, satellites, and unmanned aerial systems (UAS). In review at Marine Pollution Bulletin.
  • Kourafalou, V., Y. Androulidakis, M. Le Hénaff, and H. Kang (2017). The Dynamics of Cuba Anticyclones (CubANs) and Interaction With the Loop Current/Florida Current System. Journal of Geophysical Research-Oceans, 122(10), 7897-7923.
  • Le Hénaff, M., and V. H. Kourafalou (2016). Mississippi waters reaching South Florida reefs under no flood conditions: synthesis of observing and modeling system findings, Ocean Dynamics, 66, 435-459.
  • Le Hénaff, M., F. E. Muller-Karger, V. H. Kourafalou, D. Otis, K. A. Johnson, L. McEachron, H.-S. Kang (2019). Coral Mortality Event in the Flower Garden Banks of the Gulf of Mexico in July 2016: A Consequence of Cross-Shelf Transport of Flood Waters? In Review at Continental Shelf Research.
  • Otis, D.B., M. Le Hénaff, V.H. Kourafalou, L. McEachron, L. and F.E. Muller-Karger (2019). Mississippi River and Campeche Bank (Gulf of Mexico) Episodes of Cross-Shelf Export of Coastal Waters Observed with Satellites. Remote Sens., 11(6), p.723.