We are providing this oceanographic analysis to update the conditions in the Gulf of Mexico related to the Deepwater Horizon oil spill. Much has happened with the surface oil, the surface water - oil - dispersant mixture and the subsurface plume or cloud of the water - oil - dispersant mixture. We have been monitoring the conditions over the Gulf of Mexico on a daily basis since the oil first appeared. During the first week of August, 2010 it has become increasingly difficult to locate large surface oil slicks from any of the satellite data that we have been using including ocean color - visible (NASA's Terra and Aqua MODIS sensor, and ENVISAT MERIS sensor data) data (MODIS in realtime from the University of South Florida IMaRS and MERIS from the European Space Agency) and synthetic aperture data (many sources from Univ. Miami CSTARS and ENVISAT).
As late as August 21, 2010 we had observed some relatively narrow surface slicks that are likely to be petroleum oil from the Deepwater Horizon, the Saratoga Platform (near 88°58'W & 28°56'N), and other sources including natural seeps.
The graphic analysis that we are showing today was derived from combining the ocean color data from both the MODIS and MERIS sensors over the 20-25 August 2010 period. It provides an excellent background for showing the currents that occur over the Gulf of Mexico now. The black arrows show the direction of the surface flow of the water based on sequential image analysis using infrared (for sea surface temperature) and ocean color satellite data. The current directions that we have indicated agree with the surface drifting buoy data available online from NOAA (http://www.aoml.noaa.gov/phod/dhos/drifters.php), and Horizon Marine (http://www.horizonmarine.com/bp_buoys/) .
Red arrows are the subsurface currents at 2000 feet depths (approximately 667 meters) that were derived from the acoustic doppler current profilers (ADCP) as reported from the platforms by NOAA's National Data Buoy Center's website (http://www.ndbc.noaa.gov/maps/ADCP_WestGulf.shtml). More and deeper ADCP data would be useful, as would subsurface drifting buoy data. The color palette reflects the color- chlorophyll (plus dissolved organic material) composition of the water. Over the last few weeks we have watched Eddy Franklin clearly separate from the Loop Current and drift westward while it is rotating in a clockwise direction. The Loop Current which had a minimum intrusion into the Gulf of Mexico for an abnormally long time (based on our experience over the last 20 years) has been moving northward and the northern extent appears to be located near approximately 26°00'N & 85°00-84°30'N. The Yucatan Current water is being pulled around the Loop Current and also around Eddy Franklin. It has been a surprise to us and many others, that over the period since the end of April until now that the majority of the water and the water - oil - dispersant mixture in the northern Gulf of Mexico has not been pulled into the Loop Current and into the Gulf Stream system.
The impacts of the surface oil on the ecosystem (onshore, nearshore and offshore) of the Gulf of Mexico remain unknown and are being slowly studied. Hopefully more studies by independent scientists along with NOAA scientists will occur and that the results will be publically available for review in a relatively short time period. Damage assessment is critical for understanding the past effects and for understanding the changes that will become obvious as time moves on. With proper funding we hope to reevaluate all of our observations of the surface oil and the oil-water-dispersant mixture as it moved throughout the northern Gulf of Mexico from Florida to Texas. The goal of this effort will be to produce a temporal spatial history of the oil-water-dispersant mixture. This will facilitate ecosystem damage assessment studies. When we finish our reassessment, we will make our data available to the public again.
Our concerns now are focused on the subsurface plume or cloud of the oil-water-dispersants that occur below the surface with apparently relatively low (< 1 part per million) concentration of petroleum. From a variety of sources it appears that this cloud is irregularly shaped and extends northeastward from the Deepwater Horizon site at least as far as DeSoto Canyon and perhaps farther eastward. It also extends at least as far west as 92°00'W. The cloud is like an ameba in that it is constantly changing shape as a result of the deep water currents between 1000 meter and 1500 meter depths. Apparently the thickness varies from 50 meters to 200 meters. While no publically available maps are available, the subsurface cloud occurs south of the 1000 meter isobath at approximately 1200 meter depths. While we understand that the surface waters which we observe from the satellite data are more often decoupled from the deep water circulation, we believe that our analyses provide insight into the general motion of the water in the Gulf of Mexico. We also believe that studies should be conducted to study the relationship between the surface flow and the subsurface flow under a variety of conditions (e.g., with eddy features and without, variable thermocline depths, winds, and salinity, etc.). We remain concerned that subsurface oil will be concentrated along ocean frontal convergence boundaries and be upwelled into the surface waters again.
Based on what we are seeing now, it appears that the subsurface cloud will continue moving east-northeastward in the DeSoto Canyon and that the cloud by 92°W will continue to move westward. Remember that the ameba shaped subsurface cloud, like an atmospheric cumulous cloud, will move in a variety of directions.
