DeepWater Horizon Oil Spill

The weekend comes to a close with the gliders continuing their surveys. The northern gliders in the western Gulf are conducting high resolution surveys.  While the southern gliders continue their cross-shore surveys of the Florida continental shelf.

The NAVO gliders are on the outside of the projected oil spill zones.  The gliders are fanning out.  The backscatter plumes are dramatic and they remain 100s(!) of meters thick. The chlorophyll is continues to show a subsurface maximum directly below the thermocline which is ~50 m deep.  The CDOM shows little spatial variability except for the depth dependent variability.

The iRobot/APL Seaglider continues to show the complex spatial patterns in the CDOM.  The surface waters however are now showing some indications of the low salinity plumes with enhanced chlorophyll.  The surface plume is seen as low salinity, enhanced CDOM and chlorophyll and likely reflect plumes from the local wetlands and/or the Mississippi river.  The chlorophyll maximum and thermocline is shallower then seen by the NAVO gliders.

For the Florida shelf, the four gliders are making good progress. Starting from the North to south, all the gliders provide a consistent picture of the state of the Florida shelf.  The USF SAM glider has made good progress and is now on the inner shelf.  The particle loads are high at depth, but surprisingly the chlorophyll values are low.  The decision in the next day will be to determine what is the ideal survey given the remaining batteries.

In contrast RU23 is heading offshore into deep water.  Like SAM, the particles are higher at depth, but chlorohyll are high at depth.  We plan on following the path of the earlier RU21 flight, head to locations near the offshore eddy where there are projections suggesting the possible presence of oil. CDOM patterns match all gliders, EXCEPT THE SEAGLIDER IN THE SPILL, with enhanced values in bottom waters.

RU21 has broken free from the loop current.  Planning conitnues for the coming week.  We will fly northeast at the suggestion of the Mote Marine team.  This will facilitate recovery before we rebattery, and likely do it again. Patterns remain consistent with the last 5 days.

The UDelaware glider makes good progress offshore with the depth steadingly increasing. The main features include a strengthening density dependent stratification, with subsurface bottom water maxima in chlorophyll, particles, and CDOM.

Figure 1.  Tracks from the Horizon Drifters, the IOOS glider fleet, and today’s NOAA oil spill forecast.  The densest concentrations are now in a north-south band between the Deepwater Horizon site and the Alabama/Florida border.  Horizon Marine Drifters are on both sides of this band.  Seaglider 515 remains in the immediate vicinity of the Deepwater Horizon site.  The part of the slick that extends south along the eastern side of the Loop Current Eddy is now concentrated at the edge of the Florida continental shelf edge or deeper.  The Horizon Marine buoys indicate that this part of the slick is in the portion of the Loop Current Eddy that is recirculating.  An interesting drifter today is the one located near 27N, 85.5 W. It was moving southeast, but has reversed direction so that it is now heading northwest.  This is inside inside the slick forecast area, and an important comparison point with the HyCOM model below.

Figure 2.  Now we add the currents reported by the HF Radar networks and the gliders.  Here we plot the most recent 25-hour average HF Radar currents.  The hourly HF Radar currents are highly tidal today, so I need to use the longer term average in these google earth snapshots to show the trends.  Up in the USM networks, the  strong average currents are found in a band along the offshore side of the coverage, south of 26.5 N and heading east.  Along the Florida shelf, both glider and HF Radar currents are much lower, until you get all the way south to the UDel glider UD134.  The good news is that we broke RU21 out of the Loop Current Eddy and now have it back up in the slower currents of the Florida shelf.  Lots of tacking to get this glider back and avoid a long distance recovery.

Figure 3.  The SST gives a good picture of the Loop Current Eddy, and how the slick on its eastern side is following the edge of the warm water. But the temperatures are warming up and its getting harder to see the contrast.  We’ll need to switch over to some individually enhanced images soon.

Figure 4.  Hycom model with forecast currents  and surface temperatures. The large Loop Current eddy dominates the view. The slick that wraps around this eddy appears to be crossing more into the core of the eddy as it is advected around by the high velocities.  But not everything in this portion of the slick is moving clockwise around the eddy, The northern edge of this filament of oil is heading northwest, with the drifter and the HyCOM forecast.  Up to the north, we see that band of eastward flowing currents just south of 26.5 N, just like we saw in the HF Radar, giving us more confidence in this feature in the model.  The clockwise eddy that is up by 27 N, 90 W in the model is also well defined by the drifters.

Figure 5.  Here is an interesting validation point.  HyCOM currents, now in white, plotted on top of the oil spill forecast.  That jet south of 26.5  looks to be moving that part of the denser oil slick to the east.  In the part of the slick that wraps around the Loop Current Eddy, there are 2 regions of higher concentration.  HyCOM says the western slick is heading clockwise into the core of the eddy.  The eastern slick is moving counterclockwise back to the northwest.

Figure 6. One more comparison for tonight.  HyCOM currents and temperature, compared to HF Radar 25 hour average currents. In the southern part of the Radar coverage, both have the current jet to the east.  Way up on the northeast side of the coverage, HyCOM is running alongshore to the southeast.  HF Radar currents are in the opposite direction, indicating that average current in this region is toward the Florida shore where the oil is washing up.