Archive for July 5th, 2010

Glider data as of morning of July 5

July 5th, 2010 No comments

The gliders continue to make good progress in surveying the upper region of the oil spill and along the Florida shelf.  In the oil spill region there are four gliders that continue to map the area.  Off Florida we currently have three gliders. Kudos to NAVO, Scipps/WHOI, iRobot/APL, USF, Mote and U Del.

Both NAVO gliders show a consistent story.  The optical backscatter continues to show the highest spatial variability of any parameters and is not correlated with any of the other features mapped by the gliders.  The surface waters show a shallow low salinity plume.  The low salinity surface show enhanced CDOM and chlorophyll.  When there is no low salinity plume present the chlorophyll maximum resides at ~50-75m.  CDOM values are consistently  higher at depth.

The Scripps/WHOI Spray glider continues its survey in the oil spill region.  The system is heavily startified and the currents are consistently to the north west.  This is consistent with the reports of oil reports that Lousiana and Mississippi are bearing the brunt of the damage. The thermocline appears to be deepening over time.

The iRobot/APL Seaglider continues its survey on the inshore side of the spill site and continues to reside in the heart of the spill zone.  Data remains consistent during this high resolution survey.  A stratified system, with enhanced CDOM in the mid-water depths.  The chlorophyll maximum is close to ~50 meters consistent with the NAVO gliders.  Chlorophyll maximum is above the mid-water CDOM maximum.  Also consistent with the NAVO gliders, the optical backscatter shows a high degree of variability especially at depth.  The variability is not correlated with CDOM, hydrographic features, or chlorophyll.

The Florida gliders are doing well, despite the presence of the pesky Remoras, and the UDel Blue Hen has recoveed after an “encounter” with a marine vessel late last week. The USF BASS glider is making a series of cross-shelf surveys.  Like the other gliders in the northern gulf, the chlorophyll maximum resides at ~50m water depth and is associated with the pycnocline.  The CDOM values are highest at depth.  Optical backscatter shows the presence of “bright nepheloid layers the are not correlated with the chlorophyll.

The UDel glider is in shallow water and fighting strong southerly currents.  We will try to move it north before starting the cross shelf survey.  The data collected the last few days shows a strongly stratified system with a pycnocline at ~15m but it is increasing with any increase in water depth.  The particles, chlorophyll and CDOM are high below the pycnocline.

Waldo carries on its along shelf survey.The pycnocline is around 20m, and like the UDel glider the chlorophyll, particles, and CDOM are highest in the waters directly below the pycnocline.


The oil slick spreads west

July 5th, 2010 No comments

Figure 1: First we looks at the winds from Oceanweather. The ship observations showing winds over the Gulf from the southeast, blowing towards the northwest over the entire Gulf of Mexico.

Figure 2: Next from Oceanweather, the waves. Again, surface waves across the entire Gulf are heading to the northwest.

Figure 3: Now the NOAA forecast of the slick location. We have another day of major changes in the slick location due to the persistent winds and currents to the northwest.  We see the slick has now spread well to the west along a major portion of the southern Louisiana coast.   The heaviest slick from the drill site has moved even closer to shore.  Three Horizon Marine Drifters are in the westward moving portion of the slick.  All are moving west. One is shooting the 16 kilometer gap located directly in between the highest concentration slick and the shore.  The HF Radar network covering the northern edge of the slick provide maps of the 25-hour average  currents in this region.  Currents are generally to the northwest and west, and are strongest near the coast. The Navy  Seagliders & SIO/WHOI Spray glider remain offshore in deepweater between the slick and the Loop Current Eddy. The iRobot Seaglider remains in the slick in deepwater near the drill site. But it looks like attention is probably moving shoreward with the oil to the inner shelf, the region that could be covered with HF Radar.

Figure 4:  Here is the same figure as above but now with the potential beached oil locations turned on.  You can see why I turned them off in figure 3.  There are so many reports of potential beached oil, you can’t see the map.

Figure 5: Since our focus today is on the inner shelf, we bring in the high resolution, nested, SABGOM model rather than the global HyCOM.   In this model we see the strong coastal current running along the inner shelf from Panama City along the Florida, Alabama, Mississippi and Louisiana coasts. Many of the currents vectors north of the birdsfoot head straight at the coast on the northern side of the Mississippi Delta.  Some of the currents wrap around the birdsfoot, and join a westward flowing current along the southern coast of Louisiana. The currents turn shoreward at the western edge of the potential oil slick in the NOAA slick forecast.  Alongshore currents further west are slower in this SABGOM forecast.

Figure 6:  While seemingly trivial in comparison to the alongshore spreading of the slick in the Gulf of Mexico, here is the update on the Horizon Marine drifter that is in the Gulf Stream offshore the Middle Atlantic Bight.  It has just entered the base of the meander crest. Will it loop around, or will it be ejected at the top of the crest?