BP / Gulf Oil Spill – The Slick Is Dissipating

At long, long last.

Radarsat images taken yesterday (July 26) show the oil slick is steadily dissipating. The failed Macondo well has been tightly sealed since July 15, so no new oil has been entering the Gulf for over a week. Oil floating at the ocean’s surface has a limited lifespan – it’s been collected and destroyed by skimming, booms, chemical dispersants, evaporation, photolysis, biodegradation – and took a beating from wind and waves when tropical depression Bonnie blew through over the weekend. If the well stays plugged until the static-kill and bottom-kill efforts permanently plug it with cement, then the remaining fragments of slick should disappear within days.

The big question: what’s the fate and impact of the oil we can’t see with satellite images? Oil now buried on Gulf coast beaches, embedded in marshes, and remaining dispersed underneath the water’s surface or lying on the seafloor? It will take diligent, systematic research to find the answers. We need to make sure that this research actually gets funded, conducted and published, and not sidetracked by litigation and confidentiality.

Here’s the July 26 imagery without SkyTruth’s analysis. Wind conditions (ranging from 3-6 meters per second) were nearly ideal for detecting oil slicks on radar imagery. Scattered dark patches of slick and sheen are spread across a wide area, but it appears that the oil slick created by the Macondo well blowout is steadily dissipating, and no new oil can be found around the well site:

RADARSAT images taken July 26, 2010, without analysis. Images courtesy CSTARS.

And here’s the version with our analysis of BP-related oil slicks and sheen, delineated in orange:

RADARSAT images taken July 26, 2010, with SkyTruth analysis. Images courtesy CSTARS.

BP / Gulf Oil Spill – What Did Bonnie Do?

The center of Bonnie’s circulation appears close to the Macondo well site on a CSK radar satellite image taken July 24. CSK and MODIS satellite images the next day, July 25, show remnants of the BP oil slick scattered around the Mississippi Delta. No new oil is seen around the well site; it’s been tightly capped since July 15.

COSMO-SkyMed radar satellite image showing center of circulation of tropical depression Bonnie, July 24, 2010. CSK-1 image courtesy CSTARS. Backdrop (color) is MODIS/Aqua image from earlier the same day.

The center of circulation for tropical depression Bonnie was located about 15 miles (24 km) south-southeast of the Macondo well site when this CSK-1 radar satellite image (black-and-white) was taken, at 6:44 pm local time. Weather station 42364, on the Ram-Powell oil platform about 27 miles (43 km) northeast of the Macondo well, recorded sustained wind speed of 22 mph (10 m/s) at that time. Station 42887 on the Thunder Horse oil platform about 39 miles (63 km) south of the well recorded winds at 11 mph (5 m/s).

Radar images show the “roughness” of the ocean’s surface, revealing the pattern of Bonnie’s counterclockwise-circulating winds. The strongest winds are generally in the northeast quadrant of cyclones in the northern hemisphere. This is reflected by the overall gray tone in the radar image: the area of stronger winds north and east of the storm’s center is brighter than the area to the south and west.

Two distinct storm bands are also apparent; these are lines of strong thunderstorms with gusty winds. A narrow line of oil slick is also visible – possibly related to the BP / Deepwater Horizon spill, although we think most of the slick and sheen from that spill is obscured on the radar image by the strong wind conditions.

COSMO-SkyMed radar and MODIS/Terra satellite images taken July 25, 2010, showing remnants of BP oil slick. CSK-1 image courtesy CSTARS.

CSK radar and MODIS / Terra satellite images taken on July 25, 2010, show the effects of tropical depression Bonnie’s passage on the oil slicks and sheen from the spill. No new oil is seen in the immediate vicinity of the well. But remnants of the oil slick are visible around the Mississippi Delta.

The MODIS image also shows dozens of small oil slicks from natural oil and gas seeps. These seeps appear unusually active, possibly due to seafloor disturbance caused by Bonnie. A bright area of slicks or sheen between the spill-related oil slicks (orange line) and the area of active seeps (dashed red line) could be where oil from both sources is mingling.

See all of SkyTruth’s images related to the BP / Deepwater Horizon spill in our gallery.

BP / Gulf Spill – Buh Bye, Bonnie

More good news for the Gulf: Bonnie was a bust. She blew over the BP / Deepwater Horizon spill site Saturday morning as a rapidly weakening tropical depression. NOAA weather buoys and stations in the eastern Gulf barely registered her passing, with sustained winds at the leak site only briefly exceeding 14 meters per second (about 31 mph). Fellow weather-geeks, check out the data from Station 42364 (located on the Ram-Powell oil platform operated by Shell) and Station 42376 (on the Marlin platform operated by BP).

BP / Gulf Oil Spill – Here Comes Bonnie

3-day forecast track for Tropical Depression Bonnie, expected to strengthen over the weekend

The Bad News: Tropical Depression Bonnie is making a beeline through the eastern Gulf of Mexico, heading right for the Macondo well site. According to the National Weather Service, Bonnie should cross over the site on Saturday afternoon, strengthened by her trip over warm Gulf waters to a tropical storm with sustained winds over 40 miles per hour. Crews are being evacuated from the area, and progress on the relief wells has been brought to a halt.

GOES weather satellite image of Bonnie, taken at 5pm Central time on July 23, 2010

The Good News: The cap on the Macondo well has been shut tight for several days, and we no longer see signs of fresh oil upwelling around the site of the failed well. We have also noticed a significant reduction in the surface oil slicks in the Gulf since early July. Although we don’t know how much oil is lingering out of sight beneath the surface, we hope this means that far less oil is available to be thrown up onto the beaches and into the wetlands when Bonnie comes through.

On June 29, when Tropical Storm Alex was moving past in the southern Gulf, the area of slicks on satellite images spanned 19,000 square miles; the MODIS / Aqua image below, taken on July 21, shows a fragmented area of slicks and sheen covering 5,476 square miles:

MODIS / Aqua satellite image taken July 21, 2010

However, the large area of anomalous ocean color noted on a July 19 MODIS image is even more obvious. It shares spectral characteristics with the sediment-laden plume emerging from the Mississippi River, but it may also indicate changed water chemistry in the area affected by the spill – possibly due to oxygen depletion as a result of the elevated levels of methane (natural gas) dissolved in the water. The eastern edge of this anomaly is marked with a dashed brown line.See all of SkyTruth’s images of the BP spill here.
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Dalian Oil Spill, China

Sometime last week, two pipelines in the port city of Dalian, China, exploded and burned, and a large quantity of oil was released into the Yellow Sea. One firefighter lost his life. There are some harrowing pictures of oil-covered firemen being pulled from the water. Officials report that 165 square miles of ocean was covered with oil, but the pipelines are no longer leaking and cleanup is proceeding. Aquaculture is a huge business in China – Greenpeace estimates that 10,000 shellfish farms have been affected.

Envisat ASAR radar image (black-and-white) taken July 18, 2010

This Envisat radar satellite image appears to show patchy oil slicks spread out over a large area along the coast and islands near Dalian. China Central Television reported that the spill was estimated at about 400,000 gallons. If true this is far smaller than the BP /Deepwater Horizon spill in the Gulf of Mexico, although it’s worth noting that any spill greater than 100,000 gallons is labeled “major” by the US Coast Guard.

Some of the dark patches in this radar image may be areas of calm water rather than oil. This is a rugged coast, and strong topography can generate “wind shadows” on the downwind sides of rocky islands and coastal hills.