Variability of the Deepwater Horizon Surface Oil Spill Extent and Its Relationship to Varying Ocean Currents and Extreme Weather Conditions - Mathematical Modelling and Numerical Simulation of Oil Pollution Problems - page 15

Fig. 1.6 Map showing two areas of extent of the surface oil obtained from the NOAA National
Environmental Data and Information Services experimental Marine Pollution Surveillance Reports
(MPSR) products. These maps correspond to pre- (June 26, 2010, in dark gray ) and post- (July
2, 2010, light blue ) Hurricane Alex. Average surface SE winds of 7.4m/s during this time period
contributed to the reduction of the surface oil extent. Gray lines indicate bathymetry contours of
25, 50, 100, 200, 500, 1000, and 2000m

19-23, 2010. These locations only reflect the extent of surface oil identified in more
than one report and as a single continuous area. In addition, smaller areas of potential
surface oil slick were reported in the MPSRs. However, large uncertainties existed
in their identification and location, and their confirmation therefore relied on visual
inspection by overflights. These areas, which extended as far south and east as 24.1 ⓦ N
and 83.0 ⓦ W, were generally not sampled, and very few of them were confirmed
by overflights. Additionally, a relatively very small amount of this oil could have
originated in natural seeps or other anthropogenic sources. Observations indicated
that these areas consisted of transparent sheens, which may have been very thin oil
(

40nm) or may have been biological in origin (natural sheening of sargassum).
For example, a slick detected approximately 160km southwest of Tampa, Florida,
was confirmed as a transparent sheen by a C130 overflight conducted on June 2,
2010. No further visual analysis or sampling was carried out at later dates in this
region. In addition, there were several short-lived slicks detected around the LCR that
reached south of 27 ⓦ N between 85 ⓦ W and 87 ⓦ W at the end of May and beginning
of June. However, they were not confirmed by overflights or by in situ observations.
These could have been formed due to ephemeral surface convergence as sequential
image analysis suggested that it was possible for DWH oil to have reached this area.
However, compared with the other areas, especially those with recoverable oil, these
areas contribute to less than 5% of the total surface oil spill area.
In addition to surface currents, the surface oil extent depended on other factors,
such as the rate of oil flowing from the well, which on average was estimated to range
between 50,000 and 70,000 barrels per day [ 19 ]. A suite of recovery efforts was

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