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 17

Fig. 1.7 Maps showing the areal extent of surface oil (regions in black ) for three different dates
(May 20, June 20, and June 27, 2010), as obtained from the 5-day (centred on the referenced day)
experimentalMarine Pollution SurveillanceReports (MPSR) product. These areas are superimposed
on the altimetry-derived surface currents ( grey arrows ), showing selected sea height contours that
are associated with the main mesoscale cyclonic and anticyclonic features ( blue and red lines ,
respectively). The star placed at 88.36 ⓦ W 28.73 ⓦ N, shows the location of the Deepwater Horizon
oil spill site. a MAY 20. b JUN 20. c JUN 27

surface oil began to spread and attained its first maximum of areal extent (Fig. 1.7 b),
approximately reaching its southernmost location at 27 ⓦ N (Fig. 1.4 c). At this time,
the southern boundary of the main surface oil area, located at approximately 27 ⓦ N,
followed the shape of the northern edge of the large LCR and extended south and
east of the small cyclonic eddy centred at approximately 86.5 ⓦ W 27.5 ⓦ N as revealed
by satellite-derived surface currents (Fig. 1.4 c) and pathways of water particles using
numerical modelling (Fig. 1.1 ). However, these southern extensions of the surface
oil extent did not necessarily correspond to the maximum oil extensions, except for
mid May. These results highlight the close link between surface ocean dynamics and
the surface oil extent.
The pathways and boundaries of the LC and LCRs were also partly defined by
Lagrangian Coherent Structures (LCSs) patterns formed by passive tracers, e.g. [ 5 ],
which control transport and mixing. These features are revealed using, for example,
synoptic fields of sea surface temperature and ocean colour, or can be extracted from
current velocity fields using Lagrangian techniques. For example, LCSs can help to
explain the shape of the surface oil extent for May 20, 2010 (Fig. 1.1 ;[ 27 ]), which is
one of the dates when a maximum of surface oil extent occurred (Figs. 1.4 c and 1.5 b).
At the time of the oil spill, the dynamical conditions of the LC exhibited a marked
northern excursion with the potential of GOMwaters to get closer to theWest Florida
Shelf. Numerical experiments carried out inwhichwater particles were released at the
surface near the oil spill site indicate that none of the synthetic water particles made
their way onto the shelf (Fig. 1.1 ). This is consistent with the presence of an unbroken
barrier that partially inhibits transport across the shelf. In addition, numerical model
experiments revealed that almost no particles ( 0.1%) reached the coastal waters

near the Florida Keys (Fig. 1.1 ). The lack of agreement sometimes found between this
type of study and simulated oil distributions may be partly attributed to neglecting
the non-conservative behaviour of oil in the simulations.
After reaching its northernmost location in mid-May, the LC began shedding a
LCR, aided in part by its interaction with the cyclonic eddy centred near 85 ⓦ W25 ⓦ N

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