Natural and unnatural oil slicks in the Gulf of Mexico

TitleNatural and unnatural oil slicks in the Gulf of Mexico
Publication TypeJournal Article
Year of Publication2015
AuthorsMacDonald IR, Garcia-Pineda O., Beet A., S. Asl D, Feng L, Graettinger G, French-McCay D., Holmes J., Hu C., Huffer F., Leifer I, Muller-Karger F, Solow A., Silva M., Swayze G
JournalJournal of Geophysical Research-Oceans
Date PublishedDec
ISBN Number2169-9275
Accession NumberCCC:000369153200036
KeywordsDeepwater Horizon
AbstractWhen wind speeds are 2-10 m s(-1), reflective contrasts in the ocean surface make oil slicks visible to synthetic aperture radar (SAR) under all sky conditions. Neural network analysis of satellite SAR images quantified the magnitude and distribution of surface oil in the Gulf of Mexico from persistent, natural seeps and from the Deepwater Horizon (DWH) discharge. This analysis identified 914 natural oil seep zones across the entire Gulf of Mexico in pre-2010 data. Their approximate to 0.1 mu m slicks covered an aggregated average of 775 km(2). Assuming an average volume of 77.5 m(3) over an 8-24 h lifespan per oil slick, the floating oil indicates a surface flux of 2.5-9.4 x 10(4) m(3) yr(-1). Oil from natural slicks was regionally concentrated: 68%, 25%, 7%, and <1% of the total was observed in the NW, SW, NE, and SE Gulf, respectively. This reflects differences in basin history and hydrocarbon generation. SAR images from 2010 showed that the 87 day DWH discharge produced a surface-oil footprint fundamentally different from background seepage, with an average ocean area of 11,200 km(2) (SD 5028) and a volume of 22,600 m(3) (SD 5411). Peak magnitudes of oil were detected during equivalent, approximate to 14 day intervals around 23 May and 18 June, when wind speeds remained <5 m s(-1). Over this interval, aggregated volume of floating oil decreased by 21%; area covered increased by 49% (p<0.1), potentially altering its ecological impact. The most likely causes were increased applications of dispersant and surface burning operations.