Did Deepwater Horizon Hydrocarbons Transit to the West Florida Continental Shelf?
Hydrocarbons that originated from Deepwater Horizon were observed at the surface along west Florida's northern coastline in June 2010. The farthest eastward advance nearly to Cape San Blas occurred during the last week of June before the surface oil retreated back westward and dissipated. Surface oil was not observed on the portion of the West Florida Continental Shelf (WFS) situated to the southeast of Cape San Blas. Nevertheless, there were numerous anecdotal occurrences of reef fish caught on the WFS with lesions and other deformities. Subsequent systematic sampling of WFS reef fish provided additional evidence for damage that extended as far south as the Dry Tortugas. Here we examine the possibility that hydrocarbons of Deepwater Horizon origin transited to the WFS beneath the surface. We use a numerical circulation model simulation run for the entirety of 2010 and quantitatively gauged against in situ observations. A passive tracer is introduced into the model to mimic the movement of subsurface hydrocarbons, either dissolved or of sufficiently small particle size to effectively be dissolved. The tracer, driven primarily by an anomalously strong and persistent upwelling circulation, eventually covered most of the WFS. Using reasonable estimates of what the initial tracer concentration may have been with respect to hydrocarbons, we conclude that the transport of subsurface hydrocarbons to the WFS is both plausible and consistent with the observed distribution of fish lesions, fish liver chemistry and other chemical and ecological evidence.