On the interaction of Mississippi River waters with the deepwater horizon oil spill (Gulf of Mexico).

Yannis Androulidakis, Vassiliki Kourafalou

Thursday 2 july 2015

15:00 - 15:20h at Europe 1 (level 0)

Themes: (T) Special session, (ST) Oil spill modelling

Parallel session: 12J. Special session: Oli Spill Modelling

The 2010 Deepwater Horizon oil rig explosion caused ~7*105 m3 of oil gushing from the Northern Gulf of Mexico bottom. The important and numerous effects of the DwH oil spill on the deep and coastal environment of the Northern Gulf of Mexico motivated this study. The oil spill significantly affected the pelagic communities of the entire NGoM, while biological feedback also influenced the oil fate. The close proximity of the rig to the Mississippi Delta raised questions from disaster managers about possible influence of river induced circulation on oil patch evolution. This is a very relevant aspect of circulation and pollutant transport in the Gulf of Mexico, recipient of the largest U.S. river discharge and subject to intense oil exploration. It is also a unique topic relating the dynamics of a large scale river plume with the transport and fate of hydrocarbons. In particular, it was hypothesized that the high Mississippi River discharge in May 2010 might have helped to initially keep oil from reaching coastal marshes. We have explored this intriguing hypothesis, quantifying similar and connecting patterns in the evolution of riverine and oil covered waters. Numerical simulations, satellite and in situ data were used to show the unique influence of a large river plume on a surface oil patch resulting from a deep oil release. The buoyant plume induced circulation, modified by shelf and slope flows, was found to substantially influence the near surface transport of oil. Anticyclonic circulation within the upstream plume region created a front that restrained onshore transport. Conversely, the shoreward tendency within the downstream plume region guided oil transport along the Louisiana-Texas shelf. Periods of low discharge reduced the dominance of buoyancy-driven effects, but an interval of sustained downwelling-favorable winds, combined with river induced stratification, resulted in a strong westward current and surface oil patch extension.