Acoustic Observations of the Deep Scattering Layer During the Deepwater Horizon Oil Spill

The explosion of the Deepwater Horizon drilling rig on April 20, 2010 resulted in the release of large quantities of oil and gas from the damaged wellhead into the deep waters of the Gulf of Mexico.  During the monitoring effort that ensued, a large body of acoustic measurements with scientific echosounders was collected from May to October with the goal of mapping subsurface oil and gas and monitoring the integrity of the well head.  These measurements will be used to observe the deep scattering layer (DSL), a ubiquitous community of sound-scattering mesopelagic organisms in the vicinity of the spill site.  Preliminary observations of reduced backscatter in the near-field of the rising oil indicate that the DSL is perturbed by the rising oil close to the well head.  It is unclear whether this is highly localized effect occurring only near the well, or whether the DSL was also perturbed by a deep oil plume that spread from the well site. The acoustic measurements of the DSL will be related to fluorometric indices of hydrocarbons from CTD profiles to gauge if the there was a larger-scale perturbation on the abundance, behavior, and distribution of the midwater community.