AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Gulf of Mexico Circulation and Oil Transport Pathways
(1) Horizon Marine, Inc., Marion, MA.
(2) School of Marine Science and Technology, University of Massachusetts, Dartmouth, MA.
As the recent Deepwater Horizon (DWH) accident has shown, monitoring of oil dispersion and transport over the Gulf of Mexico (GOM) represented a significant challenge in this oceanographically dynamic region. The circulation in the northern and eastern GOM is complex, comprised of currents which, near the shelf, are driven by wind and buoyancy forcing from large volumes of freshwater and, in the open ocean, by wind stress, the Loop Current, and energetic eddies, both cyclonic and anticyclonic. In the DWH crisis the effective use of traditional methods for oil tracking methods was augmented with continuous monitoring of the ocean currents using a ship-based ADCP system along the Loop Current frontal boundary and within the associated energetic mesoscale eddies. In this paper we describe the evolution of temporarily active transport pathways between the main spill site and distant regions of the Gulf of Mexico. These were discovered through the combined use of Lagrangian drifters, satellite imagery, and vessel surveys of ocean current during mid-May and mid-June 2010. Drifter trajectories showed progressive entrainment into the strong confluence region between the Loop Current and nearby counter-rotating mesoscale eddies located over the slope and offshore of the spill site. Closely -spaced drifters that entered the same confluence region became widely dispersed over the northern GOM slope and the West Florida Shelf, and also exited the GOM. An objective analysis of the surface currents around these features provided useful synoptic spatial maps of the surface velocity and associated error fields and their evolution over time. Sequences of satellite-derived oil slick distributions showed similar trajectories and indicated potentially extensive spreading and entrainment of surface oil off the northern GOM shelf/slope and into the Loop Current. These overlapping and complementary methods provided critical and timely information for predicting the three-dimensional oceanic transport pathways of oil. Analysis of historical data and statistical trends over the past 26 years enumerates 22 separate incursions of the Loop Current or Loop Current Eddy into northern Mississippi Canyon. Such conditions could have vastly complicated the scale of response efforts. We present the potential repercussions of strong Loop Current events during the oil spill, and possible impacts of worst-case environmental scenarios on response efforts at the Macondo site.