The following is a summary of proceedings at the Oil Spill Physical Oceanography Summit on June 09, 2010, convened by representatives from Sea Grant College Programs in the South Atlantic states.
Summary prepared by Michael Voiland, Executive Director, North Carolina Sea Grant
Any assessment herein is based on best-available information at the time of writing, June 11, 2010.
Media contact: Katie Mosher, 919/515-6069,
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IN THE STATES of Florida, Georgia, and South and North Carolina, questions have arisen among the public and its legislative, executive, and business leaders regarding whether oil spilled into the Gulf of Mexico (GoM) due to the Deepwater Horizon (DH) disaster might reach South Atlantic waters and shores. These questions and concerns seemed to increase following national news reports in early June that identified potential movement of the oil through the Gulf Stream to the East Coast of the United States.
Within just the last few days, on June 9, 2010, at the Skidaway Institute of Oceanography in Savannah, GA, the four South Atlantic state Sea Grant programs jointly convened a roundtable of recognized physical oceanographic experts from the region to consider, discuss, and answer questions on if, how, and when GoM oil could arrive in regional waters. A listing of these experts is attached below.
The June 9 roundtable panel reached consensus on what is generally known and unknown about the GoM spill, and also on prospects and processes through which the Loop Current and Gulf Stream circulation mechanism could move Gulf oil to southeastern U.S. offshore and nearshore waters. Overall, the panel noted three distinct stages to consider: 1) oil released at the DH site and moving within the GoM; 2) oil in various forms that may be brought into the Loop Current and then into the Gulf Stream; and 3) potential for oil in various forms to move from the Gulf Stream toward near-shore waters and the shore in the Southeast.
The experts agreed that there are some hard realities and major questions that limit even generalizing about the movement of spilled Gulf oil to South Atlantic waters. These include:
- Despite estimates by BP and federal agencies, the amount of oil that has spilled into the Gulf is essentially unknown. The actual volume of oil spilled there will affect the chances of it reaching South Atlantic waters.
- As of this writing, authorities in the Gulf have no firm grasp as to where spilled oil — in various forms and concentrations — can be found within the GoM's water column and geographic expanse. Where oil lies, and at what depth, in the Gulf could play a substantive role in its entrainment and movement via the Loop Current.
- It is still highly speculative to pinpoint the location, depth, and amounts of GoM oil that might eventually be captured and transported by the Loop Current over specific periods of time. Understanding the sourcing, amount, and timing of spilled oil bleeding into this major GoM current is critical to understanding the oil's possible ultimate transport to the southeastern U.S. coast.
- Major questions exist about the nature of the spilled oil: How much oil has dispersed or has been degraded? How much will be degraded in coming weeks and months? And what are the physical and chemical forms that such degraded oil will take — i.e., slicks, tarballs, underwater plumes, diluted at various concentrations, etc. Such degraded oil outcomes could affect how spilled oil will move.
At the same time, the panelists agreed that:
- Much is known about how general ocean circulation typically works in the Gulf and South Atlantic Bight, due to our knowledge about the Gulf's Loop Current, the Atlantic's Gulf Stream, and the interrelationship between them. See the following URL for an explanation and depiction of that general understanding: http://www.skio.usg.edu/?p=news/showarticle&n=128.
- There was unanimous agreement that the Loop Current and Gulf Stream would be the main "conveyor" should Gulf oil move to South Atlantic waters and shorelines.
- The first major step in any movement of Gulf oil to the South Atlantic would be its entrainment in the GoM's Loop Current. In recent weeks and at present (June 11, 2010), the Loop Current has been "pinched" at its ox-bowed (loop) narrowing, creating an eddy or gyre separated from the Loop Current itself. This fluctuation, manifested as a separated eddy, has acted as a barrier to major movement of oil into the Loop Current. Thus, that action may have prevented and delayed the movement of oil toward the Atlantic. For an animated depiction of this eddy in relationship to the Loop Current, see: http://omglnx6.meas.ncsu.edu/sabgom_nfcast.
- The separated eddy now present in the Gulf, however, will likely reconnect to the Loop Current in the near future due to seasonal weather trends and perhaps other factors that are poorly understood. The more fully developed Loop Current resulting from this re-attachment could reach farther into the Gulf and closer to the spill zone center, likely capturing more oil in various forms and more fully channeling it toward the Florida Straits and the Gulf Stream. Once within the Loop Current, that oil could move from the Gulf to Cape Hatteras in about a month's time under typical weather conditions. Once oil borne by the Loop Current reaches the southeast end of the Florida peninsula, it then could become captured by the Gulf Steam and move to the north, offshore of the east coasts of FL, GA, SC and NC. (Again, see: http://www.skio.usg.edu/?p=news/showarticle&n=128)
- The risk of having oil spill residuals come ashore would be greatest along the southern portion of Florida's east coast, due to closer proximity of the Gulf Stream to that shore. Factors affecting the prospects and amounts of oil reaching the shoreline include shearing and eddy effects along the Gulf Stream's west (inshore) edge, prevailing winds and their speeds, and acute weather events.
- A second area in the South Atlantic that would be at higher risk for oil spill residuals coming ashore is at North Carolina's Cape Hatteras and neighboring Outer Banks beaches, and especially in the September to April time frame. Again, this would be mainly driven by proximity of the Gulf Stream to the shore and weather events, but also by onshore eddies and jetting actions caused by interactions of the Gulf Stream near Hatteras with southerly flowing currents of cooler water from the north.
- Shorelines and waters between south Florida and Cape Hatteras also could experience visible oil deposits, diluted concentrations of oil, and other effects. Manifestations of oil will likely be more highly dependent on acute weather events (significant coastal storms), prevailing wind direction and speeds over set periods of time, and seasonally-related perturbations (e.g., eddies, meanders, "spin-offs") along the inshore (western) edge of the Gulf Stream.
- The expert panel noted that the longer Gulf oil remains at sea, the more likely natural degradation of the oil could take place. As such, it is possible that oil reaching south Florida waters may be in more visible forms such as sheens, slugs, and tarballs; while oil that makes it to Hatteras waters may be more diluted and dissolved - and, if conspicuous at all, perhaps only seen in forms such as water color/turbidity differences, thin oily residues on contact objects, and smaller tarballs.
In addition, secondary (but highly significant and concerning) effects of oil (and chemicals used as oil dispersants) reaching southeastern U.S. waters could include impacts on coastal fish, animal, and aquatic plant health; seafood contamination issues; and compromised coastal ecosystem functioning. It could take years to observe, document, and experience these adverse effects, and the coastal observation network and infrastructure along the southeastern U.S. shore is currently inadequate to effectively monitor and measure such adverse effects in a timely manner.
The reference to Cape Hatteras is not meant to be ominous or dire. But the panel did want to note that Cape Hatteras is closer to the Gulf Stream than other parts of the North Carolina coast, or the coastlines for South Carolina, Georgia and northern Florida. Of course, the southern Florida area is closest to the Gulf Stream.
The reference to oil spill residuals is vague because we do not know what exact form degraded oil from the Deepwater Horizon would have after weeks and months of weathering as it may move. The experts did not want to speculate so far out.
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South Atlantic Sea Grant Programs' Oil Spill Physical Oceanography Summit
June 9, 2010, Skidaway Institute of Oceanography, Savannah, GA
List of Participating Experts
(In addition to participating Sea Grant personnel)
Ruoying He, North Carolina State University
Coastal and estuarine circulation dynamics; numerical modeling and data assimilation; coastal ocean observing system; bio-physical interactions; air-sea interaction; satellite oceanography.
Rick Luettich, UNC-Chapel Hill, director of the Institute of Marine Sciences
Research has dealt broadly with modeling and measurement of circulation and transport in coastal waters. Co-developed the ADCIRC circulation and storm surge model that is widely used by the academic, government and private sectors and has been applied extensively for modeling storm surge in the Southern Louisiana and New Orleans areas. Participated in the development of pieces of the SEACOOS component of the national Coastal Ocean Observing System effort.
George Voulgaris, University of South Carolina
Shoreline evolution; nearshore and beach processes; surf-zone and continental shelf sediment transport; wave- current interaction; sediment re-suspension; hydrodynamic and turbulence measurements in the field and laboratory; time-series analysis; tidal propagation in estuaries and lagoons; numerical model applications to coastal zone.
Dana Savidge, Skidaway Institute of Oceanography
Observational physical oceanography; dynamics of episodic, seasonal, and mean processes accounting for the transport of water and the material it contains through different ocean regimes, from open ocean to shelf settings. Boundary current variability, effects on coastal circulation effects, wind and buoyancy effects at subtidal, tidal, and super-tidal temporal scales.
Catherine Edwards, Skidaway Institute of Oceanography
Physical oceanography of continental margins, especially at the nearshore boundary and shelfbreak. Currently examining the interaction of winds and currents and the correlation of tides and shelf edge eddies in the South Atlantic Bight.
Note: Experts invited from Florida were unable to attend because of prior commitment, including commitments made in response to the Deepwater Horizon incident.
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