Earlier this month a group of experts from the institutions of the South Atlantic Sea Grant Program gathered at Skidaway Institute for a discussion of the Gulf of Mexico (GoM) oil spill and its potential effect on the Atlantic coast.
Here is an abbreviated summary of their conclusions.
Overall, the panel noted three distinct phenomena that must be considered:
(1) oil released at the Deep Horizon (DH) site and moving within the GoM, (2) oil in various forms that may be “captured” by the Loop Current and then transported into the Gulf Stream, and(3) the potential for oil in its various forms to move in a westerly direction from the Gulf Stream toward our nearshore waters and the southeastern coastline.
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 GoM is essentially unknown. The actual volume of oil spilled there will affect the chances of it reaching South Atlantic waters.
*Authorities in the Gulf have no firm grasp as to where spilled oil – in its various forms and concentrations – can be found within the GoM’s water column and geographic expanse. Where oil lies in the Gulf, and at what depth, could play a substantive role in its entrainment in 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. region.
* Major questions exist about the nature of the spilled oil. For instance, 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 (e.g., 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 GoM and South Atlantic Bight, due to our knowledge about the GoM’s Loop Current, the Atlantic’s Gulf Stream, and the interrelationship between them. There was unanimous agreement that the Loop Current and Gulf Stream would be the main “conveyor” of the Gulf oil should it move to South Atlantic waters.
* 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, the Loop Current has been “pinched” at its ox-bowed (loop) narrowing, creating an eddy 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. See an animated depiction of this eddy in relationship to the Loop Current here.
* The separated eddy now present in the Gulf, however, will either drift to the west (which is good), as it will take entrained oil with it, or reconnect to the Loop Current in the near future (not so good); the controlling factors being seasonal weather trends and events and perhaps other factors that are now poorly understood. A more fully developed Loop Current resulting from re-attachment could reach farther north into the GoM and therefore closer to the spill zone center, likely capturing more oil in various forms and more fully channeling it toward the Florida Straits and possibly the Gulf Stream.
Once within the Loop Current, that oil could move from the GoM to the coastal waters off Cape Hatteras, NC 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.
* The risk of having oil spill residuals come ashore along the southeastern coast would be greatest along the southern portion of Florida’s east coast, due to the close proximity of the Gulf Stream to that shoreline. 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. 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.
* Due to the greater width of the continental shelf off of South Carolina, our shoreline and waters are less likely to be impacted by Gulf oil. Deep hard-bottom reefs and fisheries would be more vulnerable in conjunction with upwelling of deep Gulf Stream waters associated with spin-off eddies, while coastal wetlands and estuaries would be the least vulnerable.
*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 be seen in forms such as water color/turbidity differences, thin oily residues on contact objects, and smaller tarballs.
The summit concluded with a brief discussion of secondary (but highly significant and concerning) effects of oil (and chemicals used as oil dispersants) reaching southeastern U.S. waters, which 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. Unfortunately, our coastal observation networks and infrastructure in and along the southeastern U.S. coastal waters and shorelines are currently inadequate to effectively monitor and measure such adverse effects in a timely manner.
As a result of the meeting, the four Sea Grant programs in the South Atlantic region will further develop a regional website regarding Gulf oil spill information, which can be found here.