Where will all the spilled oil go?

Probability of shoreline threat, courtesy of NOAA

Almost everyone wants to know, and many responders absolutely need to know, exactly where all the oil is going as it gushes out from BP’s Deepwater Horizon spill. Scientists need to know where to best sample the ocean environment for spill impacts. The Coast Guard needs to know where to deploy more booms. Local and state government officials need to know where to best disperse their staff, equipment, and other resources. Beach-goers may want to know before they head off for their seaside family vacation. Wildlife rehabilitators also need to know where they ought to set up optimal facilities for cleaning and sheltering the wildlife harmed by the oil.

But knowing where this oil is going to strike sometime into the future is no easy task. Ocean currents that transport and also weather the spilled oil are notoriously fickle. Currents change each year, each month, each week, every day. Some currents even change by the hour and minute. Because of this great uncertainty, the ocean can ultimately either help or hinder our efforts to contain at least some of the environmental damages caused by the spill.

Although we cannot predict precisely where surface oil will go in the coming months, it is certainly possible to analyze where surface oil is most likely to go from historical wind and ocean current records, and then account for both the natural processes of “weathering” and the human interventions that are currently underway to recover and remove the oil. This is exactly what the National Oceanic and Atmospheric Administration (NOAA) did last week when it released results from its pivotal study looking at the likely fate of Deepwater Horizon oil in surface waters. NOAA used a large number of computer models to produce estimates for the potential threats to U.S. coastlines that might result if oil spilling from the Deepwater Horizon site continues until a relief well successfully stops the flow.

Before getting to the final results for particular coastlines across the southeastern United States, let’s first take a closer look at how the variation in ocean currents can play out in the Gulf of Mexico. We’ll look at three different “movies” of what would have happened to the oil if it had spilled during previous years, and where it would have gone during the weeks and months afterwards. For example, if the spill had occurred on April 6, 1996, most of the oil would have stayed close to and north of the original spill site. In this case, Louisiana would have taken the brunt of the oil hitting the shorelines, but eastern Texas, Mississippi, Alabama, and the Florida panhandle would have been hard-hit by late June and July.

Another historical simulation of how the Deepwater Horizon spill would impact the Gulf had it started on April 17, 1997 shows yet another scenario for the fate of the oil. In this case, the oil would have spread much further across the Gulf, not only covering much of the continental shelf off western Florida, but with considerable amounts of oil being caught by the Loop Current and shunted all the way around Florida and up the eastern seaboard of the U.S. Another scenario for what might happen to the oil comes from a historical simulation for a spill had it occurred on April 15, 1993. With currents that behaved this way, far more oil first would have been transported westward and concentrated along the beaches of eastern Texas, with oil finally moving offshore and ultimately being caught in the Loop Current months later.

Reef at Dry Tortugas, courtesy of NPS

What do these examples mean for the fate of oil from the Deepwater Horizon spill in 2010 and later? NOAA’s study was able to take all of the scenarios that they could find using such historical data, and then map the probabilities for oil striking individual coastlines. These results show that, as is happening right now, eastern Louisiana, all of Mississippi and Alabama, and northwest Florida have coastlines that are particularly vulnerable (see map above).

But the Florida Keys, with their magnificent coral reefs  and significant number of colonial seabirds nesting at the Dry Tortugas, are also in the bulls-eye of the oil washing ashore. Southeast Florida all the way north to West Palm Beach has as much as an 80% probability of getting oiled. And yet another important seabird colony, at the Bahama’s Cay Sal Bank, has as much as a 40% likelihood of being oiled.

Those are not odds that wildlife conservationists really want to see. We can only hope that ocean currents in the Gulf of Mexico procrastinate the day of reckoning until sometime well after the spill is stopped for good.