Geoscientists say a study reveals the force of the Mississippi River emptying into the Gulf of Mexico created mounds of freshwater that pushed back against much of the oil slick from the leaking Deepwater Horizon drilling rig offshore.
"The idea is that, if the water surface is tilting a little bit, then maybe the oil will move downhill, sort of like a ball on a plate. If you tilt the plate, the ball will roll one way and then another," University of Pennsylvania researcher Douglas Jerolmack said.
"Surprisingly no one had really investigated the effect that the tilting of the water surface can have on the migration of oil," he said in a university release Thursday.
While many wetland habitats and wildlife were oiled during the three-month leak, a great part of the spreading slick never made it to the coast, the researchers said.
The National Oceanic and Atmospheric Administration used information from satellite data to issue daily forecasts of where the oil slick might travel, using computer models based on ocean currents.
"We noticed that there was a big disconnect between the forecasts of where the oil was going to be the next day and where the oil actually was the next day," Jerolmack said.
The researchers analyzed see level data from the period and confirmed the existence of several mounds and troughs in the Gulf.
"We recognized that there was a very persistent mound, a bump or a bulge, in the elevation of the sea surface in the vicinity of the Mississippi Delta," Jerolmack said, noting the oil spill coincided with the typical spring flood on the Mississippi that pushed a larger-than-normal flow of water into the Delta.
A mathematical model confirmed the slope of the mound was sufficient to direct the oil's movement, he said.
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