USF Researchers Show Need for Better Gulf Tracking

In a published article, USF researchers say the nation needs a better, more integrated system to track the Gulf of Mexico oil spill or other disasters.

By Vickie Chachere

USF News

 

ST. PETERSBURG, Fla. (Feb. 21, 2011) – From the first days of the Deepwater Horizon oil spill, the question on the minds of Gulf Coast residents was how much oil was gushing out of the well and where would it go.

Getting a good estimate to answer those questions, however, proved to be anything but easy.

For months, the Ocean Circulation Group and the Optical Oceanography Laboratory at University of South Florida’s College of Marine Science provided some of the best estimates of where the oil was headed, both on the surface and in the vast, underwater plumes of microscopic oil droplets.

Now, an article featured on the cover page of EOS Transactions, a publication of the American Geophysical Union, gives an inside look on the challenges the nation encounters in the face of such disasters. Click here to read the article.

Researchers said the current system – a conglomeration of various modeling systems which calculate currents and winds that move the Gulf waters and uses satellite imagery that can identify surface oil slicks – is imperfect and fraught with assumptions which can undermine its accuracy. The limits of the modeling system call for several future improvements, said the article authored by Yonggang Liu, Robert Weisberg, Chuanmin Hu and Lianyuan Zheng.

“No single model is adequate, either for the deep ocean or for the coastal oceans and its estuaries,” the authors said in the article. “Better coordination of real-time data among all groups that monitor the Gulf of Mexico would help improve all forecast systems. Most important, sustained funding is required for personnel and equipment to maintain and expand coastal ocean observing and modeling assets in the future.”

The challenges of tracking the spread of the oil both on the Gulf’s surface and in vast underwater plumes began with an incomplete picture of how much oil was flowing from the ruptured Macondo well and the use of dispersants in the depths of the Gulf, an unprecedented practice to combat a spill.

 USF’s Ocean Circulation Group marshaled its resources to track the spill, engaging numerical models that calculated ocean currents and satellite remote sensing resources that existed from previous ocean observing projects. Working in both Weisberg and Hu’s labs, researchers logged exhaustive, seven-day weeks for the duration of the spill taking in data from a series of observation systems feeding them information on currents, winds and water movement.

The models - developed by various federal and academic institutions and compiled by the USF groups and made available to the public online - became a familiar site alongside weather maps on the evening news: the brightly colored areas of the Gulf highlighted by the growing black stain with fingers stretching toward the Gulf’s vital Loop Current and later the development of an eddy that detached and kept millions of gallons of oil in the north central Gulf where it could be weathered, skimmed or burned.

The oil tracking modeling system is for rapid-response purposes, it’s a rough model,” said Liu, the lead author of the article. “All models in the system are trajectory models. Many assumptions go with them.”

But the forecast that allowed Gulf communities to get prepared for the oil movement were imperfect, the article notes. The forecast models have a margin of error which grows over time. Accurate oil trajectory modeling was also dependent on two crucial facts: the amount of oil flowing from the well and the fate of the oil. Those two crucial pieces of information were largely unavailable during much of the event, the scientists noted.

Scientists used six numerical ocean circulation models from different institutions to build a merged, best-estimate picture of what was occurring in the Gulf and what the forecast might be. They checked their calculations against imagery gleaned primarily from NASA satellites which produced images of the oil spill as a silvery image from sun glints on the water’s surface. 

The satellites, however, were hampered on cloudy days from getting a good view of the Gulf’s surface. On those days, the researchers continued to gather data from synthetic aperture radar satellite instruments to help delineate oil slicks. These data were made available by NOAA and USGS through collaborative efforts with other institutions.

That addressed the issue of oil on the surface, but the Deepwater Horizon spill would soon show the public that oil spills in the Gulf are three-dimensional issues.  Again, scientists were challenged to understand how deep-sea plumes might have spread from the Macondo well and at what depths.

Subsurface trajectories were prone to more errors than surface predictions, the group noted. Nonetheless, Weisberg and his group were able to estimate the plumes would follow the contours of the bottom depth of the Gulf and their predictions turned out to be right. Between June and August, following the models, USF researchers identified two large plumes of degraded oil suspended in the depths of the Gulf right at the spot near DeSoto Canyon where the Ocean Circulation Group thought the plumes would be.

Those plumes have since been identified as bearing the chemical fingerprint of Macondo well oil.

The lessons of the Deepwater Horizon spill are apparent now, they say. The limitations of current modeling systems call for the development of more integrated systems requiring various agencies with differing tools to contribute to building the model. The satellite observations are also limited to provide only the surface extent of the oil, and methods to estimate the thickness of the surface oil are required to improve the models.

To that end, Weisberg and two other institutions have received a grant through the Florida Institute of Oceanography to develop a better system.

”This work obviously demonstrates how our community can benefit from an integrated ocean observing system,” Liu said, “More resources are is needed to maintain and improve it. We have learned a lot from this work.”

To read more about the challenges of tracking the Deepwater Horizon spill, click here.

To watch a video of Robert Weisberg’s presentation to the Century Commission on tracking challenges, click here.

Vickie Chachere can be reached at 813-974-6251.