Posted on behalf of Melissa Gaskill
After 27 days at sea and 80-plus data collection stops, the Cape Hatteras pulled into Gulfport , Mississippi yesterday. Her complement of scientists from the University of Texas Marine Science Institute and the University of Georgia, Athens, broke down the on-board lab, carting instruments and equipment off the ship and into waiting U-Hauls. 
Their research contributed to an aggregate picture that the National Oceanic and Atmospheric Administration (NOAA) is creating of a hydrocarbon signature southwest of the blown well. The data also indicated that waters to the southeast of the well near the Florida shelf remain relatively oil-free, and it created a preliminary picture of hydrocarbon features around the well site. The boxes and cartons carried from the ship contain water samples (right) from across hundreds of kilometers of the Gulf, ready for further testing and analysis.
The Deepwater Horizon created an incredible scientific opportunity, a kind of giant, in-situ experiment. A chance to study, among other things, the long-term movement of oil, mixing and exchange in the water column, and geochemical effects – complex reactions, with multiple variables, taking place in a very large and dynamic system. So far, an impressive array of resources have been deployed to take advantage of that opportunity. The Hatteras, for example, was one of 11 ships stocked with a heck of a lot of scientific instruments and the people to run them.
“This is the largest environmental disaster in the US,” says Tracy Villareal, chief scientist aboard the Hatteras (left). “It’s important to understand the consequences, the effect of the oil, and its location. We now have one of the best-documented oil spills ever, but plenty of questions remain.” Given all this, the resources thrown at understanding the spill look well-spent – perhaps even inadequate.
Not that those resources are inconsequential. A day on the Hatteras costs between $15,000 and $20,000, plus the expense of her eight-person scientific crew, and a bank of instruments crammed into the ship-board lab. Funding from the National Science Foundation covered the cost of the ship, and a Rapid grant met additional expenses, including purchase of a nutrient auto-analyzer and lease of a critical piece of equipment, the Aqua Tracka, which transmits real-time data from the water column (see graph in a previous post). Many other instruments came from Villareal’s UT MSI lab. Boxes of extra machinery and spare parts provide insurance against a process or piece of equipment malfunctioning, since a lab at sea lies beyond the reach of repair services and a quick trip to the supply closet.
Villareal stresses that data from this cruise provide snapshots of specific points in a continuously changing situation, as hydrocarbons from the spill continue to move within Gulf of Mexico waters. A number of tests performed on board at each station measured gasses, pH, and nutrients throughout the water column, serving to confirm real-time data on fluorescence, which indicates the presence of hydrocarbons. Measurements of decreased oxygen indicate that bacteria are metabolizing those hydrocarbons. The preliminary data indicate that a well-documented, deep hydrocarbon feature southwest of the well is producing measurable changes in oxygen distribution and nutrient levels.
Earlier posts from the cruise explained the collection of real-time data on beam attenuation and oxygen levels, and onboard measurements of bacteria and methane. Katie Swanson (right), University of Texas at Austin, measured nutrient levels from multiple depths in the water column at each station, producing data that indicate productivity and nutrient recycling.
In hydrocarbon plumes, nutrients decrease because bacteria use them up while metabolizing the oil. “When hydrocarbons are present, we expect to see decreased nitrate and phosphate and increased ammonia,” Swanson says. “We have not seen significant increases in ammonia, but have seen the decrease in nitrate and phosphate where we expected it. The data correlate with where the plume is.” Additional analysis in the lab back at the MSI will reveal patterns, and Swanson will be able to graph specific nutrients by concentration and depth. “Nutrient levels should match our bacteria counts,” she says. “These measures are indicative of microbial or planktonic metabolic activity. We know normal levels, so can compare against those.”
In a few locations, the Hatteras collected data several days apart, known as time series, both as a “reality check” and to track movement and change of the features. For example, three stations were taken at the same location on 28 August, 30 August and 8 September. These time series also show, through variation in data from the same location, the incredible variability in the movement and chemical reactions of the released oil.
The northern Gulf likely contains pockets of oil, similar to individual clouds in a cloud bank, says Villareal, and hydrocarbon plumes with breaks and variation. The action and motion of oil as it initially boiled out of the broken well head could have introduced eddies, resulting in fingers of oil rather than a single plume. Even early efforts to cap the blow out may have sent oil in different directions. Factor in existing eddies and currents in the Gulf, and it simply isn’t possible to draw a line in the water and say, there. There is the oil. But it is possible to say, here is where some oil was yesterday, and here is where some of it is today. It is also possible to say that all the oil is not gone.
photo credits: Melissa Gaskill