Science journalist Mark Schrope is aboard the research vessel Pelican, which is spending the week studying the Deepwater Horizon oil spill in the Gulf of Mexico. Check back to The Great Beyond for daily mission updates.
Our sojourn to the far reaches of the deep-sea plume the team discovered two days ago was successful and offered the added bonus of fresh air and relatively clean waters. But, alas, according to plan we’re back to the downwind side of ground zero, and that means brown-banded water and the dreaded oil stench.
Besides completing rough delineation of the plume, the National Institute for Undersea Science and Technology team also got an unexpected boost to their work from fresh National Oceanic and Atmospheric Administration data. While not definitive, the information certainly supports the notion that what the researchers have been tracking from the ship is oil from the gushing well.
But first, some bad news. The science team got word from the NIUST chief back home that before returning to shore they would need to do a detailed inventory of all samples onboard the ship as well as those offloaded last weekend. “This is actually so we can prove later on, legally, that we did collect these samples,” says NIUST oceanographer Vernon Asper, who, like his colleagues, wasn’t especially pleased with the task. As far as they know this is just a precaution, rather than a response to any specific intended application of the data that will ultimately be gleaned from their samples.
So, the team set to work going through refrigerators and freezers to pull out and more comprehensively catalog their hundreds of water and sediment samples. “We’re making progress,” says Asper, “It’s just going to be tedious.”
But the plume work continued unabated. This morning, the researchers found that somewhere between about 45 and 50 kilometres out, the plume dissipates to barely detectible levels. Later in the day, sampling work along the northern end of the plume allowed them to estimate very roughly that the plume is some 10 kilometres wide. “As we see how narrow it is,” says NIUST chief scientist Arne Diercks, “to put [the instruments] right in the middle of it at the beginning was pretty lucky.”
Now that they know approximately where the plume goes, they’ll have to figure out what it is, based on eventual analyses of water samples collected. “We are tracking a plume of something,” says Diercks, “but what that plume is, what its exact characteristics are, we don’t know.”
This afternoon, Asper came on deck with the new bit of evidence pointing to oil in the plume. A colleague emailed him results from a NOAA Gulf survey using aerial expendable bathythermographs (AXBTs). These are tiny temperature probes connected to two very thin copper wires. They’re dropped from planes, sending back data until the wires eventually break.
Because currents cause subtle but measurable changes to temperature gradients, AXBT temperature data can be used to estimate current directions and rates. The data showed that the deep-sea current out here is running to the southwest away from the well, which is exactly the direction the plume extends out from ground zero. “It’s really exciting that they found what we found,” says Asper.
So, while this new information doesn’t settle the question, if there’s a huge, strange plume lying in the direction that the current is flowing from the oil well, it’s a reasonable bet that the plume is oil from the well. If so, that’s hefty chunk of previously unaccounted for oil in the water that could add fuel to the erupting debate over just how extensive the spill really is.
There are other potential explanations. One is that the plume is oil and associated material that sank from the surface. However, to be this deep that would require surprisingly quick sinking.
Through tonight and into tomorrow the team will be returning to sites already sampled to repeat measurements and to gather additional water samples in the precious few bottles that remain, all the while toiling away at the inventory list. Tomorrow night, we’ll begin the trek back to port in Cocodrie, a bit more appreciative of fresh air.
Posted on behalf of Mark Schrope
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