A new report from the Joint Analysis Group (JAG), which includes the US National Oceanic and Atmospheric Administration, found that oxygen levels have dropped by about 20% below average in locations around the site of the Deepwater Horizon oil spill in the Gulf of Mexico.
In an unrelated development, a team of researchers has found evidence (see photo, right) of precipitated oil on the seafloor below causing significant harm to organisms there.
The zones of depleted oxygen, called “sags” extend some 100 kilometres from the Deepwater Horizon wellhead. The sags are the result of microbial activity breaking down the oil and are not low enough to cause dead zones in the deep ocean, says Steve Murawski, Chief Science Advisor for NOAA Fisheries and head of the joint agency team.
The findings, based on data collected between 8 May and 9 August, dispel questions raised in the JAG’s second report over whether low oxygen signals were simply due to fouled instrumentation. Academic scientists have been documenting significant oxygen drops for months, but the previous JAG report raised concerns that these measurements were “false positives”.
The oxygen levels are a good indicator that microbes are munching up the oil and that the oxygen is being replenished by the surrounding oxygen-rich water. Without significant mixing of water around the oily plume, “this region would have been depleted of oxygen within a few weeks”, says Murawski.
As to the question of whether the plumes are still around, Murawski says that current monitoring efforts are “tracking the dissolution of the plume”. In other words the plume is being degraded and diluted and is at very low concentrations, he says.
Despite the upbeat government report, academic researchers at sea have some dismal news. Biogeochemist Samantha Joye, from the University of Georgia in Athens, and her colleagues have found a layer of oilburied about three centimetres deep in a canyon some 30 kilometres from the wellhead. They also spotted dead worms, shrimp and other bottom-dwelling organisms in the same region.
The oil is in the form of tiny aggregates in the sediment, which Joye and her colleagues term “marine snow”. The snow was likely produced by biological breakdown, dispersant application, or a combination of
both, Joye says. The team is doing experiments to determine how this material is generated.
“It looks like the benthic infauna [bottom burrowing creatures] were nuked by the oil snow storm,” she adds. “The only things alive in the oil impacted sediments are the microbial flora, and they seem to be happy with all the carbon to eat.”
Posted on behalf of Amanda Mascarelli
Photo courtesy Samantha Joye