Speculation on the whereabouts of wayward oil.
by Len Bahr, PhD*
Between April 20 and July 15 2010 an estimated 4.9 million barrels of crude oil was unceremoniously released a mile underwater southeast of Venice, Louisiana. The fate and effects of the escaped oil remains very much in question. I’m not a geochemist, geophysicist, oceanographer or microbiologist but I combine generalist credentials and experience as a coastal ecologist – with an avid interest in listening and reading. Thus I’m pretty well positioned to engage in educated speculation about the whereabouts of the slippery stuff – with a great excuse for being wrong!
For a mind’s-eye picture of the quantity of wayward oil visualize 27% of the volume of the Superdome. In absolute terms that’s a lot but, according to my calculation, in a relative sense it’s slightly less than the volume of freshwater added to the Gulf of Mexico by the Mississippi River every 45 seconds.**
Technical disagreements over residual oil
After the gusher had been shut off in mid-July the conversation shifted from capping the well to the quantity and fate of the oil – how much had washed inshore,*** how much remained offshore, where the missing oil was located, in what form and to what risk. The ecological, economic, cultural, legal and political implications of this giant shell game are far-reaching.
On August 14 the National Oceanographic and Atmospheric Administration (NOAA) reported (prematurely) that approximately 74% of the escaping oil had been destroyed, removed from the gulf or had dissipated naturally (see Figure 1). That assertion was quickly challenged by Chuck Hopkinson, who directs the Sea Grant Program at the University of Georgia. On August 19 Bill Lehr, a top NOAA scientist retracted the claim and acknowledged that far more oil may be out there.
That same day The Times-Picayune reporter Mark Schleifstein reported that a 22 mile-long midwater plume of oil droplets had been discovered during a research cruise by independent scientists from the Woods Hole Oceanographic Institute (WHOI). This plume was also reported on NPR’s Morning Edition by Christopher Reddy, a co-author of the study. On August 23 an editorial in The Times-Picayune criticized the feds for painting an overly rosy scenario.
Even academic colleagues differ widely about the amount of residual oil in the gulf. On September 9 the ABC-TV affiliate WBRZ-TV in Baton Rouge ran a video clip of Greg Stone, director of the LSU Coastal Studies Institute showing what he believes to be large patches of oil hovering beneath the waves. In the same clip Ed Overton, professor emeritus at the LSU Environmental Studies Institute, casts doubt on that claim but Dr. Stone insists that significant amounts of submerged oil await shoreward transport in storm-related pulses.
It’s very rare to see such a wide range of estimates on a specific technical issue, in this case the whereabouts of a family of organic compounds that have a unique fingerprint and that are traceable in very small concentrations. On the other hand, the gulf is a huge body of water that is constantly in motion and there are many poorly-understood variables in play, including the effects of chemical dispersants and physical dispersion, advection by currents, rates of evaporation and microbial degradation and a possible deep water ‘blizzard’ of flocculated oil.
Among other criticisms of NOAA’s oil budget in Figure 1, Dr. Hopkinson took exception to high estimates of evaporation, pointing out that dispersed subsurface oil could not evaporate. On the other hand lighter components of the crude oil would easily volatilize at the surface under a very warm temperature regime.
Chemical and physical dispersion
BP reportedly used 1.8 million gallons (43,000 barrels) of various types of the soap-like dispersant Corexit at the well head and on the surface to break down oil globules into tiny droplets. This practice has been particularly controversial. The subsurface application seems to have worked as hoped, effectively reducing the size of oil droplets to ‘bite size’ pieces for bacteria. Professor Overton has said that the ingredients in Corexit are not particularly toxic and that its breakdown is rapid. Nevertheless, many critics maintain that the use of this product has been an environmental travesty, although few would qualify as expert witnesses in a court hearing.
On the subject of expertise, the possible toxicity of dispersants and other residues from the blowout has generated a plethora of hyperbole, mostly by non authorities. Pontification sans credentials has been widespread throughout this sordid episode. To put the dispersant threat into perspective, on August 5 Mark Schleifstein reported in The Times-Picayune that, by an ironic coincidence, the Mississippi River discharges an equivalent volume of various chemical dispersants directly at the Macondo Well site every year.
Much oil dispersion apparently occurred independent of Corexit. Oil and methane billowing from the broken well plumbing created enormous turbulence and was seen by billions of TV viewers. This turbulence churned the oil-gas mixture into droplets too small to rise to the surface. Presumably, all the oil currently suspended as clouds of tiny droplets will ultimately be consumed by bacteria, as described below.
Hungry marine germs and gulf hypoxia
Artificially-dispersed oil diffuses into the offshore water column and sinks as tiny droplets, an irreversible process. Diffusing oil droplets are consumed by bacteria, as long as there is a sufficient oxygen to support respiration. Rebecca Mowbray’s article in the August 25 The Times-Picayune described California researcher Terry Hazen, who found an abundance of oil-chomping germs in the deep waters of the gulf. Hazen’s work is based, not on oxygen levels or samples of living bacteria but rather on residues of bacterial DNA. His work, described here in EarthSky.org, was confirmed in a report by panel of scientists, including Steve Murawski, chief science advisor to the National Oceanographic and Atmospheric Administration (NOAA). This was described by Mark Schleifstein on September 8 in The Times-Picayune.
Concerns have been expressed over whether oil released from the Macondo Well blowout would overwhelm the capacity of the gulf ecosystem to provide sufficient oxygen to support microbial degradation. Hazen’s data imply that this is not a problem, that oxygen levels remain adequate to support respiration and not contribute to gulf hypoxia.
According to Ed Overton, a large glob of oil may take three hours to rise to the surface from a mile down, smaller dollops can take a month and oil droplets the width of a human hair are neutrally buoyant and don’t rise to the surface. Thus, most of the wayward Macondo Well oil probably never reached the surface. The oil that did surface was skimmed, burned, weathered, evaporated or drifted ashore. Thus little or no surface oil exists to date.
A potentially huge pool of wayward crude was recently discovered on the deep seafloor in the gulf by Dr. Samantha Joye, from the University of Georgia. Dr. Joye was recently featured on this ABC TV videoclip. Figure 2 is a photograph of a two inch thick layer of this material and she has seen oil on bottom sediments as far as 80 miles from the blowout site. When the full extent of this find has been quantified (and assayed) it should provide a critical missing link in the budget of BP oil. The smothering impact of oil, which covers the critical benthic (bottom-dwelling) organisms, may be huge.
A final note
A colleague said he recently heard Ed Overton say that crude oil leaking from existing natural seeps into the Gulf of Mexico is roughly equivalent to two Exxon Valdez size spills a year, i.e, up to 1.5 million barrels.
Figure 3 is a crude breakdown of my thinking about how much of the original 4.9 million barrels of crude oil and oil breakdown products remains out there and its current whereabouts. An essay on thoughts about the ecological impacts of the Macondo blowout will follow.
*Founding editor, LaCoastPost firstname.lastname@example.org
**Based on an annual mean river flow of ~625,000 cubic ft/sec or 111,600 bbls/sec.
***Whatever volume of oil came inshore must be a tiny fraction of the total volume discharged into the gulf. For example, Katrina probably injected considerably more oil into Louisiana marshes than did the Macondo Well blowout.