This is the third post in a four part series discussing the ongoing – and “cascading” – effects in the Gulf, not from “oil,” but rather its toxic components and their impacts on sensitive ecosystems. Read the rest of the series.

It could well be that the now-notorious subsurface plumes contained –or contain – a mixture of tiny oil droplets (both from oil spewing, hot, under pressure into cold water, and then being dispersed into even smaller droplets courtesy of Corexit) and dissolved or partly dissolved lower-molecular weight materials, like BTEX (benzene, toluene, ethyl benzene and various xylenes).

Components of these plumes broke down – and are breaking down – not in one felled swoop from oil to not-oil, but through a series of breakdown pathways, while it was transported in various directions as the currents shifted over several months of the active oil disaster. These materials would have been exposed to biological processing by bacteria. Bacterial populations were low initially, but have grown exponentially through time within the plumes as they drifted.

There is no free lunch in the sea: Did bacteria “eat” the oil?

Many people are sighing in relief that the apparent explosion of mid-water bacteria have processed much of the original oil load of the system. The cascading impacts of that phenomenon – if verified – have yet to be established. Perhaps the “oil,” per se, is largely gone, but the array of produced materials, and their ramifying ecological effects must be fully accounted.

Full and final processing of this huge load of oil would both demand oxygen and produce carbon dioxide. While there have been some observations of adequate oxygen presence, there has as yet been no modeling of total oxygen demand and its implications for ocean ecosystems, including some already under oxygen stress. Moreover, the sea is already being subjected to acidification from absorbed carbon dioxide (the final breakdown product where oxygen is adequate from biotic degradation of hydrocarbons).

While an “Andromeda strain” scenario is far-fetched, many questions remain. What are the likely impacts of such massive loads of both oxygen-consuming organic substances and produced carbon dioxide, on oxygen levels and acidity patterns in the depths? What will happen to this large, new and artificial, biomass of bacteria, as they respire and then decompose? How will this major perturbation of mid-water biota cascade through ocean ecosystems? All unanswered questions.

This is the second post in a four part series discussing the ongoing – and “cascading” – effects in the Gulf, not from “oil,” but rather its toxic components and their impacts on sensitive ecosystems. Read the rest of the series.

I remain extremely concerned about what has happened to the out-of-sight, underwater ecosystems of the Gulf of Mexico, especially at middle depths and on the bottom. These little known but ecologically vital elements of the ocean have been heavily exposed to oil-based pollution, both rising from the bottom and sinking back down from the surface, and – at least in some places – bathed in persistent underwater toxic plumes.

Marine life in the mid-waters is so rich and profuse in places that sonar waves bounce back as a “deep scattering layer” and provides key food for many familiar, surface-diving animals, including whales, dolphins, billfishes and giant tunas. Deepwater coral reefs and other bottom dwellers have been at great risk all along, and not even the initial explorations have yet been done to assess the impacts of reefs less than twenty miles from the broken well bathing in oil-based pollution.

An actual track of a sperm whale diving through rich mid-water feeding zones (shown in green) from the northern Gulf of Mexico. Credit: Modified from Azzara, 2006.

The oil and oil-derived pollution that made it to the surface followed – and is following – one set of pathways through the Gulf ecosystem, exposing and injuring not just sea turtles and sea birds, but also near-surface marine animals and plants, large and small, and entering foodwebs through a complicated series of entry points, which we don’t yet fully understand.

Fine droplets of dispersed pollution are more likely to be adsorbed onto particulates, sinking back through the midwaters and into the abyss. The moreresistent elements, like tar balls, either float away or sink back into the abyss, and follow a different set of pathways.

The total “dump” of highly toxic oil components, including low-molecular weight aromatic hydrocarbons (known familiarly as “BTEX” – benzene, toluene, ethyl benzene and various xylenes), could have been up to 50,000,000 gallons. These are heavy-duty pollutants in their own right, including known carcinogens and reproductive toxicants, with a fair solubility in sea water. In a surface spill, pollution mostly evaporates, and the only real concern relates to emergency response workers that are exposed while on duty. In this underwater case, scientists simply do not know – yet – exactly how the massive load of pollution is being processed in the Gulf.