Each spring and summer fertilizer from the fields of the U.S. Midwest runs off into the Mississippi River. Old Muddy carries the nutrients down the length of the continent before dumping them into the Gulf of Mexico. Once introduced, the nitrogen and phosphorus prompts a bloom in algae, phytoplankton and other microscopic plants. After the plants die they drift to the bottom and their decomposition sucks the oxygen out of the seawater. The result is a vast dead zone, lethal to sea life that cannot swim out of the way, in inhabitable waters near the Gulf Coast that is sometimes as large as New Jersey—and the as much as 3.8 million liters of oil now spilling into the Gulf per day may make it worse.

"The oil is in the area of the annual low-oxygen zone that develops off the Mississippi River," says biological oceanographer Nancy Rabalais, executive director of the Louisiana Universities Marine Consortium (LUMCON), who has measured an early start to the annual dead zone this year in March. "There will be localized low-oxygen areas under the surface of the slick."

The oil spill may exacerbate the shallow-water dead zone through a variety of physical and biological processes. But it could also help minimize the dead zone through similar means. Overall, the response of the Gulf dead zone to the oil spill is quite uncertain, with oxygen levels being tugged up and down by numerous factors, leaving the future of this habitat in question.

At the same time, further from shore, the oil is having a host of potential oxygen-depleting effects from the surface waters all the way to the seafloor. So the questions remain: Will the oil spill create more dead zones in those deeper habitats? Or could it simply help to minimize the one we already have near the Louisiana coast?

Let's get physical
Oil creates a slick that rides on the water's surface. First and foremost, this physical coating prevents seawater from absorbing oxygen from the atmosphere. As the oil washes into ever-shallower waters, that barrier will particularly choke off oxygen in the estuaries and wetlands that serve as habitat and nurseries for much sea life, in essence asphyxiating larvae and other inhabitants.

Of course, the smaller Exxon Valdez oil spill never ended up creating such dead zones near shore. The 41.5 million liters of oil spilled off southern Alaska dropped oxygen levels in the water by as much as 50 percent but currents there minimized the damage to sea life, and the large-scale movements of seawater may work similarly in the Gulf. "We never saw any fish kill or other event from hypoxia there, and I'm not anticipating it here," says microbiologist Ronald Atlas of the University of Louisville, who evaluated responses to the Alaskan oil spill. "I'm not expecting with currents that we're going to go to zero or a low enough number to have a fish kill."

At the same time, however, shallow-water sediments coated in oil can help boost algal growth. "Frequently after an oil spill sediment that has become oiled will turn green—algae will proliferate," says ecologist John Fleeger at Louisiana State University. "The grazing invertebrates will die off [from the oil], and the algae has a boom. It's an unexpected situation where you think everything will be harmed, but some organisms can do better." That could mean less oxygen as the algae grows, dies and decomposes.

But the physical oil coating on the water's surface might also reduce the number of algae by blocking sunlight—potentially minimizing the near-shore dead zone. "The trick [for this sunlight-blocking] is getting the slick to stand still long enough," says marine biologist Robert Diaz of The College of William and Mary. "If the slick is just passing by, the depression in light and photosynthesis would likely be short-lived and minor," and therefore do nothing to prevent the seasonal dead zone underway.

The oil itself is directly toxic to some algae as well, and can turn even more toxic when interacting with sunlight, an effect known as phototoxicity, which could also diminish the dead zone. In a smaller spill off Panama's coast in the 1980s such phototoxicity played a key role in killing coral and other shallow-water sea life. "In retrospect, a good part of the damage was from photo-enhanced toxicity," says environmental chemist Jeffrey Short of environmental group Oceana, who has studied the after effects of the Exxon Valdez spill and others. "It's not very well understood in the field. This oil spill may give us an opportunity to learn a lot more about how much of a factor that is."

In addition, the dispersants that have been used to break up the oil, such as Correxit 9500, are toxic to phytoplankton. The National Academy of Sciences noted in a 2005 report that 20 parts per million of it depressed growth in 50 percent of Skeletonema costatum, a Gulf of Mexico diatom, within 72 hours. "If BP was over there in the area of the dead zone applying the dispersant at the same rate as they are at the wellhead, they might be on to something in terms of controlling the dead zone," Diaz says.

In deep water
Regardless of what may happen near shore, the deeper waters of the Gulf—where the oil is directly spilling—may form their own dead zones, thanks to the busy work of microorganisms breaking down the oil and consuming oxygen in the process. An example of this busy work can be found in the famous Mobile Bay jubilee—a mass migration of deeper dwelling sea life, such as crabs and shrimp, into shallower waters as a result of certain weather conditions. Jubilees happen when a low-oxygen zone rapidly forms in deeper waters as organic sediment is broken down by microorganisms, prompting deep-sea crabs, shrimp, flounder and other fish to migrate quickly to shallower, more oxygenated waters. Stunned by the low-oxygen conditions, they are easy to harvest in copious quantities—hence the name jubilee. Now, low- or no-oxygen (anoxic) conditions may follow in the wake of the oil spill and the increased microbial activity that it will spur.

Similarly, the far offshore waters of the Gulf of Mexico may see more or expanded areas of deeper waters with low or no oxygen. Low oxygen concentrations in the middle depths of the Gulf persist naturally, from roughly 100 meters to 1,000 meters, dropping as low as three milligrams per liter compared with an average concentration of as much as six milligrams per liter in other waters. (By comparison, the shallow-water dead zone has oxygen levels less than two milligrams per liter.) That means life in these depths is used to little oxygen but bacteria, fungi and other microbes chewing on the oil could expand these zones into surface or bottom waters or make low-oxygen zones anoxic—replicating the effects of a jubilee.

Less or no oxygen kills sea life that cannot move fast enough (or at all) to escape it, such as the immobile Lophelia coral anchored on the sea bottom or relatively immobile animals, such as worms and crabs. "Increased microbial respiration as the oil is broken down may expand this zone," biological oceanographer Lisa Levin of the Scripps Institution of Oceanography wrote in an e-mail. "Low oxygen zones in the water will lead to animal migrations and habitat compression, but also mortality in less motile organisms."

Already, thanks to climate change warming the waters, these zones are expanding. "You could get a similar response from oil as an organic substrate," Diaz says.

Shrimp, to take just one example, may be forced to migrate into denser clusters in different depths as a result of oxygen levels that are too low in their preferred habitat. "It's only going to make them more stressed, and the prediction would be negative in terms of the population of mobile animals," Diaz says. "Multiple stressors lead to higher levels of mortality."

Is dilution the solution?
Fortunately, the sheer volume of water in the Gulf of Mexico will help to tamp down the impacts from even the worst oil spill in U.S. history, which may have already dumped more than 150 million liters of petroleum into the ocean. "Dilution is not the solution to pollution entirely but a pretty large volume of water already has low oxygen levels as part of that deep water," LUMCON's Rabalais notes. "The volume [of water] is just too great."

Biogeochemist David Valentine of the University of California, Santa Barbara, calculates that 20,000 barrels per day added more than 30 days to an area of roughly 40,000 square kilometers of ocean with a depth of 1.5 kilometers coupled with microbial degradation rates would produce a "1 percent oxygen drawdown. On a regional scale, it's probably not going to cause mass death. Localized, it could be more of an issue."

For example, no one knows for sure what will happen on the Gulf's seafloor, a region that is not well understood by scientists. The drilling mud used in an attempt to muscle the oil back into the well at the spill site might exacerbate low-oxygen conditions in the immediate vicinity of the Macondo well. After all, much of that mud leaked back out, laced with hydrocarbons, and settled to the sediment around the wellhead. "There should be some localized drawdown of oxygen where that drilling fluid is being put out," Rabalais says. "It will have some localized effects on the benthic [deep-sea] fauna."

And dispersants are being applied directly to the oil in the subsurface, resulting in yet more rich-feeding for oil-eating microbes as well as subsurface plumes, which BP's chief operating officer Doug Suttles noted at a press conference on May 29 that the oil company would not be able to clean. Company CEO Tony Hayward continues to deny such subsurface plumes might exist.

"We're relying on dispersion to reduce concentrations below oil toxicity threshold limits," explains microbial ecologist Kenneth Lee, director of the Center for Offshore Oil, Gas and Energy Research with Fisheries and Oceans Canada, who has been assisting with the disaster in the Gulf. "Of course, the dispersants can also stimulate microbial growth."

Ultimately, an enormous science experiment is underway in the Gulf of Mexico, as oil slicks interact with the seasonal shallow-water dead zone and dispersed oil droplet plumes provide rich feeding to microbial life. A host of science expeditions hope to assess and better understand how the oil spill will impact everywhere from tidal estuaries to 1,500 meters beneath the sea's surface. "No one knows yet to what extent any of these potential problems will alter our ecosystems and their functions," Scripps's Levin says, "but significant effects are likely."

17 Comments

1. 1. Patrick 027 10:01 PM 6/3/10

   Where is BP's suggestion box? I don't know, so I'm putting this here:
   
   Use multiple lengths of pipe to 'bring the leak to the surface', then cap it.
   
   As I understand it, it is hard to seal the leaks/hole by covering it because of pressure. So how about covering it with something that has a hole in it that lets the oil through. Seal the first hole, then cover the next hole and seal that, etc. This might not seem to go anywhere, but consider using lengths of open pipe. This could be done with several lengths of pipe until the gusher is brought to the surface - where it will be easier to cap.
   
   Several lengths of pipe that readily fit into each other end-to-end, with joints easily sealed. The first pipe will be difficult to seal with the original hole because of the roughness of that hole, but let's wrap a sheet of rubber around the joint (as opposed to fitting it in between) and then wrap some metal wire around it and pull tight to seal it. After that, just keep adding lengths of pipe. The oil will continue spilling out the top of the top pipe, but that's okay for a short period - once the last pipe is put on, it will be at the surface, where it can be more easily dealt with.
   
   Maybe.
   (?)

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2. 2. JoannaPoppink 03:12 PM 6/4/10

   Rather than debate the existence of undersea plumes or, more likely, the extent and movement of undersea plumes, we need methodocial and systematic investigation.
   
   I haven't seen anything written about undersea exploration with submarines actually seeking out these plumes. We humans developed technology to seek out, find and deal with submarines and subsurface explosives during WWII.
   
   Surely that technology has evolved and could be adapted to seek, find and deal with oil plumes. I hope so.

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3. 3. hjoab in reply to Patrick 027 03:21 PM 6/4/10

   It looks like a good idea to me Patrick.

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4. 4. JoannaPoppink in reply to Patrick 027 03:36 PM 6/4/10

   This makes a lot of sense based on human scope of imagination.
   I just wonder about how much force we are dealing with when it's an earth issue and we tap into unimaginable force.
   
   Lessons reinforced: It's difficult to put the genii back in the bottle.
   
   Patrick, I think your suggestion is excellent if we have pipes
   strong enough to hold and direct the power of that hemmorage.

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5. 5. hjoab 03:39 PM 6/4/10

   We better can use microbes that eat oil. Search on google about this topic. There are studies that says the we can recover form this disaster in weeks.

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6. 6. hjoab in reply to hjoab 03:42 PM 6/4/10

   We can use micros that eat oil (peroleum). Search in Internet about studies that says we can recover from this disaster in weeks alone.

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7. 7. drachinimi in reply to Patrick 027 09:57 AM 6/5/10

   BP.com has a section on the right hand side for suggestions

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8. 8. davidburke75116 12:43 PM 6/5/10

   I think it is time that BP and our government request help from other companies and countries with expertise in this area. It is evident that they are trying to figure this out as they go. Their last gamble has drastically increased the oil flow from the oil head and has made the situation worse. I think this is a wakeup call for us to look closely at what we are doing to the Gulf, from oil exploration to toxic runoff from farming up the MS river. Not in my back yard, now it may be in the back yard of the whole east coast of America.

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9. 9. Peterson 06:36 AM 6/7/10

   Thanks for your updates .I really appreciate your work to this site.I hope you can continue this kind of good work in future also..
   <a href=http://www.sanghioxygen.com/><!--Oxygen Plant--!></a>
   

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10. 10. tombaxter 10:33 PM 6/7/10

    Nobody knows how catastrophe this will be. The article discusses oil eating microbes. It will take them decades to eat through this mess. They are the only things that will clean it up. They will help in creating dead zones.

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11. 11. davidburke75116 11:48 AM 6/9/10

    I have been on the Gulf Coast when they are dredging sand on the beach to repair errosion damage. Why don't we see large pipes that would suck oil from the coast line out through large pipes to a container ship, then separate the oil from the water, and put the clean water back in the Gulf. This could also be done out in the open water to remove oil from the surface. When I see people wiping oil from marsh grasses with paper towels and boats pulling small skimming devices behind boats to collect small amounts of oil, it seems very ineffective. We need large scale oil removing devices that can actually make a difference.

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12. 12. dgloumbia 10:14 AM 6/10/10

    i simply do not understand the reaction to this disaster on a scientific level. those scientists who study ocean chemistry and biochemistry the most carefully seem to be saying that it is virtually certain that they entire gulf will both become a "dead zone" due to toxicity, but that also the oil + corexant plumes are currently killing all the existing embryonic and microscopic life wherever they go. The fact that coastal freshwater areas and the entire Mississippi river delta are being seen the wrong way: the dead zone will spread out from the Gulf onto land, and these areas will become largely unhabitable, or at best unusable for agricultural production.
    
    why is there no hard cry from Thad Allen, NSF, etc., directing ALL our attention to every single available technology to CLEAN THE WATER and GET THE OIL OUT OF IT with all haste?
    
    is there any way a dead Gulf of Mexico does not impact the Atlantic Ocean, climate change, the gulf air and water flows??
    
    again, it is the scientists who look at the ocean most closely who seem to find this stuff the most alarming, but also to feel the most impotent. what BP is doing to the gulf is unreal and i can't believe we are watching and letting it happen.
    
    supposedly, people who work in Saudia Arabia have developed all kinds of technology for remediation and BP and US-gov aren't letting it be used or even tried! WHY?

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13. 13. CMSoilrem in reply to hjoab 10:14 AM 6/12/10

    There are naturally occurring microbes in the ocean which attack hydrocarbons however they do deplete the oxygen which can cause further problems for marine life. This becomes critical when the oil reaches the marshes where the oxygen levels are already low. There are many claims being made by many companies who produce microbial products to eat up the oil however their formulations contain only 1 or 2 of the essential components to form an effective, non-intrusive consortium. many are working on this problem and we hope that a conclusive solution is close at hand.

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14. 14. dgloumbia in reply to CMSoilrem 10:35 AM 6/12/10

    "There are naturally occurring microbes in the ocean which attack hydrocarbons"
    
    correct, and they are a big enough problem. But what we have now is a dispersed, toxic mixture of hydrocarbons, other volatile organic compounds, and the various poisons that make up the dispersants. Are there naturally occurring microbes that subsist on that mixture, created by the Corexant spray which may have been the most irresponsible decision made in the history of humankind?
    
    For all intents and purposes, much of the GOM is now a permanent dead zone, and much of the southern coastal US will no longer provide any sort of barrier against weather-driven erosion.

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15. 15. eco-steve 08:53 AM 6/14/10

    PATRICK 027 : If you have any clever ideas, look for 'BP OIL SPILL' on your search engine, then find 'technical report' and fill out the suggestions form, (less than 250 characters). Your proposal will be considered by a team of experts and you will ultimately recieve a reply, especially if your idea can be implemented. But be patient as there are many submissions, so please ensure your poprosal is practical.

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16. 16. Lu 03:41 PM 6/27/10

    Only shallow water can get oxygen from the air. The air does not oxygenate the oceans. It is the other way around. We depend on the plankton for oxygen. BP's oil and dispersant kills plankton. They are killing us all.
    
    They need to get out there and suck it up!

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17. 17. j4z 12:08 AM 7/22/10

    It doesn't take a marine biologists to know that the damage from this spill will be horendous-the bottom line is that this can not happen-I had to explain to my daughter what the big black, mis-shapen tar ball was on the beach the other day and that the rainbow sheen in the water wasn't a pretty sight to see...this is what the elite of society is doing for our children's future and our world.
    There are lots of enzymes/microbs that eat oil, phosphates, and nitrates in water: like sewer treatment plants and swimming pools, so why aren't we utilizing this valuable and natural resource? Surely there is a way to dose the gulf to speed up the process.
    And once its cleaned up take the power out of the elitests hands...I'm talkin' major regulations!!!!

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