NASA’s revealed a study detailing the location and extent of the world’s oceanic dead zones–regions where oxygen depletion stifles life. It looks like they’re growing.
First up: What is a dead zone (apart from a creepy movie starring the inimitable Christopher Walken)? It’s a region of the ocean where significantly less oxygen than normal is dissolved in the water, which stifles the normal oxygen-eating marine life that’s usually found in the area, often with a food-chain-like effect (lack of smaller fish, which either die or swim away, leads to lack of bigger fish and so on). One way they occur is when run-off water from farmland makes its way into rivers, and then into the sea, where it triggers a huge bloom of algae that revels in the excess nutrients. The algae then dies, and sinks deeper in the ocean where it starts to decompose with the aid of microbial activity, in what’s normally a totally natural process. But in the case of an algal bloom, the huge amount of extra biomass results in the microbes eating “too much” oxygen from the water, leaving not enough for other marine life.
Since they were first recorded in 1970, the number of dead zones appears to have exploded: In 2006 there were an estimated 200, compared to 149 in 2004. In 2008 the figure was estimated at 400, which would mean incredible worsening of the situation. Now NASA’s satellite study, which is the most detailed yet, looked at particulates in the ocean–in areas with much higher particle density there’s a greater risk of dead zones forming, as the process completes itself. It’s basically confirming the effect is getting worse.
There are several take-aways from the data, though. The first is one interesting dead zone is the Gulf of Mexico–an area much in the news thanks to the oil spill at the moment. This dead zone is fed by huge areas of farmland around the Mississippi river, which fed algal blooms that swirl in the circling currents off the coast and feed algal blooms. Is it possible that much of the area’s marine life was already decimated before millions of barrels of oil polluted the sea? Is this much bigger ecological crime going unreported because it’s caused by “good” farming versus “bad” oil harvesting?
Secondly, the East Coast of the U.S. would seem to be a strange place for a typical dead zone. One would find it hard to imagine farming having an affect on the U.S.’s most populous coast, and the run-off effects of other industries wouldn’t seem to encourage algae. It would suggest rather the opposite effect, with toxins killing marine life–and in fact this is very likely one component in action here. But check out this video of a computer simulation of oil dispersion from the Gulf oil spill:
It shows that large-scale oceanic currents can circle around the entire East coast, and effects that influence the waters in the Gulf can flow up the coastline before spooling off across the Atlantic. This explains the dead zone off the coast here, as well as demonstrating one important component in dead zone formation–chaos. Currents in an ocean are complex beasts, and are mathematically chaotic (meaning they have a predictably degree of, well, unpredictability)–it’s why the El Nino effect changes year to year. All sorts of natural and man-made influences change how currents work, and even how the dead zone effect works: For example, in 2009 the Gulf dead zone was much smaller than it had been, despite no particular change in mankind’s influence in the region. The upshot is that commenting about dead zone growth isn’t as simple a matter as saying “oh no, there are more square kilometers of dead zone,” because natural effects also create them–like volcanic events–and the overall behavior is unpredictable. Dead zones also come and go, and life can recover pretty quickly, as exemplified by the disappearance of the Black Sea dead zone in the years since the collapse of the USSR, and in a time when fertilizer became too expensive to use.
It’ll take many months of examining NASA’s data before we can truly say what’s causing the recently observed changes, but it’s pretty safe to assume that the U.S.’s farmland habits are pretty ecologically disastrous.
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