Ooooooh spooky! Yes The Green Man is venturing into "the dead zone" (lowering his voice and switching on the reverb).

The "Dead Zone" lies in the Gulf of Mexico just off the coast of America and, as usual, the scientists involved have failed to capitalise on its dramatic capability by referring to it as "The Gulf of Mexico Hypoxic Zone". It has this name because it has virtually no disolved oxygen in the water. Fish, who breathe oxygen, find this disconcerting and vacate the area closely followed by the fishermen.

You can see it on the map below in red and the most commonly accepted cause is nirates flowing from the Mississippi River, the catchment of which is in yellow.

Of course nature can be a fickle thing and just when a nice little academic community had established itself to investigate the phenonemon it seems that it is breaking up. Steven DiMarco, associate professor in the Department of Oceanography at Texas A&M University has observed

Strong coastal currents can develop and breakup the stratification that causes hypoxia. Another is offshore circulation features, such as eddies, that intrude onto the continental shelf. We think this could break down the hypoxia in the area as well.

It throws some doubt on the hypothesis that the mighty Mississippi is the culprit. Of course a resourceful scientist is never put off by the disappearance of his research topic. As Dr Steve observes

We need to do some further research to determine the specific mechanisms under which hypoxia is created, maintained, and ultimately dissipated

Read more about The Gulf of Mexico Hypoxic Zone at the US Geological Survey Website.
Read more about Dr Steves work here.