The Silent Suffocation of the Sea
Oceanic dead zones have been proliferating across the globe since the 1960s, forcing aquatic animals to flee from coastal waters. Whereas, indiscriminate suffocation awaits those who are unable to escape. The source of this marine misery seeps out from the world’s cities. It’s an all too cliched situation of pollution grievously harming wildlife, and we know what factors attributes to the advance of dead zones, but exactly what is a dead zone?
A dead zone in scientific jargon is a hypoxic zone: meaning a large aquatic area that has critically low levels of oxygen. The general pattern for the creation of a dead zone is an excessive input of nutrients into the area, which is known as eutrophication. Eutrophication fuels the growth of phytoplankton, the microscopic plant-like organisms in the water, which eventually die out and provide a source of food for oxygen-using (aerobic) bacteria. The aerobic bacteria consume oxygen to the point where oxygen becomes depleted and thus unsuitable for animal life1.
The process described above can occur naturally; however, natural eutrophication occurs over many generations and in isolated bodies of water. To create multiple dead zones over large coastal waters within 50 years would require a more intensive input – pollution.
The two forms of pollution that lead to the creation of these dead zones are nitrogen and phosphorous. Nitrogen pollution comes from fertiliser runoff, which is where water washes fertiliser within the soil and sewage downstream. Phosphorous pollution is exuded from our cars and is absorbed into the atmosphere, whereby it later falls into oceans through the rain. For phytoplankton, both are high in demand but naturally low in supply; so whenever modern civilisation is inadvertently generous enough to let the phytoplankton have its waste for free, you end up with a dead zone2.
The most infamous of the dead zones are the coastal waters around the Mississippi delta within the Gulf of Mexico, covering a size greater than 12,000 km2. The Mississippi Delta has polluted water flowing through it (originating from multiple states), which is then inevitably collated into the Gulf of Mexico – creating the dead zone3. Over-exploitation amplifies the damage caused by dead zones; the Bay of Bengal was regarded as a limitless source of food, but the few animals that remain after the bouts of intensive fishing cannot survive suffocation – as a result, it is now a lifeless grey mass4. Furthermore, increasing water temperature can exacerbate the creation of dead zones, as oxygen is less inclined to dissolve into water under higher temperatures. It seems like this is the death knell for marine life as a whole5.
It needn’t be so glum, as dead zones are well described in the scientific literature so they can be undone or at least managed. For instance, the European Union has banned the usage of phosphorous in detergents; these measures ought to stop the decline of the sea into a big pile of decaying flotsam – if not, then there are always swimming pools left to swim in6.
Edited by Richard Murchie