Scientists have discovered a huge dead zone in the Bay of Bengal. The zone is of an estimated 60,000 square kilometers, contains little or no oxygen.
The area supports microbial processes that remove vast amounts of nitrogen from the ocean.
Dead zones are well known off the western costs of North and South America, off the coast of Namibia and off the west coast of India in the Arabian Sea.
Laura Bristow, a former postdoc at University of Southern Denmark, said, “The Bay of Bengal has long stood as an enigma because standard techniques suggest no oxygen in the waters, but, there has been no indication of nitrogen loss as in other ‘dead zones’ of the global ocean.”
Researchers, including those from the Council of Scientific and Industrial Research’s National Institute of Oceanography (NIO) in Goa reported that though some amount of oxygen does exist in the Bay of Bengal, the Researchers, including those from the Council of Scientific and Industrial Research’s National Institute of Oceanography (NIO) in Goa. The oxygen level is stated to be around 10000 times lesser than the amount found in the air-saturated surface water.
The microbes present in the Bay of Bengal are in fact capable of removing all the nitrogen from the water but traces of oxygen stop them from doing so. Though there is some evidence of nitrogen-removing micro-organisms existing in other well-known dead zones as well, they are reported to work at a much slower rate.
“We have this crazy situation in the Bay of Bengal where the microbes are poised and ready to remove lots more nitrogen than they do, but the trace amounts of oxygen keep them from doing so,” said Bristow, now a scientist at the Max Planck Institute (MPI) in Germany.
“Remove the last amounts of oxygen, and the Bay of Bengal could become a major global player in nitrogen removal from the oceans,” said Wajih Naqvi, former director of NIO and a coauthor of the study published in the journal Nature Geosciences. Removing more nitrogen from the oceans could affect the marine nitrogen balance and rates of marine productivity.
Globally, warming of the atmosphere through climate change is predicted to lead to an expansion of ‘dead zones’ in the ocean. It is currently unclear whether climate change would lead to the removal of these last traces of oxygen from the Bay of Bengal waters.
However, the Bay of Bengal is also surrounded by a heavy population density, and expected increases in fertilizer input to the Bay may increase its productivity, contributing to oxygen depletion at depth.
“Time will tell, but the Bay of Bengal is at a ‘tipping point’, and we currently need models to illuminate how human activities will impact the nitrogen cycle in the Bay of Bengal, and also globally,” said Bristow.
Dead zones are large areas in the ocean that have low oxygen concentration. The marine life in these areas mostly suffocates and dies or if they are mobile like the fish then, they leave the area.
Though, at many times, dead zones occur naturally, scientists are also of the opinion that they are created due to increased human activity. The main cause of the zones created by human is nutrient pollution. Excess nutrients (nitrogen and phosphorus) can result in the overgrowth of algae, which later decomposes in the water consuming excess oxygen, depleting the supply available for the marine life.