Our marine life is struggling for its life! Oxygen, a gas vital to all forms of life on our planet, has been decreasing in oceans. Oceans account for half of the total oxygen in the atmosphere and trees for the other half. With unabated emissions of greenhouse gases such as carbon dioxide and other human activities, oceans are developing dead zones with no oxygen to sustain any life. The term Ocean deoxygenation, in simpler words, is just that — the reduction of oxygen in some parts of the ocean. These dead zones have been the consequences of the greenhouse gases emitting from the consumption of fossil fuels in power plants and automobiles, anthropogenic activities including poor farming practices. The increasing concentration of CO2 in the atmosphere is trapping heat and has caused a rise in temperatures of oceans. Further, the nutrients, such as nitrogen and phosphorus, released into oceans from fertilisers used in farms, agricultural activities and some from the sewage has led to blooming of phytoplankton and other animals, which when die and rot get decomposed by microbes which use up a large volume of oxygen creating oxygen-depleted areas. Not just that, the rising sea temperature has led to stratification in the ocean column where oxygen levels become low as the stratification inhibits the production of oxygen through photosynthesis. Warm ocean water loses its capacity to hold oxygen too. These dead zones find it difficult to support marine life including fish and other animals. Most of them either die or are so poorly developed that they become prone to several diseases making them weak. Some of them even lose their ability to reproduce too. When fish and other crustaceans like crabs try to move from these dead zones to other areas, they often become victim to overfishing.
Last ten years have highlighted several other deadly changes in the oceans like ocean acidification and rising sea temperature, however, the process of ocean deoxygenation has been going on for some time now and it has caught our attention only now. Oceanographers and climatologists have sounded the alarm that unless we tackle spiralling greenhouse gases emissions, we might see the development of many such dead zones in oceans in future. In the last few decades, the number of these dead zones has increased from 40 to 700! The decline in marine life will impact many whose livelihood depends on the fisheries and aquaculture output. They suggest that we still have some time to make radical changes and these include the same actions which are required for mitigating greenhouse gas emissions. Moreover, we need better farming practices and stop pouring in fertilisers from the agricultural fields into the oceans. Technology is already present to reduce the nitrogen from the atmosphere getting into the ocean. Though the scientists have been working on collecting data, improving models and awareness, it is the world leaders and the policy-makers who can contribute the most by introducing stringent rules and regulations as far as the carbon emission and poor farming practices are concerned.