The oxygen content in global oceans has reduced by more than two per cent since 1960, with large variations in oxygen loss in different ocean basins and at different depths. The current study has predicted a decline in the dissolved oxygen inventory of the global ocean of one to seven per cent by the year 2100.
Effects
Just a little loss of oxygen in coastal waters can lead to a complete change in ecosystems.
In fact, such a decline in oxygen content could affect ocean nutrient cycles and the marine habitat.
It can have detrimental consequences for fisheries and coastal economies.
It must be noted that the only organism in the ocean that thrives with little or no oxygen is bacteria.
World Distribution
While the largest volume of oxygen was lost in the Pacific Ocean, the largest percentage of oxygen loss was witnessed in the Arctic Ocean. Hence, oxygen in the world's oceans is not evenly distributed.
Southern Indian Ocean and parts of the eastern tropical Pacific and Atlantic basins have already started noticing climate-linked deoxygenation.
Western tropical Indian Ocean has been warming for more than a century and at a rate faster than any other region of the tropical oceans. It is the largest contributor to the overall trend in the global mean sea surface temperature.
Cause of depleting oxygen content in oceans:
This oxygen depletion is mostly a result of climate change.
More warming on the surface of water makes the surface water less dense. Such stratification prevents the surface water from mixing with the sub-surface water. This, in turn, prevents the sub-surface water from absorbing oxygen from the atmosphere.
At times, more rain and runoffs from rivers bring in more freshwater into the sea. Due to the lack of salinity, the freshwater floats on the surface, leading to stratification.
While ocean warming is a widely identified reason for depletion of oceanic oxygen, changes in salinity can also contribute to oxygen loss.
