New York: A new study has warned that oxygen levels in some oceans are beginning to fall and widespread evidence of the trend will likely be evident from 2030 onwards.


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While the effects of climate change on marine ecosystems are a growing concern, loss of ocean oxygen would leave fish, crabs, squid, sea stars, and other marine life struggling to breathe.


"Loss of oxygen in the ocean is one of the serious side effects of a warming atmosphere, and a major threat to marine life," said Matthew Long from US National Centre for Atmospheric Research (NCAR) and lead author of the study.


"Since oxygen concentrations in the ocean naturally vary depending on variations in winds and temperature at the surface, it's been challenging to attribute any deoxygenation to climate change. This new study tells us when we can expect the impact from climate change to overwhelm the natural variability," Long pointed out.


The entire ocean - from the depths to the shallows--gets its oxygen supply from the surface, either directly from the atmosphere or from phytoplankton, which release oxygen into the water through photosynthesis.


Warming surface waters, however, absorb less oxygen. And in a double whammy, the oxygen that is absorbed has a more difficult time traveling deeper into the ocean. That's because as water heats up, it expands, becoming lighter than the water below it and less likely to sink.


To investigate the impact of climate change on deoxygenation , the research team relied on the NCAR-based Community Earth System Model.


The scientists used output from a project that ran the model more than two dozen times for the years 1920 to 2100 on the Yellowstone supercomputer, which is operated by NCAR.


Using the simulations to study dissolved oxygen gave the researchers guidance on how much concentrations may have varied naturally in the past.


With this information, they could determine when ocean deoxygenation due to climate change is likely to become more severe than at any point in the modeled historic range.


They also determined that more widespread detection of deoxygenation caused by climate change would be possible between 2030 and 2040.


However, in some parts of the ocean, including areas off the east coasts of Africa, Australia, and Southeast Asia, deoxygenation caused by climate change was not evident even by 2100.


The research team also found that deoxygenation caused by climate change could already be detected in the southern Indian Ocean and parts of the eastern tropical Pacific and Atlantic basins.


The study has been published in the journal Global Biogeochemical Cycles.


(With IANS inputs)