Skip to main content

Oceans are fast losing oxygen, putting marine habitat at greater risk (downtoearth)





aThe 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, finds a new study by researchers at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany.

This oxygen depaAletion, the study shows, is mostly a result of climate change.

Published in Nature Journal, the study gives more teeth to previous arguments about deadly consequences of the ocean's declining oxygen levels on marine life. The three co-authors: Sunke Schmidtko, Lothar Stramma and Martin Visbeck looked into the data dating back to 1960. By using information on oxygen, temperature and other factors relating to the oceans, they estimated the overall oxygen loss.

"We were able to document the oxygen distribution and its changes for the entire ocean for the first time. These numbers are an essential prerequisite for improving forecasts for the ocean of the future," said Schmidtko.

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.

"Just a little loss of oxygen in coastal waters can lead to a complete change in ecosystems," said David Baker, assistant professor at the University of Hong Kong's Swire Institute of Marine Sciences. 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.

Is oxygen depletion true for Indian Ocean?

In an earlier study published in 2016, it was revealed that southern Indian Ocean and parts of the eastern tropical Pacific and Atlantic basins have already started noticing climate-linked deoxygenation.

Explaining the cause of depleting oxygen content in oceans, Roxy Mathew Koll, a climate scientist at the Indian Institute of Tropical Meteorology (IITM), says, “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.”

A joint study by the IITM and the France-based Sorbonne Universités had revealed that 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. The study also suggested that it is the largest contributor to the overall trend in the global mean sea surface temperature.

A situation, wherein oxygen is almost completely depleted in the depth range between 100 and 1000 metres, was observed in the northern Indian Ocean in the area of the Arabian Sea and the Bay of Bengal. While ocean warming is a widely identified reason for depletion of oceanic oxygen, changes in salinity can also contribute to oxygen loss. “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. Although I cannot say for certain, but there is a probability that this might prevent oxygen to sink into the deeper layers of the ocean,” says Koll.

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.

Comments

Popular posts from this blog

SC asks Centre to strike a balance on Rohingya issue (.hindu)

Supreme Court orally indicates that the government should not deport Rohingya “now” as the Centre prevails over it to not record any such views in its formal order, citing “international ramifications”.

The Supreme Court on Friday came close to ordering the government not to deport the Rohingya.

It finally settled on merely observing that a balance should be struck between humanitarian concern for the community and the country's national security and economic interests.

The court was hearing a bunch of petitions, one filed by persons within the Rohingya community, against a proposed move to deport over 40,000 Rohingya refugees. A three-judge Bench, led by Chief Justice of India Dipak Misra, began by orally indicating that the government should not deport Rohingya “now”, but the government prevailed on the court to not pass any formal order, citing “international ramifications”. With this, the status quo continues even though the court gave the community liberty to approach it in …

Cloud seeding

Demonstrating the function of the flare rack that carries silver iodide for cloud-seeding through an aircraft. 
Water is essential for life on the earth. Precipitation from the skies is the only source for it. India and the rest of Asia are dependent on the monsoons for rains. While the South West Monsoon is the main source for India as a whole, Tamil Nadu and coastal areas of South Andhra Pradesh get the benefit of the North East Monsoon, which is just a less dependable beat on the reversal of the South West Monsoon winds.

India’s criminal wastage: over 10 million works under MGNREGA incomplete or abandoned (hindu)

In the last three and half years, the rate of work completion under the Mahatma Gandhi National Rural Employment Guarantee Act (MGNREGA) has drastically declined, leading to wastage of public money and leaving villages more prone to drought. This could also be a reason for people moving out of the programme.

At a time when more than one-third of India’s districts are reeling under a drought-like situation due to deficit rainfall, here comes another bad news. The works started under the MGNREGA—close to 80 per cent related to water conservation, irrigation and land development—are increasingly not being completed or in practice, abandoned.

Going by the data (as on October 12) in the Ministry of Rural Development’s website, which tracks progress of MGNREGA through a comprehensive MIS, 10.4 million works have not been completed since April 2014. In the last three and half years, 39.7 million works were started under the programme. Going by the stipulation under the programme, close to 7…