PLEA Network

10 May 2017, Climate News Network, Ocean oxygen decline greater than predicted. Circulation changes caused by warming waters and melting polar ice are the most probable explanations for the rapidly falling levels of oxygen in the ocean. US scientists who have been warning that warmer oceans are more likely to be poorer in dissolved oxygen have now sounded the alarm: ocean oxygen levels are indeed falling, and seemingly falling faster than the corresponding rise in water temperature. That colder water can hold more dissolved gas than warmer water is a commonplace of physics: it is one reason why polar seas are teeming with marine life and tropical oceans are blue, clear and often relatively impoverished. In 2013, an international consortium of marine scientists warned that oxygen levels in the oceans could fall by between 1% and 7% by the century’s end. And this could, other scientists predicted, lead to what they politely called “respiratory stress” for some marine life. Ocean warming Ocean ecologists in the US and Germany warned last year that parts of the deep oceans were already showing signs of oxygen deprivation with corresponding dead zones. Earlier this year, another research group looked at the computer simulations for the years 1920 to 2100 and predicted that the hazards were likely to increasewith warming. Now the team have returned to the issue. They report in Geophysical Research Letters that they looked at data for the last 50 years and found the oxygen levels started dropping in the 1980s, as ocean temperatures began to climb – and falling unexpectedly rapidly. The trend of oxygen falling is about two to three times faster than what we predicted from the decrease of solubility associated with ocean warming,” says Takamitsu Ito, of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology, who led the study. “This is most likely due to the changes in ocean circulation and mixing associated with the heating of the near-surface waters and the melting of polar ice.” Read More here