Warming Impact On Oceans' Long-Term Ability To Produce Oxygen Not Even Mentioned In COP Draft
While some effects of climate change on the oceans — including acidification and rising sea levels — are well known, its effects on oxygen levels in the seas have largely been left out of the discussion at COP21 in Paris. “There’s lots of meetings about small island nations, thinking about rising seas, and talking about acidification, but not about deoxygenation of the ocean,” said Lisa Levin, an ocean oxygen expert at the Scripps Institution of Oceanography in San Diego.
Like acidification and rising sea levels, low oxygen zones in the ocean also appear to be expanding as a result of climate change, Levin said. But as world leaders are wrapping up talks aimed at a treaty to slow global warming, Levin said many of the negotiations failed to address the impacts of climate change on the oceans. The word “oceans” is mentioned once in the preamble of the latest draft of the agreement, Levin said.
This means climate change’s impact on oceans won't be addressed by actions agreed to in the global treaty. In the Pacific Ocean off the coast of southern California, oxygen levels have dropped between 20 to 30 percent in the past 50 years, Levin said. Globally, the losses are around 20 percent. The declines are expected to continue as ocean temperatures increase.
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The effect of ocean stratification on mixing is important, Koslow said. Deeper waters get their oxygen mostly from the atmosphere. In the winter, storms help break down the warm-water surface layer and well-oxygenated water gets mixed down with deeper waters. Unlike surface levels of the ocean, deep waters cannot get oxygen from photosynthesis because there’s not enough light, Koslow said. In fact, deeper waters are usually losing oxygen because bacteria consume oxygen while digesting dead organic material like algae or phytoplankton that has sunk. That risks undoing the balance of oxygen gained in deeper oceans and oxygen consumed by bacteria, Koslow said, which if left unchecked could have significant consequences. “The mass extinctions in the past appear to be linked to periods of deoxygenation, that’s why we’re concerned,” said Koslow, who is working with the National Oceanic Atmospheric Administration to examine ecological change in the oceans.
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http://america.aljazeera.com/articles/2015/12/11/ocean-deoxygenation-left-out-of-climate-debate.html
