Study - Link Between Warming Oceans During PETM (Last Major Extinction Spike), Low Dissolved Oxygen

Digging into our planet's past could help us prepare for a hot future. One dramatic spike in historical temperatures, the Paleocene–Eocene Thermal Maximum (PETM), occurred around 55.9 million years ago. That time was marked by changes in ocean productivity, the water cycle, ocean acidification and land animal migrations. Now a new study by researchers in the U.K. confirms the ocean held less dissolved oxygen.

Similarly, low oxygen zones caused by modern climate change threaten marine life and humans who depend on the ocean for food. Deoxygenated zones in the North Pacific and tropical oceans have expanded in the last 50 years, according to a 2009 review from researchers in Europe and the U.S.

To peek into ancient climate for a possible clue to our future, Alex Dickson, a paleoceanographer, and his colleagues at The Open University in England analyzed sediment samples gathered by the Integrated Ocean Drilling Program, an ongoing international marine research project. The sediment cores were pulled from the Lomonosov Ridge in the Arctic Ocean. The team estimated the extent of low-oxygen seawater in global oceans by measuring the ratio of molybdenum isotopes in the sediment samples. The ratios "imply a small but significantly higher level of low-oxygen marine environments compared with the present day," the team wrote in the July issue of Geology.

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Tim Lyons, a biogeochemistry professor at the University of California, Riverside, commends the researchers for the study's thoroughness and calls it one of the first studies to experimentally validate the idea that warming during the PETM led to low oxygen levels in the ocean. Lyons, who was not involved in the study, specifies that the study does not prove that low oxygen levels were causing massive marine organism death, but it does indicate something in the ocean environment was "potentially quite different. And the missing part of the record could be even more dramatic." (Lyons co-wrote a commentary on the Dickson team's work.) The findings are important in the face of today's changing climate, Lyons says. "We hope it resonates," he adds, this kind of broad-scale phenomenon could potentially have a big effect on the ocean and our relationship with the ocean."

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http://www.scientificamerican.com/article.cfm?id=bottom-line-ocean-floor