Oxygen levels in the ancient oceans were surprisingly resilient to climate change, new research suggests. An international team of scientists led by ETH Zurich used geological samples to estimate ocean oxygen during a period of global warming 56 million years ago - and found limited expansion of seafloor anoxia (absence of oxygen). Global warming - both past and present - depletes ocean oxygen, but the new study suggests warming of 5°C in the Paleocene Eocene Thermal Maximum (PETM) led to anoxia covering no more than 2% of the global seafloor. However, conditions are different today to the PETM - today's rate of carbon emissions is much faster, and humans are adding nutrient pollution of the oceans - both of which could drive more rapid and expansive oxygen loss. "The good news from our study is that the Earth system was resilient to seafloor deoxygenation 56 million years ago despite pronounced global warming," said lead author Matthew Clarkson, of ETH Zurich. Today's framework conditions more pessimistic. "However, there are reasons why things are different today.
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