Changing resilience of oceans to climate change
Oxygen levels in the ancient oceans were surprisingly resilient to climate change, new research suggests.
Scientists 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 we are adding nutrient pollution to the oceans - both of which could drive more rapid and expansive oxygen loss.
The study was carried out by an international team including researchers from ETH Zurich, the University of Exeter and Royal Holloway, University of London.
"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 Dr Matthew Clarkson, of ETH Zurich.
"However, there are reasons why things are different today.
"In particular, we think the Paleocene had higher atmospheric oxygen than today, which would have made anoxia less likely.
"Additionally, human activity is putting more nutrients into the ocean through fertilisers and pollution, which can drive oxygen loss and accelerate environmental deterioration."
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