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Current increases in anthropogenic carbon dioxide emissions and related ocean acidification trends have parallels in an event 55 million years ago.
The Paleocene Eocene Thermal Maximum (PETM) was a period when the earth warmed by 5°C due to a rapid increase in the levels of atmospheric carbon dioxide. This led to ocean acidification, as the oceans absorbed some of the increase in carbon dioxide (CO2) from the air.
A recently solved riddle was why ocean acidification during this period was greater in the Atlantic than other oceans around the world. Research published last year in Nature Geoscience revealed that the shape of the ocean basin and nature of ocean currents in the Atlantic was key.
These findings highlight the complexities of ocean and atmospheric systems, and provide valuable insights for scientist grappling with the current ocean acidification challenge.
How did they discover something from 55 million years ago? A computer model was developed which simulated the ocean basins and currents at that time. Sediment cores have reveal that the bottom layers of water in the Atlantic were particularly acidic and corrosive. When the model was programmed to take into account the rapid atmospheric temperature increase of 5°C during the PETM, a funny thing happened.
The corrosive water warmed and started circulating upwards, flowing towards the surface and then southwards towards the South Atlantic, and eventually the Pacific, creating an enormous, corrosive deep water current. By corrosive I mean creatures which sought protection from a calcium carbonate skeleton (like coral) or shell (many molluscs), didn’t stand a chance.
While this prehistoric event shares parallels with todays oceans under climate change, there is one big difference. The PETM event occurred when increases in atmospheric carbon dioxide were one tenth of the current rate of emissions. The changes back then took thousands of years to unfold and caused one of the largest mass extinction events in the deep ocean. Indicators suggest we are facing more rapid and more devastating changes, making research like this vital to understanding and managing the future of our oceans.
The original article ‘Solution to corrosive ocean mystery reveals future climate’ by Alvin Stone for the AMSA Bulletin is available here: https://www.amsa.asn.au/sites/default/files/%23196_3_AMSA_Bulletin.pdf