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2019 was a record year: the third in a row of the warmest years on record for the world’s oceans, researchers reported in January 2020 in the journal “Advances in Atmospheric Sciences”.

A team of researchers at the Museum für Naturkunde Berlin is exploring the fossil record of an ancient episode of ocean warming and its effects on marine life. One of the goals is to develop better predictive frameworks for long-term responses to current human-caused climate change.

Oceans, short of breath

“We focus on a marine extinction event that took place about 183 million years ago, in the early Jurassic”, says Veronica Piazza, who is working on her PhD thesis, supervised by Martin Aberhan. At the time of the “Early Toarcian Oceanic Anoxic Event” (TOAE), earth experienced an episode of global warming, with a mean temperature increase of up to 3.5 degrees Celsius in subtropical seas.

This strongly impacted marine ecosystems, as the oceans took up a large share of the excess heat. Increased water temperatures affected organisms directly and indirectly, often coupled with deoxygenation, acidification of seawater or both.

In many places, low oxygen levels were the main cause of the observed mass extinction. However, in what is today south-western Europe, oxygen deficiency did not occur and fossils from those places have not been explored to the same extent so far. “We want to get a better understanding of how climate change affected ground-dwelling organisms in the shallow sea that covered these regions”, says Piazza.

In particular, the team is investigating the temperature-related effect on the body size of brachiopods and molluscs and on the taxonomical and ecological structure of the benthic communities: which species were present on the seafloor and how they lived.

The fossils are today on land, in ancient seafloor beds in Portugal and Spain. The researchers are trying to achieve a fine resolution of the temporal changes in the species communities to be able to tie them to the temperature-related drivers. They measure the size of the shells of brachiopods and molluscs and analyse the data.

Results indicate that body size decreases as an early response to stress before and during the environmental crisis. Larger-sized species are more affected than smaller-sized species. “And we are seeing that organisms are affected for a long time”, says Piazza. The time span of the environmental perturbations related to the TOAE lasted up to 900.000 years. “This may be a relatively short time in geological terms, but for human time scales it is like forever”, the researcher adds.

Project-title

Response of Early Jurassic (Pliensbachian-Toarcian) benthic marine faunas from south-western Europe to temperature-related stresses (EvoBiv)

Partners

Funding

Deutsche Forschungsgemeinschaft - DFG