Shallow Seas May Have Offered Refuge for Life

Ore geologists at Luleå University of Technology are part of an international collaboration that sheds new light on oceanic extinction events during the mid-Permian time period. Analyses of limestone layers from Bolivia suggest that shallow marine environments may have served as unexpected refuges for life during times when the ocean was low in oxygen, conditions similar to the later mass extinction event at the end of the Permian period. The findings also raise important questions about today’s oceans and their future.

During the mid-Permian, around 270 million years ago, marine life suffered from low-oxygen conditions. But there may have been glimmers of hope even during the catastrophe as shallow waters appear to have acted like lifeboats for certain organisms.

"Shallow, oxygen-rich marine environments may have served as oases for life during the Permian period," says Lidia Mabel Nina Quiroz, PhD student in ore geology at Luleå University of Technology and the main contributor to the international research project.

Her doctoral thesis, Geochemical Signatures of Permian Carbonates in the Copacabana and Chutani Formations, Bolivia, is based on geochemical analyses of limestone layers from western Bolivia. The samples were collected during fieldwork in what is now a high-altitude region near Lake Titicaca and were studied through a collaboration between Bolivia and Sweden.

Traces of Life in Stone

More than 100 samples were collected from the bedrock at three different locations during fieldwork. Thin sections of limestone were studied through a range of different microscopy techniques, where the researcher examined mineral grains, fossils, and signs of how the rock formations had changed since they were first formed and deposited on the seafloor. Advanced analyses of carbon and oxygen isotopes were also carried out, along with measurements of trace metals and rare earth elements.

The laboratory work was done at Luleå University of Technology and at for instance the LABISE lab in Recife, Brazil. The methods allowed researchers to look back ca. 270 million years and map how oxygen levels and the chemistry of seawater changed over millions of years.

Fossil Fingerprints of Resilience

The results show that parts of the ancient seabed in what is now Bolivia had better oxygen conditions than many other parts of the world’s oceans at the time. This is evident from the presence of marine organisms — such as corals, brachiopods, and foraminifera — and from chemical patterns that point to freshwater influence and higher oxygen levels.

"The amount of cerium we measured suggests that oxygenated conditions may have existed in shallow marine areas, despite widespread oxygen depletion in the oceans," she explains.

In the Chutani Formation, signs were found that oxygen levels gradually decreased — but even there, intervals of re-oxygenation occurred. This paints a picture of an ocean where some zones offered a lifeline, while others became uninhabitable.

A Reminder of Ocean Vulnerability

Although the thesis focuses on prehistoric geology, the findings are highly relevant today. Our modern oceans are facing a crisis of their own — with oxygen loss in deep waters, mass mortality of marine species, and shifting water chemistry driven by climate change.

"By understanding how life survived past crises, we can better interpret what’s happening in our oceans today — and maybe also how to protect them," says Lidia Mabel Nina Quiroz.

Her thesis is part of the project Non-Metallic Mineral Resources for the Development of Poor Bolivian Regions, funded by Sida. The research shows that even under extreme conditions, nature can find a way — but also that such opportunities depend on delicate chemical balances. Balances that are now increasingly under threat.