Today's ocean oxygen levels may have cascading impacts

Scientists have uncovered a crucial connection between ocean oxygen levels and one of the most catastrophic marine extinction events in Earth’s history. 

The research not only illuminates our understanding of past global changes but also issues a stark warning about the current fragility of marine ecosystems.

Triassic–Jurassic mass extinction

The study was focused on the Triassic–Jurassic mass extinction, which occurred approximately 200 million years ago. This event is among the Earth’s major mass extinctions, periods characterized by significant global ecosystem collapses and widespread species extinctions. 

Historically, these events have been closely associated with global environmental disturbances, frequently resulting in reduced oxygen levels (anoxia) in oceanic waters.

Focus of the study

A common hypothesis has been that greater extents of ocean deoxygenation would naturally lead to larger scale extinctions. However, the current study challenges this assumption by demonstrating that the level of euxinia (an extreme form of deoxygenation) during the Triassic–Jurassic extinction was similar to what we observe today.

The research team, including experts from Royal Holloway (UK), Trinity College Dublin (Ireland), and Utrecht University (Netherlands), analyzed chemical data extracted from ancient mudstone deposits in Northern Ireland and Germany. 

Critical insights 

The results of the analysis highlight the role of anoxia in the marine extinctions during this period. The study also reveals a surprising limitation in the global extent of extreme deoxygenation at the time.

The experts found a correlation between increased extinction rates and spikes in deoxygenation across shallow marine environments along European continental margins. 

Cautionary tale 

Upon further investigation, the team determined that the global extent of extreme deoxygenation was rather limited, and similar to the present day. 

The research serves as a cautionary tale about the current state of our oceans, suggesting that they may be more vulnerable than previously thought. 

The study of past global change events is invaluable in understanding the consequences of modern climate change, as well as in predicting and possibly mitigating future ecosystem tipping points.

Cascading impacts

“Scientists have long suspected that ocean deoxygenation plays an important role in the disturbance of marine ecosystems, which can lead to the extinction of species in marine environments,” said study co-author Professor Micha Ruhl.

“The study of past time intervals of extreme environmental change indeed shows this to be the case, which teaches us important lessons about potential tipping points in local, as well as global ecosystems in response to climatic forcing.”

“Crucially however, the current findings show that even when the global extent of deoxygenation is similar to the present day, the local development of anoxic conditions and subsequent locally increased extinction rates can cascade in widespread or global ecosystem collapse and extinctions, even in areas where deoxygenation did not occur.” 

Assessing ecosystem stability 

Professor Ruhl said the research shows that global marine ecosystems become vulnerable, even when only local environments along the edges of the continents are disturbed.

“Understanding such processes is of paramount importance for assessing present day ecosystem stability, and associated food supply, especially in a world where marine deoxygenation is projected to significantly increase in response to global warming and increased nutrient run-off from continents.”

The study is published in the journal Nature Geoscience

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