Mercury and carbon cycling linked to terrestrial ecosystem collapse at the Permo-Triassic boundary

Mercury and carbon cycling linked to terrestrial ecosystem collapse at the Permo-Triassic boundary

A new study shows for the first time that the collapse of terrestrial ecosystems during Earth’s most deadly mass extinction event was directly associated with disrupting ocean chemistry.

The international study published today in Nature Communications, and co-authored by Oxford Earth Sciences Professor Tamsin Mather, highlights the importance of understanding the inter-connectedness of ecosystems as our modern environment struggles with the devastating effects of a rapidly warming planet.

The Permian–Triassic extinction, also known as the Great Dying, took place roughly 252 million years ago. It saw the loss of an estimated 90% of marine species, 70% of land species, widespread loss of plant diversity and extreme soil erosion.

While the exact cause of the terrestrial mass extinction is still debated, recent developments suggest that the terrestrial ecosystems were wiped out prior to the marine ecosystems. However, it has been unclear if or how the terrestrial extinction impacted the chemistry of Earth’s ancient oceans.

The team built a computer model that mapped the chemical changes in the Earth’s oceans during the period of the Permian–Triassic extinction. The model tracks the cycling of the poisonous element mercury, which is emitted from volcanoes but also gets incorporated into living organisms. By tracing both the mercury and carbon cycles, and comparing to measurements in ancient rocks, the team were able to separate out biological and volcanic events.

The study revealed that a massive collapse of the Permo-Triassic terrestrial ecosystems led to organic matter, nutrients, and other biologically-important elements cascading into the marine system. Many marine species rely on chemical stability in their environment in order to survive and therefore an influx of this kind is likely to have had major consequences for the marine ecosystems at the time.

Prof. Mather said: ‘Previously, we have studied levels of the element mercury in the geological record in order to unlock more about key episodes of volcanism and their effects on the environment over Earth history. One of the exciting things about this study is that it shows the potential for mercury measurements to tell us more than this and also to yield crucial information about the exchange of biomass between the land and the oceans hundreds of millions of years ago.’

Dr Benjamin Mills, from the School of Earth and Environment at Leeds and co-author said: ‘252 million years ago the effects of mass plant death and soil oxidation appear to have seriously altered the chemistry of the oceans. This is an uncomfortable parallel with our own human-driven land use change, and we too are transferring large quantities of nutrients and other chemicals to the oceans.

‘As we look to re-start the world’s economies in the wake of the current pandemic, protecting our life-sustaining ecosystems should be a priority.’

The paper: Permo-Triassic boundary carbon and mercury cycling linked to terrestrial ecosystem collapse (DOI: 10.1038/s41467-020-16725-4) can be downloaded here.

Featured image:

Siberian flood-basalt flows in Putorana, Taymyr Peninsula. These rocks form part of a gigantic volcanic area that erupted 250 million years ago contemporaneously with the end-Permian mass extinction. Photo by co-author Paul Wignall.