Extreme temperatures following Earth's greatest mass extinction driven by the loss of siliceous ecosystems

Global climate and biotic recovery in the aftermath of Earth’s most severe mass extinction was sluggish, taking over 5 million years. Our study demonstrates that the decline of silica secreting ecosystems and subsequent increase in marine clay formation contributed to this mysterious climate trend.
Extreme temperatures following Earth's greatest mass extinction driven by the loss of siliceous ecosystems

Global warming at the end-Permian ~252 million years ago initiated the most devastating and extended environmental crisis in Earth’s history. During this event the eruption of large volumes of lava was accompanied by the injection of CO2 into the atmosphere, causing a 15 degree C increase in surface temperature and more acidic and oxygen depleted global oceans. This drove the extinction of ~85-95% of all marine species on Earth.

Notably, climate and biotic recovery in the wake of this mass extinction event was extremely sluggish taking over 5-6 million years. This recovery time is dramatically longer than the expected timescale of recovery based on our current understanding of the global carbon cycle. During this multi-million-year interval the planet was effectively trapped in a greenhouse climate state. This mysterious climatic trend sets the end-Permian mass extinction event apart from all other known global warming events in Earth’s history, and has puzzled scientists for over a decade.

In our paper published in Nature Communications, we demonstrate that the global decline of marine silica secreting ecosystems (e.g., sponges and radiolarians) likely played a role in sustaining elevated greenhouse conditions in the aftermath of the mass extinction. It has been previously observed that silica secreting organisms essentially vanished from all low and mid latitude sites globally for ~5 million years post the mass extinction, corresponding to the anomalous greenhouse interval. This would have driven seawater to be more silica rich and in turn increased the amount of clay formation in global oceans, a process that releases CO2. Overall, this process would have reduced the efficiency of the Earth system in sequestering carbon, and consequently kept CO2 levels and temperatures elevated.

We demonstrate this using two independent methods. First, we employ a global carbon-silica cycle model, to show that the traditional framework of global carbon cycling cannot explain the sustained high temperature trend following the end-Permian. Next, we expand on the traditional framework by allowing for marine biogeochemical silica processes to feedback into the carbon cycle. Specifically, the formation of in-situ (authigenic) marine clay minerals is dependent on the chemistry of seawater, and contributes to CO2 release. Simply, this allows for dynamic carbon recycling within the ocean and atmosphere system and provides us with a more realistic representation of global carbon cycle feedbacks. From this modeling work, we are able to estimate the change in marine clay formation required to explain the climate trend across the end-Permian event.

Our second method involves determining the different minerals preserved in marine shales that span this time interval via X-ray diffraction (XRD). Specifically, through this technique we are able to quantify changes in the amount of silica being buried in marine sediments as a clay mineral phase versus a biogenic silica phase. We find that the results from the mineralogical analysis are consistent with the estimates from our global carbon cycle model. This supports the idea that enhanced CO2 release from marine clay formation played a prominent role in sustaining the prolonged greenhouse conditions.

Overall, this framework provides a novel and unique self-consistent link between the lethally hot temperatures, delayed climate recovery, and the widespread loss of silicifying organisms across the end-Permian mass extinction event. While solid-Earth degassing may have acted as a trigger, subsequent biotic feedbacks likely exacerbated and prolonged the environmental crisis.

The End-Permian mass extinction event is the only known event in Earth’s history with carbon release rates similar to that of modern rates and the only carbon injection event to result in the widespread disappearance of marine siliceous organisms. This provides an impetus to better quantify modern rates of marine authigenic clay formation and CO2 release. It also promotes the need to better quantify the synergistic effects of environmental change (warming, deoxygenation, and acidification) on siliceous organisms and vice versa. This will give us a more complete understanding of how marine ecosystems respond to and shape climatic events.

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