Digging Through Disaster: Bioturbation’s Impact on Ocean Nutrient Cycling Across Mass Extinctions

The loss of seafloor sediment mixing by burrowing animals across mass extinctions is often seen as a symptom of environmental crisis, but rarely a driver. In this talk I will explore how bioturbating animals may have acted as “chemical engineers” of the oceans across mass extinctions, via their effect on nutrient exchange between sediment and seawater. I will present results from a regional case study focusing on Permian??"Triassic marine sedimentary rocks in Svalbard, Arctic Norway, which span Earth’s greatest mass extinction ca. 252 million years ago. Using combined ichnological and geochemical analyses of samples collected across a wide range of shallow marine depositional environments, I demonstrate statistically significant relationships between bioturbation intensities and carbon, sulfur, and phosphorus contents, pointing towards a close coupling between bioturbation and nutrient cycling across broad areas of the continental shelf. My results reveal a hierarchical recovery pattern: efficient carbon and sulfur cycling resumed within tens to hundreds of thousands of years after the extinction, coincident with the return of shallow, simple styles of bioturbation, while restoration of phosphorus cycling to its pre-extinction state lagged by up to one million years, coincident with the return of deeper, more complex styles of bioturbation. As a next step, I plan to use Earth system modeling to test whether bioturbation-induced changes to seafloor organic carbon burial can substantially impact global climate over geologically rapid timescales (thousands of years). I also aim to explore whether longer-term changes in the global extent of bioturbation across the Phanerozoic may have led to differences in Earth system sensitivity across various climate events, including how modern patterns of bioturbation may influence future climate change.

Speaker: Brian Beaty, Stanford University

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