In a new study published in One Earth (Cell Press), Aske L. Sørensen and Tais W. Dahl demonstrates that the Earth system tipped into a state of widespread marine anoxia during the Cambrian SPICE event. A self-cascading mechanism involving anoxia-dependent nutrient release from seafloor sediments has been documented regionally and hypothesized to operate globally. The new study shows that the rate of changes in the global marine carbon and molybdenum cycles requires a self-perpetuating feedback to operate at the global scale.
The study also proposes that the anoxia-nutrient feedback is sedimentation sensitive, which means that coastal anoxia is particularly dangerous – and in fact, a massive expansion of oceanic anoxia associated the Cambrian SPICE event might well have been driven by shorewards migration of the anoxic zones, perhaps associated with a sudden sea level rise.
Using the new formulation of the anoxia-nutrient feedback – calibrated in the SPICE event – the study also finds that the current Earth system is more than 100,000 yr away from passing the tipping point today.
Importantly, the study demostrates that we can learn about climate change risks from geochemical reconstructions of the geological past.