Mass Extinction Events
Ocean mixing led to recovery
At the same time, there were major changes in ocean chemistry and carbon cycling, the team found. Vertical mixing of oceanic water had stopped during or soon after the mass extinction, causing widespread depletion of oxygen in the oceans. Carbon isotopes in the Majiashan rock layers suggest the oldest marine reptiles appeared just after a return to healthy ocean circulation, which could have prompted the ecosystem recovery, the researchers suggest. The rocks recorded more vigorous mixing of ocean waters, which would have brought nutrient-rich waters to the surface to fuel tiny organisms at the bottom of the ocean's food chain.