Quantifying ocean anoxic event severity using isotope mass balance

Since Earth reached near-modern atmospheric and marine oxygen levels, transient perturbations have occurred in which ocean anoxia has expanded. These events are often associated with enhanced rates of weathering and volcanism, which impact climate and ocean circulation, and also set off feedbacks involving nutrient cycling under anoxic conditions. Quantifying the severity of these events is critical, as it allows us to discern the impact of climatic changes on ocean redox, as well as the impact of ocean redox on animal life. Only recently have quantitative proxies emerged that are up to this task; we recently explored the most promising of these - uranium isotopes - by developing an inverse modeling framework to estimate seafloor anoxia given a paleo-d238U record.