BIOSPHERIC PRODUCTIVITY AND THE TRANSITION TO A VENTILATED OCEAN (Invited Presentation)

Ocean chemistry, marine fauna, and ecosystem structure on the modern Earth are fundamentally different from those that characterized the majority of Earth’s history. However, the nature of the transition to this modern state—the basic patterns and drivers of ocean oxygenation and accompanying changes in nutrient cycling and biospheric productivity—remain uncertain. Using an Earth system model of ocean biogeochemistry and climate (CANOPS), we explore the levels of nutrient availability and primary productivity that are consistent with atmospheric oxygen levels ranging from those of the modern Earth to those estimated for the Neoproterozoic.

We aim to: (1) improve quantitative constraints and uncertainties on the Earth system scaling between rates of biospheric productivity and atmospheric O₂ abundance; (2) evaluate the sensitivity of changes in phosphorus scavenging efficiency and the impact of this parameter across the transition to a ventilated ocean; (3) evaluate the control of upper limitations on nitrogen fixation on biogeochemically feasible Earth system states; (4) quantify expected changes in vertical carbon fluxes and energy flow to the benthic realm across the transition to an oxygenated deep ocean. To this end, we employ a stochastic approach to explore biogeochemically stable regimes of nutrient availability, productivity, and marine redox at atmospheric oxygen abundance ranging from 0.1 – 100% of the present atmospheric level.