Constraining the Extent and Intensity of Ocean De-oxygenation During Global Carbon Cycle Perturbations

The extent and intensity of oxygen minimum zones have a first order relationship with the efficiency of nutrient and trace metal recycling in the oceans, global burial rates of organic carbon, and the availability of aerobe habitat. Reconstructing how the extent and intensity of oxygen depletion has varied with past changes in climate and global carbon cycle perturbation would enable something of the sensitivity of de-oxyenation (and its attendant impacts) to CO₂ release to be quantified. However, even the extent of past de-oxygenation is notoriously difficult to constrain from the scattered and generally ocean margin and interior seaway dominated availability of observations.

Spatially resolved global biogeochemical models can help, as by placing the distribution of records of any particular proxy into a global, mechanistic framework, one can make a more quantitative assessment of the observations. Moreover, multiple proxies with differing controls and sensitivities to redox state can be assessed simultaneously to help further constrain the interpretation.

In this talk I will illustrate this (model-data) approach, taking examples from OAE2 and OAE1a, proxy records of seafloor anoxia and photic zone euxinia, and using the ‘GENIE’ Earth system model (http://mycgenie.seao2.org). I will also discuss what records and model-data approaches might be used to help better understand much subtler de-oxygenation events such as the PETM.