The School of Earth and Atmospheric Sciences Presents Dr. Taka Ito, Georgia Tech

Ocean Deoxygenation

Broadly speaking the oxygen content of the ocean is controlled by the downward transport (ventilation) of the O2-rich surface waters and the microbial O2 consumption. The balance between these two processes determines the patterns of O2 in the oceans. 

The concentration of O2 varies globally from the ventilation-dominated high latitude waters to the O2-deficient mid-depth waters at low latitudes. Global energy imbalance due to the increasing levels of greenhouse gases and the resultant rise in ocean heat content are expected to cause gradual decline of oxygen content with profound influences on marine biogeochemistry, ecosystem and fisheries. 

Increasing temperature lowers the solubility of gases in the seawater. In addition, increased vertical stratification weakens the rate of ventilation, thus the physical supply of O2. Earlier studies have shown multi-decadal declines of O2 superimposed with natural variability in many regions, but the global assessment remains challenging due to sparse and irregular sampling. 

We developed a time-varying, globally mapped O2 dataset from 1958 to present based on historic observations. In this presentation, we examine the observed O2 decline using this new dataset, compare it to earth system model simulations, and explore underlying mechanisms using both models and observations.