Abstract:

The coupled cycling of oxygen, carbon, and heat influences the health and trajectory of our ocean climate. The oceans are the major sink of anthropogenic carbon and heat, while declining dissolved oxygen levels have been observed in all ocean basins. On the global scale, the three tracers are clearly coupled, however, little is understood about their regional-scale coupling. This talk addresses three unresolved questions. How well do we know about the long-term change of dissolved oxygen? Can earth system model reproduce observed deoxygenation trend? Why are ocean heat and oxygen tightly coupled globally but not locally? We approach these questions by comparing observational datasets from two different ways of checking data quality, and nine different methods for filling in data gaps. We also analyzed 14 CMIP6 earth system models and compared them to the observational datasets. Mapping methods are likely the largest contributor of the observational uncertainty for annual mean, but both mapping and QC methods are important for the seasonal cycle and the long-term trends. The models’ climatological annual mean oxygen matches observations well near the surface. However, significant biases remain in the tropics and in the thermocline, and the models tend to underestimate deoxygenation trends, except for the North Atlantic basin. Finally, we show the global coupling of heat and oxygen through a quasi-conservative tracer, PO. Different modes of regional O2-heat coupling are revealed by the observational reconstruction of heat and oxygen. Continued collaboration across disciplinary boundaries will be necessary to tackle unresolved questions about the co-evolution of physical and biogeochemical tracers in the warming ocean. 

Biography:

Taka Ito (he/him) is an oceanographer, interested in ocean biogeochemistry and climate. He is a native of Japan and received his PhD degree from Massachusetts Institute of Technology (2005). He was at University of Washington and Colorado State University before joining Georgia Institute of Technology in 2011 where he currently serves as a professor in School of Earth and Atmospheric Sciences and teaches physical and chemical oceanography and other courses. His research group uses theoretical, observational and modeling approaches, and the past research projects included circulation and carbon cycle of the Southern Ocean, ocean carbon pumps, and the global cycling of nutrients and dissolved oxygen.