Collaborative Research: Assessing Global Oxygen Inventory, Trends and Variability through the Intercomparison of Observation-based Gridded Datasets

Dissolved oxygen is essential for supporting life in marine habitats and for controlling the cycling of carbon and nutrients in the global ocean. Historical observations have shown that oxygen concentrations are declining in many parts of the oceans, termed “ocean deoxygenation”. The causes of the decline are linked to changes in surface water temperature and its impact on oxygen solubility, along with variations in the strength of the biological pump, ocean circulation, vertical mixing, ventilation, and biochemical processes.

It is difficult to calculate exactly how much ocean oxygen has been lost to the atmosphere and how much has been redistributed within the ocean interior. This project will compare observation-based gridded oxygen datasets with the purpose of generating comparable four-dimensional (space and time) estimates of global oxygen distribution, assessing their similarities and differences and promoting scientific understanding of the drivers of ocean deoxygenation.

The project will promote workforce development through support of an early career investigator, a postdoctoral researcher, a graduate student, and several undergraduate interns.

The project has two primary goals. The first goal is to identify the causes of disagreements between different gridded oxygen datasets by conducting an intercomparison of oxygen datasets from common in situ observational and model-based profiles. Many factors can affect estimates of a deoxygenation trend: existing observational studies use different sets of raw data, measurement platforms, data quality control metrics, land-ocean masks, vertical and horizontal grids and interpolation methods.

Because variations in any of these factors can lead to different estimates, it is difficult to make direct comparisons and determine the causes of disagreements among datasets. Standardized protocols will be applied to isolate the interpolation method as the only source of discrepancy and to assess uncertainties in global oxygen inventory trends. The second goal is to test hypotheses for the underlying causes of ocean deoxygenation.

The suite of new datasets will be used to evaluate the roles of oxygen solubility, the biological pump, and physical and biogeochemical processes driving global ocean deoxygenation. Further, the mechanisms driving the expansion of the tropical ocean oxygen minimum zones will be explored. The use of novel datasets with unprecedented spatio-temporal resolution in these analyses will enable new insights into global and regional oxygen content changes.

The suite of gridded oxygen datasets will be made available via public data repositories, and the results of the product intercomparisons and deoxygenation analyses will be disseminated via open-access papers. Collaboration with the Scientific Committee on Oceanic Research (SCOR) Working Group 168 will enhance access and utility of gridded oxygen datasets through sharing and exchange of ideas, experimental protocols and data products.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.