Project: Decadal trends in oceanic anthropogenic CO2 from the CLIVAR and GO-SHIP d13C datasets and in an ocean biogeochemistry model

NSF Award Abstract:
The ocean has absorbed about a third of the fossil fuel carbon dioxide (CO2) that humans have emitted, slowing the accumulation of CO2 and its associated trapping of thermal energy in the atmosphere. The research aims to improve our understanding of how this ocean uptake of CO2 will change when ocean circulation responds to continuing changes in climate. Researchers will use observations of the isotopic ratio of carbon (13C/12C) of seawater and atmospheric samples, as a high signal/noise method to determine air-sea transfer rates and storage in the ocean interior of fossil-fuel CO2. Also, a state-of the art ocean C-cycling model will be used to validate the model's air-sea exchange rates and upper ocean storage of fossil-fuel CO2. The additional information provided by 13CO2 will establish important benchmarks on ocean-atmosphere and biosphere-atmosphere C exchanges in models used for forecasting future changes in climate. Results would be incorporated into an outreach program through the University of Washington's Program on Climate Change to educate the public on the impact of human activity and climate on the ocean, atmosphere, and earth. One postdoc would be supported and trained as part of this project.

To better understand the processes that control the evolution of the anthropogenic carbon dioxide (CO2) signal in the ocean, we will utilize two characteristics of dissolved inorganic 13Carbon (DIC13) that distinguish it from DIC. First, the 10x longer air-sea equilibration time for DIC13 yields a well-constrained air-sea 13CO2 flux in all basins that is resolvable on decadal time scales. Second, the anthropogenic DIC13 accumulation in the ocean is quantifiable to better signal to noise than anthropogenic DIC itself. The availability of ocean del13C and DIC data from WOCE, CLIVAR and GO-SHIP provide the opportunity to quantify, based on observations alone, the evolution and transports of the anthropogenic DIC and DIC13 signal on regional and global scales in the ocean. Implementation of the anthropogenic DIC and DIC13 perturbations into an ocean model, driven by interannually varying winds, will yield simulations of the DIC and DIC13 evolution that we will compare to observations, helping to identify likely processes causing interdecadal shifts in the rate of this evolution. The combination of observations and model analysis tracking the decadal DIC13 and DIC perturbations are designed to improve our insight into the ocean's important role in modulating climate by taking up and storing anthropogenic CO2.

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.