Collection of High-Resolution Carbon Isotope Data on GO-SHIP Cruises in the Indian and Pacific Oceans for Constraining Ocean Carbon Uptake and Storage

There are two common versions of carbon in carbon dioxide, carbon-13 and carbon-12. The ratio of carbon-13 to carbon-12 (13C/12C) in petroleum is very different from that ratio in seawater. One of the most sensitive ways we have of finding petroleum-based carbon in the ocean is by looking for changes in 13C/12C of carbon dioxide dissolved in seawater. Unfortunately, this is seldom done because 13C/12C measurements are expensive and not regularly done at sea. In this project, the 13C/12C ratio of ocean carbon dioxide will be measured in the Pacific and Indian Oceans using a new instrument that is much less expensive to run and can run many more samples than previous methods. The new measurements will be compared to old ones in order to estimate how much man-made carbon dioxide has entered the ocean. In coming decades changes in ocean behavior should be detectable by comparison with the data collected in this project. PIs have developed a seagoing dissolved inorganic carbon (DIC) extraction system coupled with a laser spectrometer that can be deployed at sea. The combination can provide unprecedented coverage and state-of-the-art precision and accuracy for 13C/12C of DIC. The project centers on instrument deployment, with personnel, on 3 cruise legs along a meridional line in the Pacific Ocean and on one meridional cruise in the Indian Ocean. The data will be compared with prior datasets using established statistical techniques to quantify decadal changes in 13C, providing a powerful window into upper ocean turnover and anthropogenic CO2 uptake rates. The project supports a graduate student over the four-year duration of the project and a postdoctoral scholar for 2.5 years. Both will participate and be trained in collection and analysis of the 13C datasets. 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.