ABSTRACT

This project supports the global measurement of carbon isotope tracers as part of the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP). The US component of GO-SHIP typically occupies 2 or 3 major oceanic hydrographic sections per year. The team will sample a subset of these to determine changes in 14C and 13C of dissolved inorganic carbon (DIC). These data provide key metrics for climate and earth-system models and can be used by the broader research community for a diverse set of scientific applications, such as climate model development and calibration. Both institutions will also endeavor to engage postdoctoral researchers supported under separate funding, contributing to the training of the next generation of scientists.

Carbon isotopic data affords key insights into ocean processes that are not available from any other measurements: 14C provides high signal/noise quantification of decadal-scale penetration of anthropogenic perturbation through the bottom of the thermocline and into the deep sea. It also provides key insights into the global overturning circulation by documenting return flow of Southern Ocean intermediate waters to the sea surface. Delta 14C is critical to quantifying the air-sea CO2 gas exchange rate. For 13C, the air-sea 13C disequilibrium is readily measured, thus quantifying the uptake of the anthropogenic CO2 perturbation at the sea surface. When combined with the accumulation of anthropogenic 13C changes in the ocean interior, it is possible to quantify basin-scale redistribution of anthropogenic CO2 in the ocean interior from observations alone. These processes are difficult, if not impossible to examine with synthetic anthropogenic tracers like Chlorofluorocarbon and with conventional C system measurements. The availability of carbon isotope data will aid a wide range of studies including climate change, oceanic anthropogenic CO2, thermocline ventilation, thermohaline overturning rates, air-sea gas exchange rates, biological cycling rates, and model evaluation or calibration. As GO-SHIP cruise schedules are planned, the team will carefully evaluate which legs would yield the best science return from the limited analytical capacity. Sampling will likely focus on long, meridional sections in the Atlantic and Pacific oceans where a strong signal is anticipated, and on any other areas where measurements have been lacking. The water samples will be transported to the National Ocean Sciences Accelerator Mass Spectrometry facility (NOSAMS) for analysis. The sampling design, final quality control, and submission of the data to the CLIVAR and Carbon Hydrographic Data Office (CCHDO) and to the Ocean Carbon Data System (OCADS) will be performed at the University of Washington.

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.

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