Collection and Analysis of Radio- and Stable Carbon Isotopes along Selected CLIVAR Repeat Hydrography Lines

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

OCE-0223434 DI14C and DI13C samples will be collected and analyzed along selected Repeat Hydrography cruises where there has never been radiocarbon sampling or where 15-20 years have passed since the last sampling. The isotopic data will be promptly provided to the community; and will contribute to the establishment of good reference materials for the measurement of both isotopes. Radiocarbon in DIC has long been recognized and used as an important tracer in studies of ocean processes and, in particular, of the ocean carbon cycle. Data collected as part of this study will be used to study mixing, ventilation rates and residence times in the deep ocean, air-sea gas exchange, thermocline ventilation rates, and to calibrate ocean general circulation models (OGCMs). Tracer studies of anthropogenic sources of carbon rely heavily on a precise knowledge of the oceanic bomb inventory and its changes over time. This can only be done globally with confidence if there are good datasets with good spatial representation of the oceans. Direct calculations of the bomb inventory penetration depth changes on a global basis are only possible with repeated global measurements over time. The sampled locations have been selected to reflect both the spatial and the time-series requirements for a successful ocean carbon study. DI13C tracks the input of anthropogenic CO2 in a complementary fashion to DIC. The d13C of CO2 added from fossil fuel and biomass burning (approx. -25 ) is significantly lower than that of atmospheric CO2 (approx. -7 , pre-industrial). The atmospheric change can be tracked in the surface ocean waters with the precise measurements of DI13C proposed here. The samples collected here will allow the modeling community to combine DIC, DI13C and DI14C in OGCMs. This will greatly improve the accuracy of the reconstructions possible and, consequently, increase confidence in the predictions made from these models. One cannot emphasize enough the importance of conducting these isotopic measurements in conjunction with the measurement of carbon parameters and other transient tracers. The combined amount of information possible will be far greater than that available alone. This project is contribution to NSF's Integrated Carbon Cycle Research Program and the CLIVAR Program.