The composition and transport of organic carbon in rainfall:: Insights from the natural (13C and 14C) isotopes of carbon -: art. no. L14402

The dilute nature and compositional complexity of rainwater organic carbon (OC) has made it difficult to determine the role of rainwater OC in regional and global carbon budgets. Here I present the delta(13)C and Delta(14)C signatures of OC in rainfall, including two hurricanes, which indicate that OC in rain originates from multiple sources including a significant fraction from fossil fuels and marine OC. These samples demonstrate that atmospheric wet deposition of OC from fossil fuels can supply significant quantities of relic carbon to ecosystems. In addition, rainfall events that originate over the ocean can be dominated by marine OC, arguing for a significant transfer of marine OC to the continents and a large recycled marine OC component to marine rain. A conceptual model of the direct transfers of OC in rainfall concludes that the net transfer of continental OC to the ocean could be close to zero due to a significant marine to continental flux.