Oceanic export of relict carbon by small mountainous rivers

Small mountainous rivers (SMR) export globally significant quantities of particulate organic carbon (POC) to the oceans, the composition of which may be distinct from POC delivered by major world rivers. To better constrain the controls on the Delta(14)C signatures of POC suspended in SMR, we examined the temporal variability of Delta(14)C and delta(13)C of POC suspended in the Santa Clara River, a SMR in California, USA. Our data suggest mixing of bedrock and contemporary soil, which can be applied to other SMR in contrasting climate zones and with varying land cover. The data also suggest that chemical denudation is incomplete, but effective to the point that only the most recalcitrant moieties of the parent POC are exported. We further propose sediment yield as a potentially useful proxy for the Delta(14)C of riverine POC. A preliminary analysis of the existing data for a spectrum of rivers supports this hypothesis.