Flux and age of dissolved organic carbon exported to the Arctic Ocean: A carbon isotopic study of the five largest arctic rivers

The export and Delta C-14-age of dissolved organic carbon (DOC) was determined for the Yenisey, Lena, Ob', Mackenzie, and Yukon rivers for 2004 - 2005. Concentrations of DOC elevate significantly with increasing discharge in these rivers, causing approximately 60% of the annual export to occur during a 2-month period following spring ice breakup. We present a total annual flux from the five rivers of similar to 16 teragrams (Tg), and conservatively estimate that the total input of DOC to the Arctic Ocean is 25 - 36 Tg, which is similar to 5-20% greater than previous fluxes. These fluxes are also similar to 2.5 x greater than temperate rivers with similar watershed sizes and water discharge. Delta C-14-DOC shows a clear relationship with hydrology. A small pool of DOC slightly depleted in Delta C-14 is exported with base flow. The large pool exported with spring thaw is enriched in D14C with respect to current-day atmospheric Delta C-14-CO2 values. A simple model predicts that similar to 50% of DOC exported during the arctic spring thaw is 1 - 5 years old, similar to 25% is 6 - 10 years in age, and 15% is 11 - 20 years old. The dominant spring melt period, a historically undersampled period, exports a large amount of young and presumably semilabile DOC to the Arctic Ocean.