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

[1] The export and Δ 14 C-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 ∼16 teragrams (Tg), and conservatively estimate that the total input of DOC to the Arctic Ocean is 25-36 Tg, which is ∼5-20% greater than previous fluxes. These fluxes are also ∼2.5 x greater than temperate rivers with similar watershed sizes and water discharge. Δ 14 C-DOC shows a clear relationship with hydrology. A small pool of DOC slightly depleted in Δ 14 C is exported with base flow. The large pool exported with spring thaw is enriched in Δ 14 C with respect to current-day atmospheric Δ 1 C-CO 2 values. A simple model predicts that ∼50% of DOC exported during the arctic spring thaw is 1-5 years old, ∼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.

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