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

TLDR

The study measured DOC export and Δ14C age from the Yenisey, Lena, Ob', Mackenzie, and Yukon rivers (2004–2005) and modeled that roughly half of spring‑thaw export is 1–5 yr old, with the remainder older, indicating a large flux of young, semilabile DOC during the melt period. DOC concentrations rise with discharge, concentrating ~60% of the annual export within two months after spring ice melt, yielding a total annual flux of ~16 Tg and an Arctic input of 25–36 Tg—5–20% higher than prior estimates and 2.5× that of comparable temperate rivers—while Δ14C data reveal a hydrologically linked age distribution, with a slightly depleted base‑flow pool and a spring‑thaw pool enriched relative to contemporary atmospheric Δ14C.

Abstract

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× 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 14 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.