Major flux of terrigenous dissolved organic matter through the Arctic Ocean

Opsahl, Stephen, Ronald Benner, Ranier M. W. Amon

Limnol. Oceanogr., 44(8), 1999, 2017-2023 | DOI: 10.4319/lo.1999.44.8.2017

ABSTRACT: High-latitude rivers supply the Arctic Ocean with a disproportionately large share of global riverine discharge and terrigenous dissolved organic matter (DOM). We used the abundance of lignin, a macromolecule unique to vascular plants, and stable carbon isotope ratios ( d13C) to trace the high molecular weight fraction of terrigenous DOM in major water masses of the Arctic Ocean. Lignin oxidation products in ul-trafiltered DOM (UDOM; >1,000 Da) from Arctic rivers were depleted in syringyl relative to vanillyl phenols (S/V = 0.3- 0.5) compared to UDOM in temperate and tropical rivers (S/ V = 0.5-1.2), indicating that gymnosperm vegetation is a ma-jor source of terrigenous UDOM to the Arctic Ocean. High concentrations of lignin oxidation products (83-320 ng L-1 )\ and a depletion of 13C (d13C = -23.0 to -21.9) in UDOM throughout the surface Arctic Ocean indicate that terrigenous UDOM accounts for a much greater fraction of the UDOM in the surface Arctic (5-33%) than in the Pacific and Atlantic oceans (0.7-2.4%). In contrast, UDOM in deep water from the Arctic Ocean as well as waters from throughout the Greenland Gyre had relatively low concentrations of lignin oxidation products (24-45 ng L-1 ) and was enriched in 13C (d13C = -21.0 to -20.8). Terrigenous UDOM has a relatively short residence (~1-6 yr) in surface polar waters prior to export to the north Atlantic Ocean. Assuming that the bulk of Arctic-derived DOM is compositionally similar to the UDOM frac-tion, we estimate that 12-41% of terrigenous DOM (2.9-10.3 Tg C yr-1 ) discharged by rivers to the Arctic Ocean is exported to the North Atlantic via surface waters of the East Greenland Current. It appears very little terrigenous DOM from the Arc-tic is incorporated into North Atlantic Deep Water and distrib-uted globally via deep thermohaline circulation.

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