Major flux of terrigenous dissolved organic matter through the Arctic Ocean

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 (δ13C) to trace the high molecular weight fraction of terrigenous DOM in major water masses of the Arctic Ocean. Lignin oxidation products in ultrafiltered DOM (UDOM; >1,000 Da) from Arctic rivers were depleted in syringyl relative to vanillyI 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 major source of terrigenous UDOM to the Arctic Ocean. High concentrations of lignin oxidation products (83-320 ng L-1) and a depletion of 13C (δ13C = -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 (δ13C = -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 fraction, 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 Arctic is incorporated into North Atlantic Deep Water and distributed globally via deep thermohaline circulation.