Limnol. Oceanogr., 44(8), 1999, 2017–2023

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 ultrafiltered DOM (UDOM; .1,000 Da) from Arctic rivers were depleted in syringyl relative to vanillyl phenols (S/V 5 0.3– 0.5) compared to UDOM in temperate and tropical rivers (S/ V 5 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 L21) and a depletion of 13C (d13C 5 223.0 to 221.9) 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 L21) and was enriched in 13C (d13C 5 221.0 to 220.8). 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 Arcticderived DOM is compositionally similar to the UDOM fraction, we estimate that 12–41% of terrigenous DOM (2.9–10.3 Tg C yr21) 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. The Arctic Ocean receives ;10% of the freshwater and dissolved organic matter (DOM) supplied globally by rivers (Aagaard and Carmack 1989; Gordeev et al. 1996; Macdonald et al. 1998; Anderson et al. 1998), yet it represents only 1% of the global ocean volume (Menard and Smith 1966). Thus, the flux of terrigenous DOM to the Arctic Ocean is much greater on a volume basis than corresponding fluxes to the Atlantic, Indian, and Pacific oceans. Furthermore, the supply of terrigenous DOM to the Arctic Ocean may be