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 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 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.

The optics of chromophoric dissolved organic matter (CDOM) in the Greenland Sea: An algorithm for differentiation between marine and terrestrially derived organic matter

“…Dissolved organic carbon studies in the Arctic Ocean and surrounding seas have concluded that despite the number of large rivers that supply the region, in situ production is the largest source of dissolved organic carbon (Wheeler et al 1997). Lignin tracer studies in Arctic water masses have shown that the dissolved organic carbon in the Greenland Sea gyre contains a low amount of lignin oxidation products and was enriched in 13 C (Opsahl et al 1999). From this it was deduced that terrestrial dissolved organic matter plays a relatively insignificant role in carbon cycling in the Greenland Sea.…”

“…This is one of the driving forces in the global thermohaline circulation, which has considerable control over Earth's climate (Broeker 1997) and the global carbon cycle. There is an ongoing debate about how much of the DOM pool has its origin from land and how much is produced autocthonously in the marine environment both in coastal areas and in the open oceans, like the Greenland Sea (Wheeler et al 1997;Opsahl et al 1999). The differentiation has previously been quantified by in-depth chemical analyses (e.g., Opsahl et al 1999).…”

“…There is an ongoing debate about how much of the DOM pool has its origin from land and how much is produced autocthonously in the marine environment both in coastal areas and in the open oceans, like the Greenland Sea (Wheeler et al 1997;Opsahl et al 1999). The differentiation has previously been quantified by in-depth chemical analyses (e.g., Opsahl et al 1999). The objective of the present study was to characterize the optical properties of CDOM in the Greenland Sea and to develop an algorithm that can distinguish between CDOM of marine and terrestrial origin, respectively.…”

Deciphering associations between dissolved organic molecules and bacterial communities in a pelagic marine system

“…From a molecular perspective, terrigenous components can be traced in aquatic systems by lignin-derived phenols (Opsahl and Benner, 1997;Hernes and Benner, 2006) and pyrogenic black carbon, a product of biomass burning (Dittmar and Paeng, 2009;Jaffé et al, 2013). Mobilized from soils and subsequently transported to the oceans by rivers, terrigenous DOM contributes between o1% of the dissolved organic carbon (DOC) in the Pacific and up to 33% of the DOC in the Arctic Ocean (Opsahl and Benner, 1997;Opsahl et al, 1999;Hernes and Benner, 2002). The decomposition pathways of terrigenous DOM in the ocean are still not fully constrained.…”

Diversity of Arctic pelagic <i>Bacteria</i> with an emphasis on photoheterotrophs: a review

“…The Arctic Ocean has the most extensive shelves of any ocean basin, covering about 50 % of its total area. Relative to other ocean basins, rivers play a disproportionately important role in the Arctic Ocean, which contains only about 1 % of the volume of the world's oceans yet receives approximately 10 % of the global terrigenous dissolved organic carbon (DOC) load (Aagaard et al, 1985;Opsahl et al, 1999). The DOC concentrations in coastal Arctic waters are twice higher than those in the Atlantic and Pacific oceans (Cauwet and Sidorov, 1996), highlighting the tight coupling of the Arctic Ocean with terrestrial catchments (Meon and Amon, 2004).…”