Terrigenous dissolved organic matter in the Arctic Ocean and its transport to surface and deep waters of the North Atlantic

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Abstract

[1] Surface waters of the Arctic Ocean have the highest concentrations of dissolved organic carbon (DOC) and terrigenous dissolved organic matter (DOM) of all ocean basins. Concentrations of dissolved lignin phenols in polar surface waters are 7-fold to 16-fold higher than those in the Atlantic and Pacific oceans, and stable carbon isotopic compositions of DOM are depleted in 13C by 1–2‰ relative to those in the Atlantic and Pacific. The large contribution of terrigenous DOM from Arctic rivers is responsible for the elevated concentrations of DOC in polar surface waters. The distribution of terrigenous DOM in polar surface waters is very heterogeneous, but on average we estimate 14–24% of the DOC is of terrestrial origin. Stable nitrogen isotopic compositions were useful for distinguishing DOM of Pacific and Atlantic origins as well as terrigenous and marine origins. The size distribution and composition of lignin phenols provide some evidence of photochemical transformations of terrigenous DOM, but it appears this process is not extensive in polar surface waters. The extent to which terrigenous DOM is removed from the Arctic Ocean by microbial degradation is less clear and warrants further study. Physical transport of terrigenous DOC to the North Atlantic is a major mechanism for its removal from the Arctic. The East Greenland Current alone exports 4.4–6.6 Tg of terrigenous DOC annually to the North Atlantic. Terrigenous DOC of Arctic origin was identified for the first time in components of North Atlantic Deep Water. Preliminary estimates indicate that ∼1 Tg of terrigenous DOC is exported from the Arctic in Denmark Strait Overflow Water with an additional ∼0.7 Tg in Classical Labrador Sea Water. Together, these exports compose approximately 25–33% of the terrigenous DOC discharged annually to the Arctic via rivers.

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