Evidence for terrigenous dissolved organic nitrogen in the Arctic deep sea

Abstract

To trace the fate of terrigenous dissolved organic nitrogen (DON) in the Arctic Ocean, principal-components analyses (PCA) was used on a data set of 13 amino acids released via hydrolyses from a total of 110 water samples from Russian rivers, adjacent near-shore locations, and the Laptev Sea. The first component of the PCA distinguished significantly between terrigenous DON from the rivers (1.2 Ϯ 0.1) and marine-derived DON in the deep central Arctic Ocean (Ϫ1.1 Ϯ 0.2). The significance of this distinction was validated with amino acid data from seawater and river samples from other regions. The second PCA component correlated significantly with the proportion of D-alanine, a tracer for microbial degradation. The percentage of terrigenous DON in the Arctic Ocean was assessed from the first PCA component. The model was calibrated using data from the rivers (100% terrigenous) and the deep central Arctic Ocean (ϳ0% terrigenous) as end members. Terrigenous DON accounted for 28 Ϯ 13% of the total DON on the Laptev Sea shelf, which is in good agreement with independent, lignin-based estimates. High proportions of terrigenous DON (up to 100%) were calculated for the continental slope down to 2,000 m depth and are probably due to downward convection of brine-enriched shelf waters. The model presented here provides the first direct evidence of terrigenous DON in the deep sea. The model may be directly applied to trace the fate of terrigenous DON in other terrestrially dominated marine environments.

Tracing the transport of colored dissolved organic matter in water masses of the Southern Beaufort Sea: relationship with hydrographic characteristics

“…This phenomenon was demonstrated in laboratory experiments (Amon, 2004), and observed over Russian shelves in autumn as a significant mechanism for the export of terrigenous dissolved organic nitrogen (Dittmar, 2004). The similar positive correlation between a CDOM (440) and salinity was also found in the PSW.…”

Absorption and fluorescence properties of chromophoric dissolved organic matter of the eastern Bering Sea in the summer with special reference to the influence of a cold pool

“…10f and 11f) corresponded to elevated salinity in the cold pool, low S and slightly elevated a g 355 (Figs. 5e, f and 6e, f) likely the effects of brine rejection during ice formation in winter and the subsequent remineralization of the organic matter in these waters (Dittmar, 2004;Granskog et al, 2012;Matsuoka et al, 2012). Elevated negative AOUs (Figs.…”

Influence of terrestrial organic matter in marine food webs of the Beaufort Sea shelf and slope

“…The potential of terrigenous carbon to influence food webs on the outer Beaufort shelf and slope is high: satellite images have captured the sediment plume exiting the Mackenzie River extending more than 400 km off-shelf (Macdonald et al 1999) and large fluxes of terrestrially derived carbon have been recorded in the water column over the 500 m isobath of the slope (Forest et al 2007). The substantial mobility of Mackenzie-derived OM terr across the Beaufort shelf and into the Canada Basin has been explored thoroughly in sedimentary markers (Goñi et al 2013), yet consideration of how this OM terr influences the biota of offshore and deep-sea communities in the Arctic Ocean has been inadequate, especially given the potential of terrestrially derived food subsidies for deep-sea consumers elsewhere (Dittmar 2004). OM terr from high-latitude rivers enters the Arctic Ocean in 2 forms: the majority as dissolved organic matter (DOM) and the remainder as particulate organic matter (POM) (Macdonald et al 1998).…”

“…Furthermore, considering the high seasonality of both particulate (Forest et al 2015) and dissolved , Raymond et al 2007, Holmes et al 2012) fractions of OM terr input from rivers into the Beaufort Sea, the late summer sampling dates of this study mean that our results are likely an underestimate of the potential contributions of terrestrial organic matter to marine food webs in these areas. The transport and advection of OM terr from the Mackenzie River down the Beaufort slope (Goñi et al 2000) may be facilitated by the morphology of the Beaufort Sea's relatively narrow shelf and steep slope compared to the broad shelves of the Eurasian Arctic, frequent upwelling and resuspension processes (Forest et al 2013), and vertical convection of brine-enriched waters from sea ice melt (Dittmar 2004). The equivalent lengths of shelf and slope food webs in the regions near the Mackenzie River indicate that the trophic effect of OM terr appears to be equally important on the eastern Beaufort shelf and slope regardless of water depth or the differing benthic community composition (Nephin et al 2014).…”