Production of fluorescent dissolved organic matter in Arctic Ocean sediments

Abstract

Little is known about the production of fluorescent dissolved organic matter (FDOM) in the anoxic oceanic sediments. In this study, sediment pore waters were sampled from four different sites in the Chukchi-East Siberian Seas area to examine the bulk dissolved organic carbon (DOC) and their optical properties. The production of FDOM, coupled with the increase of nutrients, was observed above the sulfate-methane-transition-zone (SMTZ). The presence of FDOM was concurrent with sulfate reduction and increased alkalinity (R² > 0.96, p < 0.0001), suggesting a link to organic matter degradation. This inference was supported by the positive correlation (R² > 0.95, p < 0.0001) between the net production of FDOM and the modeled degradation rates of particulate organic carbon sulfate reduction. The production of FDOM was more pronounced in a shallow shelf site S1 with a total net production ranging from 17.9 to 62.3 RU for different FDOM components above the SMTZ depth of ca. 4.1 mbsf, which presumably underwent more accumulation of particulate organic matter than the other three deeper sites. The sediments were generally found to be the sources of CDOM and FDOM to the overlying water column, unearthing a channel of generally bio-refractory and pre-aged DOM to the oceans.

Figure 1. Sampling sites for sediment pore waters in the Chukchi Shelf (JPC-1a or S1), Northwind Basin (JPC-2 or S2), East Siberian continental slope (JPC-3 or S3), and Chukchi Basin (JPC-4 or S4) of the Arctic Ocean.

The sea ice concentration data from August 27^th to September 5^th, 2015 were obtained from http://www.meereisportal.de (grant: REKLIM-2013-04) (Refer to Spreen et al.70). The map was created by using Ocean Data View.

Figure 2. Downcore profiles of the sediment pore water in the Arctic (BS: Bering Strait).

Figure 3. Contour plots of four identified EEM-PARAFAC components (upper panel) and downcore profile of the absolute abundance (RU, lower panel).

Figure 4

Inverse correlation between EEM-PARAFAC components and sulfate (a) concurrent with positive correlation with alkalinity (b) and ammonium (c) in Arctic pore waters. Positive correlations between net FDOM production and modeled POCSR reaction rates (d). The inset in (d) indicates the correlations for the clustered data.