Eroding permafrost coasts release low amounts of dissolved organic carbon (DOC) from ground ice into the nearshore zone of the Arctic Ocean

Abstract

Ice-rich permafrost coasts in the Arctic are highly sensitive to climate warming and erode at a pace that exceeds the global average. Permafrost coasts deliver vast amounts of organic carbon into the nearshore zone of the Arctic Ocean. Numbers on flux exist for particulate organic carbon (POC) and total or soil organic carbon (TOC, SOC). However, they do not exist for dissolved organic carbon (DOC), which is known to be highly bioavailable. This study aims to estimate DOC stocks in coastal permafrost as well as the annual flux into the ocean. DOC concentrations in ground ice were analyzed along the ice-rich Yukon coast (YC) in the western Canadian Arctic. The annual DOC flux was estimated using available numbers for coast length, cliff height, annual erosion rate, and volumetric ice content in different stratigraphic horizons. Our results showed that DOC concentrations in ground ice range between 0.3 and 347.0 mg L À1 with an estimated stock of 13.6 ± 3.0 g m À3 along the YC. An annual DOC flux of 54.9 ± 0.9 Mg yr À1 was computed. These DOC fluxes are low compared to POC and SOC fluxes from coastal erosion or POC and DOC fluxes from Arctic rivers. We conclude that DOC fluxes from permafrost coasts play a secondary role in the Arctic carbon budget. However, this DOC is assumed to be highly bioavailable. We hypothesize that DOC from coastal erosion is important for ecosystems in the Arctic nearshore zones, particularly in summer when river discharge is low, and in areas where rivers are absent.

Transformation of terrestrial organic matter along thermokarst-affected permafrost coasts in the Arctic

“…A major process is the dilution and mixing with melted massive ice beds that underlie the RTS or ice wedges that intersect the permafrost exposures in the headwall. Both consist of nearly pure ice (~99%), contain very low amounts of OC, and take up~28% of the total sediment volume at our study site (Couture and Pollard, 2015;Fritz et al, 2015;Tanski et al, 2016). With initial slumping, the massive ice melts and dilutes OC derived from the active layer and thawed permafrost, partially explaining the loss of OC in the disturbed zone.…”

“…Leaching of POC is supported by the studies of Artinger et al (2000), who reported that DOC in the form of humic acids can originate from sediment OC, as well as by Dou et al (2008) who showed that different solutions have the potential to leach DOC from POC. Tanski et al (2016) showed a very strong correlation between sediment contents and DOC concentrations within massive ice, most likely due to prolonged contact of meltwater during segregation. Also, showed that DOC can be taken up by water flowing over thermokarst into the ocean.…”

“…For this approach, we assumed a non-conservative mixing from active layer, permafrost and massive ice sources, disregarding processes such as in situ production, flocculation and degradation of OM (Stedmon and Markager, 2005). In addition to known DOC concentrations of active layer and permafrost (this study), DOC concentrations for massive ice (n = 16) were taken from Tanski et al (2016). The volume of each feature in the headwall was calculated using its height.…”

Towards an assessment of riverine dissolved organic carbon in surface waters of the western Arctic Ocean based on remote sensing and biogeochemical modeling

“…This flux is 4 orders of magnitude lower than the tDOC supply from the Mackenzie River specified as boundary conditions in the model (2.54 Tg C yr −1 ). Similarly, tDOC eroded from permafrost stored in the North American shores accounts for only ∼ 0.5-1.6 × 10 −4 Tg C yr −1 (Tanski et al, 2016;Ping et al, 2011, using a DOC : particulate organic carbon, POC, ratio of 1 : 900 as in Tanski et al, 2016) to ∼ 2 × 10 −3 Tg C yr −1 (McGuire et al, 2009). With regard to these flux values, tDOC originating from both melted sea ice and eroded permafrost, not taken into account in the model, are hence not believed to explain the model-satellite discrepancies (Fig.…”

Contribution of Coastal Retrogressive Thaw Slumps to the Nearshore Organic Carbon budget along the Yukon Coast

“…We estimated mobilized SOC and DOC stocks and fluxes from RTSs based on the values provided in Couture (2010) and Tanski et al (2016). OC values were derived from in-situ measurements (Tanski et al, 2016;Couture, 2010) and were available for each coastal segment.…”