High biolability of ancient permafrost carbon upon thaw

Abstract

Ongoing climate warming in the Arctic will thaw permafrost and remobilize substantial terrestrial organic carbon (OC) pools. Around a quarter of northern permafrost OC resides in Siberian Yedoma deposits, the oldest form of permafrost carbon. However, our understanding of the degradation and fate of this ancient OC in coastal and fluvial environments still remains rudimentary. Here, we show that ancient dissolved OC (DOC, >21,000 14C years), the oldest DOC ever reported, is mobilized in stream waters draining Yedoma outcrops. Furthermore, this DOC is highly biolabile: 34 ± 0.8% was lost during a 14 day incubation under dark, oxygenated conditions at ambient river temperatures. Mixtures of Yedoma stream DOC with mainstem river and ocean waters, mimicking in situ mixing processes, also showed high DOC losses (14 days; 17 ± 0.8% to 33 ± 1.0%). This suggests that this exceptionally old DOC is among the most biolabile DOC in any previously reported contemporary river or stream in the Arctic.

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

“…The narrow ratios, especially for the DOC fraction in the mudpool and transition zone, reflect the high mineralization rates of OM. DOC/DN-ratios in the thaw stream are extremely low (4) indicating strong mineralization, which is typical for aerobic streams draining permafrost areas Vonk et al, 2013). However, in contrast to C/Nratios, degradation is not reflected by δ 13 C-TOC and δ 13 C-DOC signatures, which did not change considerably in the disturbed zone.…”

“…It is of particular importance for the mobilization of OM, as it triggers its release by disturbing the frozen ground Bowden et al, 2008;Vonk et al, 2013). Thermokarst in upland, inland, sub-Arctic, and High Arctic permafrost regions, was intensively studied focusing on the lability of permafrost carbon, greenhouse gas emissions, release of nutrients (e.g., nitrogen, phosphorus, sulfur), and impacts on aquatic systems Cassidy et al, 2016;Frey et al, 2007;Turetsky et al, 2007).…”

Optical properties and bioavailability of dissolved organic matter along a flow-path continuum from soil pore waters to the Kolyma River mainstem, East Siberia

“…Recent research suggests that Arctic watersheds may increasingly augment the role of freshwater ecosystems in the global flux of terrestrial carbon to the atmosphere (Walter et al, 2006;Denfeld et al, 2013;Vonk et al, 2013;Hayes et al, 2014;Spencer et al, 2015) and ocean (Frey and Smith, 2005;Frey and McClelland, 2009;Schreiner et al, 2014;Tesi et al, 2014) as a result of climate warming and changing regional hydrology. Terrestrial sources of organic matter generally dominate the energy and carbon fluxes through stream, riverine, and estuarine ecosystems (Mulholland, 1997;Holmes et al, 2008), but the lability and composition of this carbon remain poorly characterized.…”

Spatial and temporal dynamics of biogeochemical processes in the Fraser River, Canada : a coupled organic-inorganic perspective

“…A stepwise freshet may lead to a more complex transition between base flow and freshet DOC. Furthermore, the lack of extensive permafrost in the Fraser basin excludes significant inputs from a potential pool of relatively degraded and aged soil DOC during late spring and summer months (Neff et al, 2006;Raymond et al, 2007;Wickland et al, 2007;O'Donnell et al, 2010), though this DOC is often found to be labile Vonk et al, 2013). In small streams, on the other hand, storm-driven discharge events are short-lived and may deliver fresh DOC to stream channels more efficiently than the long, relatively gradual rising limb of the spring freshet in the Fraser.…”