Abstract
Northern high-latitude rivers are major conduits of carbon from land to coastal seas and the Arctic Ocean. Arctic warming is promoting terrestrial permafrost thaw and shifting hydrologic flowpaths, leading to fluvial mobilization of ancient carbon stores. Here we describe 14C and 13C characteristics of dissolved organic carbon from fluvial networks across the Kolyma River Basin (Siberia), and isotopic changes during bioincubation experiments. Microbial communities utilized ancient carbon (11,300 to >50,000 14C years) in permafrost thaw waters and millennial-aged carbon (up to 10,000 14C years) across headwater streams. Microbial demand was supported by progressively younger (14C-enriched) carbon downstream through the network, with predominantly modern carbon pools subsidizing microorganisms in large rivers and main-stem waters. Permafrost acts as a significant and preferentially degradable source of bioavailable carbon in Arctic freshwaters, which is likely to increase as permafrost thaw intensifies causing positive climate feedbacks in response to on-going climate change.
Highlights
Northern high-latitude rivers are major conduits of carbon from land to coastal seas and the Arctic Ocean
Elucidating the fate of permafrost-derived dissolved OC (DOC) is crucial for establishing if on-going thaw is currently impacting Arctic fluvial networks and in determining whether its turnover may result in a positive carbon feedback to climate change[7]
Our findings indicate that terrestrial permafrost organic carbon (OC)
Summary
Climate-induced Arctic warming has led to increased soil temperatures, causing a succession of changes associated with permafrost degradation and widespread ground collapse or thermokarst, including deepening of the seasonally thawed surface active layer[1,2] and alterations to watershed hydrology[3,4]. These changes threaten to destabilize ancient (Pleistocene-aged) northern circumpolar terrestrial permafrost, which contains vast quantities of organic carbon (OC) comprising as much as 50% of global below-ground soil carbon stocks[5]. Thawing Yedomaderived OC is thought to be highly susceptible to biological degradation in fluvial networks[19,24], and has been proposed as a key feedback upon global climate[20]
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