Rivers across the Siberian Arctic unearth the patterns of carbon release from thawing permafrost

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Wild, Birgit, Andersson, August, Bröder, Lisa, Vonk, Jorien, Hugelius, Gustaf, McClelland, James W., Song, Wenjun, Raymond, Peter A., Gustafsson, Örjan
• Format: Text
• Language: English
• Published: National Academy of Sciences 2019
• Subjects: Physical Sciences; Arctic; Kolyma; Yenisey; Global warming; permafrost; Thermokarst; Siberia
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6535028/; http://www.ncbi.nlm.nih.gov/pubmed/31061130; https://doi.org/10.1073/pnas.1811797116

Climate warming is expected to mobilize northern permafrost and peat organic carbon (PP-C), yet magnitudes and system specifics of even current releases are poorly constrained. While part of the PP-C will degrade at point of thaw to CO(2) and CH(4) to directly amplify global warming, another part will enter the fluvial network, potentially providing a window to observe large-scale PP-C remobilization patterns. Here, we employ a decade-long, high-temporal resolution record of (14)C in dissolved and particulate organic carbon (DOC and POC, respectively) to deconvolute PP-C release in the large drainage basins of rivers across Siberia: Ob, Yenisey, Lena, and Kolyma. The (14)C-constrained estimate of export specifically from PP-C corresponds to only 17 ± 8% of total fluvial organic carbon and serves as a benchmark for monitoring changes to fluvial PP-C remobilization in a warming Arctic. Whereas DOC was dominated by recent organic carbon and poorly traced PP-C (12 ± 8%), POC carried a much stronger signature of PP-C (63 ± 10%) and represents the best window to detect spatial and temporal dynamics of PP-C release. Distinct seasonal patterns suggest that while DOC primarily stems from gradual leaching of surface soils, POC reflects abrupt collapse of deeper deposits. Higher dissolved PP-C export by Ob and Yenisey aligns with discontinuous permafrost that facilitates leaching, whereas higher particulate PP-C export by Lena and Kolyma likely echoes the thermokarst-induced collapse of Pleistocene deposits. Quantitative (14)C-based fingerprinting of fluvial organic carbon thus provides an opportunity to elucidate large-scale dynamics of PP-C remobilization in response to Arctic warming.