Detecting the Signature of Permafrost Thaw in Arctic Rivers, Siberia, Russia 2012 - 2014

• Main Author: Spencer, Robert
• Format: Dataset
• Language: English
• Published: Arctic Data Center 2017
• Subjects: Carbon, Rivers, Arctic; Arctic; Kolyma; Climate change; Detecting the Signature of Permafrost Thaw in Arctic Rivers; Global warming; permafrost; Siberia
• Online Access: https://dx.doi.org/10.18739/a2j960930; https://arcticdata.io/catalog/#view/doi:10.18739/A2J960930

Permafrost soils in the Arctic contain vast quantities of ancient organic matter. If thawed, the decomposition of this aged organic carbon will release the greenhouse gases CO2 and CH4 to the atmosphere, fueling a positive feedback between permafrost thaw and global warming. The term “carbon bomb” has been used to describe this process, primarily in the popular press but also within journals such as Nature and Science. Numerous studies have shown extensive permafrost thaw and degradation in the Arctic, but dissolved organic carbon (DOC) exported from the mouths of large Arctic rivers – which are expected to integrate processes and changes occurring through their watersheds – has been shown to be predominantly modern. This raises the question, where is the ancient organic carbon that is mobilized from permafrost degradation and the deepening of the active layer? Research supported by this grant highlighted fundamental new insights into the fate of permafrost thaw derived DOC in Arctic inland waters. A major focus was placed on the period of maximum permafrost thaw in the fall at the time of deepest active layer depth. Four full field campaigns were undertaken examining the field sites in the Kolyma watershed (Siberia). Our results highlighted mobilization of ancient (>20,000 ybp) DOC in streams draining from permafrost landscapes. We showed for the first time direct utilization of ancient (>20,000 ybp) permafrost thaw DOC in stream networks along with concurrent shifts in the molecular structure of the dissolved organic matter (DOM) resulting in the remaining DOM looking similar to modern sources of DOM from terrestrial inputs in the Kolyma Basin. Additionally, microbial demand was supported by progressively younger carbon downstream through the Kolyma fluvial network, with predominantly modern carbon pools subsidizing microorganisms in large rivers and main-stem waters. Our results add significant weight to the argument that any permafrost inputs will be rapidly degraded in small thaw streams and the loss of molecular signature along with high biolability of permafrost derived DOC makes the permafrost inputs difficult to study using samples from major rivers. Permafrost was shown to act 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.