Eight Mile Lake Research Watershed, Thaw Gradient: Geochemistry of soil pore waters sampled in May 2018 (0 - 20 cm depth) and August 2019 (0-120 cm depth) at Gradient site, 2018-2019

In this larger study, we are asking the question: Is old carbon that comprises the bulk of the soil organic matter pool released in response to thawing of permafrost? We are answering this question by using a combination of field and laboratory experiments to measure radiocarbon isotope ratios in soil organic matter, soil respiration, and dissolved organic carbon, in tundra ecosystems. The objective of these proposed measurements is to develop a mechanistic understanding of the SOM sources contributing to C losses following permafrost thawing. We are making these measurements at an established tundra field site near Healy, Alaska in the foothills of the Alaska Range. Field measurements center on a natural experiment where permafrost has been observed to warm and thaw over the past several decades. This area represents a gradient of sites each with a different degree of change due to permafrost thawing. As such, this area is unique for addressing questions at the time and spatial scales relevant for change in arctic ecosystems. Analysing the geochemistry of soil pore waters at Gradient site complements the overarching aim of this study. The dissolved organic carbon and mineral elements are determined in soil pore waters from sites of minimum, moderate and extensive permafrost degradation during the spring thaw (0-20 cm depth) in May 2018 and during late summer (0-120 cm depth) in August 2019. Soil pore waters were collected from sites approximately 15 m uphill of the highly monitored Gradient sites. The geochemical data was used to assess the mineral element-organic carbon associations in soil pore waters between contrasting sites of permafrost degradation.