Arctic permafrost soils are estimated to hold approximately 1,440-1,600 petagrams (Pg) of organic carbon (OC), which is equivalent to more than twice the carbon content of the current atmospheric carbon (C). As this permafrost OC thaws into the contemporary C cycle, it can be decomposed by soil microorganisms and subsequently transported to aquatic ecosystems where further microbial degradation and photochemical processes can occur. Climate warming is predicted to accelerate the release of northern permafrost carbon with 24-69% of permafrost soils expected to thaw by 2100. As a result, around 5% of permafrost soil organic carbon has been estimated to being lost annually through hydrological pathways, thus leading significant positive feedback to global warming. However, the mechanisms of these carbon releases are not well-defined. Recent research highlights that shoulder seasons, particularly spring thaw and autumn freezing, are pivotal for the lateral movement of soil constituents into Arctic rivers. As soil active layers freezes and thaws during yearly shoulder seasons, their contribution to riverine export changes, yet no clear data exists as to indicate when a biogeochemical connection exists between permafrost soils and rivers. In this study, we used radiogenic strontium (Sr) isotopes to trace the sources of mineral nutrients in Panguigue creek, a first-order river, directly draining permafrost soils near Eight Mile Lake, Healy, Alaska, USA. The data reveal a distinct mixing pattern between surface and subsurface inputs from nearby permafrost soils, which gradually decreases during the Autumn shoulder season, transitioning to a baseflow likely originating from deeper groundwater. Conversely, this trend reverses during Spring thaw. These findings demonstrate a clear biogeochemical disconnection between permafrost soils and river systems throughout the winter, a pattern that can be effectively traced using Sr isotopes. This provides a timely approach to detect ongoing and future changes in biogeochemical connectivity between permafrost soils and rivers in a warming Arctic.
Roux et al. (Mon,) studied this question.