Impacts of Changes in Winter Precipitation on C Stocks and Fluxes in Arctic Tussock Tundra

The alteration of winter precipitation patterns in Arctic regions represents a potentially important climate forcing agent. However, climate/carbon (C) cycle forcing feedbacks from Arctic regions remain largely unresolved due to uncertainties in the strength, form (CO2 and CH4), direction and timing of ecosystem C fluxes under future precipitation scenarios. I combined C flux measurements and soil organic carbon (SOC) inventories with stable isotope and radioisotope methods in a multi-year, multi-level snow manipulation experiment in Arctic tundra to investigate: i) the rate at which permafrost C will become available for decomposition and will be released relative to ecosystem C inputs under future precipitation scenarios, ii) the magnitude, form and direction of derived climate/C-cycle feedbacks, and iii) the mechanisms driving long-term impacts of changes in winter precipitation on Arctic tundra C budget and fluxes. Results indicated the potential of Arctic tundra to become a transient C source through accelerated soil organic carbon (SOC) mineralization rates under future precipitation scenarios, but also to act as an additional long-term C sink with persistent increases in winter precipitation, as recently thawed SOC may remain largely immobilized over decades under thaw-induced near-water saturated conditions. This additional C sink however, may come at the cost of a substantial positive feedback on climate derived from increases in the net CH4 source strength of Arctic tundra, as warmer and wetter active layer stimulate CH4 production above CH4 oxidation further subsidized by enhanced plant-mediated transport associated to transitions in supported vegetation over the course of progressive permafrost degradation. Results suggested that much of current divergence among model predicted Arctic climate/C-cycle feedbacks may stem from inaccurate representations of the sensitivity of both physical and biological processes to changes in winter precipitation over time. Findings presented here indicate that projected precipitation scenarios will drive the Arctic tundra C budget and shape the radiative forcing from Arctic regions, critically affecting future climate.