Ancient CO2 Emissions from the High Arctic-Svalbard in Winter: Responses to Deeper Winter Snow in a Permafrost Dominated Landscape

Abstract:

High Arctic tundra landscapes are underlain by globally significant pools of ancient carbon (C) in the form of permafrost that today is beginning to thaw, as evidenced by deepening active layers. The degree to which this ancient C is diffusing as CO₂ into the modern atmosphere during winter is a key climate feedback uncertainty today. Quantifying the magnitude and patterns of these ancient CO₂ emission are critical as we begin to fully understand how, as a consequences of climate changes, these emissions might increase even further, accelerating the rise in atmospheric CO₂ concentrations and thus global temperatures. In order to do so, we measured fall and winter ecosystem respiration, soil pore space CO₂ concentrations and bulk soil C at different depths along with their radiocarbon (¹⁴C) contents under ambient and experimentally manipulated deeper snow conditions in mesic tundra of Svalbard, in Adventdalen. Abiotic parameters such as air and soil temperature and water content were continuously monitored for the entire study period.

Our findings reveal that: a) soils in these landscapes have permafrost that is up to 25,000 years old at 1.5 m depth; b) in late fall, once plants are dormant, CO₂ emissions are dominated by ancient C with older values under deeper snow conditions c) that respiration rates are higher in winter under deeper snow, due to soils being up to 8^oC warmer than ambient conditions; d) winter emissions of respired CO₂ are dominated by ancient C at all times with effect of snow depth. For the first time our results show that ancient C, previously disconnected from the C cycle, is continuously emitted into the atmosphere during the long High Arctic winter. This new biosphere-atmosphere C cycle interaction may accelerate over time as permafrost active layers continue to deepen, increasing the CO₂ concentration of the atmosphere, further distributing global temperatures and leading to subsequent changes in the Arctic and global climates. Our findings are integrated into a synthetic High Arctic annual cycle model of the ages and rates of CO₂ emissions from the northerly most landscapes on earth.