Impacts of wildfire on biogeochemistry and energy balance of the North Slope of Alaska

Wildfires are historically rare and novel occurrences in Northern Alaska, but have increased in frequency, severity, and area burned within the past decade. One fire, the Anaktuvuk River (AR) Burn, consumed >1000 km2 on the North Slope of Alaska in 2007, releasing ~ 2M tonnes of C directly to the atmosphere and more than doubling the area burned in this region since 1950. In the three years since the AR Burn the burned lands have continued to release C to the atmosphere and C, N, and P to streams although at decreasing rates due to regrowth of the burned vegetation. Surface energy balance was also changed by the fire, lowering albedo and increasing soil heat flux; this has led to greater annual depth of soil thaw and, in several instances, to local thermokarst and other surface failures. As a result of these changes the AR Burn has become a “hot spot” of element turnover and surface energy exchange on the North Slope of Alaska, with an impact on the element and energy exchange of the entire region that is disproportionate to its 0.5% of the area of the North Slope. These biogeochemical changes following wildfire are much larger and more rapid than expected in response to relatively slow, uniform increases in temperature as the regional climate warms and suggest that further increases in arctic wildfire will lead to a new dynamics of interaction between the arctic land surface and the atmosphere.