VEGETATION AND FIRE: FEEDBACKS TO PLIOCENE ARCTIC CLIMATE
Climate, vegetation and fire regime were reconstructed at four early to mid-Pliocene localities in the Canadian High Arctic. These were then used to test the influence of climate-vegetation-fire feedbacks in the Arctic using climate simulations of the mid-Piacenzian Warm Period (MPWP). Climate reconstructions suggest mean annual temperatures (MAT) ~3°C with warmer winter temperatures contributing most to the higher MAT, and mean summer temperatures ~15°C. Reconstructed precipitation was variable between sites, but significantly higher than present. Atmospheric CO2 concentration averaged over the deposition of one key site, Beaver Pond, was 439 ± 47 ppm. Charcoal analyses indicate fires in the Arctic were widely distributed and likely frequently recurring during the Pliocene.
Climate simulations of the MPWP for northern high latitudes found ~3°C warming attributable to strong surface albedo feedback from higher boreal tree line. Consistent with paleorecords, simulations found elevated fire in the northern high latitudes under MPWP climate. The enhanced emissions of fire aerosols strongly altered the Arctic radiation budget, primarily through changing cloud microphysics. Model runs show enhanced cloud formation and a cloud cooling effect in the Arctic region during the warm months, with a mild warming effect in the sub-Arctic, likely related to the enhanced transport of black carbon, during cool months. Thus, our preliminary results suggest amplification of Arctic Pliocene surface temperature was strongly influenced by vegetation albedo and that fire emissions contributed to reduced seasonality of surface temperatures. Our results highlight the complexity of both direct and indirect climate-vegetation feedbacks in understanding the sensitivity of Arctic climate.