Late Quaternary paleoclimatic reconstructions for interior Alaska based onpaleolake-level data and hydrologic models

Hydrologic models are developed for two lakes in interior Alaska to determi ne quantitative estimates of precipitation over the past 12,500 yrs. Lake l evels were reconstructed from core transects for these basins, which probab ly formed prior to the late Wisconsin. Lake sediment cores indicate that th ese lakes were shallow prior to 12,500 yr B.P. and increased in level with some fluctuation until they reached their modern levels 4,000-8,000 yr B.P. Evaporation (E), evapotranspiration (ET), and precipitation (P) were adjus ted in a water-balance model to determine solutions that would maintain the lakes at reconstructed levels at key times in the past (12,500, 9,000 and 6,000 yr B.P.). Similar paleoclimatic solutions can be obtained for both ba sins for these times. Results indicate that P was 35-75% less than modern a t 12,500 yr B.P., 25-45% less than modern at 9,000 yr B.P. and 10-20% less than modern at 6,000 yr B.P. Estimates for E and ET in the past were based on modern studies of vegetation types indicated by fossil pollen assemblage s. Although interior Alaska is predominantly forested at the present, polle n analyses indicate tundra vegetation prior to about 12,000 yr B.P. The lak es show differing sensitivities to changing hydrologic parameters; sensitiv ity depends on the ratio of lake area (AL) to drainage basin (DA) size. Thi s ratio also changed over time as lake level and lake area increased. Small er AL to DA ratios make a lake more sensitive to ET, if all other factors a re constant.