Combining lake core records with the limnologic model DYRESM-CAEDYM to evaluate lake response during the Little Ice Age and Medieval Climate Anomaly

Abstract

The Little Ice Age and Medieval Climate Anomaly are two climatic intervals within the last 2000 years that had distinctive conditions in many North American paleoclimate reconstructions. During each of these intervals, the Crevice Lake, Montana paleorecord shows distinctive limnological characteristics inferred from fossil diatoms that reflect changes in temperature seasonality and lake thermal structure. A thermodynamic-ecological model, DYRESM-CAEDYM, was used to estimate climatic conditions during these time intervals and to explore the potential for linking paleo-records with lake models to evaluate the dynamic interactions of environmental variables in influencing diatom populations over time. The model effectively simulates the timing and distribution of Stephanodiscus and Cyclotella populations evident in the modern Crevice Lake observational data. In sensitivity tests altering multiple weather inputs had a greater effect on lake temperature isotherm patterns compared with changing only single variables, which suggests the interactive effect of multiple climate variables in affecting lake thermal structure. The model simulations show the importance of the rate of climate change in affecting lake thermal structure and diatom community structure, particularly during spring and early summer. The model also provides constraints on the range of changes in solar radiation, temperature, and wind speeds that may have produced the diatom communities characteristic of the Medieval Climate Anomaly, Little Ice Age, and contemporary times.