This study contributes to the long-term perspective on natural climate variability that is needed to understand historically unprecedented changes now occurring in the Arctic. Rapid changes in the Arctic climate system that occurred in the relatively recent past can be compared with the output of climate models to improve the understanding of the processes responsible for nonlinear system change. This study focuses on the transition between the Holocene thermal maximum (HTM) and the onset of Neoglaciation, and on the step-like changes that occurred subsequently during the late Holocene.
During the HTM, summer sea-ice cover over the Arctic Ocean was likely the smallest of the present interglacial period, and therefore affords an opportunity to investigate a period of warmth similar to what is projected during the coming century. The millennial-scale cooling trend that followed the HTM coincides with the decrease in Northern Hemisphere summer insolation driven by slow changes in Earth’s orbit. Despite the nearly linear forcing, the transition from the HTM to the Little Ice Age (1500-1900 AD) was neither gradual nor uniform. To understand how feedbacks result in rapid changes, we are assembling a geographically distributed network of proxy climate records to study the spatial and temporal patterns of change, and to quantify the magnitude of change during these transitions.
This collaborative project focuses on lacustrine sediments for high-resolution proxy climate records of the past 8000 years. Lakes are the most widely distributed sources of proxy climate records that consistently extend through the post-glacial interval. The study sites include two focus regions: eastern Beringia and the NW Atlantic.