A HIGHLY-RESOLVED, 900-YEAR NEW ENGLAND PALEOTEMPERATURE RECONSTRUCTION

Paleotemperature reconstructions are essential for distinguishing anthropogenic climate change from natural variability. Despite the social and economic prominence of the Northeastern USA, little is known about its long-term climate history. An emerging method in paleoclimatology is the use of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in lacustrine sediments, but their application is hindered by a limited understanding of their sources, seasonal production, and transport. We report seasonally resolved measurements of brGDGT production in catchment soils, within the water column, and in a sediment sequence from a small, deep inland lake in Maine, USA. BrGDGT distributions in the water column are distinct from catchment soils but similar to the distributions in lake sediments, suggesting that (1) brGDGTs are produced within the lake and (2) this in situ production dominates the downcore sedimentary signal. Seasonally, water depth-resolved measurements indicate that the dominant production of brGDGTs occurs in deep waters in late fall. We apply these observations to the interpretation of a 900-year-long brGDGT-based temperature reconstruction and find that it shows similar trends to a pollen record from the same site and to regional and global syntheses of terrestrial temperatures and hydroclimate over the last millennium. The record also contains higher-frequency variability, potentially attributed to the North Atlantic Oscillation and volcanic/solar activity. Furthermore, the record deviates from observed temperatures in the modern era, which may be related to human impact in the lake and catchment area. This is the first brGDGT- based multi-centennial temperature reconstruction from this region and contributes to our understanding of the production and fate of brGDGTs in lacustrine systems, and also extends the temperature history of the Northeastern USA beyond the brief period of instrumental measurements.