LAGGED LAKE-TEMPERATURE RESPONSES TO DEGLACIAL AND EARLY HOLOCENE ENVIRONMENTAL CHANGES AT BIG PEA PORRIDGE POND, MADISON, NEW HAMPSHIRE

Big Pea Porridge Pond (BPPP), a 48-ha lake situated at 197 m asl (43.941 N, 71.188 W), yielded a 10-meter sediment core from about 14-m water depth in early 2008. Two AMS 14C ages from the lower-most 4.5 meters reveal a late-glacial to early-Holocene sedimentation rate of 0.08 cm/yr. During this interval, organic content (from loss-on-ignition) increased by an order of magnitude while mid-summer lake surface temperatures (from chironomid models) increased by over 10°C. The transition was apparently rapid but asynchronous, with different aspects of the lake environment experiencing high rates of change at different times. We compare these findings with the regional record, especially with respect to the Younger Dryas, 9.2 ka and 8.2 ka climate oscillations. In BPPP, the lake productivity increased rapidly within a 50-cm interval, just after 13,500 cal yr BP, while lake temperatures increased after 12,000 cal yr BP. This apparent lag in lake temperature response may result from localized sources of glacial meltwater, from cold groundwater influencing the lake or from modeling constraints within the chironomid data set. The Younger Dryas cold interval appears to be represented merely as a weak dip in the LOI data and is not associated with visible variations in the core sediments. A later, more obvious feature in the core is a pair of 3-cm thick, finely laminated, yellowish bands, associated with small decreases in LOI at about 9660 cal yr BP. ICP geochemical analyses on these bands is underway.