PRELIMINARY ANALYSIS OF SUBFOSSIL MIDGE REMAINS (DIPTERA: CHIRONOMIDAE) IN SEDIMENTS FROM BIG PEA PORRIDGE POND, EAST-CENTRAL NEW HAMPSHIRE

In March, 2008, a 10.2 meter sediment core was extracted through the ice from the deepest spot (14.6 m) in Big Pea Porridge Pond, a 48 hectare lake in Carroll County New Hampshire, just southeast of the White Mountains. An AMS radiocarbon age of 14,010±70 cal yr BP (at 9.35 m) lies 10-30 cm above the no-organic/organic-matter transition (interpreted as the onset of ice-free conditions at this site). Here we report preliminary results from chironomid (midge) analyses from the late glacial and early Holocene sediments from this core.

Community assemblages of midge larvae from various depths in sediment cores serve as quantitative proxy indicators of past temperatures, through transfer-function modeling (Walker et al., 1997). Samples (3 cc each) for analysis of larval midge communities were taken from 5.85 – 10.15 m sediment depth at 10 cm intervals. Higher resolution sampling (2 cm intervals) was used in core regions of potentially greater value for climate reconstructions (e.g., based on LOI analysis or on visual changes in sediment characteristics). We followed standard procedures (Brooks et al., 2007) in the extraction and identification of midge larvae remains.

Work to date suggests mid-summer, surface-water temperatures decreased about 5oC at the Allerød-Younger Dryas transition, and increased by 8oC between the Younger Dryas and the subsequent Holocene period. We plan to use other independent proxies derived from this core (i.e., data from LOI and pollen analyses) to substantiate and assess the applicability of the chironomid-temperature inference model to lakes both deeper and especially larger in surface area than those used in its original calibration dataset.