PALEOCLIMATE RECONSTRUCTION USING PHYSICAL SEDIMENTOLOGY AND ORGANIC MATTER BIOGEOCHEMISTRY OF VARVED SEDIMENTS, BASIN POND, FAYETTE, ME

Late Quaternary records of environmental change in Northern New England reveal a complex climatic history. A great deal of focus has been given to the existence, timing, and magnitude of late glacial and Holocene climatic intervals, including the Younger Dryas, Postglacial Hypsithermal, Little Ice Age, and 20th Century Warm Period, in proxy records. However, climate reconstructions to date have mainly relied on radiocarbon dating and often, chronologies are loosely constrained. The need for accurate, long-term and high-resolution proxy records is evident.

Basin Pond is a small, 34-acre, meromictic pond in Fayette, Maine. Previous studies utilized the pond’s laminated sediments for late Holocene reconstructions. In this study, sediment cores as long as 2.8 meters were obtained to extend the Basin Pond sedimentary record to late glacial times. Varved gyttja persists for much, or all, of the Holocene before grading down-core to minerogenic, massive late glacial sediments. The regular deposition of light-dark biogenic couplets suggests that the laminae are annual, or varved. Physical sedimentology and organic matter biogeochemistry were used to reconstruct a continuous, high-resolution paleoenvironmental record from the last ~12ka. Varve counts were performed on thin sections of impregnated sediment to act as a discrete stratigraphic chronometer for the length of the varve record. Radiocarbon analysis of terrestrial macrofossils was employed to re-affirm the annual nature of the varved sediments. Biogeochemical analysis of organic matter was performed on decalcified sediment samples every 3 cm down-core.

Percent LOI and organic carbon values show minimum rates of organic matter deposition in late glacial sediments, rising to maximum sustained rates in the early to mid Holocene. Sedimentological evidence for a late glacial climate reversal may exist in a zone of relatively coarse, organic-poor sediment that occurs within a zone of generally increasing organic matter content up-core. Similar horizons have been observed in late glacial sediments from Maine and Atlantic Canada associated with the Younger Dryas cooling event. Low C/N ratios (11-13) and δ¹³C values ranging from –33 to –30 per mil suggest organic matter production in the basin is dominated by C₃ algae with some input from terrestrial C₃ vegetation.