TOWARD A VARVE RECONSTRUCTION OF HOLOCENE CLIMATE AND ENVIRONMENTAL VARIABILITY FROM CONROY LAKE, ME
Previous data from a 2009 piston core (Morissette et al. 2010) showed shifts in multiple proxies below and above 40 cm (mean below: mean above): volume magnetic susceptibility (1.3x10-5SI: 2.8x10-5SI), CaCO3 (16%: 10%), ∑RGB (169: 159), δ13C (-33.9‰: -23.6‰), and a stepwise shift of δ15N. Previous pollen analyses done on Conroy Lake (Gajewski, 1987) show increases of the Ambrosia and Rumex horizons at ~1830 AD, which can be attributed to the settlement and town incorporation of Monticello in 1846 AD. Historical accounts show that early settlers utilized the land for farming and logging. The shifts in proxies at 40cm are hypothesized to be due to land use change associated with the pollen shifts previously identified. Varve counts from this core show a statistically significant increase in lamination thicknesses between pre-settlement (mean= 0.045 cm) and post appearance (mean= 0.162 cm) (t-test= -11.4; p<<0.0001). This shift is hypothesized to also be due to changes ~40cm; however, due to core deformation, a significant stratigraphic interval (30.9cm-60.5cm) could not be counted previously. Ongoing analyses are bridging stratigraphic gaps in the record and will likely yield climatic significance.
Continuous petrographic thin sections were made from three 2010 freeze cores and lamination counts are on-going. The freeze cores preserve the upper flocculent sediments in situ, and help to increase varve resolution as compared to piston cores.