TOWARD A VARVE RECONSTRUCTION OF HOLOCENE CLIMATE AND ENVIRONMENTAL VARIABILITY FROM CONROY LAKE, ME

Lacustrine sediments can be exceptional archives of paleoclimatological and paleoenvironmental conditions, and recent approaches to studying climate parameters include providing absolute dates to varve chronologies. The two main research questions addressed for this project were 1.) What relationships do varve properties at Conroy Lake, ME have with modern climate conditions; and 2.) How do the thicknesses of sedimentary laminations preserved in Conroy Lake relate to instrumental data? It is hypothesized that a correlation will be found between climate instrumental records and varve characteristics (i.e. thicknesses).

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.