LATE HOLOCENE ORGANIC CARBON VARIABILITY IN CONROY LAKE, ME

Conroy Lake is a small meromictic lake in Monticello, ME that has proven in previous studies to have largely undisturbed sediments that preserve high-resolution records of environmental change in the region. The purpose of this study is to utilize the sediment record of Conroy Lake to reconstruct environmental variability in the lake during the Late Holocene, specifically with regard to organic carbon deposition. During the summer of 2009, a modified Kullenberg corer was used to obtain a sediment core from the deep hole of the lake (CL09KC1, l=239.7cm; z=35m). This core was split, and a multiproxy approach was used to interpret the environmental history of the lake. Loss on ignition analyses were used to obtain records of dry/wet bulk density, organic carbon (LOI at 550°C), and carbonate content (LOI at 1000°C). Magnetic susceptibility and image analysis (i.e. RGB) were used to corroborate with organic carbon variability. Loss on ignition results have shown that organic carbon percentages through the core ranged from 15% to 23% throughout the 240cm core, with a gradually increasing trend from 239 – 82cm (range 15.6% – 18.7%), increasing rapidly from 82 – 44cm (range 16.6% - 22.5%), followed by an decreasing trend for the remaining 44 - 0cm (range 22.5% – 17%). Image analysis displays high frequency variability interpreted to represent the laminated nature of sediment. An apparent negative correlation is noted between organic carbon and the green spectrum, suggesting that the RGB data may provide a higher-resolution record of organic matter deposition than the LOI can afford. Magnetic susceptibility results ranged from -.05 to 5.5 SI units, with noticeable peaks at or near vivianite layers. A slight positive correlation between magnetic susceptibility and organic content suggests a common control over magnetic input and organic matter input to the sediment. One possible explanation of this observation may involve the role of magnetotactic bacteria in the water column. Ongoing work is utilizing carbon and nitrogen stable isotope ratios, as well as carbon/nitrogen elemental ratios, to determine the origin of the organic matter preserved in the sediment. In addition, pending radiocarbon dates from terrestrial macrofossils are expected to provide age constraints to the variability observed.