AN ORGANIC MOLECULAR RECORD OF POST-GLACIAL CLIMATE AND FIRE OCCURRENCE IN A SOUTHERN NEW ENGLAND WETLAND CORE

Southern New England has experienced considerable changes in climate and vegetation since the end of the last glacial period. These changes have produced a shift in the distribution of fire-prone plant types and the frequency of fires; however, there still remains uncertainty as to how climate change and/or humans impacted the history of fires in this region. We collected a ~6 meter core from a paleo-channel wetland at the confluence of the Ten Mile River and Housatonic River in western Connecticut to develop organic molecular records of long-term changes in climate, vegetation, and fluvial history. ¹⁴C dates from this core show a nearly continuous record of deposition for the past 12,500 years. Sediments transition from lacustrine units with abundant gastropods at the base of the core (>12,000 ka) to prolonged deposition of peat, followed by a shift to a shallow marshland subject to continual infilling from upslope land areas.

We extracted and analyzed polycyclic aromatic hydrocarbons and plant waxes preserved in the core to evaluate temporal changes to environmental conditions. Polycyclic aromatic hydrocarbons (PAHs) are composed of multiple benzene rings produced during combustion. PAHs provide a potential chemical marker of fire history within a sedimentary sequence. Plant waxes are produced by vegetation to provide protection from predation and to minimize water and/or nutrient loss and are preserved in sediments over geologic time. The hydrogen and carbon isotope records of these plant waxes are influenced by precipitation isotopes and plant-specific responses to changing environmental conditions. The distribution of high molecular weight PAHs in our sedimentary core shows a maximum between 11,500 and ~9000 years ago with progressive decrease over time, punctuated by several spikes in concentration. This time interval coincides with decreased n-alkane average chain length (ACL), which can be interpreted to reflect cooler conditions, as well as high carbon preference index (CPI). These data will be paired with C and H isotopes of n-alkanes to evaluate links between PAH abundance and environmental conditions. Peak PAH abundances are contemporaneous with peak charcoal abundances in other New England sites and suggest potentially higher fire occurrence in the early post-glacial.