Broad climate variability based on seismic stratigraphy and sediment cores in Willsboro Bay, Lake Champlain.

Abstract

Seismic profiles and sediment cores provide researchers with abundant information about the Earth's climate history. Seismic profiling generates subsurface images of stratigraphy that reveal large-scale changes in sediment type as well as events in depositional history. Sediment cores can be analyzed with various proxies in order to determine the sedimentological history of a particular region. This study focuses on correlating fourteen seismic profiles with four piston cores collected in Willsboro Bay, a finger-like bay on the western shore of Lake Champlain.Seismic profiles were collected using a swept frequency CHIRP sonar. The profiles were analyzed and digitized using SonarWizMap technology. A sedimentological record of Willsboro Bay was constructed using magnetic susceptibility, electric resistivity, color spectrophotometry, physical properties, grain size, 210 Pb and 137 Cs dating, spectral analysis on grain size, and microfossil analysis of the sediment cores. Correlation of seismic stratigraphy with sediment cores confirm the presence of the Champlain Basin's three main sediment units (proglacial Lake Vermont sediments, marine Champlain Sea sediments, and present day Lake Champlain sediments) in Willsboro Bay. Shifts in physical properties and spectral analysis reveal a 1500-yr climate cycle in the sediment record of Willsboro Bay. This is a well-documented climate cycle of the Holocene that is thought to correspond with changes in the Arctic Oscillation.Thanks to the rest of the Middlebury Geology Department (Ray Coish, Tom Manley, Jeff Munroe, and Dave West) for their help with various aspects of this project. These individuals have been extremely knowledgeable and helpful resources throughout this project. In particular, thank you to Tom for sharing his computer expertise and for solving any and all technology-related problems that I encountered. Special thanks go to Ray for getting me hooked on geology in the first place. I am thoroughly convinced that this is the best department at Middlebury and I feel very lucky to have been a small part of it.My gratitude extends to my family and friends for their consistent support, encouragement, and patience -especially this year! Although I am certain that all are glad to hear my incessant chatter about sediment units finally come to an end, I appreciate your listening. Extra special thanks go to my suitemates, teammates, and bi-hall buddies who kept me laughing, motivated, and (generally) sane. I could not ask for a better bunch. Thanks also to my fellow geology majors for their hard work -it kept me going. Special recognition goes to Tom Cronin, Richard Bopp, and Kathryn Hayo for their help with data processing. I am especially grateful to Kathryn for her help with the many tedious hours of lab work. This project would not be complete without her contribution.