A COMPARISON OF DENDROCHRONOLOGICAL AND SEDIMENTOLOGICAL DATASETS AND THEIR APPLICABILITY FOR THE INTERPRETATION OF ANNUAL AND DECADAL SCALE CLIMATE FLUCTUATIONS IN THE GREAT LAKES

Numerous techniques have been used to identify paleoclimatic conditions on a variety of time scales. These studies have also revealed patterns of warmer and cooler temperatures within the Great Lakes. For example, a paleo-lake level curve for Lakes Huron and Michigan has been constructed from beach ridge studies conducted in fourteen embayments around the Great Lakes region. The resulting curve indicates that beach ridges form in response to quasi-periodic changes in climate that occur approximately every 33- and 160-years for the last 4200 calendar years BP. Similarly, dendrochronological datasets have been used to interpret past climate fluctuations with recent research also identifying a longer-term climate pattern similar to that found in the beach ridge based studies.

We collected approximately 160 vibracores of beach ridges and 110 tree-core samples from two sites in the Lake Michigan / Huron basin. We are examining the datasets for possible annual and decadal scale similarities in the timing of beach ridge formation (from vibracore data) and climatic variability as displayed by tree ring growth patterns.

Preliminary results suggest decadal scale cycles are present in both vibracore and tree ring datasets, and annual scale cycles (<10 years) may be present in the tree ring datasets. Furthermore, the data also suggests that an impermeable subsurface layer in some locales exaggerate the magnitude of climate change observed through the annual tree ring patterns by restricting groundwater availability. This interpretation is in agreement with data collected by continuously recorded water levels in one study area.