Why should we care about lake mud? Part II
The Great Lakes hold 20% of the Earth’s surface fresh water, and are important natural and economic resources for the US and Canada. During the past several thousand years they have been strongly influenced by climate change and the evolving glacial landscape of the Great Lakes region. Lake Erie, the shallowest, has been very sensitive to environmental changes during its Holocene evolution and also to human influences during the modern era.
Lake level changes impact erosion rates; temperature shifts affect productivity and water chemistry; precipitation changes influence inflow from rivers and the Upper Great Lakes. Understanding these relationships and predicting future trends is important to maintaining these crucial natural resources. Also, understanding Lake Erie’s past climate is essential to predicting how the Great Lakes region will respond to both natural and human-induced climate change in the future.
My senior thesis project investigates Lake Erie’s history by analyzing sediments deposited in the lake’s eastern basin during the Holocene (to about 3,500 years ago). Since changes in the physical, biological, and chemical proxies found in these lake sediments can be influenced by a variety of factors, clear identification of the primary factor or factors acting at the time of deposition is not always possible. However, good interpretations can be made based on a critical analysis of the combined data. In these Lake Erie sediments, we use a variety of proxies, looking at relationships between them to better understand the lake’s paleo-depositional environment.
How do we know when proxy changes happen? (Or, how do we date mud?)
Cores can be correlated by matching magnetic susceptibility peaks that appear in sediment across the central and eastern basins. Radiocarbon dates from above the magnetic susceptibility shift are out of stratigraphic order, indicating contamination or sediment re-working. An approximate age for the shift in our Station 23 sediment was estimated from 2900 14C yrs BP from immediately above and below the shift.
CONCLUSIONS (so far)
Multi-proxy data from a Lake Erie sediment core indicate a warm climate event, peaking at about 2900 14C years BP, followed by a period of greater climate variability.
Lake Erie’s climate record differs from New York lake records, potentially indicating high regional variability.
Understanding the response of Lake Erie to climate change is crucial to predicting and preparing for future changes. Because it has such a shallow basin, Lake Erie’s water levels are particularly sensitive to climate. As we continue to see shifts in regional and global temperatures, and as human impact on the Great Lakes increases, we need to prepare for major environmental consequences.
Lake level fluctuations will impact coastal wetlands, commercial shipping, pleasure boating, and beach erosion. Temperature and water chemistry changes will impact primary productivity, fisheries, and invasive organisms. Further high-resolution paleo-climate work needs to be done in order to address these concerns.