The study of Holocene climate change is vital to understanding present and future
climate conditions in the Upper Midwest region of the United States. Varved sediments
from Elk Lake, Clearwater County, Minnesota provide an archive of multiple climate
sensitive proxies and past climate conditions, particularly related to the balance of
precipitation and evaporation (available moisture) for the North Central United States.
Studies conducted in the past using Elk Lake sediments have established large scale and
long term changes in the climate history of the region, but were done at a resolution that only allowed for a discussion of events on time scales of hundreds to thousands of years.
Scanning XRF is a new analytical technique that allows for much higher
resolution, geochemical data to be gathered from sediment cores for the characterization
of climate variability with resolution on the order of decades to inter-annual changes.
This study seeks to repeat, using new analytical and higher resolution methods, the work
done by previous researchers. One centimeter resolution XRF scans were used to
describe changes that occurred during the Holocene, and 200 micron scans were used to
identify the nature of varve deposition during major periods in the Holocene and to
characterize the timing and relationships between the laminations that make up individual
varves. With higher resolution data with which to work, time series analysis provides
insight into high frequency cycles during the Holocene record including El Nino
Southern Oscillation (ENSO) and solar activity cycles.
With the addition of the first known geophysical data set from Elk Lake, this
study also illustrates the usefulness of obtaining multiple records from an individual lake. Through the use of both geochemical and geophysical data, it is shown that events seen
separately in each data set can be correlated to one another and an accurate estimate for the timing of major climate events can be obtained.
University of Minnesota M.S. thesis. September 2010. Major: Geological sciences. Advisor: Erik T. Brown. 1 computer file (PDF); x, 138 pages, appendix p. 131-138
Rush, Robert Allen.
High Resolution geochemical XRF data from Elk Lake, Minnesota: A Holocene paleoclimate record from varved lacustrine sediments..
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