Holocene Climate Change Interpreted from Lake
Reconstructions, Bighorn Mountains, WY
December 3, 2010
Fundamentals of Research
Outline for today’s talk
Motivation for research: Why study Holocene climate change?
Brief background: What do we need to estimate
Study site: the Bighorn Mountains!
Methods and Results: What we will produce and how we will do it.
Motivation/Relevance of Research
Why study Holocene climate change?
Water resource planners are very interested in quantifying the possible effects
of future climate changes on their state’s or municipality’s water supply.
changes to lake levels caused by climate
changing events during the past, we
a better understanding of the
effect that a similar event would have on our water supply in the future.
Retrieved from www.usgs.go
do we need
We need a lake with the following characteristics:
Small lake (<50 hectares) located at the outlet of a small catchment.
Shallow and wide (<10 m deep).
Minimal surface water inputs/outputs; a ‘quiet’ hydrology dominated by
Solid, homogenous bedrock under basin sediments.
These characteristics help us isolate climatic inputs to lake level change from
local inputs, as well as…
…allow for the preservation of lacustrine
Specifically, we need to observe
Forms in the shallow waters near the lake’s current shoreline, due to wave
action and currents.
Contains relatively coarse sediment, minimal organic content, and a higher
Contains macrofossils unique to shallow freshwater environments; e.g.
(lily pads) and
Relatively low sedimentation rate.
should extend nearly continuously around the lake.
Proposed Study Sites
Lower Paint Rock Lake
3) Trigger Lake
4) Bear Lake
Proposed Research/Expected Results
Here are the results that we expect to generate during completion of this
D lake basin profiles
, using ground penetrating radar (GPR), for both Lower
Paint Rock Lake and Trigger Lake (Lower Medicine Lodge Lake and/or Bear Lake if
alternate sites are selected).
along a transect for each lake identifying past
shifts of the shoreline.
identification will be based
on laboratory analysis for grain size distribution, organic content, bulk density,
macrofossil content, and sedimentation rate.
line of lake
throughout the Holocene for
Analysis of contemporaneous changes in lake
levels with previously studied
within the Northwest Rocky Mountain region, indicating past climate
changing events during the Holocene.
1) GPR profiles
We can generate 3
D GPR profiles fairly quick (within 1 to 2 days), and thus
analyze them immediately in the field for:
Lake basin characteristics
If the GPR images look good, we can continue with collecting sediment
cores along a transect on that lake.
If the GPR images look poor, we can move on to one of the alternate lake
Light and dark contrasts indicate boundaries between
sediments with different dielectric constants.
Thickness of bands gives an idea of sedimentation
Light colored bands
2) Analyses of Sediment Cores /
Transects of sediment cores will be collected with a 70mm
piston corer, and taken back to the
will be identified based on:
Coarse sediment content (>63µm)
measure wt. % of subsample (+/
after wet sieving and drying.
measure % loss on ignition (+/
measured by gamma ray attenuation (+/
measured by radiocarbon dating of sedimentary
identification of plant macrofossils unique to shallow freshwater
Now, with the
The final correlation produced for each lake will indicate both magnitude
and direction of past shifts in the lake shoreline.
It should agree fairly well with observations from the 3
D GPR profiles…
…we can correlate the
along our transects, extending from the current
shoreline out to the lake’s
Courtesy of J.
line of Holocene lake
Thus, the end result is a Holocene time
line of lake
level changes, produced
for each lake.
Each shift of the shoreline corresponds to a change in lake
level. We can then
bracket the time that these changes occurred using
radiocarbon dating of
in western lacustrine sediments).
4) Contemporaneous changes in lake
level with previously studied sites
Analyzing for past climate change during the Holocene
We will isolate climatic inputs to lake
level change from local inputs by correlating
with multiple lakes in different watersheds, but within the same climate region.
This should provide us with an improved understanding of climate change within
Wyoming during the Holocene.
Previously studied sites:
Foy Lake, MT (Shuman et al.,
Park Pond, WY (Lynch,
Bear Lake, ID
Lake, WY (Shuman et al., in
Hidden Lake, CO
(Shuman et al., 2009)
Lynch, E.A. (1998). Origin of a park
forest vegetation mosaic in the Wind River Range,
Rosenbaum, J.G. (2010).
lake levels of Bear Lake (Utah/Idaho): a record of Holocene
2010 GSA Denver Annual Meeting
3 November 2010
Shuman, B., Henderson, A.K., Colman, S.M., Stone, J.R., Fritz, S.C., Stevens, L.R., Power, M.J.,
Whitlock, C. (2009). Holocene lake
level trends in the Rocky Mountains, U.S.A.