The Philip M. Smith Graduate Research
Grant for Cave and Karst Research
2021 Grants
Bryce K. Belanger ($2,750)
Department of Earth and Environmental Sciences
Vanderbilt University
Reconstructing mid-Holocene
hydroclimate conditions in the Rocky Mountains, USA: Implications for
seasonality and monsoon influence during past warm periods
Abstract: Examining patterns
of precipitation and drought during warm periods in Earth’s past is
critical in the effort to predict future climate changes due to
human-induced global warming. Precisely-dated, high-resolution
speleothem records provide the opportunity to examine the driving
factors of these hydroclimate shifts. The mid-Holocene (6,000 years
before present) was ~0.7°C warmer than the pre-Industrial (Marcott et
al. 2013; Kaufman et al., 2020), yet models and proxies disagree as to
what effect this warming had on precipitation regimes throughout the
western United States. In the Rocky Mountains, evidence suggests that
winters were drier, but the extended influence of the North American
Monsoon may have increased summer rainfall. Previously developed
paleoclimate records from this region are seasonally biased, and
therefore do not provide the opportunity to assess competing moisture
sources on an annual timescale. To this end, I will produce a
multi-proxy, semiquantitative record of past precipitation from Titan
Cave, Wyoming using trace element, stable isotope (𝛿𝛿18O
and 𝛿𝛿13C) and novel proxy (𝛿𝛿44Ca and Δ17O)
techniques. This multi-proxy approach will allow for the reconstruction
of precipitation amount, source location, and possible seasonal
influences, providing a holistic view of climate change during a time
considered to be an effective analog for near-future 21st century
warming (Burke et al., 2018). The record developed from Titan Cave has
the potential to be the best-dated, continuous, semi-quantitative
record of past climate during a period of warming that bears important
similarities to the 21st century.
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Rachel Bosch ($1,300)
Department of Geology
University of Cincinnati
Speleothem and charcoal dating to
constrain the pace of denudation of the Sinkhole Plain, Central
Kentucky Karst
Abstract: We propose to date
sediments and speleothems to relate geochronology of the Mammoth Cave
System to landscape evolution of the Sinkhole Plain, Kentucky, USA.
Previous geochronology studies have focused on Mammoth Cave, dating the
earliest incision events to ~3.25 Ma. Before that period, drainage
likely consisted of stream networks over clastic bedrock. During early
karstification in this region, caves developed in the Girkin limestone
(elevation >250 m ASL) in the area that is now ~10 km south of the
Green River and ~30 km east of the Barren River. We hypothesize that
this occurred about 1–10 Ma before the development of the oldest
passages in Mammoth Cave, and that the paleo cave system was part of a
karst drainage feeding the Barren River to the west. In this work, we
will use uranium series cosmogenic dating of speleothems from Crystal
Onyx Cave, a relict passage in Prewitts Knob, and radiocarbon dating of
charcoal from Little Sinking Creek on the Sinkhole Plain. These
analyses will provide dates to determine the abandonment age of Crystal
Onyx Cave and provide indication of the average modern rate of Sinkhole
plain erosion, supplementing cosmogenic dating in progress. These
results will place the development of Crystal Onyx Cave and the
denudation of the Sinkhole Plain in the context of the Mammoth Cave
System geochronology. This has implications for revealing timescales of
the evolution of karst systems as well as the interaction of
hydrological flow paths in karst areas with the transience of drainage
networks.
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Andrew Oberhelman ($3,000)
Department of Geological Sciences
University of Florida
Organic carbon and methane dynamics in
a carbonate karst aquifer
Abstract: Methane (CH4)
is a potent greenhouse gas and a common solute in groundwater, yet the
magnitude, range, and atmospheric flux of groundwater CH4
remain poorly understood, particularly in carbonate karst aquifers
(CKA) where hydrology permits the rapid exchange of water and solutes
between surface and subsurface. Availability of exchangeable electrons
(redox potential) plays an important role in cycling of CH4
and in other processes critical to groundwater quality. Quantity and
bioavailability of organic carbon (OC), also poorly understood in CKAs,
can greatly influence redox potential. Four research questions are
proposed to clarify linkages between CH4 cycling, OC
dynamics, and hydrology in CKAs: (1) how do hydrologic conditions
impact the quantity and bioavailability of dissolved OC in groundwater
and spring effluent, (2) how do relative variations in OC quantity and
bioavailability alter CH4 dynamics, (3) what is the
magnitude and range of CH4 concentrations in discharging
waters, and (4) to what extent does groundwater act as a CH4
sink or source? These questions will be explored by investigating OC
and CH4
dynamics in the Upper Floridan Aquifer (UFA), which is an ideal system
due to its numerous springs and a well-studied sinking stream system.
Comparisons of hydrologic characteristics including flow conditions and
groundwater residence time in the UFA with the cycling of CH4
and OC will reflect how changing hydrologic conditions influence CKA
redox processes. Results will help elucidate controls on variations in
CKA redox conditions, aid management of water quality related to redox
variations, and refine global CH4 budgets.
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last updated or validated on November 12, 2021