PALEOCLIMATE
RECONSTRUCTIONS FOR
THE SOUTHEASTERN U.S.A. FROM SPELEOTHEMS OF DESOTO CAVERNS,
CHILDERSBURG, ALABAMA
Abstract:
Abstract:
The southeast United States is severely lacking of high-resolution paleoclimate reconstructions that would aid in the understanding of past, present, and future local and global climate teleconnections. Researchers often use proxy information from tree rings, pollen, speleothems, lake levels, etc. to infer past continental climate conditions for multiple regions around the Earth. Current research at the Alabama Stable Isotope Laboratory located in the Department of Geological Sciences of the University of Alabama is aimed at deriving a climate (precipitation) record for the Southeast spanning the past 30,000+ years. The proxy record of choice is speleothems collected from DeSoto Caverns in Childersburg, Alabama.
Cave deposits, such as stalagmites, are widely accepted as proxies for records of precipitation (and potentially temperature and tropical storm) variations by means of interpreting changes in stable carbon and oxygen isotopes. In many cases these carbonate deposits form with annual bands that represent the mean climate of the environment above the cave. High humidity levels inside caves often allow for the stalagmites to form in isotopic equilibrium with the drip-water (sourced in precipitation). Variability of δ18O in the drip-water and stalagmite is influenced by temperature, amount, and source of precipitation. Changes in δ13C, on the other hand, are influenced by the type of vegetation above the cave or varying microbial activity, which in turn is related to the climatic conditions. Therefore, cave deposits have the potential of providing a continuous annual record of continental climate conditions based on the interpretation of carbon and oxygen isotope variations.
Because of the close proximity of the study area to the University of Alabama campus, extensive sampling and cave monitoring is possible. A data logger is currently recording cave air temperature and relative humidity values at 15-minute increments to ensure the cave environment is stable. Trips are made to the cave every two months to collect drip water and to measure the rate of water dripping into the cave. Once brought back to the laboratory, the drip water is analyzed for isotopic and chemical composition. Local precipitation is also collected at the University of Alabama campus and is monitored for both amount of precipitation and isotopic composition. Such monitoring of both the precipitation and drip water is crucial to properly interpreting a climate record derived from speleothems collected for this study.
To date, two stalagmites have been collected from DeSoto Caverns. Each will undergo isotope analysis, multiple dating techniques, and petrographic examination. A 5.5-cm sample, that was actively forming when collected in 2002, contains approximately 800 years of proxy climate information. A more recently collected 50-cm stalagmite began forming over 30,000 years ago and stopped “growing” near 6,590 B.C. based on initial radiocarbon ages. The large stalagmite will provide precipitation variability data spanning the peak of the last major glaciation, the deglaciation, up to the mid-Holocene Optimum. A high-resolution continental climate record for the Southeast during this time span does not currently exist. Future plans may involve collecting a third stalagmite to fill in the missing time interval of ~7,000 B.C. to present. Additionally, such a sample could potentially provide a multi-millennia record of tropical systems to impact the Gulf Coast.
Aside from radiometric dating, all sample analysis is being performed at the University of Alabama. The Alabama Stable Isotope Laboratory houses a suite of equipment specifically developed for the complete analysis of cave material. Data and climate interpretations will be published in professional scientific journals as the research project progresses.
Locations of continental U.S.
sites from which climate records have been reconstructed from cave
deposits (not absolutely inclusive). Southeast U.S. is outlined
in bold. The star denotes the study site location for this
project relative to the University of Alabama campus (X). DeSoto
Caverns will be one of the first caves to be studied in the Southeast
in terms of paleoclimate reconstructions.
_______________________________________________________________________
Our study site, DeSoto Caverns
(Childersburg, AL), lies directly in the path of moisture that is
carried over
eastern North America from the Gulf of Mexico. DeSoto Caverns has experienced a rich history as an
Indian shelter, a hidden saloon during the prohibition, and is currently a popular state attraction. Map above
shows locations (red stars) of samples collected for this study. The cave is capped by Ordovician age dolomite.
_______________________________________________________________________eastern North America from the Gulf of Mexico. DeSoto Caverns has experienced a rich history as an
Indian shelter, a hidden saloon during the prohibition, and is currently a popular state attraction. Map above
shows locations (red stars) of samples collected for this study. The cave is capped by Ordovician age dolomite.
Thin-section image of sample
DSSG-1 under transmitted light at 20X magnification. The sample
is mostly aragonite. The band couplets (light and dark) are
annual in nature meaning they represent one year of "growth."
_______________________________________________________________________(left) Currently, drip-water in
the cave is collected every two months for isotope and chemical
analysis.
Future plans include high-resolution sampling, especially after tropical systems pass over the area. (right) Local precipitation is collected each day and measured at weekly-resolution for δ18O and δD variability. This will allow for calibration of isotopic variation to forcing mechanisms such as precipitation amount, temperature, etc.
_______________________________________________________________________Future plans include high-resolution sampling, especially after tropical systems pass over the area. (right) Local precipitation is collected each day and measured at weekly-resolution for δ18O and δD variability. This will allow for calibration of isotopic variation to forcing mechanisms such as precipitation amount, temperature, etc.
Weekly precipitation amount
relative to δ18O (‰ V-SMOW). Note that the δ18O
scale has been
reversed to better illustrate the correlation (r2= 0.50)
with
precipitation amount. Gaps in data represent lack of
precipitation. A portion of the water samples are awaiting
isotope analysis.
_______________________________________________________________________Variability of d18O at two-month
sampling intervals for different cave drips and pool water in DeSoto
Caverns. Lack of variability of d18O may be due to either 1) low
sampling resolution, or 2) homogenization of precipitation in the cap
rock water reservoir above the cave. Future work is planned to
address this issue.
_______________________________________________________________________
(left) Staggering sampling
locations allowed for ~ 200 mm resolution and ~ 50 mg of powder.
(right) A Micro-Milling device will be implemented in the future to
achieve resolution of 20 to 40 mm and sub-annual isotopic variability.
_______________________________________________________________________Related Publications (click title for abstract/paper)
2011, Lambert, W.J. and Aharon,
P., Controls on Dissolved
Inorganic
Carbon and δ13C in Cave Waters from DeSoto Caverns:
Implications for Speleothem δ13C Assessments. Geochimica
et Cosmochimica Acta, v. 75, p. 753-768.
2010, Lambert, W.J. High Resolution, U/Th Dated (32,000 to 11,000 Years), Oxygen and Carbon Isotope Proxy Climate Records from a Stalagmite in DeSoto Caverns, Alabama, USA. PhD Dissertation, University of Alabama
2010, Lambert, W.J., Aharon, P., and Hellstrom, J., The Response of Extratropical Westerlies to Climate Change (31.9-11.3 ka) Revealed by a Speleothem from DeSoto Caverns, Alabama (USA). EOS Transactions, AGU, v. TBA, no. TBA, Fall Meeting Suppl., Abstract A33A-0098.
2010, Lambert, W.J. and Aharon, P., Oxygen and Hydrogen Isotopes of Rainfall and Dripwater at DeSoto Caverns (Alabama, USA): Key to Understanding Past Variability of Moisture Transport from the Gulf of Mexico. Geochimica et Cosmochimica Acta, v. 74, p. 846-861.
2008, Lambert, W.J. and Aharon, P., Oxygen and Hydrogen Isotope Time-Series Data in the Hydrologic Cycle of the Gulf Coast, USA. in Gulf Coast Association of Geological Societies Transactions, v. 58, p. 589-600
2008, Lambert, W.J. and Aharon, P., An Initial Baseline Study of Stable Isotope Hydrology in Alabama: Potential Applications to Water Management. Alabama Water Resources Conference.
2010, Lambert, W.J. High Resolution, U/Th Dated (32,000 to 11,000 Years), Oxygen and Carbon Isotope Proxy Climate Records from a Stalagmite in DeSoto Caverns, Alabama, USA. PhD Dissertation, University of Alabama
2010, Lambert, W.J., Aharon, P., and Hellstrom, J., The Response of Extratropical Westerlies to Climate Change (31.9-11.3 ka) Revealed by a Speleothem from DeSoto Caverns, Alabama (USA). EOS Transactions, AGU, v. TBA, no. TBA, Fall Meeting Suppl., Abstract A33A-0098.
2010, Lambert, W.J. and Aharon, P., Oxygen and Hydrogen Isotopes of Rainfall and Dripwater at DeSoto Caverns (Alabama, USA): Key to Understanding Past Variability of Moisture Transport from the Gulf of Mexico. Geochimica et Cosmochimica Acta, v. 74, p. 846-861.
2008, Lambert, W.J. and Aharon, P., Oxygen and Hydrogen Isotope Time-Series Data in the Hydrologic Cycle of the Gulf Coast, USA. in Gulf Coast Association of Geological Societies Transactions, v. 58, p. 589-600
2008, Lambert, W.J. and Aharon, P., An Initial Baseline Study of Stable Isotope Hydrology in Alabama: Potential Applications to Water Management. Alabama Water Resources Conference.
2007, Lambert, W.J., Aharon, P.,
and Hellstrom, J., Last
Deglaciation Events
(16.1-11.4 cal-Ka) Recorded in a Speleothem from DeSoto Caverns,
Alabama,
U.S.A. EOS
Transactions, AGU, v. 88, no. 52, Fall Meeting Suppl., Abstract
PP12A-04.
2006 Lambert, W. J., and Aharon, P., Paleoclimate Reconstructions for the Southeastern U.S.A. from Speleothems in DeSoto Caverns, Alabama. Archives of Climate Change in Karst, Karst Waters Institute Special Publication 10, p. 128-130.
2004 Lambert, W.J., and Aharon, P., Climate Change Recorded in Aragonite Speleothems from Central Alabama. EOS Transactions, AGU, v. 85, no. 47, Fall Meeting Suppl., Abstract PP43A-0610.
2006 Lambert, W. J., and Aharon, P., Paleoclimate Reconstructions for the Southeastern U.S.A. from Speleothems in DeSoto Caverns, Alabama. Archives of Climate Change in Karst, Karst Waters Institute Special Publication 10, p. 128-130.
2004 Lambert, W.J., and Aharon, P., Climate Change Recorded in Aragonite Speleothems from Central Alabama. EOS Transactions, AGU, v. 85, no. 47, Fall Meeting Suppl., Abstract PP43A-0610.
Poster Presentations (click for image)
American Geophysical Union Fall
Meeting, San Francisco, CA, December 13-17, 2010 (see abstract
above)
GCAGS/GSA Joint Meeting,
Houston, Texas, October 5-9, 2008 (see abstract above)
Alabama Water Resources Conference, Orange Beach, Alabama, September 3-5, 2008 (see abstract above)
Alabama Water Resources Conference, Orange Beach, Alabama, September 3-5, 2008 (see abstract above)
Climate Change: The Karst Record (IV) Băile Herculane, Romania. May 26-29th, 2006 (see abstract above)
American Geophysical Union Fall Meeting, San Francisco, CA, December 13-17, 2004 (see abstract above)
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