Hydroclimate time-series archived in a 4300 year old stalagmite from Desoto Caverns (Alabama, USA)

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University of Alabama Libraries

Recently published climate studies have implicated the Atlantic Multidecadal Oscillation (AMO) as the dominant factor modulating the precipitation in the regions adjacent to the Atlantic Ocean and the Gulf of Mexico but long range, land-based paleoclimate proxies, are notably lacking. Here I report the results of a new stalagmite- derived ä18O and ä13C ( / VPDB) time series and petrographic study from DeSoto Caverns, Alabama, spanning the interval from recent to 4025 years BP. The new data document AMO as having a pervasive controlling influence on the Southeastern USA region's hydroclimate during the Late Holocene. Ten precise 230Th/234U age determinations, from an 11.3 cm section of stalagmite, spanning the interval from 1883 to 4025 years BP, were used to construct an age model for the stable isotopes time-series containing 882 determinations. Analysis of the stalagmite's ä18O time-series in the frequency domain exhibits dominant periodicities of 30.8 ± 1.4 years and 27.4 ± 0.8 years at the Chi Squared 95% confidence interval that match the instrument-derived AMO half cycle periodicity of approximately 30 years. At the Chi Squared 90% confidence interval, the stalagmite's ä18O time-series frequency analysis reveal a periodicity of 58.0 ± 2.7 years, matching the instrument derived AMO full cycle of approximately 60 years. Starting about 1883 years BP a series of anomalous black laminations appear in the stalagmite and continue, with short interruptions, until a return to normal deposition at approximately 49 years BP. Petrographic investigations reveal that the section of the stalagmite that contains the black laminations also features intense dissolutional unconformities that are predominately composed of detrital material. Both the detrital material and dissolutional unconformities, likely resulted from intense landscape modifications by the pre-Columbian Native American and European societies inhabiting the region during the time.

Electronic Thesis or Dissertation
Geology, Paleoclimate science, Geochemistry