ATLANTIC MULTIDECADAL OSCILLATION ARCHIVED IN THE δ18O TIME SERIES OF A LATE HOLOCENE STALAGMITE FROM DESOTO CAVERNS, ALABAMA, USA

Spectral analysis of recently published paleoclimate proxies have implicated the Atlantic Multidecadal Oscillation (AMO) as the dominant factor modulating the precipitation in regions adjacent to the Atlantic Ocean and the Gulf of Mexico, but stalagmites have not been so far utilized in these investigations. Here, we report the results of a new stalagmite derived δ¹⁸O time series from DeSoto Caverns, Alabama, spanning the interval from 2030 to 4200 years BP.

DeSoto Caverns' stalagmites consist of nearly monomineralic botryoidal aragonite that have U concentrations in the ppm range, affording precise ²³⁰Th/²³⁴U dating of 10-20 mg samples. The overwhelming majority of the moisture that reaches DeSoto Caverns is sourced in the Gulf of Mexico hence, the stalagmites there contain reliable records of rainfall variability in a continental setting.

Eleven precise ²³⁰Th/²³⁴U age determinations, from a 15.5 cm section of stalagmite, were used to construct an age model for the δ¹⁸O (‰ VPDB) time series containing 1091 determinations. Combining high sampling resolution with precise and frequent dating afford for an average sampling resolution of 3.3 years per sample. Analysis of the stalagmite δ¹⁸O time series in the frequency domain exhibits a dominant periodicity of 60 ± 6 years that matches the instrument-derived AMO periodicity. This discovery suggests that AMO has controlled the region's precipitation for much longer than is revealed by the instrumental record.