What was done
The authors constructed a multi-decadal-scale history of east-central North America's hydroclimate over the past 7,000 years, based on Sr/Ca ratios and δ¹³C data obtained from stalagmite BCC-002 of Buckeye Creek Cave (BCC) in West Virginia, USA.

What was learned
Springer et al. report detecting seven significant mid- to late-Holocene droughts that "correlate with cooling of the Atlantic and Pacific Oceans as part of the North Atlantic Ocean ice-rafted debris [IRD] cycle, which has been linked to the solar irradiance cycle," as per Bond et al. (1997, 2001). In addition, they find that "the Sr/Ca and δ¹³C time series display periodicities of ~200 and ~500 years," and that "the ~200-year periodicity is consistent with the de Vries (Suess) solar irradiance cycle," and that the ~500-year periodicity is likely "a harmonic of the IRD oscillations." They also report that actual "cross-spectral analysis of the Sr/Ca and IRD time series yields statistically significant coherencies at periodicities of 455 and 715 years," which latter values "are very similar to the second (725-years) and third (480-years) harmonics of the 1450 ± 500-years IRD periodicity."

What it means
The five researchers conclude by stating that their findings "corroborate works indicating that millennial-scale solar-forcing is responsible for droughts and ecosystem changes in central and eastern North America (Viau et al., 2002; Willard et al., 2005; Denniston et al., 2007)," and that their high-resolution time series "provide much stronger evidence in favor of solar-forcing of North American drought by yielding unambiguous spectral analysis results."

References
Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I. and Bonani, G. 2001. Persistent solar influence on North Atlantic climate during the Holocene. Science 294: 2130-2136.

Bond, G., Showers, W., Cheseby, M., Lotti, R., Almasi, P., deMenocal, P., Priore, P., Cullen, H., Hajdas, I. and Bonani, G. 1997. A pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates. Science 278: 1257-1266.

Denniston, R.F., DuPree, M., Dorale, J.A., Asmerom, Y., Polyak, V.J. and Carpenter, S.J. 2007. Episodes of late Holocene aridity recorded by stalagmites from Devil's Icebox Cave, central Missouri, USA. Quaternary Research 68: 45-52.

Viau, A.E., Gajewski, K., Fines, P., Atkinson, D.E. and Sawada, M.C. 2002. Widespread evidence of 1500 yr climate variability in North America during the past 14,000 yr. Geology 30: 455-458.

Willard, D.A., Bernhardt, C.E., Korejwo, D.A. and Meyers, S.R. 2005. Impact of millennial-scale Holocene climate variability on eastern North American terrestrial ecosystems: pollen-based climatic reconstruction. Global and Planetary Change 47: 17-35.