PARENT SESSION
Poster Session #15: Paleoecology.
Monday, August 5. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC
148
Periodic climate forcing in a 672-year drought severity reconstruction from Ponderosa pine in west-central Montana.
HUNZICKER, DAVE*,1, CAMILL, PHIL1, BICE, DAVID1, 1 Carleton College, Northfield, MN
ABSTRACT- Recent tree-ring reconstructions of droughts suggest that large-scale climate periodicities may occur over extensive regions of western North America. In this study, we established a new 672-year drought severity record from Ponderosa pine (Pinus ponderosa) growth rings and compared it to existing proxy data from the western United States to examine the spatial and temporal variability of local and regional scale climate change. A master chronology with mean interseries correlation value = 0.620 and mean sensitivity = 0.243 was constructed using samples from 61, old-growth Ponderosa pines from western Montana. Response function analysis indicated that annual Palmer Drought Severity Index (PDSI) correlated best with growth (r2 = 0.22). Reconstructed PDSI back to calendar year 1330 AD showed significant correlation with previously published regional climate reconstructions, including major decadal-scale droughts during the 1580's and 1930's and shorter-duration droughts in the 1750's and 1840's. Spectral analysis of reconstructed PDSI with bootstrapped 95% confidence intervals revealed significant peaks at the 3, 10-12, 18-26, and 42-45 yr wavelengths. Applying a sliding window analysis to the power spectrum, we found patterns of temporal variation within these wavelength ranges, which can partially account for the observed variation in this and other published datasets. The 3, 10-12, and 18-26 yr periods may represent the El Nino Southern Oscillation (ENSO), Schwabe (sunspot), and Hale (double sunspot) cycles, respectively. The longer cycles (e.g., 42-45 yr) lack well-defined forcing mechanisms but have been detected previously. Applying band pass filters, we found that PDSI periodicity from 2.5-8 yr showed a strong in-phase relationship with sea surface temperature records of ENSO cycles through most of the time series, while the PDSI periodicity from 8-13 yr was consistently out of phase and lagged behind the sunspot cycle. These results suggest broad spatial correlation in climatic forcing across the western US.
KEY WORDS: PDSI, climate, dendroclimatology, Ponderosa pine