1300 years of climatic history for Western Central Asia inferred from tree-rings

Abstract

More than 200 000 ring-width measurements from 384 trees were obtained for 20 individual sites ranging from the lower to upper local timber-lines in the Northwest Karakorum of Pakistan and the Southern Tien Shan of Kirghizia. Samples were obtained predominantly from juniper species (Juniperus) and were analysed to reconstruct regional climatic variation patterns in Western Central Asia since ad 618. Site distri bution represents diverse ecological conditions (e.g., combinations of temperature and moisture stress) within the Karakorum and Tien Shan mountains, permitting both intra-montane and inter-montane comparisons of chronologies. Three different types of chronologies reflecting interannual-, decadal- and centennial-scale ring- width variations were calculated: a statistic skeleton-plotting technique was used to identify ring-width pointer years (interannual); a 101-year kernel filter was used to identify decadal-scale variations; and, for a subset of long-lived trees, the mean ring-width of the entire single series was used to identify centennial trends. After extracting and calibrating each of these three distinct wavelengths in ring-width variation, the results were combined into a comprehensive reconstruction reflecting primarily temperature fluctuations in Western Central Asia since ad 618. The nature and the temporally changing strength of the climatic signals of this reconstruction are discussed in detail. A maximum latewood density record of Pinus tienschanica from Central Tien Shan was used as a predictor series to calibrate and validate tree-ring-width variation. In so doing, we link our results to the circumpolar maximum latewood-density network (Briffa et al., 1998a; 1998b; Schweingruber and Briffa, 1996).