Temporal stability in bristlecone pine tree-ring stable oxygen isotope chronologies over the last two centuries

The absolutely dated bristlecone pine (Pinus longaeva) tree-ring chronology spans almost 9000 years, offering great potential for inferring past environmental change. Existing ring width chronologies have been widely used to produce some of the most influential millennial length temperature reconstructions for the Northern Hemisphere. A recently published delta O-18 record from two bristlecone pine trees growing at Methuselah Walk in the White Mountains of California showed a dramatic decrease in d(18)O between AD 1850 and 1920 (c. 13 parts per thousand), interpreted as indicating a major shift in Pacific storm tracks over the past 300 years. Here we present new bristlecone pine d(18)O time series from 15 trees at three White Mountains sites, including two series from Methuselah Walk. Whilst occasional high interannual variability is observed in our d(18)O series, none of our chronologies exhibit an equivalent pronounced or sustained twentieth-century decrease, suggesting the earlier results are anomalous and may require palaeoclimatic re-interpretation.