A 2,000-YEAR VARVED RECORD OF HYDROLOGIC CHANGE FROM ISLA ISABELA, SUBTROPICAL NORTHEAST PACIFIC

The persistence and recurrence of dominant climate periodicities remains a concern in predicting future variations across the Pacific Basin. We reconstructed a 2,000-year record of changes in water availability from the oxygen isotope composition of a continuous varved sequence from Isla Isabela, a small volcanic island in the subtropical northeast Pacific. Comparing the oxygen isotope (δ¹⁸O) record to the observed Pacific Decadal Oscillation (PDO) index, we found that shifts toward more elevated δ¹⁸O corresponded to negative phases of the PDO, indicating that these phases are marked by increased evaporation and/or decreased precipitation at Isabela Crater Lake. Wavelet analysis of the δ¹⁸O record indicates that strength in the dominant PDO periodicities is intermittent over the past 2,000 years, with the greatest strength in the PDO bands appearing from AD 1200 to 1400 and 1850 to 1900. Our record suggests that the PDO has changed several times in the past two millennia, and is both a critical and nonstationary component of climate variability in the subtropical Pacific.