| Tropical Pacific sea-surface temperature fluctuations associated with the El Niño-Southern Oscillation (ENSO) are known to drive climate patterns around the globe on interannual timescales. However, our understanding of the low-frequency variability exhibited by the tropical Pacific climate system is severely limited by the lack of long, high-resolution records of tropical Pacific climate. In this dissertation, I use modern and fossil corals to generate century-long, monthly-resolved records of tropical Pacific climate during five intervals of the last millennium.; Chapter 2 characterizes the signature of 20th century interannual, decadal, and secular tropical Pacific climate variability as recorded in a 112-yr modern coral oxygen isotopic (δ18O) record from Palmyra Island (6°N, 162°W). The calibration exercise demonstrates that the Palmyra modern coral δ18O is an accurate proxy for regional-scale interannual and decadal-scale tropical Pacific climate variability. Chapter 3 investigates the global footprint and frequency characteristics of a decadal climate cycle that is captured by the modern coral. The ∼12–13yr signal is associated with an SST pattern that strongly resembles that of ENSO.; I use fossil corals from Palmyra to reconstruct tropical Pacific climate from the 10th, 12th, 14–15th, and 17th centuries. Chapter 4 presents several techniques that improve the accuracy of the fossil coral U/Th dates such that overlapping coral sequences can be spliced together. Chapter 5 addresses the reproducibility of overlapping fossil coral δ18O records, and presents 30- to 150yr-long, monthly-resolved, fossil coral-based reconstructions of tropical Pacific climate from the 10th, 12th, 14th–15th, and 17th centuries.; The coral δ18O records document interannual and decadal variability with amplitude and frequency characteristics that are much more variable than those observed during the 20th century. The results suggest that El Niño events of the mid-17th century were more frequent and more severe than those of the late 20 th century. There is no evidence of cooling in the central tropical Pacific during the “Little Ice Age”, whereas relatively cool conditions are indicated for the “Medieval Warm Period”. The Palmyra reconstruction suggests that the late 20th century trend towards warmer, wetter conditions in the tropical Pacific is likely without precedent in the last millennium. |
