Collaborative Research: Testing Mechanisms of Tropical Climate Change and Variability Using New Cores from the Line Islands

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Coupled ocean-atmosphere interactions in the tropical Pacific are the leading source of modern global interannual climate variability. This variability, expressed as the El Niño-Southern Oscillation (ENSO), extends far beyond the tropical Pacific, affecting climate and human populations globally. Understanding how climate change alters these interactions is therefore critical for human societies to mitigate and adapt to future change. Discovering whether external forcing or internal variability determines ENSO behavior will greatly deepen our theoretical understanding of ENSO and improve our ability to accurately forecast ENSO behavior under altered climates. In addition to these broad scientific and societal benefits, this project will provide research opportunities for graduate and undergraduate students. The project also provides a platform for the development of K-12 teaching modules, which will be designed in collaboration with public school teachers as well as an undergraduate science teacher in training at the University of California, Santa Cruz.This project is developing records of equatorial Pacific Ocean sea-surface temperature variability during the past 250,000 years to test factors that alter tropical climate and the behavior of the El Niño-Southern Oscillation (ENSO). ENSO is the dominant cause of interannual climate variability globally, yet it is not known how its behavior could change with future climate change. Understanding past changes in the behavior of ENSO, when global temperatures were different, will be a significant advance in this regard. ENSO behavior is reconstructed from the variability of sea-surface temperatures determined by the chemistry of fossil foraminifera shells in deep-sea sediments near the Line Islands, in the central Pacific. The Mg/Ca ratio and oxygen isotope composition of each individual planktonic foraminifera shell records a one-month snapshot of sea-surface temperature. Measurement of many individual shells from a single sediment layer documents the variability of sea surface temperatures over the time of deposition. Because ENSO is the primary cause of sea-surface temperature variability near the Line Islands, past changes in temperature variability show how ENSO behavior changed in the past. These data will test the dynamic response of the equatorial Pacific to changes in solar insolation from Earth's orbit, and to glacial-interglacial changes in global temperature and greenhouse gas (pCO2) forcing, improving our understanding of the ENSO phenomenon and how it might change in the future.