ENSO flavors during the Last Glacial Maximum: Assessing spatial variability under varying climate background conditions

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ENSO flavors during the Last Glacial Maximum: Assessing spatial variability under varying climate background conditionsThe largest source of interannual climate variability on Earth is the El Niño Southern Oscillation (ENSO), characterized by distinct spatial patterns of tropical Pacific sea surface temperatures. These patterns (or ‘flavors’) are linked to climatic changes through powerful coupled ocean-atmosphere interactions that reverberate globally and can adversely affect human societies. Recent observations suggest these patterns may be changing, limiting societies’ ability to forecast and mitigate ENSO impacts. However, it remains unclear whether changes to ENSO’s spatial expression and climatic effects are related to background climate conditions such as mean global temperature or tropical ocean surface and subsurface temperatures. This project will use ocean sediments deposited approximately 20,000 years ago to study how ENSO ‘flavors’ – the spatial pattern of temperatures – change during a colder background climate state. The results will advance our theoretical understanding of the ENSO system and enable better predictions of global ENSO impacts under future climate conditions. This project will offer climate research opportunities for undergraduate and graduate students and will facilitate creation of online content to highlight the importance of ENSO-related climate variability at the regional and national level. The nature of the relationship between background climate conditions and the patterns of ocean temperature anomalies, or ‘flavors’ that characterize the El Niño Southern Oscillation (ENSO) remains unclear. This project will test hypotheses that background climate state, such as mean temperature and tropical Pacific surface and subsurface ocean conditions, influence the spatial pattern of ENSO variability, and that the thermocline plays a key role in modulating ENSO. The spatial variability of the tropical Pacific under differing climate background conditions will be assessed by developing records of variability spanning the last glacial maximum (20,000 years ago) from key locations in the central and eastern tropical Pacific. The geochemistry of planktic foraminifera shells will be analyzed to reconstruct oceanic conditions at these sites. Population distributions of trace elemental and stable isotopic ratios from individual shells will provide estimates of surface and subsurface ocean variability. These data will reconstruct ENSO’s spatial expression during the last glacial maximum and test whether background climate and/or thermocline conditions influence ENSO ‘flavors’. This research will advance our knowledge of climate system processes, mechanisms, and dynamical ocean-atmosphere interactions during different climate states with implications for predicting future ENSO behavior. This project incorporates undergraduate and graduate student research and will produce online content for public education.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.