OS021-03
Is Modern El Niño Southern Oscillation (ENSO) Variability Unprecedented? Resolving ENSO Variability of the 17th Century Using Coral Data from Genovesa Island, Galápagos
Wednesday, 9 December 2020: 19:08
Virtual
Jake Okun, University of Michigan Ann Arbor, Ann Arbor, MI, United States, Julia E Cole, University of Michigan Ann Arbor, Earth and Environmental Sciences, Ann Arbor, MI, United States, Kelsey Dyez, University of Michigan Ann Arbor, College of Literature, Science and the Arts, Ann Arbor, MI, United States, Diane M Thompson, University of Arizona, Department of Geosciences, Tucson, AZ, United States, Emma Reed, University of Arizona, Geosciences, Tucson, AZ, United States, Alexander William Tudhope, Univ Edinburgh, Edinburgh, United Kingdom and R. Lawrence Edwards, Nanjing Normal University, Dept. of Geography, Nanjing, China
Abstract:
High variability in the El Niño/Southern Oscillation (ENSO) phenomenon during the modern era has led to the hypothesis that enhanced greenhouse forcing may contribute to increased ENSO variability. Increased variability would greatly impact regions that experience drought, flooding, or rising temperatures during ENSO events. To expand the observational record of ENSO variability and evaluate whether past periods have experienced such high variability, we present new coral records from the Galápagos Islands (Ecuador). ENSO history can be reconstructed from the geochemistry of corals’ carbonate skeletons, which record ~monthly SST over time. The Galápagos Islands represent a uniquely suitable location to conduct paleoclimate studies related to ENSO. Sea surface temperature (SST) in the region is sensitive to primary ENSO signals, as the islands lie in a zone of intense upwelling in the eastern Pacific that warms dramatically during El Nino events.
Here we present an analysis of past SST variability based on oxygen isotopic data from several Galapagos corals, including new records from Genovesa Island, during the interval 1610-1710. We exclude seasonal variability in the records to isolate the inter-annual variability of ENSO. Initial results suggest that this interval experienced strong, near-modern levels of inter-annual variability in the absence of anthropogenic forcing. These results agree with central Pacific coral records that also exhibit high variance in this interval. Documenting high ENSO variance during a period without anthropogenic forcing can improve our understanding of natural ENSO variability, motivating further investigation of the roles of external forcing vs the natural background variation of ENSO. Moreover, other tropical Pacific records display divergent results that have led to contradictory interpretations of ENSO behavior during the Little Ice Age. Our new multi-core assessment of eastern Pacific variability during this interval will allow evaluation of whether variability across the tropical Pacific is changing synchronously or displaying spatial diversity, and will provide a benchmark for climate model simulations of the recent past.
