Reconstructions of central tropical Pacific climate during the 19th to early 20th centuries

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The tropical Pacific Ocean has a strong influence on global climate. This influence is evident during El Niño-Southern Oscillation (ENSO) events. Interannual ENSO variations in the tropical Pacific drive large shifts in global weather patterns, including regional rainfall extremes that can lead to floods, droughts, and wildfires. Decade-to-decade changes in the tropical Pacific also have large impacts on global climate, including the rate and pattern of global warming. Thus, to predict future changes in global climate and weather extremes we must know about the long-term state of the tropical Pacific and about changes in ENSO variability. However, the impacts of human activities since the start of the Industrial Revolution on conditions in the tropical Pacific are poorly known. This limits our ability to predict climate for the coming decades. Direct climate observations from the central equatorial Pacific are sparse prior to 1950, but this data gap can be filled by records of climate from geologic archives such as corals, tree rings, and ice cores. This project will use precisely dated coral records from the central equatorial Pacific to produce a record of ocean temperature since about 1800. This temperature record will be compared with climate model simulations to understand the observed trends and variability in ocean temperature, and their impact on climate. The project will support research by both graduate and undergraduate students. It will also develop outreach videos aimed at K-12 students and teachers.The project aims to generate up to 20 new precisely-dated records of monthly-resolved sea-surface temperature and hydrological variability in the central tropical Pacific during the period from 1800-1950CE using paired oxygen isotope and trace element measurements in modern and fossil corals from Kiritimati Island (2N, 157W). The proposed work builds on the success of recent "ensemble" approaches to coral-based climate reconstruction that allow for the development of high-fidelity, monthly-resolved records tropical Pacific climate with explicit quantification of uncertainties, grounded in calibration of modern corals against instrumental climate records over recent decades. Moreover, the application of paired coral d18O and Sr/Ca analyses allows for the separate identification of temperature and hydrological trends over the last centuries - filling critical data gaps and allowing for detailed data-model intercomparison with advanced ocean state reanalyses products. The proposed work includes the application of a wide variety of strategies to assess the robustness of the coral-based climate records, including detailed analysis of sample preservation, as geochemical alteration can introduce significant artifacts into coral-based climate reconstructions if it goes undetected. If successful, the proposed work would provide a blueprint for the extension of the short instrumental climate record throughout the Pacific Ocean, utilizing samples from extensive coral rubble fields that are present on many ocean islands.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.