Multicentury records of ENSO and rainfall in corals from northern Australia

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This project integrates two fundamental issues of global environmental change, tropical climate variations and coral reef vitality. By developing linked histories of reef climate and coral growth on the remote northern Great Barrier Reef, this research will illustrate how the region's climate has changed over the past 200+ years and how coral growth has varied in response. Corals in this region can survive for centuries, and a core from the top to the bottom of a long-lived coral colony reveals annual banding that documents the rate of coral growth over that time. The coral's skeletal chemistry tracks the environmental conditions (temperature, salinity, sedimentation) under which the coral grew. Because the corals grow at a rate of a centimeter or more each year, cores can be sampled at a scale of weeks to months to determine short-term (seasonal) as well as long-term (century) trends in growth and environment. The project takes advantage of cores already recovered from northern Australia, where temperature and salinity are closely tied to the state of the El Niño system. El Niño influences climate around the world. This research will help climate scientists understand how El Niño is changing as the world warms and whether recent strong El Niño events are unusual or within the range of natural behavior. By linking the climate record to a history of coral growth from the same core, this project will help coral ecologists to see the connections between climate variations and coral growth rates from seasonal to century time scales. The research includes collaboration with the Australian Institute of Marine Sciences (AIMS), which advises the Australian government on reef management and conservation. By spending a summer at AIMS, a graduate student will receive high-level experience in issues of coral health, growth, and conservation that are critical for managing reefs here in the US as well as abroad. Project participants will engage in interdisciplinary climate research at the University of Arizona, including climate model analysis, the global impacts of El Niño, and communicating their work to a broader audience through public presentations at Biosphere-2. The specific goals of this project include the following:- Use multicentury, subseasonal measurements of coral δ18O and Sr/Ca to define the natural variability of temperature and salinity in this region, and their relationship to regional climate; - Extract seasonally specific histories of El Niño and Australian monsoon rainfall to compare with other records and evaluate for long-term variability; - Compare geochemical histories with luminescent and growth band properties to evaluate agreement and sensitivity as proxies for environmental change; - Use the multivariate information from corals to assess relationships among environmental variations (SST, SSS, and sedimentation) and coral growth (extension, calcification); - Incorporate records into broader analyses of tropical variability, e.g. long-term variations and trends, large-scale patterns, multiproxy syntheses, and comparisons to GCM simulations. This project represents a major advance in climate and coral studies. Despite the long history of coral paleoclimatology, this will be the first integration of geochemical and growth-band characteristics at a subseasonal, multicentury scale. Multiple paleoclimate proxies will yield broadly useful reconstructions of El Niño and monsoon rainfall and reveal how environmental changes influence coral growth. These results will be incorporated into large-scale syntheses to improve understanding of long-term tropical variability. All results will be publically shared with reef managers and other stakeholders, as part of the AIMS mission of science-based conservation, and presented in Arizona to the thousands of visitors that pass through the University of Arizona's Biosphere-2.