Global surface warming markedly slowed between 2000 and 2014 despite a continued increase in greenhouse gases in the atmosphere. Both climate models and observations suggest that this slowdown or "hiatus" in warming may be attributed (at least in part) to strong trade-winds in the tropical Pacific. These strong winds transport heat into the subsurface ocean, leaving less heat to warm the atmosphere. Because wind strength changes on a decade-to-decade timescale (associated with natural variability in the Pacific), other periods of both accelerated and reduced warming over the last 100 years are likely tied to these changes in tropical trade-winds. Thus, warming will likely accelerate in the coming decade(s) when the cycle reverses and trade-winds weaken once again. However, our understanding of the link between global air temperatures and tropical Pacific wind strength to date has been limited by the scarcity of historical wind observations. This project will utilize the chemical fingerprints of changes in tropical Pacific winds captured in the skeleton of living and fossil corals to investigate past wind variability - and its link to global air temperatures - across the past century and preindustrial era. The research will also extend the application of this novel wind archive, providing key groundwork for such records to be extended to additional sites and time periods. These natural archives of tropical Pacific wind strength over the recent past have the potential to dramatically improve our understanding of the impact of wind variability on the rate of global climate change. This project will also contribute to broadening participation and diversity in science by supporting two early career female scientists, a minority postdoctoral researcher and two undergraduates, who will together develop programs to promote race, gender, and LGBTQ diversity, equity and inclusion at Boston University.
Tropical Pacific coral records have dramatically improved our understanding of the oceanic response to changes in climate forcing over the past millennium, but our understanding of the associated atmospheric response remains limited by uncertainties in the interpretation of (often indirect and/or remote) hydrological proxies. This project leverages existing modern and fossil coral cores and a promising new coral proxy to investigate tropical Pacific trade wind variability across changes in natural and anthropogenic forcing. Building off pioneering studies linking westerly wind anomalies and coral skeletal Mn/Ca at Tarawa Atoll, the project will calibrate and extend this new proxy across sites (Tarawa, Kiritimati, Butaritari, and Palmyra) and time periods (20th century and Little Ice Age/preindustrial). Initial results demonstrate that coral Mn/Ca from Kiritimati and Butaritari capture the westerly winds observed at these sites during the 1997/98 El Niño event, supporting the causal link between wind variability and coral Mn/Ca at atolls with west-facing lagoons, and thus the potential for extending Mn/Ca-based trade-wind reconstructions across space and time. This project will produce the first robust, well-replicated, and quantitative reconstructions of Pacific trade wind strength spanning the 20th century and Little Ice Age (LIA) to preindustrial period (1400-1850CE) using overlapping modern and fossil corals from the western and central equatorial Pacific. This project also lays the foundation for coral Mn/Ca-based trade-wind reconstructions to be expanded to other sites and time periods by exploring the strengths and limitations of this novel proxy. Such trade-wind reconstructions have the potential to dramatically improve our understanding of trade-wind variability and its impact on global climate change in response to both natural and anthropogenic forcings.
