Deciphering Microscale Elemental Variations in Coral Skeletons: Towards Robust Paleoclimate Reconstruction and Beyond

Reconstructing Earth’s climate history provides the context for the ongoing climate change and is essential for advancing our understanding of the climate system and for validating climate model predictions. Many of these reconstructions rely on analyses of the chemical composition of various climate archives such as coral skeletons, but they can be impacted by the non-climatic factors that can also influence the chemical composition of these archives. This research will directly address this challenge by developing a mechanistic understanding of the key factors affecting the elemental composition of coral skeletons and thus provides a new method for robust climate reconstruction. In addition, this research will yield new insights about how corals build their skeletons and their responses to environmental changes such as thermal stress. Such knowledge is much needed for predicting the fate of coral reefs in the changing climate. This project will also support the education and training of undergraduate students and a graduate student, and include outreach activities to local K-12 schools and the general public. The elemental compositions of coral skeletons are among the most important proxies for reconstructing past seawater physicochemical conditions and are instrumental for advancing our understanding of Earth’s dynamic climate system. However, the presence of physiological influences (so-called vital effects) can complicate the interpretation of coral elemental compositions. This is especially prevalent at the microscale, hindering robust reconstructions of past environmental changes and limiting most coral element-based paleo-reconstructions to monthly and coarser resolutions. This project seeks to develop a quantitative physicochemical framework to accurately interpret elemental variations in coral skeletons, especially on microscale, and thus enable robust paleoclimate reconstruction and estimations of coral physiological regulation across a range of temporal resolutions. Specifically, the project will consist of three main tasks: (1) construct a physicochemical model to quantitatively simulate microscale (e.g., micrometer-scale) elemental variations (such as magnesium, lithium, strontium) in coral skeletons; (2) develop a multi-element Bayesian method to robustly reconstruct changes in seawater temperature and coral physiological regulation (e.g., enzymatic proton pumping) from coral elemental records; (3) extend the model to simulate uranium and boron incorporation into coral skeleton and explore their potential for improving the Bayesian method and for reconstructing seawater carbonate chemistry. This project is expected to produce a suite of numerical models and methods that can be readily used by the community for robust paleoclimate reconstruction and beyond. 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.