Project: Validation of the Strontium-Uranium Thermometer Against Instrumental Records of Ocean Temperature

NSF abstract:
Anthropogenic CO2 emissions are changing Earth's climate. Yet climate also varies naturally on timescales of decades to millennia. Characterizing this variability is critical to both quantifying the anthropogenic influence and projecting future change. Sea surface temperature (SST) plays a major role in climate yet the instrumental record is too short to enable a robust evaluation of natural variability. Proxy data generated from coral skeletons have potential to fill these gaps but generation of lengthy records requires use of dead colonies that grew before the instrumental era, for which existing geochemical SST proxies are not well-suited. A new thermometer, Sr-U, has been developed for application to non-living corals but the calibration to SST requires testing. This project seeks to validate Sr-U by reconstructing a record for the central Red Sea and comparing against well-constrained observational SSTs for the region. A successful outcome will benefit the scientific community by opening the global archive of non-living corals for SST reconstructions. Improved SST reconstructions will provide a target for the same numerical models used to predict future oceanographic and climate change.

Coral-to-coral geochemical variability is a major obstacle to SST reconstructions from non-living corals and Sr-U is based on a robust understanding of the processes that cause this variability. This project will generate Sr/Ca and U/Ca data for the last 50 years from an existing Porites coral core sampled in the central Red Sea and apply a calibration derived from Atlantic species to reconstruct the SST record. Heavy ship traffic in the region means the pre-satellite observational record is well-constrained. Additionally, Red Sea SSTs over the last 50 years are characterized by decadal variability superimposed on a long-term warming trend, and thus present an ideal test of the ability of Sr-U to capture both variability and trends in an unknown coral. The goal is a proof-of-concept, to demonstrate the universal application of Sr-U as a tool with which to reconstruct accurate SST records using modern and fossil corals alike.