The Red Sea is a semi-enclosed basin where surface winds cause high evaporative cooling and create north-south gradients in sea surface temperature (SST) and salinity (SSS). This regime results in northward transport where surface waters become colder and more saline, and thus dense enough to sink into the subsurface in the far north, forming Red Sea Overflow Water (RSOW). Understanding the hydrography and climate of the Red Sea provides valuable insight into the factors controlling this circulation pattern. Although there are numerous instrumental datasets constraining global SST, there are limited products available to study SSS, especially in narrow marginal seas such as the Red Sea. Corals, however, serve as natural hydrographic archives by incorporating the chemical composition of the surrounding seawater into their skeletons, recording changes in conditions during growth. Strontium-calcium (Sr/Ca) and oxygen isotope (δ18O) ratios can be used to reconstruct variability in SST and SSS across spatial scales where reliable SSS data do not exist. In this study, we investigate Porites sp. coral records along the length of the Red Sea, from the inflow of waters through the Strait of Bab-al-Mandeb in the south, to the site of RSOW formation in the north. Monthly-resolution measurements of coral Sr/Ca and δ18O during the satellite calibration period trace the evolution of surface temperature and salinity at multiple temporal scales. The mean annual coral δ18O values reflect spatial gradients of SST, SSS, and seawater potential density as the waters flow north. Further, the average coral δ18O-SST slope from each site in the basin (-0.10) captures realistic coral SSS reconstructions. This work provides insight into how Red Sea surface waters evolve and will improve our understanding of how regional hydrography contributes to overturning circulation through time.
Acknowledgements: This work was funded by the U.S. National Science Foundation (Grant No. OCE-2303246 to SAM, DPG, KAH, and VVM). We thank the MC&G Department and the Guest Student Program at WHOI for their support. We are also grateful to everyone who assisted in obtaining and sampling cores from all six sites. Special thanks to Stable Isotope Laboratory Technician Juliana Guimaraes Ribeiro Souza for her help processing samples. This work was additionally supported by the NYS/UUP Joint Labor-Management Committees through the Dr. Nuala McGann Drescher Leave Program award to SAM.