Proxy interpretation of coral-recorded seawater 18O using 1-D model forced by isotope-incorporated GCM in tropical oceanic regions

Abstract

The oxygen isotopic ratio in the seawater (δ18Osw) recorded in δ18O of coral skeleton for several centuries in tropical regions is an important variable for reconstructing the past climate. However, the relationship between δ18Osw and hydrological balance has not been clearly uncovered yet. In this study, a one-dimensional ocean budget model forced by the global quasi-reanalysis isotope data, which is the output of an isotope-incorporated global spectral model, is employed to simulate δ18Osw. The results from the simulations are compared with 31 coral records in tropical oceanic regions. The 1-D model successfully reproduces δ18Osw in 21 coral records, indicating these corals have the potential to reconstruct the local hydrological budget. The results also confirm that the reproducibility of the 1-D model generally increases with the annual precipitation variability. However, in the regions where the precipitation variability is less, it is more difficult to reconstruct climatic information from the δ18Osw, since the nonlocal physical processes unaccounted for in the 1-D model may affect δ18Osw. The sensitivity analysis of the 1-D model shows that in tropical oceanic regions, the large-scale precipitation is the dominant factor for δ18Osw, confirming that δ18Osw recorded in the coral records is a proxy for the precipitation anomaly. This study implies that δ18Osw is more closely associated with precipitation and local water isotope budget in tropical oceanic regions than elsewhere, and that the 1-D model is a useful approach for the proxy interpretation in tropical oceanic regions.