Oxygen Isotopes as a Key Proxy of Equatorial Pacific SST Variability in a Multiparametric Tree-Ring Approach in the Low-Latitude Andes

Sea surface temperature (SST) variability in the equatorial Pacific plays a crucial role in shaping global climate patterns. As El Niño–Southern Oscillation (ENSO)-related extremes intensify, understanding SST fluctuations and their connection to ENSO becomes increasingly important. However, limited instrumental records hinder the ability to simulate SST variability and distinguish natural variability from anthropogenic trends. Tree rings provide annual data essential for reconstructing past SST and ENSO dynamics. While previous research has successfully reconstructed SST variability in the central equatorial Pacific, capturing signals from the eastern Pacific remains more challenging. This study analyzes P. rodolfovasquezii trees from the central Peruvian Andes (11.72°S, 75.14°W) using ring width and stable oxygen and carbon isotopes to assess their sensitivity to Pacific SST variability. We focus on the two leading modes of SST variability derived from Empirical Orthogonal Functions: EOF1 representing SST variability in the Niño 3.4 region, and EOF2 depicting a west-east dipole between the Niño 4 and 1 + 2 regions, explaining 66.22% and 10.79% of the variance in tropical Pacific SSTs, respectively. We developed a 129-year multiproxy tree-ring record. Trees' sensitivity to local and regional hydroclimate is reflected in the temporal variability of their isotopic content. Tree-ring oxygen isotopes showed significant correlations with both SST modes, although their ability to capture EOF2 variability was limited—likely due to the trees' distance from the influence region of the Niño 1 + 2. Overall, oxygen isotopes outperformed ring width and carbon isotopes, underscoring their potential for future SST reconstructions in the tropical Andes.