Climate variability and precipitation isotope relationships in the Mediterranean region

This study investigates the links between Mediterranean precipitation δ 18 O and Mediterranean sea level pressure (SLP) anomalies during the winter months and over the years 1960–present. Previous studies have considered only the influence of the North Atlantic Oscillation (NAO) on rainfall δ 18 O at Mediterranean sites, but Mediterranean winter SLP variability evolves with at least three degrees of freedom, which means that other climate patterns may be equally important in influencing Mediterranean rainfall δ 18 O. In this study, Multivariate Linear Regression (MLR) is employed to identify the ‘coupled patterns’ in the Mediterranean winter SLP and δ 18 O fields. The multivariate linear model is estimated in two different ways, using Principal Components Regression (PCR) and regularized Canonical Correlation Analysis (regCCA), resulting in two different models which are compared. In both models two main patterns are identified, that explain 50% of the shared variance in the SLP and δ 18 O fields. Subspace projection of various regional and Northern Hemisphere climate indices shows that the two main patterns are more closely related to local Mediterranean climate indices than to other Northern Hemisphere climate indices. Analysis of the predicted and residual fields from the two models suggests that the regCCA model provides better predictability for rainfall δ 18 O at central Mediterranean sites, while both models explain relatively less of the rainfall δ 18 O variance at eastern Mediterranean sites. These results can potentially aid the interpretation of the climate‐isotope signal preserved in high‐resolution natural archives from different parts of the Mediterranean.