Oxygen Isotopic Composition of Miocene Meteoric Water (δ18Ow) in Alpine Foreland Basins

Abstract

The reconstructed stable oxygen isotopic composition of meteoric water (δ18Ow) is widely used for paleoclimate reconstructions. Understanding past environmental factors that drove changes in δ18Ow is essential for interpreting past climate conditions. Here, we investigate the spatial and temporal variations of δ18Ow in the Miocene Alpine foreland basin from multiple proxy materials with isotope‐enabled climate model simulations. Based on δ18O values and clumped isotope‐based temperatures of pedogenic carbonate nodules, we compare Middle Miocene δ18Ow records from the Northern Alpine Foreland Basin (NAFB) in Switzerland and its counterpart in the Mediterranean Alpine foreland (Digne‐Valensole Basin, SE France). Additionally, we analyze isotope‐tracking atmospheric general circulation model outputs of δ18O in precipitation for the Middle Miocene and present‐day to assess changes in distributions. Our results highlight a latitudinal δ18Ow gradient in the Middle Miocene that is similar to the present‐day. The occurrence of distinct N‐S differences in δ18Ow values during the Miocene are likely the result of a similar‐to‐present climate divide (North‐Atlantic vs. Mediterranean climates). Concurrently, we suggest that shifts in atmospheric circulation over the Alpine region during certain time intervals of the Middle Miocene led to rapid high‐amplitude variations in δ18Ow. We note significant differences in δ18Ow values between proxy‐based reconstructions and climate model simulations that we attribute to (a) proxy biases toward higher δ18Ow values and (b) inappropriate model resolution and topography for the Miocene Alpine region. Our study advances the use of multiproxy data‐model comparison for paleoclimate and paleoaltimetry reconstructions and points out the importance of integrating proxy and modeling approaches.