Meteoric water δ18O across the Dinarides: Role of topography, air-mass mixing, and precipitation seasonality

Streams in the Dinarides ranging from coastal Croatia across the high-elevation basins of Bosnia and Herzegovina to the lee of the Dinarides. The topographic evolution of the Dinarides is poorly-constrained and its controlling geodynamic mechanisms remain unclear. The oxygen-isotope composition (δ 18 O) of authigenic minerals is a common paleo-altimeter for reconstructing past topography, proper interpretation requires thorough constraints on mechanisms modifying modern meteoric-water δ 18 O. To constrain modern δ 18 O patterns across the Dinarides, we collected new stream samples and integrated them with published water stable isotope data. Meteoric-water data show δ 18 O is higher at the coast (∼-6 ‰) and lower at the peak (∼-11 ‰). We use moisture trajectory models to show isotopic patterns across the Dinarides reflect two distinct moisture sources. The dominant source of moisture on the windward side originates from the Mediterranean and the leeward side has a continental source. This difference in moisture sources is reflected in d‐excess values, which are high along the windward margin—reflective of Mediterranean moisture—and low in the lee, reflective of summertime, continental-sourced moisture. We interpret orographic rainout as the primary-driver of modern precipitation and surface water δ 18 O with secondary influences from moisture sources and precipitation seasonality. Our findings have implications for understanding the climatic processes that deliver moisture as well as our understanding of the past topography of the Dinarides. • HYSPLIT and WAM modeling identify two distinct sources of moisture to the Dinarides. • Orographically forced rainout is the primary control on δ 18 O patterns. • Secondary influences include shifts in precipitation and moisture source variability. • d‐excess analysis suggests 17O-excess offers a robust proxy for paleoelevation, improving paleotopographic reconstructions.