Meteoric water δ$^{18}$O across the Dinarides: Role of topography, air-mass mixing, and precipitation seasonality

Study region: Streams in the Dinarides ranging from coastal Croatia across the high-elevation
basins of Bosnia and Herzegovina to the lee of the Dinarides. Study focus: 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. New hydrological insights for the region: 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,
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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.