Desert flashfloods recorded by Ba/Ca in benthic marine foraminifera (Operculina ammonoides)

River discharge proxies are essential for reconstructing terrestrial precipitation patterns and long-term climatic variability. Unfortunately, easily distinguishable direct proxies such as the presence of terrestrial muds in the sea are often missing after being winnowed and removed from the near-shore stratigraphy, or altered due to mixing and bioturbation. Barium, which is abundant in terrestrial sediments, is delivered to the sea via these runoff events in dissolved and particulate forms. Barium-to-calcium (Ba/Ca) ratios in carbonate skeletons of marine organisms have proven to be an indicator of discharge events, though their application in benthic foraminifera remains under-studied. In particular, their capacity to resolve individual events in perennial systems where seasonal contrasts are often muted has not been explored. This study investigates Ba/Ca ratios in live benthic foraminifera (Operculina ammonoides) from the shallow marine shelf of the hyper-arid Gulf of Aqaba–Eilat. This setting provides a unique natural laboratory where ephemeral river (wadi) floods are rare and brief, potentially providing an isolated geochemical runoff signal. Our results demonstrate that foraminiferal chambers precipitated within five months of a flood event exhibit Ba/Ca ratios approximately double the background levels (∼8 versus ∼4 μmol/mol). Stable Mg/Ca ratios and historical water parameters negate temperature and pH as drivers of this enrichment. These findings suggest that Ba/Ca ratios in shallow-shelf benthic foraminifera are controlled by post-flood changes in the porewater, thereby successfully archiving desert flash floods. Consequently, and with added calibration this may provide a potent proxy for reconstructing high-resolution paleohydrology in arid coastal regions and offers a potential framework for developing paleo-environmental proxies in coastal settings generally.