oa Messinian Flash Floods & Mediterranean Gateway Changes Detected by Plant Biomarkers Along the Southern Iberian Margin

International Ocean Discovery Program Expedition 401 drilled on both sides of the Mediterranean-Atlantic gateway. We discovered woody debris and continuous, stratified lake-like conditions in the Alborán Basin during the Messinian including during the interval during which the Mediterranean experienced the Messinian Salinity Crisis (MSC; 5.97–5.33 Ma). Plant biomarkers including plant wax and lignin characterize terrestrial ecosystems and hydroclimate, as well as the fluvial regimes that transport woody debris to the marine realm. Angiosperms dominate the lowlands with gymnosperms only at higher altitudes in SE Spain. These diagnostic components of Mediterranean lignin therefore serve as a tracer of Mediterranean overflow, that ceased when the gateway closed during the MSC. Precipitation isotopes are invariant on the Portuguese margin, but SE Spain received Mediterranean storms in the early Messinian and early Pliocene, contrasting with Atlantic-only winter rainfall in the MSC when the Mediterranean desiccated. Woody debris records flashy fluvial transport on the margin of SE Spain. The Messinian flashy fluvial regime provides geological precedent for the extreme precipitation and flood events seen in 2024 in this region that are predicted to worsen with future warming.