Geology Club Seminar

International Ocean Discovery Program (IODP) Expedition 401 drilled four sites on both sides of the Mediterranean-Atlantic gateway. Onboard, we identified woody debris and continuous, stratified lake-like conditions in the Alborán Basin, the westernmost basin of the Mediterranean, during the Messinian including during the interval during which the Mediterranean experienced the Messinian Salinity Crisis (MSC; 5.97–5.33 Ma). In subsequent organic geochemical analyses of sediments from all four sites, we quantified the changing delivery and burial of plant material through analysis of lignin phenols and plant wax n-alkanes, n-alkanoic acids and their carbon and hydrogen isotopic composition across the late Miocene and early Pliocene. Increased terrestrial inputs were detected in the Alborán Sea sediments and the Atlantic site, closest to the Mediterranean gateway relative to more distal sites. Late Miocene vegetation on the Iberian Peninsula was, like today, mostly angiosperm, open canopy and C3-dominated, with gymnosperm inputs detected from the high mountain ranges bordering the western Alborán Sea. Precipitation isotopic composition was found to be invariant in all three Atlantic sites, suggesting a consistent Atlantic-winter rainfall regime on the Portuguese margin. In the Alborán Sea, we detect the Mediterranean Sea as an additional source of summer rainfall to SE Spain, with Atlantic-only winter rainfall during the MSC. Our multi-biomarker approach characterizes changing conditions in the western Alborán Sea during the Messinian and identifies changes in Mediterranean Overflow Water outside the gateway at the defining boundary between Miocene and Pliocene climate states.