The existence of late Miocene evaporites beneath the Mediterranean Sea was one of the major early discoveries of scientific ocean drilling in the 1970s. The Messinian Salinity Crisis (MSC; 5.97 5.33 Ma) produced Earth¿s youngest salt giant deposit and documents a period of extreme environmental change for the Mediterranean basin, with potentially global implications. Recently, International Ocean Discovery Program (IODP) Expedition 401 built on this legacy by successfully recovering near-continuous records of the late Miocene to early Pliocene in the Mediterranean¿Atlantic gateway region. These cores will be used to resolve some of the outstanding questions about the MSC, including the history of water exchange, dense bottom currents, and environmental conditions on both sides of the gateway before, during, and after the event. Site U1611 in the western Alborán Sea yielded an unexpected result: routine shipboard analyses revealed high-salinity interstitial water, with a maximum of S = 70 just over a kilometer below the seafloor. The salinity maximum occurs less than 100 m below the sediments deposited during the MSC and includes parallel increases in both chloride and bromide ion concentrations. Based on the behavior of these highly conservative ions, we interpret the interstitial water to be the remnants of a Messinian-aged paleobrine that developed during the lead-up to evaporite deposition elsewhere in the Mediterranean. A similar subsurface brine documented at nearby ODP Site 976 suggests that this feature may be present regionally, even where Messinian sediments are not well preserved. The existence of this paleobrine, a result that was uniquely enabled by scientific ocean drilling and the analytical protocols developed by IODP, places key constraints on salinity changes within the Alborán Sea and gateway water exchange during the MSC.

Comunicación oral presentada en AGU Fall Meeting, del 9 al 13 de diciembre de 2024, en Washington D.C.