International Ocean Discovery Program
Expedition 401 Preliminary Report
Mediterranean–Atlantic Gateway Exchange1
10 December 2023–9 February 2024
Rachel Flecker, Emmanuelle Ducassou, Trevor Williams, and the Expedition 401 Scientists
1 Flecker, R., Ducassou, E., Williams, T., and the Expedition 401 Scientists, 2024. Expedition 401 Preliminary Report: Mediterranean–Atlantic Gateway Exchange. International Ocean Discovery Program. https://doi.org/10.14379/iodp.pr.401.2024
Abstract
Marine gateways play a critical role in the exchange of water, heat, salt, and nutrients between oceans and seas. Changes in gateway geometry can significantly alter both the pattern of global ocean circulation and climate. Today, the volume of dense water supplied by Atlantic–Mediterranean exchange through the Gibraltar Strait is among the largest in the global ocean. For the past 5 My, this overflow has generated a saline plume at intermediate depths in the Atlantic that deposits distinctive contouritic sediments and contributes to the formation of North Atlantic Deep Water. This single gateway configuration only developed in the Early Pliocene. During the Miocene, two narrow corridors linked the Mediterranean and Atlantic: one in northern Morocco and the other in southern Spain. Formation of these corridors followed by progressive restriction and closure resulted in extreme salinity fluctuations in the Mediterranean, leading to the precipitation of the Messinian Salinity Crisis salt giant. International Ocean Discovery Program (IODP) Expedition 401 is the offshore drilling component of a Land-2-Sea drilling proposal, Investigating Miocene Mediterranean–Atlantic Gateway Exchange (IMMAGE). Its aim is to recover a complete record of Atlantic–Mediterranean exchange from its Late Miocene inception to its current configuration by targeting Miocene offshore sediments on either side of the Gibraltar Strait. Miocene cores from the two precursor connections now exposed on land will be obtained by future International Continental Scientific Drilling Program (ICDP) campaigns.
Plain language summary
Today, Mediterranean–Atlantic seawater exchange takes place exclusively through the Gibraltar Strait. Around 8 million years ago, however, there were another two gateways: one in northern Morocco and the other through southern Spain. Both connections have subsequently closed and been tectonically uplifted and preserved on land. Extreme narrowing of these pre-Gibraltar Strait connections raised salinity in the Mediterranean substantially, leading to the precipitation of more than 1 km of salt on the Mediterranean’s seafloor. This process may have contributed to a major episode of global cooling. The chemical and physical properties of the sediments preserved in and on either side of these corridors are key to understanding and quantifying this global cooling. International Ocean Discovery Program (IODP) Expedition 401 is the offshore drilling component of the Land-2-Sea drilling proposal, Investigating Miocene Mediterranean–Atlantic Gateway Exchange (IMMAGE). The expedition recovered records of exchange preserved off shore in the Atlantic and Mediterranean. Future drilling on shore will target the fossil gateway records that are now preserved on land.