by Rachel Flecker

Marine gateways play a critical role in the exchange of water, heat, salt and nutrients between oceans and seas. The advection of dense waters helps drive global thermohaline circulation and, since the ocean is the largest of the rapidly exchanging CO2 reservoirs, this advection also increases the sensitivity of the ocean to atmospheric carbon changes. Changes in gateway geometry can therefore significantly alter both the pattern of global ocean circulation and associated heat transport and climate, as well as having a profound local impact. Today, the volume of dense water supplied by Atlantic-Mediterranean exchange through the Gibraltar Strait is amongst the largest in the global ocean. For the past five million years this overflow has generated a saline plume at intermediate depths in the Atlantic that deposits distinctive contouritic sediments in the Gulf of Cadiz. This Pliocene gateway configuration evolved during the Miocene from a wide, open seaway to two narrow corridors: one in northern Morocco; the other in southern Spain. These more restricted connections permitted Mediterranean salinity to rise and a distinct, dense water mass to form and overspill into the Atlantic for the first time. Further restriction and closure of these marine corridors resulted in extreme salinity fluctuations in the Mediterranean, leading to the formation of a salt giant, the Messinian Salinity Crisis. This amphibious drilling proposal is designed to recover a complete record of Atlantic-Mediterranean exchange from its Late Miocene inception to its present-day configuration which was achieved in the Early Pliocene. This will be achieved by targeting with IODP, off-shore sediments on either side of the Gibraltar Strait, and, with ICDP, recovering core from Gibraltar’s two precursor connections, the Rifian and Betic corridors which are now exposed on land in Morocco and Spain. The scientific aim of the IMMAGE is to constrain quantitatively the consequences for ocean circulation and global climate of the inception of Atlantic-Mediterranean exchange, to explore the mechanisms for high amplitude environmental change in marginal marine systems and to test physical oceanographic hypotheses for extreme high-density overflow dynamics that do not exist in the world today on this scale.

• The objectives of the IMMAGE research program are: Objective 1:
• To document the time at which the Atlantic first started to receive a distinct overflow from the Mediterranean and to evaluate quantitatively its role in Late Miocene global climate and regional environmental change. Objective 2:
• To recover a complete record of Atlantic-Mediterranean exchange before, during and after the Messinian Salinity Crisis and to evaluate the causes and consequences of this extreme oceanographic event, locally, regionally and globally. Objective 3:
• To test our quantitative understanding of the behavior of ocean plumes during the most extreme exchange in Earth’s history. These objectives require sediments that can only be recovered by undertaking both on-shore drilling in Morocco and Spain and offshore drilling in the Alborán Sea and on the Atlantic margin. The drilling strategy for IMMAGE is therefore amphibious.

Africa, Contourites, Europe, Gibraltar, IMMAGE, Marine Gateway, Morocco, Paleoclimate, Salt Giant, Spain

Latitude: 36.00000, Longitude: -6.00000