Discriminating Deep Water Deposits for IODP Expedition 401: "Mediterranean-Atlantic Gateway Exchange" (Acronym: DISCRIMINATE)

Ocean basins are connected by gateways (e.g., Drake Passage), sometimes referred to as seaways, passages, straits, and corridors. 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 affects atmospheric carbon concentration.

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, generates bottom currents distinctive deposits (called "contourites") in the Gulf of Cadiz and contributes to the formation of North Atlantic Deep Water.

This single gateway configuration only developed in the early Pliocene, however. During the Miocene, a wide, open seaway linking the Mediterranean and Atlantic evolved into two narrow corridors: one in northern Morocco; the other in southern Spain. Formation of these corridors permitted Mediterranean salinity to rise and a new, distinct, dense water mass to form and overspill into the Atlantic for the first time.

Further restriction and closure of these connections resulted in extreme salinity fluctuations in the Mediterranean, leading to the formation of the Messinian Salinity Crisis salt giant. The International Ocean Discovery Program (IODP) Expedition 401: "Mediterranean-Atlantic Gateway Exchange" is planned to recover a complete record of Atlantic-Mediterranean exchange from its Late Miocene inception to its current configuration.

This IODP expedition is the offshore component of the Land2Sea Proposal IMMAGE "Investigating Miocene Mediterranean-Atlantic Gateway Exchange", which aims 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 JOIDES Resolution Science Operator (JRSO) was pleased to invite my participation as a Sedimentologist on IODP Expedition 401. This proposal "Discriminating Deep Water Deposits for IODP Expedition 401: "Mediterranean-Atlantic Gateway Exchange" (DISCRIMINATE) would support my participation in the IODP Exp 401 covering my participant's cost; staff, travel and subsistence, and moratorium period research.

This research project aims the discrimination d of deep marine deposits, with special emphasis on possible deposits generated by bottom currents (contourites) or sediment reworked by currents (as reworked turbidites), on the Atlantic sites from IODP Expedition 401. The specific research objectives of the proposed research based on than general aim are: a) recognise and discriminate bottom current deposits, for estimate the bottom current variability and circulation before, during and after the Messinian Salinity Crisis; b) Understand the long- and short-term dynamics and exchange of water masses during key intervals during the Late Miocene (as the early and Late Messinian), and c) determine the key events and their significance for basin analysis and palaeocirculation.

The growing interest in, and implications of, contourite and sediment reworked by currents deposits demonstrates that these sediments represent significant deep-marine sedimentary environments.