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Reconstructing Mediterranean-Atlantic exchange during the Miocene

Final Report Summary - MEDGATE (Reconstructing Mediterranean-Atlantic exchange during the Miocene)

MEDGATE’s objectives were to train ten researchers, address specific scientific problems relating to the Mediterranean-Atlantic gateway during the Miocene and develop a European Network that leads international ocean gateway research. Here we detail how the project has met all these objectives fully and has had both direct and indirect socioeconomic implications.
Objective 1: To train nine Early Stage Researchers (ESR) and one Experienced Researcher (ER) in a wide variety of geological skills.
The MEDGATE programme included extensive training in field geology and biostratigraphic techniques, for which there is specific demand from the geoscience industries in Europe and globally. The training programme also included state-of-the-art geochemistry and numerical modelling that are sought-after academic research skills. The training was front-loaded both to ensure that the researchers had the skill set they required for the projects early on, and to give them time to develop into subject experts.
Objective 2: To expose the researchers to a multidisciplinary working environment and thus equip them for careers in both academia and industry.
The multidisciplinary training programme was supported by a strong ethos of collaborative research which involved extensive secondments to other institutions in the network. The effectiveness of MEDGATE’s training in equipping its researchers for careers in both academia and industry has been demonstrated by job offers to our researchers from both sectors. For example, the Experienced Researcher who was hosted by Repsol, MEDGATE’s full industrial partner, has transferred directly onto a full employment contract with them. Several of the ESRs close to completing their PhD theses have applied for, and been offered postdoctoral positions at prestigious academic institutions across the world.
Objective 3: To involve the researchers in all aspects of the project including its management and the dissemination of results to a wide community of academic and industrial stakeholders and the public.
MEDGATE’s earliest complementary skills training focussed on developing their ability to contribute to the technical training of the network as a whole. As their skills and experience grew, the researchers transitioned progressively to leading the technical training in their specialist field. This culminated in an international conference held in Morocco where, as well as contributing to the science presented, they designed the schedule, identified and solicited the keynote speakers, encouraged participants, convened the sessions, judged the prizes and led the fieldtrips. The high standard of their professionalism elicited unprompted praise from senior international participants at that meeting who included both academics and industrial scientists.
Objective 4: To address MEDGATE’s scientific aims concerning the Mediterranean-Atlantic gateway
Marine gateways play a critical role in the exchange of water, heat, salt and nutrients between oceans and seas. They have an important impact on both regional and global climate. MEDGATE focused on the two marine gateways, the Rifian (Morocco) and Betic (Spain) corridors that linked the Mediterranean with the Atlantic 5-10 million years ago, before the Gibraltar Strait formed. During closure of these two fossil gateways, the Mediterranean experienced massive salinity fluctuations and ~6% of global ocean salt was precipitated on its sea floor in an event known as the Messinian Salinity Crisis. The scientific aims of the network were to:
(1) Identify the location and geometry of the fossil corridors and the timing of exchange
An outstanding question is the identity of the corridor which fed Atlantic water into the Mediterranean during the Messinian Salinity Crisis. Detailed planktic foraminiferal analysis of previously undated strands of both the Rifian and Betic corridors demonstrated that neither of these were open during the crisis. Synthesising all existing evidence from the entire gateway region, MEDGATE concludes that, contrary to existing hypotheses, the Gibraltar Strait must have been open during the Messinian and supplying Atlantic water to the Mediterranean during salt precipitation. This has important implications for the location of hydrocarbon reservoirs.
MEDGATE research has also estimated the dimensions of the fossil gateway connecting the Mediterranean Sea and the Atlantic Ocean for the first time, using numerical theory of sea straits. During the Messinian Salinity Crisis the connection must have had a minimum depth of 30–45 m, a maximum width of 0.7–2 km and been up to 500 km long.
(2) Reconstruct the patterns of exchange through the fossil corridors
During extensive fieldwork in Morocco, we identified the first large-scale, siliciclastic contourites ever found preserved on land. These sediments form when dense water flows over a bathymetric barrier into the open ocean. The contourites in the Rifian Corridor demonstrate that the connection with the Atlantic was sufficiently restricted to allow Mediterranean water to become more saline than ambient ocean water, two million years before the first evaporite precipitated. MEDGATE research also demonstrated that younger, earliest Pliocene sediments deposited in the Gulf of Cadiz were the product of similar Mediterranean outflow processes through the Gibraltar Strait.
MEDGATE’s modellers have generated an innovative suite of climate simulations to quantify different aspects of the Mediterranean’s freshwater budget 5-10 million years ago. Combining these results with salinity information preserved in the rock record means we can reconstruct the Mediterranean-Atlantic density contrast, which is a major control on the vigour of exchange. These results have also led to new quantitative hypotheses for large fluctuations in Mediterranean salinity that occurred during the Messinian Salinity Crisis, involving freshwater input from the precursor lake that linked the Black and Caspian seas. These large-scale models are complemented by high resolution geochemistry which has allowed us to reconstruct the patterns of exchange between Mediterranean sub-basins over a 20 thousand year climate cycle. A strontium isotopic record from Spain, challenges accepted ideas on the interplay between freshwater input, water column stratification and the timing of exchange.
(3) Evaluate the local and global consequences
The main drivers of Mediterranean environmental change are the interplay between tectonic alteration of the gateway and climatic cycles driven by periodic changes to the earth’s orbit. MEDGATE’s multidisciplinary approach to this problem has allowed us to disentangle these two controls and reconstruct exchange during the lead up to the Messinian Salinity Crisis and at its termination. This provides a much better understanding of the record of both high amplitude and subtle environmental change in the Mediterranean, as well as having direct consequences for oil and gas exploration in the gateway region. Globally, MEDGATE’s work also has implications, the most important of which derives from the Late Miocene contourites found in the Rifian Corridor. These indicate that the outflow of dense Mediterranean water began earlier than previously thought and hence contributed to the enhanced formation North Atlantic Deep Water which led to the onset of Northern Hemisphere Glaciation in the Late Miocene.
Objective 5: To build a new European multi-sector network that will benefit researchers, the participating institutions and allow Europe to take the lead in studies of oceanic gateways.
MEDGATE has supported the development of both its researchers and staff. Two major international research drilling initiatives with direct relevance to MEDGATE science are being led by mid-career, female staff involved in the network. If funded, these will result in the investment of more than $100 million in gateway research. These projects build on and diversify MEDGATE’s cross-sectoral relationships with academia and industry. MEDGATE’s ESRs are being asked to participate in these projects and in existing and proposed ITNs.