NERC-FAPESP: the Marine Gateways Project - Quantifying the causes and climatic consequences of the opening of the South Atlantic

Ocean circulation is driven by water masses with different densities. Much of this is generated at the ocean-continent boundary where near landlocked seas have a restricted connection with the global ocean, allowing them to evolve a different temperature or salinity. These marginal basins often form when continental plates coalesce - the Mediterranean today is a good example of this - or disaggregate - the opening of the South Atlantic around 100 million years as Gondwana broke apart is another. The evolution of these marine gateways therefore has a profound impact on the patterns of ocean circulation and its vigour. Changing palaeogeography is known to play a key role in major climate reorganisations such as the transition from greenhouse to icehouse conditions, and marine gateways are therefore the focus of several upcoming international scientific drilling projects.

When marine gateways allow only very limited exchange, large volumes of evaporites may precipitate in the marginal seas. These salt giants, which are not forming in the world today can be sufficiently large to change the salinity of the global ocean. The most recent salt giant formed around 5 million years ago in the Mediterranean. Using isotopes that respond to the different proportions of ocean and river water feeding the marginal basin, integrated with box modelling and global climate simulations, it has been possible to reconstruct and quantify Mediterranean-Atlantic exchange and show that the major climate impact of this gateway evolution precedes evaporite precipitation by several million years.

In this project we propose to develop and apply these techniques to the older and larger South Atlantic salt giant where there is still controversy over the location and timing of gateway evolution and hence the climatic impact of opening the South Atlantic. To do this we are extending an existing collaboration between Bristol and Utrecht where researchers have led much of the Atlantic-Mediterranean gateway research, to include researchers at the University of Sao Paulo who have essential expertise in the palaeogeography and chronology of the South Atlantic salt-bearing successions. This is therefore a joint NERC-FAPESP global partnership seedcorn application.

Over two years we propose to undertake fieldwork in Brazil led by the University of Sao Paulo, pilot isotope analyses and GCM analysis of existing global climate simulations at the University of Bristol, in parallel with box-modelling at Utrecht University. An early meeting in Bristol to review the initial pilot data will be followed by a mid-project model-data integration workshop in Sao Paulo. The workshop will be open to the wider research community in South America and we will particularly encourage the involvement of Early Stage Researchers. In addition, we will support Sao Paulo PhD students to apply for internship scholarships (FAPESP-BEPE) in order to be actively involved in the project. The last phase of this project will draw in researchers involved in marine gateway research associated with current scientific drilling projects, three of which are led by UK scientists. The final meeting in Bristol will be a forum both for presenting the scientific results of the project and for initiating an EU COST-Action application to support on-going community-building and collaborative research activities. This is designed to support and expand the scientific community engaged with long-term scientific drilling projects focused on marine gateways.