OSCAR - Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge

The cooling of young oceanic crust is the main physical process responsible for removing heat from the solid Earth to the hydrosphere. Close to the mid-ocean ridge rapid cooling is dominated by hydrothermal circulation of seawater through the porous and fractured basalt crust. This hydrothermal fluid is then discharged into the ocean mainly along the ridge. In this interdisciplinary project we will investigate the effects of this heat loss and hydrothermal circulation in both the solid Earth and the ocean. We will, for the first time, derive an integrated model which will be constrained by geophysical, geological and physical oceanography data that includes pathways in both the solid Earth and the ocean including fluxes through seabed.

The most rapid heat exchange occurs close to the fast-spreading ridges, where there are little or no sediments, driven by hydrothermal flow. Cold ocean water enters the fractured basalt in areas on the ridge flanks and flows through the permeable crust becoming super-heated in the proximity of the axial magma chamber. This highly buoyant water ascends rapidly and escapes into the oceans along the ridge axis and is known to form distinct vents called black smokers. Once in the ocean the hot water mixes with the ambient cold water through entrainment and forms a plume that rises to its point of neutral density. The entrainment process may increase the volume of the water in the plume by several orders of magnitude thereby providing a mechanism to heat and lift the densest waters away from the bottom boundary layer. These waters are then more readily available for further mixing and heating as part of the global thermohaline circulation system. The intensity of the hydrothermal fluid flow in the crust decays with distance from the ridge axis because of clogging of the pathways by geochemical alteration products which changes the geophysical properties of the crust and with age, pelagic sediments isolate the fractured basaltic upper crust from the overlaying water preventing direct water exchange. Here conductive heat loss is determined by the thickness and structure of this layer of sediment.

The project will acquire an interdisciplinary dataset which integrates physical oceanography and geophysics into a single data acquisition cruise. Using these data we will build and parameterise new integrated models that will provide valuable insight and new constraints of the thermal processes close to ocean ridges that includes a permeable seabed. These data and resultant models will set a new benchmark for integrated multi-physics experiments and will result in a new understanding of the fluid and heat fluxes at ocean ridges and, as importantly a better understanding of what geophysical and oceanographic data actually resolve in the context in an oceanic axial ridge setting, and a predictive model that can be applied to similar ocean ridge systems world-wide.

The main beneficiary of knowledge arising from this research is anticipated to be the academic community working on a diverse range of problems related to ocean ridge processes, in particular those interested in the formation of the ocean crust and hydrothermal circulation and transport of minerals from the solid Earth to the hydrosphere and biosphere. There may also be commercial interest from mineral extraction industry 1) to determine the mode of formation and hence mode of extraction of seabed located mineral deposits and 2) the better understanding of the origin and development of ore resources generated by the flow of fluids though host rocks, which extract and then enrich specific minerals at specific locations along that particular fluid flow path.

As part of the project we will convene a number project meetings and workshops. In particular, we plan an interdisciplinary workshop in the fourth year of the project which will bring together all interested parties to discuss the results and their wider implications for understanding fundamental processes. Results will be presented through seminars at other institutions and at national and international conferences. Collaborative science papers with other interest groups will be encouraged, together with joint applications for further funding for cross-disciplinary research based on the results of this project. We will use the web to publish work package summaries, progress updates and results, both in "academic speak" and in language and presentation style for stimulating general public's interest in the project and the associated research areas. We will also establish a web-forum to enable inter-researcher discussion with the wider community.

We will encourage public interest in the research throughout as exploration of the deep oceans and geological processes that shape the planet are of general interest. This research project involves a major sea campaign of data acquisition using a wide and diverse range of equipment, therefore, while at sea the science party will engage in "blogging", including video and sound clips as well as images, to convey their experiences of the research activities as they happen. We will also participate in the Classroom at Sea scheme (see http://www.classroomatsea.net/index.html) to encourage real-time interaction with teachers and school children of all ages.

The following milestones will measure the success of this impact plan:
1)web site with both public and private sites - monitor usage;
2)setting up teacher at sea and class room at sea - monitor websites;
3)a list of seminars will be maintained, together with abstracts and science papers (these too will be placed on the web);
4)establishing links with free-lance science writer early in project and involve them at project workshops - popular science article in year 3 and/or 4;
5)a 2-day interdisciplinary workshop hosted at Durham with invited keynote speakers on ridge formation, evolution, and associated hydrosphere and biosphere.