Fluid Fluxes and Manganese Nodules

Hydrothermal fluids can withdraw significant amounts of heat from the oceanic lithosphere by lateral fluid flow through permeable basaltic crust of an age of up to 65 Ma. Basement out- crops in-between impermeable pelagic sediments permit fluid recharge and discharge. A recharge site has been detected on the flank of one of the numerous seamounts in the work- ing area in the equatorial E-Pacific. Moreover, successions of small basins typical for "hydro- thermal pits" occur which could be interpreted as fossil discharge sites. The objective of this project will be to investigate the regional pattern of fluid circulation based on heat flow meas- urements and pore-water geochemistry. Recharge of oxic seawater causes upward oxygen diffusion into the sediments overlying the permeable basalt in areas proximal to the recharge sites. The prolonged oxygen exposure time is suggested to have a strong impact on biogeo- chemical processes in the sediments and the element inventory of Mn nodules. The quantita- tive investigation of such processes and element enrichments and their range of influence around recharge sites is thus the second objective of this project. An additional goal will be to investigate whether fluid circulation through 21 Million years old crust can mobilize metals and affect metal flux rates into sediments and nodules at possible discharge sites.