Timing and magnitude of C02 uptake by ocean crust through seawater interaction and carbonate veining

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Fluid flow within the flanks of mid-ocean ridges is now recognized as one of the principal processes that control the budgets of many elements in the oceans and the aging ocean crust on long time scales. This includes CO2 for which carbonate veins in basalt crust impose an important sink, yet little is known about the respective global flux. In over thirty years of ocean drilling, ocean crust of all ages has been sampled to depths that allow an assessment of CO2 uptake in the uppermost crust, but flux estimates exisit only for a few sites. Old crust indicates global oceanic uptake fluxes of 2-4•1012 moles CO2/yr, whereas young crustal sections indicate uptake rates that are an order of magnitude smaller. These observations can only be reconciled if the crust takes up CO2 continuously throughout much of its life time, which is at odds with seismic and heat flow evidence suggesting progressive sealing of permeability and virtual shut down of circulation in crust older than 20-50 Myrs. We propose that this major conundrum in ocean floor research can be resolved by comprehensive and systematic analyses of carbonate veins from crustal sections that cover a range of ages of both slow and fast spread crust. Our approach is fourfold:(1) Logging of core archives to establish carbonate vein crustal inventories, (2) determination of trace element abundances in carbonate veins by laser ablation ICP-MS to determine the maturity of fluids from which the carbonate precipitated, (3) Sr isotope dating by laser ablation MC-ICP-MS analyses of suitable carbonate veins, and (4) determination of geochemical changes in vein halos. The expected results will lead to better estimates of the global CO2 flux between ocean crust and oceans and to a more comprehensive understanding of the timing and processes involved in setting this flux. The data will be merged with isotopic data (Ca, Sr, O, C) to be obtained within the framework of a companion proposal.