HR: 08:45h
AN: T31F-04    [Abstracts]
TI: Temporal Evolution of the Earth's Deep Water and Carbon Cycles
AU: * R\"upke, L H
EM: lruepke@ifm-geomar.de
AF: IFM-GEOMAR, SFB 574, Wischhofstr. 3, Kiel, 24148 Germany
AU: Phipps Morgan, J
EM: jp369@cornell.edu
AF: Department of Earth and Atmospheric Sciences, Cornell University, Snee Hall, Ithaca, NY 14853-1504 United States
AU: Hort, M
EM: hort@dkrz.de
AF: Abteilung f\"ur Geophysik, Universit\"at Hamburg, Bundesstr. 55, Hamburg, 20146 Germany
AU: Connolly, J
EM: james.connolly@erdw.ethz.ch
AF: Institut f\"ur Mineralogie und Petrographie, ETH-Zentrum, Sonneggstr. 5, Z\"urich, 8082 Switzerland
AB: Most investigation techniques for determining the Earth's hydration state only allow to constrain the present-day conditions. However, to understand the geodynamical and geochemical evolution of the Earth, an approach needs to be taken that includes time. We address the question of how the Earth's hydration state and CO$_2$ content may have evolved through time by the using geodynamic models. These models solve for the two main processes that control the global water and carbon cycles: outgassing at mid-ocean ridges and hotspots and deep recycling at subduction zones. We have recently presented a possible scenario on how the Earth's deep water cycle may have evolved through time (R\"upke et al., 2004). In that scenario the Earth's mantle has been largely, but not completely outgassed ($\sim$93%). Due to slab recycling, it contains about $\sim$49% of the exosphere's water content and $\sim$33% of its initial water content, of which $\sim$80% has been recycled back from the exosphere. Here we present new results from a follow-up study in which we have linked and put into relation our predicted mantle water concentrations to geochemically determined water concentrations in OIB and MORB as recently determined by (Dixon et al., 2002). We find that in a plum-pudding type mantle, the most primitive components (FOZO) are the wettest; recycling associated components like the EM&HIMU components are much dryer but contain still more water than the dry depleted mantle source that melts beneath mid-ocean ridges to make MORB. These findings are in striking agreement with the geochemical data, so that our modelling approach appears to be a valid approximation to the evolution of the Earth's water cycle. Furthermore, we will present first results from new models that will solve for the global carbon cycle. These new models will use a 2-D subduction zone model that solves for decarbonification (and thereby deep CO$_2$ recycling) at subduction zones and a parameterized mantle convection model to solve for CO$_2$ outgassing at mid-ocean ridges and hotspots. This type of modelling approach can help to reconcile data from different fields of geosciences in order to better understand how the Earth's hydration and carbonification state may have evolved through time to form the present-day conditions.
DE: 1749 Volcanology, geochemistry, and petrology
DE: 1025 Composition of the mantle
DE: 1635 Oceans (4203)
DE: 1010 Chemical evolution
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting