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BREAKOUT SESSION 2: DEEP CARBON FLUXES What are the key unanswered questions?

What are abundances and chemical states with depth of key species in the mantle? Carbon (COx, graphite, recycled from surface, other?), related species (Fe, H, Nb, redox state [fO2], 3He)

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BREAKOUT SESSION 2: DEEP CARBON FLUXES What are the key unanswered questions?

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  1. What are abundances and chemical states with depth of key species in the mantle? Carbon (COx, graphite, recycled from surface, other?), related species (Fe, H, Nb, redox state [fO2], 3He) What is the nature of the major processes that deliver carbon toward the surface? Under MOR? OI? Arc? Fore-arcs? Back-arcs? How do vertical fluxes vary over various timescales? Modern fluxes versus longer timescales. Tectonics variations over deep time (spreading rates, geothermal gradient, etc). MOR: how do C fluxes vary along the ridges (80 to 90 percent of global magma production today)? OI: Present versus past fluxes (episodicity)? Overall long-term fluxes? Subduction zones: C budget wrt to re-injection vs loss to surface (effect of C species, carbonitized basalt vs sedimentary C, slab PvsT trajectories [wrt plate age, long-term changes, etc.]) Flux methodology: C/3He C/Nb BREAKOUT SESSION 2: DEEP CARBON FLUXESWhat are the key unanswered questions?

  2. Where do we want to be in 10 years? • Improved quantitative understanding of modern mantle effluxes in MOR, OI, arcs, continents (magnitudes, geographic variations) • Improved quantitative understanding of modern influxes in arcs, continents (chemical states of C, magnitudes, geographic variations) • Variations of fluxes over time (Holocene) • Relationships between heat flow and C fluxes (modern) • Chemical states of C in upper mantle

  3. Where do we want to be in 25 years? Quantitative understanding of modern effluxes in MOR, OI, arcs, continents (magnitudes, geographic variations) Improved quantitative understanding of modern influxes in arcs, continents (magnitudes, geographic variations) Carbon abundances and speciation in igneous oceanic crust Variations of fluxes over time (up to Ga timescales) Relationships between heat flow and C fluxes (up to Ga timescales) Quantify basalt carbonatization of igneous oceanic crust, fate of this C along plate trajectory Chemical states of C in lower mantle Comparisons with other planets (e.g., Venus, Mars) Early atmosphere composition, evolution, losses to space 5

  4. What do we need to do to get there: Experiments and new instrumentation? • Carbon partitioning between mantle and core (experiments at relevant T, P, fO2 and compositions) • Carbon partitioning associated with formation of melts and volatile fluids (MOR, subduction zones) • Nanoscale observations of experimental samples and specific field samples (e.g., melt inclusions, etc.) • Basalt carbonatization • Instruments for remote sensing, deep sea platforms

  5. What do we need to do to get there: Field observations? • Existing ODP cores • Drilling programs into igneous crust away from ridges • Subduction zone carbon budget • Serpentinites: measure C contents, heterogeneities • Composition, redox budget and permeability of the underlying oceanic crust along trajectory from MOR to subduction zones • Improved methodology for determining fluxes (remote sensing, deep sea cable networks) • Episodic fluxes (seismicity, ice core records, etc.)

  6. What do we need to do to get there: Theoretical advances? • High pressure C phases (e.g., deep mantle, core) • Partitioning of carbon and other volatiles between mantle and core • Equations of state for C-O-H in fluids and minerals • Flux proxies (e.g., C/Nb, others): understanding principles, identifying new proxies • Transport models

  7. BREAKOUT SESSION 2: DEEP CARBON FLUXESCONCLUSIONS • Systematic studies identified that will improve estimates of fluxes • Modern geographic variations • Through geologic time

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