1. Arcs – a critical sink in the global C cycle? Interesting features Ca, Mg rich compositions Fast kinetics in volc rocks Tectonically active Wet High erosion rates Frequent resurfacing Underrepresented in our data and our thinking No big rivers Large groundwater fluxes (unmeasured!) Milliman: sed yields are ≈10x global average MgSiO 3 + 2CO 2 + 3H 2 O Mg ++ + 2HCO 3 - + H 4 SiO 4 “MgCO 3 ” + SiO 2 + CO 2 net = -1 CO 2 per mol Ca or Mg weathered Climate sensitivity?

2. Arc rivers are different …. n=74 n=156

3. Basalt weathering shows strong climate sensitivity. (data mostly from Dessert et al., 2003) T dependence: exponent ≈ 0.08 is similar to laboratory Arrhenius rates, e.g. for labradorite. Is this too good to be true …?