RESUMO
Earth's climate may be stabilized over millennia by solubilization of atmospheric carbon dioxide (CO2) as minerals weather, but the temperature sensitivity of this thermostat is poorly understood. We discovered that the temperature dependence of weathering expressed as an activation energy increases from laboratory to watershed as transport, clay precipitation, disaggregation, and fracturing increasingly couple to dissolution. A simple upscaling to the global system indicates that the temperature dependence decreases to ~22 kilojoules per mole because (i) the lack of runoff limits weathering and retains base metal cations on half the land surface and (ii) other landscapes are regolith-shielded and show little weathering response to temperature. By comparing weathering from laboratory to globe, we reconcile some aspects of kinetic and thermodynamic controls on CO2 drawdown by natural or enhanced weathering.
RESUMO
The electrical conductivities of aqueous solutions of Na(2)SO(4), H(2)SO(4), and their mixtures have been measured at 373-673 K at 12-28 MPa in dilute solutions for molalities up to 10(-2) mol kg(-1). These conductivities have been fit to the conductance equation of Turq et al.(1) with a consensus mixing rule and mean spherical approximation activity coefficients. Provided the concentration is not too high, all of the data can be fitted by a solution model that includes ion association to form NaSO(4)(-), Na(2)SO(4)(0), HSO(4)(-), H(2)SO(4)(0), and NaHSO(4)(0). The adjustable parameters of this model are the dissociation constants of the SO(4)(-) species and the H(+), SO(4)(-2), and HSO(4)(-) conductances (ion mobilities) at infinite dilution. For the 673 K and 230 kg m(-3) state point with the lowest dielectric constant, epsilon = 3.5, where the Coulomb interactions are the strongest, this model does not fit the experimental data above a solution molality of 0.016. Including the species H(9)(SO(4))(5)(-) gave satisfactory fits to the conductance data at the higher concentrations.
