Mineral weathering rate constants, r, depend on temperature and on mineral surface age. I use expressions for r(t) for major silicate minerals (Table 16.1), and the carbonate (calcite) weathering rate constant, from Morse & Arvidson (2002), is kept constant in time. The rate constants are adjusted from laboratory temperatures (20°C) to T = 0°C with the Arrhenius relationship

r |
" E |
' 1 |
111 |

— = exp r0 |
V T |
- T1 |

where r is the rate at temperature T (in kelvin), r0 is the rate at temperature T0, Ea is the activation energy of the reaction (energy/mol), and R is the gas constant (energy/mol/T). The apparent activation energy (Ea) used for plagioclase, K-feldspar and hornblende is 55kJmol-1, for biotite is 27kJmol-1 (White et al., 1999), and for calcite is 9kJmol-1 (Morse & Arvidson, 2002). Solute fluxes are computed over a range of sediment ages (t), which affect values of r and l.

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