Relationship between mechanical erosion and atmospheric CO2 consumption in the New Zealand Southern Alps

To examine the influence of mountain uplift on the long-term carbon cycle, we used geochemical, hydrologic, and suspended-load data for 12 streams draining the New Zealand Southern Alps to quantify rates of erosion, weathering, and atmospheric CO2 consumption. Rapid uplift in the western Southern Alps elevates mechanical erosion rates by a factor of similar to13 relative to those on the tectonically stable eastern side [125 x 10(8) vs. 9.4 x 10(8) g/(km(2.)yr), respectively]. Similarly, the average chemical weathering rate is 5 times higher on the western compared to eastern side of the mountain range[9.8 x 10(7) vs. 2.0 x 10(7) g/(km(2.)yr), respectively]. However, because the proportion of stream-water Ca2+ and Mg2+ from carbonate weathering increases as the rate of mechanical erosion increases, the long-term atmospheric CO2 consumption rate on the western side is similar to2 times higher than that on the eastern side [14 x 10(4) vs. 6.9 x 10(4) mol/(km(2.)yr), respectively] and only similar to1.5 times higher than the global mean value [similar to9 x 10(4) mol/(km(2.)yr)]. Data for major world rivers (including Himalayan rivers) provide a consistent interpretation regarding the relationship between mechanical erosion intensity and the ratio of silicate to carbonate weathering. Thus, we conclude that mountain building increases atmospheric CO2 consumption rates by only a factor of similar to2, which is much lower than previous estimates.