Relationship between mechanical erosion and atmospheric CO (sub 2) 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 CO (sub 2) consumption. Rapid uplift in the western Southern Alps elevates mechanical erosion rates by a factor of approximately 13 relative to those on the tectonically stable eastern side [125X10 (super 8) vs. 9.4X10 (super 8) g/(km (super 2) .yr), respectively]. Similarly, the average chemical weathering rate is approximately 5 times higher on the western compared to eastern side of the mountain range [9.8X10 (super 7) vs. 2.0X10 (super 7) g/(km (super 2) .yr), respectively]. However, because the proportion of stream-water Ca (super 2+) and Mg (super 2+) from carbonate weathering increases as the rate of mechanical erosion increases, the long-term atmospheric CO (sub 2) consumption rate on the western side is approximately 2 times higher than that on the eastern side [14X10 (super 4) vs. 6.9X10 (super 4) mol/(km (super 2) .yr), respectively] and only approximately 1.5 times higher than the global mean value [ approximately 9X10 (super 4) mol/(km (super 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 CO (sub 2) consumption rates by only a factor of approximately 2, which is much lower than previous estimates.