SOIL PHYSICAL AND CHEMICAL DENUDATION RATES IN THE RAPIDLY UPLIFTING WESTERN SOUTHERN ALPS, NEW ZEALAND

The lack of soil production and weathering rate data from Earth’s most rapidly uplifting mountains has made it difficult to determine whether weathering rates increase or decline in response to rapid erosion. Understanding the relationship between erosion and weathering rates is critical for evaluating whether mountain uplift can influence the geological carbon cycle and climate. We measured beryllium-10 concentrations in soils from the western Southern Alps, New Zealand, which demonstrate that soil is produced from bedrock more rapidly than previously recognized, at rates from 0.1 to 2.5 mm yr^-1. Weathering intensity data further indicate that soil chemical denudation rates increase proportionally with erosion rates. We also used beryllium-10 to determine catchment-scale denudation rates, which reach as high as 12 mm yr^-1. Published river solute flux data suggest that catchment-scale weathering rates are comparable to the soil weathering rates, despite the much higher rates of catchment denudation. These high weathering rates suggest that soils may be a key location for denudation in tectonically-active mountains and support the view that mountains play a key role in global-scale chemical weathering.