Soil chemical depletion and dust deposition rates along an altitudinal climate transect at San Jacinto Peak, southern California

Silicate weathering supplies life-sustaining nutrients to ecosystems, modulates Earth's topographic evolution, and regulates Earth's long-term climate. To quantify the sensitivity of silicate weathering to climate and dust, we measured denudation rate, soil chemical depletion, and dust deposition rate along a steep climatic gradient on the granitic San Jacinto Peak in southern California, which spans nearly 3 km in elevation. We collected samples of soil and its parent rock at 18 soil-mantled ridgetop sites spanning 483-3281 m in elevation, which we used to measure chemical and physical erosion rates. We deployed a network of 8 climate monitoring stations to measure soil climate over the past 1-4 years. Six of these sites include passive dust traps, from which we retrieved seasonal dust samples to measure dust deposition rates and elemental composition. Soil denudation rates derived from 10Be concentrations in soil-borne quartz vary more than fivefold among the sample sites, from 70.4 g yr-1 m-2 at 3281 m to 376 g yr-1 m-2 at 1242 m. Dust deposition rates are highly variable in space and time, ranging from 5.4 g yr-1 m-2 at 1552 m (3-year average: 2019-2022 ) to 63.9 g yr-1 m-2at 1084 m (1-year average: 2021-2022). Our measurements show that dust contributes a significant mass influx to the soils at our field sites. Our climate observation data show mean annual soil temperature declines systematically with elevation from 24.1℃ at 483 m to 7.4℃ at 2883 m, while mean annual soil volumetric water content in the top 10 cm increases systematically with elevation from 0.028 (m3/m3) at 483 m to 0.076 (m3/m3) at 2883 m. These measurements also reflect the seasonal decoupling of soil temperature and soil moisture, with cool wet winters and dry hot summers. Our preliminary estimates of soil chemical depletion factor (CDF) derived from soil and bedrock chemistry range from -0.33 to 0.54, and are consistent with a weak sensitivity to both temperature and water availability. Together, these measurements provide new constraints on the considerable variations in environmental factors across our field sites at San Jacinto Peak. Our analysis suggests that soil chemical weathering is sensitive to multiple aspects of climate and to rates of mineral supply from bedrock and atmosphere.