The Chilean Coastal Cordillera features a spectacular climate and vegetation gradient, ranging from arid and unvegetated areas in the north to humid and forested areas in the south. The DFG Priority Program "EarthShape" (Earth Surface Shaping by Biota) uses this natural gradient to investigate how climate and biological processes shape the Earth's surface. We explored the critical zone, the Earth's uppermost layer, in four key sites located in desert, semidesert, mediterranean, and temperate climate zones of the Coastal Cordillera, with the focus on weathering of granitic rock. Here, we present first results from four ~2m-deep regolith profiles to document: (1) architecture of weathering zone; (2) degree and rate of rock weathering, thus the release of mineral-derived nutrients to the terrestrial ecosystems; (3) denudation rates; and (4) microbial abundances of bacteria and archaea in the saprolite.
From north to south, denudation rates from cosmogenic nuclides are ~10 t km-2 yr-1 at the arid Pan de Azúcar site, ~20 t km-2 yr-1 at the semi-arid site of Santa Gracia, ~60 t km-2 yr-1 at the mediterranean climate site of La Campana, and ~30 t km-2 yr-1 at the humid site of Nahuelbuta. A and B horizons increase in thickness and elemental depletion or enrichment increases from north (~26 °S) to south (~38 °S) in these horizons. Differences in the degree of chemical weathering, quantified by the chemical depletion fraction (CDF), are significant only between the arid and sparsely vegetated site and the other three sites. Differences in the CDF between the sites, and elemental depletion within the sites are sometimes smaller than the variations induced by the bedrock heterogeneity. Microbial abundances (bacteria and archaea) in saprolite substantially increase from the arid to the semi-arid sites.
With this study, we provide a comprehensive dataset characterizing the Critical Zone geochemistry in the Chilean Coastal Cordillera. This dataset confirms climatic controls on weathering and denudation rates and provides prerequisites to quantify the role of biota in future studies. The data are supplementary material to Oeser et al. (2018).
All samples are assigned with International Geo Sample Numbers (IGSN), a globally unique and persistent Identifier for physical samples. The IGSNs are provided in the data tables and link to a comprehensive sample description in the internet.
The content of the eight data tables is:
Table S1: Catena properties of the four primary EarthShape study areas.
Table S2: Major and selected trace element concentration for bedrock samples.
Table S3 Normative modal abundance of rock-forming minerals.
Table S4: Major and selected trace element concentration for regolith samples and dithionite and oxalate soluble pedogenic oxides.
Table S5: Weathering indices CDF and CIA, and the mass transfer coefficients (𝛕) for major and trace elements along with volumetric strain (ɛ).
Table S6: Chemical weathering and physical erosion rates
Table S7: Relative microbial abundances in saprolite of the four study areas.
Table S8: Uncorrected major and trace element concentration.
The data tables are provided as one Excel file with eight spreadsheets, as individual tables in .csv format in a zipped archive and as printable PDF versions in a zipped archive.