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| Titel |
Sr isotope characterization of atmospheric inputs to soils along a climate gradient of the Chilean Coastal Range |
| VerfasserIn |
Ralf Oeser, Jan A. Schuessler, Geerke H. Floor, Friedhelm von Blanckenburg |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250148756
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| Publikation (Nr.) |
 EGU/EGU2017-13043.pdf |
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| Zusammenfassung |
| The rate and degree of rock weathering controls the release, distribution, and cycling of
mineral nutrients at the Earth’s surface, being essential for developing and sustaining of
ecosystems. Climate plays an important role as water flow and temperature determine both
the biological community and activity, and also set the speed of weathering. Because of this
double control by climate, the impact of biological activity on rock weathering and
the feedbacks between the geosphere and the biosphere under different climatic
conditions are not well understood. We explore the impact of biota on rock weathering
in the four EarthShape primary study areas which are situated along the Chilean
Coastal Range, featuring an outstanding vegetation gradient controlled by climate,
ranging over 2000 km from hyper-arid, to temperate, to humid conditions. The study
sites are within 80 km of the Pacific coast and are located in granitic lithology.
Moreover, the sites were unglaciated during the last glacial maximum. However, as
substrates get depleted in mineral nutrients, ecosystems are increasingly nourished by
atmospheric inputs, sources, such as solutes contained in rain, dust, and volcanic
ash.
We aim to quantify the primary nutrient inputs to the ecosystem from these different
potential sources. Radiogenic strontium (Sr) isotope ratios are a powerful tool to trace
chemical weathering, soil formation, as well as cation provenance and mobility [1]. We
determined 87Sr/86Sr ratios on bulk bedrock, saprolite, and soil and performed sequential
extractions of the the easily bioavailable soil phases up to 2 m depth on two soil depth profiles
in each of the four study sites.
Our first results from the La Campana study site indicate that the radiogenic Sr isotope
ratios of saprolite samples decrease from 0.70571 (n = 4) at the base of the profile to lower
values of 0.70520 (n = 4) at the top of the immobile saprolite, indicating increasing biotite
weathering. 87Sr/86Sr increases in the mobile soil layer to 0.70571 (n = 25). We find that
atmospheric sources (87Sr/86Srseawater = 0.709234; [2]) contribute about 13 % of Sr to the
soil and are a minor but not negligible fraction in comparison to weathering supply from
saprolite. Furthermore, the 87Sr/86Sr ratios determined for saprolite samples are in good
agreement with the values reported for the local Illapel Plutonic Complex [3]. Hence,
the top-soil atmospheric inputs are potentially influencing the plant’s strategies of
nutrient uplift, ultimately controlled by the plants’ nutrient demand as a function of
climate.
[1] Capo, R. C., Stewart, B. W., and Chadwick, O. A., 1998, Strontium isotopes as
tracers of ecosystem processes: theory and methods: Geoderma, v. 82, no. 1-3, p.
197-225.
[2] DePaolo, D. J., and Ingram, B. L., 1985, High-resolution stratigraphy with strontium
isotopes: Science, v. 227, no. 4689, p. 938-941.
[3] Parada, M. A., Nyström, J. O., and Levi, B., 1999, Multiple sources for the Coastal
Batholith of central Chile (31–34˚ S): geochemical and Sr–Nd isotopic evidence and tectonic
implications: Lithos, v. 46, no. 3, p. 505-521. |
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