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| Titel |
Calcium isotopes in a proglacial weathering environment: Damma glacier, Switzerland |
| VerfasserIn |
Ruth S. Hindshaw, Ben C. Reynolds, Jan G. Wiederhold, Ruben Kretzschmar, Bernard Bourdon |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041903
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| Zusammenfassung |
| Calcium is a key element in global biogeochemical cycles. It is an essential nutrient and the
dissolution of Ca from silicate minerals is intimately linked to the global carbon cycle. Yet
relatively few studies have utilized the potential of stable Ca isotopes to directly investigate
(as opposed to using Sr isotopes) processes affecting Ca during initial weathering and
subsequent cycling within the ecosystem.
The Damma glacier fieldsite (Central Swiss Alps) provides an ideal opportunity to study
the early stages of silicate weathering processes and is the site of a larger multidisciplinary
research project (BigLink). The catchment is underlain by Central Aar granite, which does
not contain detectable carbonates. The Damma is a small, glacial catchment (10.7 km2)
where the glacier has retreatred since 1850 creating a 1.5 km long chronosequence which
spans approximately 150 years of soil development and exhibits a strong vegetation gradient
along its length.
In order to investigate the biogeochemical Ca cycle in the forefield, extensive sampling of
the main reservoirs of Ca was undertaken. Soil samples from two different depths (0-5
and 5-10 cm) were collected at 23 randomly selected sites across the forefield in
addition to six bulk rock samples. To further investigate potential fractionation
between different soil pools, sequential extractions were performed. Stream water was
collected at three different locations in the forefield on a biweekly basis throughout the
sampling season, in addition to precipitation (snow and rain) and porewater samples.
To investigate the effect of biological cycling on Ca, leaves from Rhododendron
ferrugineum were also analysed. Analyses of all samples were performed using a Triton
TIMS with a 43Ca-46Ca double spike, after a 4-step chromatographic separation
procedure.
During this very early stage of weathering, the young soils which have formed were
isotopically identical in δ44-42Ca to the rock from which they were derived, indicating that
primary dissolution of the bulk rock does not strongly fractionate Ca isotopes. This is further
corroborated by the analyses of the streamwaters which were within error of the average soil.
Only one time point, coinciding with the end of the main snow melt period, was significantly
different in δ44-42Ca from bulk rock. The only Ca pool which was significantly
fractionated from bulk rock was vegetation, which exhibited an enrichment of light Ca
isotopes.
Significant calcium isotope fractionation between bulk rock and soils is likely to only
occur where the soils are no longer buffered by primary mineral dissolution and secondary
processes such as biological cycling and secondary mineral precipitation become dominant. |
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