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| Titel |
Application of the flow-through time-resolved analysis technique to trace element determination in ostracod shells |
| VerfasserIn |
Nicole Börner, Bart De Baere, Roger François, Peter Frenzel, Antje Schwalb |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097614
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| Publikation (Nr.) |
 EGU/EGU2014-13214.pdf |
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| Zusammenfassung |
| Trace element analyses of ostracod shells are a vital tool for paleoenvironmental
reconstructions from lake sediments (Börner et al., 2013). Conventional batch dissolution
ICP-MS is the most common way for analyzing trace elements in ostracod shells. However,
due to dissolution or secondary overgrowth the primary signal may be masked. Resulting
variations in trace element composition have been identified to be in the order of a magnitude
range. Therefore, the application of the newly developed flow-through technique will be
assessed.
The flow-through time-resolved analysis technique allows to chemically separate
mineral phases of different solubility such as, in particular, original shell calcite from
overgrowth calcite, and thus to correct the measurements for the biogenic signal. During a
flow-through experiment, eluent is continuously pumped through a sample column,
typically a filter in which the ostracod valves are loaded. The gradual dissolution of the
substrate is controlled by a combination of eluent type, eluent temperature and eluent
flow rate. The dissolved sample then flows directly to a mass spectrometer. The
resulting data is a chromatogram, featuring different mineral phases dissolving as time
progresses. Hence, the flow-through technique provides a detailed geochemical
fingerprint of the substrate and therefore additional data relative to conventional
methods.
To calibrate this technique for the application to ostracods we use ostracod shells from
Southern Tibetan Plateau lakes, which feature an alkaline environment but show highly
diverse hydrochemistry. Cleaned as well as uncleaned ostracod shells show similarity in their
trace element signals, allowing measurements without prior cleaning of the shells, and thus
more time-efficient sample throughput. Measurements of unclean shells are corrected for the
biogenic signal using an equation from Klinkhammer et al. (2004). Another advantage is that
the measurements can be carried out on single ostracod shells, as not every single sediment
sample contains enough adult intact specimens of all required genera, making batch cleaning
dissolution impossible.
The flow-through time-resolved analysis technique gives an accurate and high-resolution
dataset. The trace elemental data for living ostracods compared to the hydrological data from
each sampling site provides a calibration dataset for further hydrological and thus
climatological reconstruction of a sediment core from Nam Co. Mg/Ca and Sr/Ca ratios in
ostracod shells will provide information about past water temperature and salinity resulting
from changes in precipitation vs. evaporation ratios and monsoon activity. Further, we will
exploit Mn/Ca, Fe/Ca and U/Ca ratios as redox indicators to reconstruct oxygenation cycles
and Ba/Ca ratios to detect changes in productivity and/or salinity. This reconstruction should
provide a more extensive insight in past climatic change, e.g. precipitation – evaporation
balance, lake level and circulation changes, and the recording of environmental signatures by
ostracod shells.
Börner, N., De Baere, B., Yang, Q., Jochum, K.P., Frenzel, P., Andreae, M.O., Schwalb,
A., 2013. Ostracod shell chemistry as proxy for paleoenvironmental change. Quaternary
International 313–314, 17-37.
Klinkhammer, G.P., Haley, B.A., Mix, A.C., Benway, H., Cheseby, M., 2004.
Evaluation of automated flow-through time-resolved analysis of foraminifera for Mg/Ca
paleothermometry. Paleoceanography 19, PA4030. |
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