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| Titel |
Molybdenum behaviour in the low salinity zone during estuarine mixing |
| VerfasserIn |
Rebecca A. Neely, Hanne Wouters, Alex J. Dickson, Christopher R. Pearce, Don Porcelli, Sigurður R. Gíslason, Kevin W. Burton |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250111163
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| Publikation (Nr.) |
 EGU/EGU2015-11249.pdf |
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| Zusammenfassung |
| Molybdenum is the most abundant trace metal in the oceans (~10Âppb) [1], with a residence
time of ~800Âka, and an almost uniform isotope composition of 2.1ÂoÂ[2] and it has been
thought to behave conservatively upon mixing between rivers and oceans [3]. However, more
recent studies have shown examples of non-conservative behaviour in estuaries [4], [5]. In
order to improve the quantitative interpretation of the Mo palaeo-proxy for redox conditions
this study presents preliminary data from two estuaries, with a view to understanding the
potential for estuarine modification of rivers, the most dominant source of Mo to the
oceans.
The Kalix and Råne rivers, drain into the Bothnian Bay, Sweden. Samples are from three
locations along each estuary at 0.5, 5.0 and 10.0Âm depths, collected under ice conditions.
The salinity range was 0.1-2.3 PSU (Kalix) and 0.04-2.5 PSU (Råne). Mo concentrations
increase with salinity from 0.3 to 1.0Âppb (Kalix) and 0.4 to 0.9Âppb (Råne) (±10%). In the
Kalix, the measured [Mo] values fit closely with the theoretical conservative mixing line
between the river and sea water endmembers (measured R2=0.93) whilst in the Råne estuary
the measured [Mo] have a poor fit (measured R2=0.25). The dissolved load was analysed for
Mo isotopes relative to NIST 3134 with the Kalix δ98Mo of 1.07-1.97ÂoÂ(2s.e.
0.02Â) with an R2=0.51 (against 1/[Mo]) and Råne δ98MoÂof 1.54-2.16 oÂ(2s.e.
0.05) with an R2=0.01 (against 1/[Mo]). It is clear from concentration and isotope
data that non conservative behaviour is observed in these estuaries with isotope
exchange that has not greatly altered Mo concentration. This is especially notable in
the Råne estuary. Similar non-conservative behaviour has been observed in Li
isotopes in the same estuaries [6]. This work explores the interactions between
the dissolved and suspended phases, and processes controlling Mo input to the
oceans.
[1] Collier, R. W. 1985. Limnology and Oceanography, 1351-1354
[2] Nakagawa, Y et al., 2012. Geochemical Journal, 46, 131
[3] Archer, C. & Vance, D. 2008. Nature Geoscience, 1, 597-600
[4] Pearce, C. R., et al., 2010. Earth and Planetary Science Letters, 295, 104-114
[5] Rahaman, W., et al., 2014. Geochimica et Cosmochimica Acta, 141, 407-422
[6] Murphy, M. J., 2014. Procedia Earth and Planetary Science, 10, 204-207 |
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