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| Titel |
Fate of colloids during estuarine mixing in the Arctic |
| VerfasserIn |
O. S. Pokrovsky, L. S. Shirokova, J. Viers, V. V. Gordeev, V. P. Shevchenko, A. V. Chupakov, T. Y. Vorobieva, F. Candaudap, C. Causserand, A. Lanzanova, C. Zouiten |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 10, no. 1 ; Nr. 10, no. 1 (2014-02-24), S.107-125 |
| Datensatznummer |
250116926
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| Publikation (Nr.) |
 copernicus.org/os-10-107-2014.pdf |
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| Zusammenfassung |
The estuarine behavior of organic carbon (OC) and trace elements (TE) was
studied for the largest European sub-Arctic river, which is the Severnaya
Dvina; this river has a deltaic estuary covered in ice during several
hydrological seasons: summer (July 2010, 2012) and winter (March 2009)
baseflow, and the November–December 2011 ice-free period. Colloidal forms of
OC and TE were assessed for three pore size cutoffs (1, 10, and 50 kDa)
using an in situ dialysis procedure. Conventionally dissolved
(< 0.22 μm) fractions demonstrated clear conservative
behavior for Li, B, Na, Mg, K, Ca, Sr, Mo, Rb, Cs, and U during the mixing of
freshwater with the White Sea; a significant (up to a factor of 10)
concentration increase occurs with increases in salinity. Si and OC also
displayed conservative behavior but with a pronounced decrease in
concentration seawards. Rather conservative behavior, but with much smaller
changes in concentration (variation within ±30%) over a full range
of salinities, was observed for Ti, Ni, Cr, As, Co, Cu, Ga, Y, and heavy REE.
Strong non-conservative behavior with coagulation/removal at low salinities
(< 5‰) was exhibited by Fe, Al, Zr, Hf, and light REE.
Finally, certain divalent metals exhibited non-conservative behavior with a
concentration gain at low (~ 2–5‰, Ba, Mn) or intermediate
(~ 10–15‰, Ba, Zn, Pb, Cd) salinities, which is most likely
linked to TE desorption from suspended matter or sediment outflux.
The most important result of this study is the elucidation of the behavior of
the "truly" dissolved low molecular weight LMW< 1 kDa
fraction containing Fe, OC, and a number of insoluble elements. The
concentration of the LMW fraction either remains constant or increases its
relative contribution to the overall dissolved
(< 0.22 μm) pool as the salinity increases. Similarly,
the relative proportion of colloidal (1 kDa–0.22 μm) pool for the
OC and insoluble TE bound to ferric colloids systematically decreased
seaward, with the largest decrease occurring at low
(< 5‰) salinities.
Overall, the observed decrease in the colloidal fraction may be related to
the coagulation of organo-ferric colloids at the beginning of the mixing zone
and therefore the replacement of the
HMW1 kDa–0.22 μm portion by the
LMW< 1 kDa fraction. These patterns are highly reproducible
across different sampling seasons, suggesting significant enrichment of the
mixing zone by the most labile (and potentially bioavailable) fraction of the
OC, Fe and insoluble TE. The size fractionation of the colloidal material
during estuarine mixing reflects a number of inorganic and biological
processes, the relative contribution of which to element speciation varies
depending on the hydrological stage and time of year. In particular,
LMW< 1 kDa ligand production in the surface horizons of the
mixing zone may be linked to heterotrophic mineralization of allochthonous
DOM and/or photodestruction. Given the relatively low concentration of
particulate versus dissolved load of most trace elements, desorption from the
river suspended material was less pronounced than in other rivers in the
world. As a result, the majority of dissolved components exhibited either
conservative (OC and related elements such as divalent metals) or
non-conservative, coagulation-controlled (Fe, Al, and insoluble TE associated
with organo-ferric colloids) behavior. The climate warming at high latitudes
is likely to intensify the production of LMW< 1 kDa organic
ligands and the associated TE; therefore, the delivery of potentially
bioavailable trace metal micronutrients from the land to the ocean may
increase. |
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