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| Titel |
The influence of Lena River water inflow and shelf sediment-sea water exchange for the Nd isotopic composition in the Laptev Sea and Arctic Ocean. |
| VerfasserIn |
Per-Olov Persson, Per S. Andersson, Don Porcelli, Igor Semiletov |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250045989
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| Zusammenfassung |
| It has been suggested that the isotopic composition of Neodymium (Nd) in sea water can be
affected by chemical exchange processes between water and sediments, which is generally
termed boundary exchange. During the International Siberian Shelf Study in 2008 (ISSS-08)
filtered (0.22μm) sea water, suspended particles and surface sediment samples were collected
from the Laptev Sea and East Siberian Arctic Shelves (ESAS). The ESAS is the world’s
largest continental shelf and our main objective is to improve our understanding
of the vast ESAS influence on trace element and isotope behavior in the Arctic
Ocean.
Measurements of Nd isotopic composition (ÉNd) and concentration (CNd) are
presented for filtered seawater samples, sediments and suspended particles. The
samples were collected in a transect stretching from the Lena River mouth to 77Ë
N in the Laptev Sea. The surface water above 20 m depth is strongly affected by
the fresh water inflow from the Lena River, with a salinity ranging from 0 to 21
PSU.
The Lena River water show high CNd, ~600 pmol/kg and ÉNd -15, which are similar to
previously reported values, though the isotopic composition is slightly less radiogenic. In the
Laptev Sea salinity gradient, the CNdin the filtered water above the halocline, at 3 m depth,
drop and reach a CNd of 294 pmol/kg whereas the value of ÉNd -15 remains similar to the
Lena River water. For deeper water samples, below the halocline, the salinity reaches 32 psu
showing a CNd of 52 pmol/kg and ÉNd -11.4. The loss of dissolved Nd along the salinity
gradient will be discussed along with the results form sediments and suspended particulate
matter.
Sequential leaching, in four steps, was carried out on sediments and suspended
particles to determine the potential influence of mobile Nd from the sediment on the
concentration and isotopic composition of the dissolved Nd. The sequential leaches include
separation of (i) easily exchangeable species (ii) reducible species released from a low
concentration reducible agent, (iii) reducible species released from a high concentration
reducible agent and (iv)Â oxidisable species. The major fraction released during
leaching of sediments is associated with the reducible fraction, presumably in Fe- and
Mn oxyhydroxides, carrying up to ~15% of the total Nd in the sediments. The
oxidisable fraction released up to ~5% of the total Nd. If the major part of Nd
in the oxidisable fraction comes from Nd bound to organic material, a large part
might be released if the organic material is degraded on the shelf. The fraction
released as easily exchangeable corresponds only to ~1% of the total amount in the
sediments.
The result will be discussed in terms of how the Nd behaves during estuarine mixing and
how the underlying sediments modify the isotopic composition of the shelf waters. Data from
the sequential leach will be used to constrain the processes controlling Nd interaction with the
sediments. |
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