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| Titel |
Ocean colour remote sensing in the southern Laptev Sea: evaluation and applications |
| VerfasserIn |
B. Heim, E. Abramova, R. Doerffer, F. Günther, J. Hölemann, A. Kraberg, H. Lantuit, A. Loginova, F. Martynov, P. P. Overduin, C. Wegner |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 15 ; Nr. 11, no. 15 (2014-08-12), S.4191-4210 |
| Datensatznummer |
250117542
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| Publikation (Nr.) |
 copernicus.org/bg-11-4191-2014.pdf |
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| Zusammenfassung |
Enhanced permafrost warming and increased Arctic river discharges have
heightened concern about the input of terrigenous matter into Arctic
coastal waters. We used optical operational satellite data from the ocean
colour sensor MERIS (Medium-Resolution Imaging Spectrometer) aboard the ENVISAT satellite mission for synoptic
monitoring of the pathways of terrigenous matter on the shallow Laptev Sea
shelf. Despite the high cloud coverage in summer that is inherent to this
Arctic region, time series from MERIS satellite data from 2006 on to 2011
could be acquired and were processed using the Case-2 Regional Processor
(C2R) for optically complex surface waters installed in the open-source software ESA BEAM-VISAT.
Since optical remote sensing using ocean colour satellite data has seen
little application in Siberian Arctic coastal and shelf waters, we assess
the applicability of the calculated MERIS C2R parameters with surface water
sampling data from the Russian–German ship expeditions LENA2008, LENA2010
and TRANSDRIFT-XVII taking place in August 2008 and August and September
2010 in the southern Laptev Sea. The shallow Siberian shelf waters are
optically not comparable to the deeper, more transparent waters of the Arctic
Ocean. The inner-shelf waters are characterized by low transparencies, due
to turbid river water input, terrestrial input by coastal erosion,
resuspension events and, therefore, high background concentrations of
suspended particulate matter and coloured dissolved organic matter.
We compared the field-based measurements with the satellite data that are
closest in time. The match-up analyses related to LENA2008 and LENA2010
expedition data show the technical limits of matching in optically highly
heterogeneous and dynamic shallow inner-shelf waters. The match-up analyses
using the data from the marine TRANSDRIFT expedition were constrained by
several days' difference between a match-up pair of satellite-derived and
in situ parameters but are also based on the more stable hydrodynamic
conditions of the deeper inner- and the outer-shelf waters. The relationship
of satellite-derived turbidity-related parameters versus in situ suspended matter from
TRANSDRIFT data shows that the backscattering coefficient C2R_bb_spm can be
used to derive a Laptev-Sea-adapted SPM algorithm. Satellite-derived Chl a
estimates are highly overestimated by a minimum factor of 10 if applied to
the inner-shelf region due to elevated concentrations of terrestrial organic
matter.
To evaluate the applicability of ocean colour remote sensing, we include the
visual analysis of lateral hydrographical features. The mapped
turbidity-related MERIS C2R parameters show that the Laptev Sea is dominated
by resuspension above submarine shallow banks and by frontal instabilities
such as frontal meanders with amplitudes up to 30 km and eddies and
filaments with horizontal scales up to 100 km that prevail throughout the
sea-ice-free season. The widespread turbidity above submarine shallow banks
indicates inner-shelf vertical mixing that seems frequently to reach down to
submarine depths of a minimum of 10 m. The resuspension events and the
frontal meanders, filaments and eddies indicate enhanced vertical mixing
being widespread on the inner shelf.
It is a new finding for the Laptev Sea that numerous frontal instabilities
are made visible, and how highly time-dependent and turbulent the Laptev Sea
shelf is. The meanders, filaments and eddies revealed by the ocean colour
parameters indicate the lateral transportation pathways of terrestrial and
living biological material in surface waters. |
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