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| Titel |
From the shape of the vertical profile of in vivo fluorescence to Chlorophyll-a concentration |
| VerfasserIn |
A. Mignot, H. Claustre, F. D'Ortenzio, X. Xing, A. Poteau, J. Ras |
| 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 ; 8, no. 8 ; Nr. 8, no. 8 (2011-08-31), S.2391-2406 |
| Datensatznummer |
250006091
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| Publikation (Nr.) |
 copernicus.org/bg-8-2391-2011.pdf |
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| Zusammenfassung |
| In vivo fluorescence of Chlorophyll-a (Chl-a) is a potentially useful property
to study the vertical distribution of phytoplankton biomass. However the
technique is presently not fully exploited as it should be, essentially
because of the difficulties in converting the fluorescence signal into an
accurate Chl-a concentration. These difficulties arise noticeably from
natural variations in the Chl-a fluorescence relationship, which is under the
control of community composition as well as of their nutrient and light
status. As a consequence, although vertical profiles of fluorescence are
likely the most recorded biological property in the open ocean, the
corresponding large databases are underexploited. Here with the aim to
convert a fluorescence profile into a Chl-a concentration profile, we test
the hypothesis that the Chl-a concentration can be gathered from the sole
knowledge of the shape of the fluorescence profile. We analyze a large
dataset from 18 oceanographic cruises conducted in case-1 waters from the
highly stratified hyperoligotrophic waters (surface Chl-a = 0.02 mg m−3)
of the South Pacific Gyre to the eutrophic waters of the Benguela upwelling
(surface Chl-a = 32 mg m−3) and including the very deep mixed waters in
the North Atlantic (Mixed Layer Depth = 690 m). This dataset encompasses
more than 700 vertical profiles of Chl-a fluorescence as well as accurate
estimations of Chl-a by High Performance Liquid Chromatography (HPLC). Two
typical fluorescence profiles are identified, the uniform profile,
characterized by a homogeneous layer roughly corresponding to the mixed
layer, and the non-uniform profile, characterized by the presence of a Deep
Chlorophyll Maximum. Using appropriate mathematical parameterizations, a
fluorescence profile is subsequently represented by 3 or 5 shape parameters
for uniform or non-uniform profiles, respectively. For both situations, an
empirical model is developed to predict the "true" Chl-a concentration from
these shape parameters. This model is then used to calibrate a fluorescence
profile in Chl-a units. The validation of the approach provides satisfactory
results with a median absolute percent deviation of 33 % when comparing
the HPLC Chl-a profiles to the Chl-a-calibrated fluorescence. The proposed
approach thus opens the possibility to produce Chl-a climatologies from
uncalibrated fluorescence profile databases that have been acquired in the
past and to which numerous new profiles will be added, thanks to the recent
availability of autonomous platforms (profiling floats, gliders and animals)
instrumented with miniature fluorometers. |
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