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| Titel |
Optical Characterization of an Eddy-induced Diatom Bloom West of the Island of Hawaii |
| VerfasserIn |
F. Nencioli, G. Chang, M. Twardowski, T. D. Dickey |
| 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 ; 7, no. 1 ; Nr. 7, no. 1 (2010-01-13), S.151-162 |
| Datensatznummer |
250004370
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| Publikation (Nr.) |
 copernicus.org/bg-7-151-2010.pdf |
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| Zusammenfassung |
| Optical properties were collected along a transect across cyclonic eddy Opal
in the lee of Hawaii during the E-Flux III field experiment (10–27 March 2005). The eddy
was characterized by an intense doming of isopycnal surfaces, and by an enhanced Deep
Chlorophyll Maximum Layer (DCML) within its core. The phytoplankton bloom was diatom
dominated, evidencing an eddy-induced shift in ecological community. Four distinct
regions were identified throughout the water column at Opal's core: a
surface mixed layer dominated by small phytoplankton; a layer dominated by "senescent"
diatoms between the bottom of the upper mixed layer and the DCML; the DCML; and a deep
layer characterized by decreasing phytoplankton activity. We focused on two parameters,
the ratio of chlorophyll concentration to particulate beam attenuation coefficient, [chl]/cp,
and the backscattering ratio (the particle backscattering to particle scattering ratio), b~bp,
and tested their sensitivity to the changes in particle composition observed through
the water column at the eddy center. Our results show that [chl]/cp is not a good
indicator. Despite the shift in ecological community, the ratio remains controlled
primarily by the variation in chlorophyll concentration per cell with depth (photoadaptation),
so that its values increase throughout the DCML. Steeper increase of [chl]/cp below the
DCML suggest that remineralization might be another important controlling factor. On the
other hand, b~bp clearly indicates a shift from a small phytoplankton to a
diatom dominated community. Below an upper layer characterized by constant values, the
b~bp showed a rapid decrease to a broad minimum within the DCML. The higher
values below the DCML are consistent with enhanced remineralization below the eddy-induced
bloom. Both the "senescent" and the "healthy" diatom layers are characterized by
similar optical properties, indicating some possible limitations in using optical
measurements to fully characterize the composition of suspended material in the
water column. The inverse relationship between b~bp,
reported by others for Case II waters, is observed neither for the background
conditions, nor in the presence of the eddy-induced diatom bloom. Between the
two parameters, only the backscattering ratio showed the potential to be a
successful indicator for changes in particle composition in Case I waters. |
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