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| Titel |
MODIS observed phytoplankton dynamics in the Taiwan Strait: an absorption-based analysis |
| VerfasserIn |
S. Shang, Q. Dong, Z. Lee, Y. Li, Y. Xie, M. Behrenfeld |
| 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. 4 ; Nr. 8, no. 4 (2011-04-06), S.841-850 |
| Datensatznummer |
250005686
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| Publikation (Nr.) |
 copernicus.org/bg-8-841-2011.pdf |
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| Zusammenfassung |
| This study used MODIS observed phytoplankton absorption coefficient at 443 nm
(Aph) as a preferable index to characterize phytoplankton variability in
optically complex waters. Aph derived from remote sensing reflectance
(Rrs, both in situ and MODIS measured) with the Quasi-Analytical Algorithm
(QAA) were evaluated by comparing them with match-up in situ measurements,
collected in both oceanic and nearshore waters in the Taiwan Strait (TWS).
For the data with matching spatial and temporal window, it was found that
the average percentage error (ε) between MODIS derived Aph and field measured
Aph was 33.8% (N=30, Aph ranges from 0.012 to 0.537 m−1), with a root mean
square error in log space (RMSE_log) of 0.226. By comparison, ε was 28.0%
(N=88, RMSE_log = 0.150) between Aph derived from ship-borne Rrs and Aph measured from water
samples. However, values of ε as large as 135.6% (N=30,
RMSE_log = 0.383) were found between MODIS derived chlorophyll-a (Chl, OC3M algorithm)
and field measured Chl. Based on these evaluation results, we applied QAA to
MODIS Rrs data in the period of 2003–2009 to derive climatological
monthly mean Aph for the TWS. Three distinct features of phytoplankton dynamics
were identified. First, Aph is low and the least variable in the Penghu Channel,
where the South China Sea water enters the TWS. This region maintains
slightly higher values in winter (~17% higher than that in the
other seasons) due to surface nutrient entrainment under winter wind-driven
vertical mixing. Second, Aph is high and varies the most in the mainland
nearshore water, with values peaking in summer (June–August) when river
plumes and coastal upwelling enhance surface nutrient loads. Interannual
variation of bloom intensity in Hanjiang River estuary in June is highly
correlated with alongshore wind stress anomalies, as observed by QuikSCAT.
The year of minimum and maximum bloom intensity is in the midst of an El
Niño and a La Niña event, respectively. Third, a high Aph patch appears
between April and September in the middle of the southern TWS, corresponding
to high thermal frontal probabilities, as observed by MODIS. Our results
support the use of satellite derived Aph for time series analyses of
phytoplankton dynamics in coastal ocean regions, whereas satellite Chl
products derived empirically using spectral ratio of Rrs suffer from
artifacts associated with non-biotic optically active materials. |
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