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| Titel |
Inter-annual variation of chlorophyll in the northern South China Sea observed at the SEATS Station and its asymmetric responses to climate oscillation |
| VerfasserIn |
K.-K. Liu, L.-W. Wang, M. Dai, C.-M. Tseng, Y. Yang, C.-H. Sui, L. Oey, K.-Y. Tseng, S.-M. Huang |
| 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 ; 10, no. 11 ; Nr. 10, no. 11 (2013-11-20), S.7449-7462 |
| Datensatznummer |
250085426
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| Publikation (Nr.) |
 copernicus.org/bg-10-7449-2013.pdf |
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| Zusammenfassung |
| It is widely recognised that the variation of average surface chlorophyll a
concentration (Chl) in the South China Sea (SCS) is closely related to wind
forcing, especially during the intense winter monsoon. In this study, we
demonstrate that after removal of the seasonal cycles, the variation of Chl
showed strong asymmetric responses to wind speed under El Niño or La
Niña conditions. The analysis was based on a time-series of Chl in the
study area (115–117° E, 17–19° N) around the SEATS
(South-East Asian Time-series Study) station located in the central northern
SCS from September 1997 to the end of 2011, which was constructed by merging
the SeaWiFS data (1997–2006) and MODIS data (2003–2011). The merged daily
data were validated by shipboard observations at the SEATS station. The
non-seasonal variations of monthly mean Chl, wind speed, sea surface height
(SSH) and sea surface temperature (SST) were examined against the
multivariate ENSO index (MEI). The analysis reveals strongly asymmetric
correlations of Chl and SST with positive MEI (El Niño) or negative MEI
(La Niña). Under El Niño conditions, both showed significant
correlations with MEI or wind speed; under La Niña conditions, both
showed weak or insignificant correlations. The contrast was more pronounced
for Chl than for SST. The subdued responses of Chl to wind forcing under La
Niña conditions were attributable to a deepened thermocline, for which
wind driven nutrient pumping is less efficient. A deeper thermocline, which
was observed during the 1999–2000 La Niña event and inferred by positive
SSH anomalies during other La Niña events, was probably caused by reduced
SCS throughflow under La Niña conditions. Intrusion of the
nutrient-depleted Kuroshio water in the surface layer as observed during the
1999–2000 La Niña could be partially responsible for the suppressed Chl
response. |
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