Inter-annual variation of chlorophyll in the northern South China Sea observed at the SEATS Station and its asymmetric responses to climate oscillation
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...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2013-11-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/10/7449/2013/bg-10-7449-2013.pdf |
| _version_ | 1818176442758856704 |
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| author | K.-K. Liu L.-W. Wang M. Dai C.-M. Tseng Y. Yang C.-H. Sui L. Oey K.-Y. Tseng S.-M. Huang |
| author_facet | K.-K. Liu L.-W. Wang M. Dai C.-M. Tseng Y. Yang C.-H. Sui L. Oey K.-Y. Tseng S.-M. Huang |
| author_sort | K.-K. Liu |
| collection | DOAJ |
| description | 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. |
| first_indexed | 2024-12-11T20:16:16Z |
| format | Article |
| id | doaj.art-909a00ccc2154ba2993416730d70980c |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-11T20:16:16Z |
| publishDate | 2013-11-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-909a00ccc2154ba2993416730d70980c2022-12-22T00:52:10ZengCopernicus PublicationsBiogeosciences1726-41701726-41892013-11-0110117449746210.5194/bg-10-7449-2013Inter-annual variation of chlorophyll in the northern South China Sea observed at the SEATS Station and its asymmetric responses to climate oscillationK.-K. Liu0L.-W. Wang1M. Dai2C.-M. Tseng3Y. Yang4C.-H. Sui5L. Oey6K.-Y. Tseng7S.-M. Huang8Institute of Hydrological and Oceanic Sciences, National Central University, Chungli, TaiwanInstitute of Hydrological and Oceanic Sciences, National Central University, Chungli, TaiwanState Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, ChinaInstitute of Oceanography, National Taiwan University, Taipei, TaiwanTaiwan Ocean Research Institute, National Applied Research Laboratories, Kaohsiung, TaiwanDepartment of Atmospheric Science, National Taiwan University, Taipei, TaiwanInstitute of Hydrological and Oceanic Sciences, National Central University, Chungli, TaiwanInstitute of Hydrological and Oceanic Sciences, National Central University, Chungli, TaiwanInstitute of Hydrological and Oceanic Sciences, National Central University, Chungli, TaiwanIt 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.http://www.biogeosciences.net/10/7449/2013/bg-10-7449-2013.pdf |
| spellingShingle | K.-K. Liu L.-W. Wang M. Dai C.-M. Tseng Y. Yang C.-H. Sui L. Oey K.-Y. Tseng S.-M. Huang Inter-annual variation of chlorophyll in the northern South China Sea observed at the SEATS Station and its asymmetric responses to climate oscillation Biogeosciences |
| title | Inter-annual variation of chlorophyll in the northern South China Sea observed at the SEATS Station and its asymmetric responses to climate oscillation |
| title_full | Inter-annual variation of chlorophyll in the northern South China Sea observed at the SEATS Station and its asymmetric responses to climate oscillation |
| title_fullStr | Inter-annual variation of chlorophyll in the northern South China Sea observed at the SEATS Station and its asymmetric responses to climate oscillation |
| title_full_unstemmed | Inter-annual variation of chlorophyll in the northern South China Sea observed at the SEATS Station and its asymmetric responses to climate oscillation |
| title_short | Inter-annual variation of chlorophyll in the northern South China Sea observed at the SEATS Station and its asymmetric responses to climate oscillation |
| title_sort | inter annual variation of chlorophyll in the northern south china sea observed at the seats station and its asymmetric responses to climate oscillation |
| url | http://www.biogeosciences.net/10/7449/2013/bg-10-7449-2013.pdf |
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