Seasonal and inter-annual changes in the surface chlorophyll of the South China Sea (original) (raw)
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Geophysical Research Letters, 2009
Anomalous biogeochemical conditions were observed at the SouthEast Asian Time-series Study (SEATS) station in the northern South China Sea (SCS) during the 1997-98 and 2002-03 El Niño events. The time-series records showed decreases of monthly mean sea surface chlorophylla (S-chl) (and integrated primary production, IPP) by 42% (and 42%) and 13% (and 10%), respectively, below the climatological mean in the winter months (DJF) of the two events. The negative anomalies in S-chl and IPP corresponded to elevated sea surface temperature by 1.2°C and 0.4°C, respectively, above the climatological mean, while the mean wind speed was reduced by about 20% and 11%, respectively. Statistical analysis demonstrated the reduction in S-chl and IPP during El Niño events was caused by the diminished vertical mixing and strengthened stratification. Regional anomalies in hydrographic and biological conditions in the northern SCS (15-21°N and 112-119°E) were consistent with those found at the SEATS site.
Paleoceanography and Paleoclimatology, 2021
Limited instrumental records of sea surface temperature (SST) have hindered our ability to fully understand the natural long-term climate variability driven by surface ocean-atmosphere interactions, particularly in Southeast and East Asia where approximately 30% of the world's population resides (Morton & Blackmore, 2001; United Nations, 2019). Recent modeling studies have begun to document the uncertainty in the centennial-scale behavior of SST in the Western Pacific Ocean and surrounding seas, further emphasizing our need to reconstruct ocean hydrography at a high temporal resolution over longer periods (Karnauskas et al., 2012; Samanta et al., 2018). Complicating our understanding of climate in the marginal seas of the Maritime Continent are the changing interactions between climate drivers of surrounding areas. Climate drivers in Southeast Asia and the marginal seas, including the South China Sea (SCS), are complex and operate at multiple frequencies. For example, the East Asian Monsoon (EAM) varies primarily on a seasonal timescale, whereas the El Niño Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO) exert influence on interannual to interdecadal timescales, respectively. The EAM is defined by seasonal shifts in winds and moisture delivery to East Asia from the Indian and Pacific Oceans. In the summer, winds blow from the Indian Ocean over the SCS onto the Asian continent, driving precipitation. In the winter, winds reverse, delivering cold, dry air from the Pacific Ocean across the East Asian continent to the SCS. These winds have a significant impact, driving seasonal changes in ocean circulation, temperature and precipitation (Lau & Li, 1984; B.
Detailed spatiotemporal impacts of El Niño on phytoplankton biomass in the South China Sea
Journal of Geophysical Research: Oceans, 2017
The lagging and leading correlations among satellite observations, reanalyzed biogeophysical data, and the Nino3.4 El Niño index were investigated to reveal the impacts of El Niño on the phytoplankton biomass (chlorophyll a [Chl a]) in the South China Sea (SCS), in an attempt to identify the probable responsible factors in greater spatiotemporal detail. A basin-scale high Chl a concentration during the developing phase of El Niño changed to basin-scale low Chl a during the weakening phase. Cyclonic wind circulation in the northern basin, increased wind speed in the southern basin, and strengthened upwelling off the Vietnamese coast likely caused a basin-scale nutrient increase during the developing phase of an El Niño event; the opposite conditions led to low nutrient levels during the weakening phase. Decreases in Chl a east of the Vietnamese coast and northwest of Borneo Island were due to decreases in nutrients supplied by rivers. These spatiotemporal changes are considered biogeophysical responses to a variety of types of El Niño. Regardless of the El Niño type, reanalyzing biogeophysical data sets during central Pacific warming separately from those during eastern Pacific warming is recommended for a more robust understanding of the detailed spatiotemporal impacts of different El Niño types on the biogeophysical environment of the SCS.
The Effect of the ENSO on the Variability of SST and Chlorophyll-a in the South China Sea
IOP Conference Series: Earth and Environmental Science, 2019
The South China Sea (SCS) is one of the western marginal oceans of the Pacific Ocean, surrounded by South China, the Indo Peninsula of China, Peninsular Malaysia, the Philippines, and Borneo Island. The effect of the ENSO on the Variability of SST and chlorophyll-a has been investigated by many researchers. However, in the study, there were not still a small number of researchers who studied in this SCS area using high-resolution satellite imagery data. Chlorophyll-a and SST data taken from MODIS data, and wind analysis data from CCMP (Cross Calibrate Multi-Platform). The results obtained, wind speed affects over changes SST and Chlorophyll-a at SCS. The influence of wind speed against the variability of SST is very strong, but otherwise, over variability of Chlorophylla is less impact. There is a high correlation between ENSO (El Nino) with the SST which tends to be dominant throughout the west season due to the influence of wind speed in the South China Sea from the Pacific towards Australia throughout the west season. However, this is in contrast to the correlation between ENSO and Chlorophyll-a which appears less dominant, which is suspected of other factors that may affect Chlorophyll-a anomalies in addition to wind and SST factors.
Seasonal and interannual variability of chlorophyll in the East China Sea
2010
Monthly chlorophyll-a (Chl-a) concentrations derived from SeaWiFS data for 1997-2005 and chlorophyll measurements from the Atlantic Meridional Transect for 1995-2001 have been analysed to describe seasonal and inter-annual variability of surface Chl-a in the Mauritanian upwelling. There was a moderate to strong correspondence between the seasonal cycles of surface Chl-a and the seasonal cycles of ocean physical and meteorological fields (such as sea-surface temperature, seasurface height, and prevailing wind), with a noticeable exception in 1998 that corresponded to a strong anomalous Chl-a event ($250% increase) in the Mauritanian upwelling. Alongshore wind-stress and wind-stress curl were found to be the most significant factors controlling the variability of Chl-a (jointly explaining more than 50% of total variance). The biological response to the alongshore wind-stress was immediate, but it lagged the wind-stress curl by 1-2 months (each explaining more than 40% of the total Chl-a variability). These observations also demonstrate a link, hitherto unreported, between the Pacific El-Nin˜o Southern Oscillation (ENSO) and anomalous Chl-a field in the Mauritanian upwelling. The multivariate ENSO index was shown to account for a significant part of the variability of the autumn-winter Chl-a anomaly (r ¼ À0.52, po0.01). A cold event, following an intense El Nin˜o in the Pacific during summer, was found to mirror the intensity of wind forcing and phytoplankton concentration in the Mauritanian upwelling a few months later. Therefore, ENSO-related changes in the local atmospheric fields are considered as the preferred candidates for explaining the observed biological changes in the Mauritanian upwelling during 1998Mauritanian upwelling during -1999
The forced and free response of the South China Sea to the large-scale monsoon system
Non-tidal sea level anomalies (SLAs) can be produced by many different dynamical phenomena over many time scales, and they can induce serious damages in coastal regions especially during extreme events. In this work, we focus on the SLAs in the South China Sea (SCS) to understand whether and how they can be related to the large-scale, seasonal monsoon system which dominates the SCS circulation and dynamics. We have two major objectives. The first one is to understand whether the NE (winter) and SW (summer) monsoons can be responsible for the persistent SLAs, both positive and negative, observed at the SCS ends along the main monsoon path. The second objective is to understand the SCS response as a free system upon onset/relaxation or sudden changes in the forcing wind. It is well known that sudden changes in the forcing mechanism induce free oscillations, or seiches, in closed, semi-enclosed basins and harbors, and we want to identify the possible seiche modes of the SCS. To our knowledge, these two objectives have not been previously addressed. We address these objectives both through observational analysis and modeling simulations. Multi-year tide-gauge data from stations along the coastal regions of the SCS are analyzed examining their spatial correlations. Strong negative correlations are found between the northeast and southwest stations at the two ends of the SCS under the path of the NE/SW monsoons. They correspond to wind-induced positive/negative sea level set-ups lasting for the entire monsoon season and changing sign from winter to summer. Short periods of negative correlations are also found between the SLAs at eastern and western stations during El Niño years in which the monsoons are weaker and have an enhanced E/W component inducing corresponding sea level set-ups. The tide-gauge station at Tanjong Pagar at the southwest SCS end near Singapore is chosen to study four extreme SLAs events in the observational record during 1999. Modeling simulations are carried out to reproduce them. The observed and modeled extreme SLAs agree quite well, both in the amplitude of the highest peak and in phase. Three main peaks are identified in the observational energy spectrum of the de-tided SLAs at the same station in 1999. Using Merian’s formula to evaluate the periods of seiches in idealized basins Wilson (Adv Hydrosci 8:1–94, 1972) the first two peaks (24.4 h and 11.9 h) are found to correspond to the first two seiche modes in the direction of the main, longer axis of the SCS. The third peak (8.5 h) is found to correspond to the seiche in the transversal, shorter axis. Finally, modeling simulations are carried out by suddenly dropping a circular bump of water in the quiescent basin at different locations to excite the seiches. The periods of the modeled peaks agree quite well with the observational ones, the first two periods being actually identical.
IOP Conference Series Earth and Environmental Science, 2019
The South China Sea (SCS) is one of the western marginal oceans of the Pacific Ocean, surrounded by South China, the Indo Peninsula of China, Peninsular Malaysia, the Philippines, and Borneo Island. The effect of the ENSO on the Variability of SST and chlorophyll-a has been investigated by many researchers. However, in the study, there were not still a small number of researchers who studied in this SCS area using high-resolution satellite imagery data. Chlorophyll-a and SST data taken from MODIS data, and wind analysis data from CCMP (Cross Calibrate Multi-Platform). The results obtained, wind speed affects over changes SST and Chlorophyll-a at SCS. The influence of wind speed against the variability of SST is very strong, but otherwise, over variability of Chlorophyll-a is less impact. There is a high correlation between ENSO (El Nino) with the SST which tends to be dominant throughout the west season due to the influence of wind speed in the South China Sea from the Pacific towards Australia throughout the west season. However, this is in contrast to the correlation between ENSO and Chlorophyll-a which appears less dominant, which is suspected of other factors that may affect Chlorophyll-a anomalies in addition to wind and SST factors.
Mesoscale eddies are observed each year in the South China Sea (SCS); however, their contributions to the biogeochemical cycles have never been systematically quantified. Here, we use a coupled three-dimensional physical-biogeochemical model to evaluate the eddy impact. We first track the modeled mesoscale eddies in the SCS and then analyze the biogeochemical responses to these eddies individually. Compared with the SCS basin mean, modeled depth-integrated (0-125 m) chlorophyll, zooplankton, new production, and silicate uptake are significantly enhanced in the cyclonic eddies and reduced in the anticyclonic eddies. Following the movements of the eddy center, temporal variations of phytoplankton community structure suggest that diatoms respond to cyclonic eddies strongly first and the responses last longer; then picoplankton grow after the diatoms. In the cyclonic eddies, modeled new production is 1.87 ± 0.37 mmol N m −2 d −1 , which is 28% higher than the SCS basin-averaged value, while in the anticyclonic eddies, modeled new production is about 32% lower than the SCS basin mean. As a consequence, modeled detrital nitrogen export for cyclonic eddies is 41% higher than the SCS basin mean, and that for anticyclonic eddies is 31% lower than the SCS basin mean. These values experience strong interannual variations with anomalously low magnitudes found during El Niño conditions for both of the eddies and the SCS basin mean. Our results indicate that cyclonic eddies in the SCS are important sources of nutrients to the euphotic zone and therefore play a significant role in regulating biological productivity and the carbon cycle.
Seasonal and intraseasonal variability of surface chlorophyll a concentration in the South China Sea
Aquatic Ecosystem Health & Management
Seasonal and intraseasonal variability of surface chlorophyll a concentration in the South China Sea is explored using the NASA standard Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) monthly and 8-day level-3 products from 1997 to 2007. The link between the seasonal and intraseasonal variability of the chlorophyll and physical forcing is revealed. Continuous wavelet transform indicates that chlorophyll in the South China Sea presents pronounced seasonal, as well as intraseasonal, variability. Chlorophyll a variability shows significant correlation with wind speed in all five sub-regions, while significant correlation with sea surface temperature only appears in the northern Sea. Intraseasonal variability of chlorophyll appears mainly in the winter, with spectral peaks around 32–64 days. It shows high commonalities for some periods in the intraseasonal cycle between chlorophyll a and sea surface temperature, wind stress curl or wind speed using cross wavelet transform.
Interannual variability in the South China Sea from expendable bathythermograph data
Journal of Geophysical Research, 1999
Using 29 years of expendable bathythermograph data, we studied the interannual temperature variability in the upper 300 m of the South China Sea (SCS). It is found that the temperature field has significant quasi-penta-annual variability throughout the 29 years. The interannual variability has a large decadal modulation. Although outside the SCS, in the Kuroshio, significant interannual variability extends to a much deeper layer beyond the 300 m depth, inside the SCS, especially in the central SCS, strong interannual variability is located near the 100 m depth and is capped by a surface layer of much weaker interannual variability. Similarities and differences in the temporal characteristics between the interannual variability inside and outside the SCS suggest that the interannual variability inside the SCS is primarily generated locally inside the SCS. In addition to the strong interannual variability, there exist strong decadal variability and a linear trend, which are also stronger in the subsurface than near the surface. It is found that below 100 m, the SCS has been cooling (linear trend) at a rate of-•0.4øC per decade, decreasing from the eastern to the western basin. 1. Introduction The tropical western Pacific region has increasingly become the focus of both theoretical and observational studies, given its pivotal role in the E1 Nino, Indonesian throughflow, and low latitude and midlatitude exchange. Lukas et al. [1996] gave a comprehensive review of studies related to the three-dimensional circulation and its temporal variability in the tropical western Pacific region. Most studies on interannual to decadal variability have focused on variabilities outside the South China Sea (SCS) in the open ocean [e.g., Rasmusson et al., 1990; Miller et al., 1997; Zhang and Levitus, 1997a, b; Miller et al., 1998], even though the SCS is one of the largest marginal seas in the world (the rim of the SCS is the most heavily populated region in the world) and is connected to the western North Pacific through the Luzon Strait between Taiwan and the Philippines, as shown in Figure 1. The SCS is under the Southeast Asian Monsoon [Lau and Yang, 1997], which reverses its direction between summer and winter.