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The concentration of chlorophyll-a (CHL) is an important proxy for the amount of phytoplankton biomass in the ocean. Characterizing the variability of CHL in the Pearl River Plume (PRP) is therefore of great importance for the understanding of the changes in oceanic productivity in the coastal region. By applying quantile regression analysis on 21-year (1998&ndash, 2018) near-surface CHL data from satellite observations, this study investigated the long-term trend of CHL in the PRP. The results show decreasing trends (at an order of 10&minus, 2 mg m&minus, 3 year&minus, 1) for all percentiles of the CHL in the PRP, suggesting a decrease in productivity in the past two decades. The trends differ fundamentally from those in the open regions of the northern South China Sea with mixed signs and small magnitudes (10&minus, 4 mg m&minus, 1). The magnitudes of the trends in high quantiles (&gt, 80th) are larger than those in low quantiles (&lt, 50th) in the PRP, indicative of a decrease in the variance of the CHL. The area with apparent decreasing trends is restricted to the PRP in summer and extends to the entire coastal region in winter. This decrease in CHL is possibly attributed to the decrease in nutrient input from the river runoff and the weakening of wind-forced mixing rather than the changes in sea surface temperature. This study extends our knowledge on the variability of CHL in the PRP and provides references to the investigation of the changes of the coastal ecological environment.

Spatio-temporal variability of the suspended sediment concentration (SSC) in the Pearl River Estuary (PRE) is analyzed over 13 years (2003–2015) using MODIS-Aqua Level-1B data. A unique seasonal SSC variability was found. During the wet season, the SSC in the northwestern estuary (NWE) is high, which could reach up to 100 mg/L, while during the dry season it suffers from a markedly decrease. Over the southeastern estuary (SEE), however, the pattern is reversed. This seasonality is mainly affected by freshwater discharge, winds and water column stratification. During the wet season, freshwater discharge dominates the SSC in the NWE while stratification and water discharge control the SSC variation in the SEE. During the dry season, freshwater discharge also plays a more important role in changing the SSC in the NWE, while the combined effect of wind mixing and tidal mixing dominates the SSC in the SEE. The interannual variability of the SSC is revealed by an EOF analysis. The first mode is highly related to water discharge of the Pearl River, indicating that the interannual variability is mainly subject to the rainfall over the Pearl River basin. The long-term SSC trend is characterized by a general decrease across the entire estuary and proved to be closely related to human activity. The reduction rate of the SSC varies spatially and seasonally. Spatially, the northern West Shoal and upper eastern part of the PRE suffer from a much greater SSC decrease, while the rest of the estuary, especially the southern West Shoal, is relatively less influenced. Seasonally, the decreasing rate in the dry season (49.3%) is higher than that in the wet season (30.1%).

River plumes play an important role in the cross-margin transport of phytoplankton and nutrients, which have profound impacts on coastal ecosystems. Using recently available Soil Moisture Active Passive (SMAP) sea surface salinity (SSS) data and high-resolution ocean color products, this study investigated summertime high-frequency variations in the Pearl River plume of China and its biological response. The SMAP SSS captures the intraseasonal oscillations in the offshore transport of the Pearl River plume well, which has distinct 30&ndash, 60 day variations from mid-May to late September. The offshore transport of freshwater varies concurrently with southwesterly wind anomalies and is roughly in phase with the Madden&ndash, Julian Oscillation (MJO) index in phases 1&ndash, 5, thus implying that the MJO exerts a significant influence. During MJO phases 1&ndash, 2, the southwest wind anomalies in the northeastern South China Sea (SCS) enhanced cross-shore Ekman transport, while the northeast wind anomalies during MJO phases 3&ndash, 5 favored the subsequent southwestward transport of the plume. The high chlorophyll-a concentration coincided well with the low-salinity water variations, emphasizing the important role of the offshore transport of the Pearl River plume in sustaining biological production over the oligotrophic northern SCS. The strong offshore transport of the plume in June 2015 clearly revealed that the proximity of a cyclonic eddy plays a role in the plume&rsquo, s dispersal pathway. In addition, heavy rainfall related to the landfall of tropical cyclones in the Pearl River Estuary region contributed to the episodic offshore transport of the plume.

Zhang, T.; Tang, S., and Zhan, H., 2018. Using satellite sensors and in situ observations to monitor phytoplankton blooms in the Pearl River Estuary. Eutrophication in the Pearl River Estuary (PRE) has become severe with the rapid urbanization of the Pearl River Delta in recent years. As a result, large-scale phytoplankton blooms occur frequently because of eutrophication. This study investigated a massive Cochlodinium geminatum bloom near the mouth of the Pearl River in August 2011 based on data from both in situ measurements and satellites. Both methods provided a useful approach for monitoring phytoplankton blooms. The in situ measurements illustrated a high concentration of algal cells (1.5 × 107 cells L−1) in the study area, and the bloom reached dimensions of approximately 10 to 15 km in length, 8 to 10 km in width, and 100 km2 in area based on continuous field measurements. A chlorophyll algorithm for satellite sensors was developed based on in situ chlorophyll concentrations and remote se...

This study investigated boreal wintertime phytoplankton blooms in the western equatorial Indian Ocean (WEIO) and the underlying physical mechanisms. The Sea viewing Wide field of View sensor (SeaWiFS) chlorophyll-a (Chla) concentrations show that phytoplankton blooms occur in the WEIO during December-March. The development of these blooms is not only a seasonal process but also consists of 2-3 intraseasonal events induced by the Madden-Julian Oscillation (MJO). During a typical intraseasonal event, enhanced cross-equatorial wind induces strong upwelling and ocean mixing, thus increasing the supply of nutrients to the surface in equatorial regions. Argo profiles clearly show various responses to the intraseasonal wind bursts, including shoaling of the thermocline and deepening of the mixed layer. Further analysis reveals that the former is the dominant mechanism for the blooms along the equator, while the latter controls the high Chla concentrations off the coast of Somalia. Surface ocean circulations not only account for the blooms south of the equator but also modulate the thermocline depth in the WEIO. The shallower thermocline during the early period of the northeast monsoon season provides favorable conditions for a stronger Chla response to intraseasonal forcing.

Ocean current is one of the major drivers of water mass, energy, and biogeochemical cycles in the global ocean–atmosphere boundary layer and also a key variable in the formation of extreme climate events (e.g., El Nino). Direct measurement of the global ocean surface current is of great scientific interest and application value for understanding multiscale ocean dynamics, air-sea interaction, ocean mass and energy balance, and ocean carbon budget, as well as their variabilities under climate change. This paper reviews the state-of-the-art developments of ocean dynamics and technology on the observation of multiscale ocean circulation and related scientific frontiers. Presently, measurements of global ocean surface currents, which are mainly geostrophically derived from satellite altimeter data, are only available to resolve quasi-geostrophic current at large- to meso-scale in the off-equatorial open ocean. This becomes a bottleneck impeding the application and the development of ocean circulation dynamics. With the ambition of breaking the bottleneck, Ocean Surface Current multiscale Observation Mission (OSCOM) will launch a satellite equipped with a Doppler Scatterometer to directly measure ocean surface currents for the first time with a very high horizontal resolution of 5–10 km and a 3-day global coverage. Through carrying a Surface Temperature Infrared Radiometer and a Surface Temperature Microwave Radiometer, the OSCOM satellite is supposed to have the capability of observing ocean surface current, ocean surface vector wind, and sea surface temperature simultaneously. With a cutting-edge design, OSCOM will provide an in-depth picture of non-equilibrium ocean state and air-sea interaction from mesoscale to submesoscale, and helps to construct the fine structure of deep ocean current through a combination with Array for Real-time Geostrophic Oceanography profiling. Those direct measurements and derived dynamic parameters will further facilitate analyses of ocean carbon budget and ocean biogeochemical cycle, and provide a novel and improved pathway to data assimilation, coupling of General Circulation Models, and the Earth System Modelling for ocean prediction and climate change.

The deterioration of dissolved oxygen conditions in the Pearl River Estuary (PRE) in summer has recently attracted considerable-scientific and political-attention. This paper documents the development, calibration, and verification of a coupled three-dimensional hydrodynamic and water quality model for the PRE. A comparison of the model's performance against field observations indicated that the model is capable of reproducing key hydrodynamic and water quality characteristics of the estuary within an acceptable range of accuracy. Furthermore, a scenario analysis showed that the extent of the hypoxic zone responds differently to changes in the river discharge at different inlets. Moreover, the hypoxic zone also changes in response to variations in the southwest wind in summer; specifically, a larger hypoxic zone develops as southwest winds blow in a more southward direction. However, the hypoxic conditions are much more sensitive to changes in the wind speed than changes in the wind direction.

The effects of interannual variability in chlorophyll concentrations on sea surface temperatures in the east tropical Indian Ocean (ETIO) during two positive Indian Ocean Dipole (IOD) events (in the boreal fall of 1997 and 2006) are investigated; this is done through two ocean model experiments, one with and one without the interannual variability of chlorophyll concentrations. A comparison of the two chlorophyll perturbation experiments reveals that, in contrast to the cooling effects at the seasonal timescale, increased chlorophyll concentrations during positive IOD events leads to an increase in the sea surface temperatures within the ETIO. Although upward velocity is enhanced (with a cooling effect), this does not counterbalance the increase in solar heating caused by the increased chlorophyll concentrations. This interannual variability of chlorophyll concentrations in the ETIO could reduce the amplitude of the IOD by about 6%. This article is protected by copyright. All rights reserved.

As an unwanted by-product in the power plants, cooling water (CW) discharge may induce harmful effects on the coastal environment. In this paper, to accurately predict the CW transport in the Daya Bay, China, we develop a three-dimensional hydrodynamic and temperature model to simulate the transport of the CW from nuclear power plant into coastal waters. Specifically, we use the flow velocity produced by the model to locate Lagrangian coherent structures (LCSs) hidden in ocean surface currents. Result show that the transport of the CW is quite strongly tied to the simulated LCSs. The LCSs constitute fluid barriers that accurately demarcate potential pathway for CW transport. Thus, LCSs in velocity fields from a coastal model is an extremely useful way to monitor and interpret the transport of CW.

Four climatologies on a monthly scale (January, April, May and November) of chlorophyll a within the South China Sea (SCS) were calculated using a Coastal Zone Color Scanner (CZCS) (1979-1983) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) (1998-2002). We analyzed decadal variability of chlorophyll a by comparing the products of the two observation periods. The relationships of variability in chlorophyll a with sea surface wind speed (SSW), sea surface temperature (SST), wind stress (WS), and mixed layer depth (MLD) were determined. The results indicate that there is obvious chlorophyll a decadal variability in the SCS. The decadal chlorophyll a presents distinct seasonal variability in characteristics, which may be as a result of various different dynamic processes. The negative chlorophyll a concentration anomaly in January was associated with the warming of SST and a shallower MLD. Generally, there were higher chlorophyll a concentrations in spring during the SeaWiFS period compared with the CZCS period. However, the chlorophyll a concentration exhibits some regional differences during this season, leading to an explanation being diffi cult. The deepened MLD may have contributed to the positive chlorophyll a concentration anomalies from the northwestern Luzon Island to the northeastern region of Vietnam during April and May. The increases of chlorophyll a concentration in northwestern Borneo during May may be because the stronger SSW and higher WS produce a deeper mixed layer and convective mixing, leading to high levels of nutrient concentrations. The higher chlorophyll a off southeastern Vietnam may be associated with the advective transport of the colder water extending from the Karimata Strait to southeastern Vietnam.

More than ten years of satellite-derived net primary production (NPP) data were used to investigate the interannual variations of NPP associated with two different types of El Niño in the South China Sea (SCS). Results of the empirical orthogonal function analysis (EOF) showed that the first two modes had significant interannual variations and were sensitive to two types of El Niño. The first mode is highly correlated to the canonical El Niño. This mode is characterized by basin-scale decreased NPP during the canonical El Niño years, predominantly diminished off the east coast of Vietnam and the northwest coast of Luzon. The second mode is well correlated to the El Niño Modoki, showing increased NPP in the central and eastern SCS during the El Niño Modoki years. The interannual NPP variability is linked to anomalous atmospheric and oceanic conditions associated with these two types of El Niño. During the developing phase of El Niño Modoki, enhanced western North Pacific summer monsoon and moderate northeasterly wind divergence gave rise to the positive wind stress curl anomalies in the central and eastern SCS, inducing strong Ekman upwelling and increased upward nutrient supply. The moderate Ekman upwelling in the mature phase of El Niño Modoki also sustained the ocean primary productivity. Basin-scale decreased NPP in the SCS was attributed to anomalous weakened wind and abnormal warm sea surface temperature throughout the period of canonical El Niño.

Satellite imagery of SeaWiFS from October 1997 to November 2007 is used to investigate the dominant seasonal and interannual variations of the surface light absorption due to Colored Dissolved Organic Materials (CDOM) in the South China Sea (SCS). Results show that the spatial distribution of CDOM mimics the major features of the SCS basin-scale circulation. High values of CDOM are found in upwelling regions like southeast of Vietnam in summer and northwest of Luzon in winter. At a basin scale, CDOM is high in winter when upwelling is strong, solar shortwave radiation and stratification weak, and vertical mixing intense. Opposite conditions exist in spring and summer. Interannual variability of the basin-wide CDOM is characterized by abnormal troughs during the El Nino events. A strong relationship exists between the time series of the first EOF mode (for both winter and summer) and Nino 3.4 Index. Associations of these events with climatic and hydrographic properties (i.e. wind forcing, solar shortwave radiation, Ekman pumping, vertical mixing, sea surface height and temperature) are discussed.

A major task of ocean colour observations is to determine the distribution of phytoplankton primary production. At present, the global coverage of the sea surface chlorophyll concentration, sea surface temperature, photosynthetically available radiation (PAR) can nominally be achieved every 1 to 2 days with standard algorithms from satellite data. From these standard products, a variety of bio-optical algorithms has been developed to estimate ocean primary productivity. In this communication, we have investigated the possibility of using a novel universal approximator-support vector machine (SVM) as the nonlinear transfer function between ocean primary productivity and the information that can be retrieved from satellite data, including chlorophyll concentration, PAR, maximum carbon fixation rate and day length, which is the same as the vertically generalized production model (VPGM). The VGPM dataset was used to evaluate the proposed approach. The primary production algorithm round robin 2 (PPARR2) dataset was used to further compare the precision between the VGPM and the SVM model. The results suggest that the SVM model is more accurate than the VGPM. Using the SVM model to calculate the global ocean primary productivity, the result is 45.5 Pg C yr-1, which is a little higher than the VGPM result.

A general three-component ocean colour model was used For simulation of water reflectance by inputting sea water component data measured in the Pearl River,er estuary of southern China. Based on the simulated reflectance data and Dissolved Organic Carbon (DOC) sea water component data a local algorithm for estimation of DOC concentration has developed. The application of the local algorithm shoal's that the estimated DOC is in close agreement in terms of concentration and distribution pattern with the sea water component data.

A key component of the East Asian climate system is seasonally varying monsoon wind. Its interannual and interdecadal variability, as well as underlying oceanic processes, is the subject of a recent project completed by the Chinese Academy of Sciences. A series of research progress in the areas of monsoon winds, ocean responses, upwelling and productivity has been made and reviewed by this paper.

Neural networks (NNs) for the inversion of chlorophyll concentrations from remote sensing reflectance measurements were designed and trained on a subset of the SeaBAM data set. The remaining SeaBAM data set was then applied to evaluating the performance of NNs and compared with those of the SeaBAM empirical algorithms. NNs achieved better inversion accuracy than the empirical algorithms in most of chlorophyll concentration range, especially in the intermediate and high chlorophyll regions and Case II waters. Systematic overestimation existed in the very low chlorophyll (

The influence of big rivers' discharge on the ocean is an important theme for land-ocean interaction studies. The Yangtz River (Chang Jiang) is the longest river in China and Asia, and the third-longest in the world. It has a mean annual runoff of 905 billion m3, and averagely carries about 0.433 billion tons of sediments and 0.15 billion tons of dissolved matters to the East China Sea (ECS) each year. The terrestrial materials provide rich substrates for biological activities in the ocean. In this study, the monthly average discharge data of the Yangtze River were collected from 1997 to 2002, and the monthly average water-leaving radiance (Lw) and the chlorophyll_a concentration (Chl_a) in the ECS were processed and calculated from SeaWiFS data acquired from December 1997 to December 2002. Then the correlations of the monthly average discharge to the monthly average Lw at 555nm and Chl_a were analysed respectively. And a series correlative coefficient image maps were achieved.

Nine years of weekly Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data from 1998 to 2006 are used to investigate the temporal correlations in chlorophyll fluctuations by means of detrended fluctuation analysis. Chlorophyll fluctuations are found to exhibit scaling behavior on time scales from several weeks to more than two years over the global ocean between 50 degrees S and 50 degrees N. The scaling exponent varies in a wide range from 0.51 to 1.26, with an average value of 0.83. Long range correlated fluctuations occur over large parts of the ocean, while uncorrelated random fluctuations tend to concentrate in the western margins of the Pacific and Atlantic. The global distribution of the scaling exponent is similar to that of the ratio of interannual to total variability. A greater percentage of interannual to total variability is generally associated with a larger scaling exponent and hence stronger long range correlation.

Euphotic layer of the sea refers to the layer where the phytoplankton can photosynthesize. Therefore the retrieval of the euphotic depth is in favor of estimating ocean primary productivity. This paper introduces an algorithm for retrieval of euphotic depth from ocean color remote sensing data, and dig out the relationship between the euphotic depth of the northern South China Sea (SCS) and the diffuse attenuation coefficient Kd (490) from theoretical deduction and in situ measurement data, then the remotely-sensed estimation of Kd (490) was used for computation of the euphotic depth of this area. A series of monthly and seasonal euphotic depth maps in the northern SCS were obtained and the seasonal variation of euphotic depth and its impact factors were analyzed.

Chlorophyll-a is the pigment presented in living plants or phytoplankton responsible for the photosynthesis, and it is a very important ecological and environmental parameter of waters, not only used for estimation of ocean primary productivity, but also for detection of red tides and for water quality. The chlorophyll-a concentration in coastal waters is generally overestimated from ocean color satellite data with common algorithm. In order to improve the remotely-sensed estimation of chlorophyll-a, many efforts have been made. In this study, six cruises for in situ data collection were conducted in lower reaches of the Pearl River and its estuary, the Lingdingyang, from 2003 to 2006. And the variables such as temperature, salinity, chlorophyll-a, total suspended matters (TSM), nutrients and gelbstoff absorption coefficient (Ag) were collected. The in situ remote sensing reflectance (Rrs) were measured from above waters with an ocean optics USB2000 spectrometer, which covers wavelength from 200 to 850 nm with spectral resolution of 0.38 nm. The original in situ Rrs data were processed to EO-1/hyperion bands (at resolution about 10 nm), and the derivative spectra with the different spectral resolutions were analyzed. The statistic analysis shows that the relative coefficient between derivative spectrum and chlorophyll-a is higher than that between original spectrum and chlorophyll-a. The band with highest relative coefficient to chlorophyll-a was employed for development of chlorophyll-a retrieval algorithm. A derivative spectrum algorithm was developed, and then applied to EO-1/hyperion data, which were acquired in December 16, 2006. The distribution image maps of chlorophyll-a concentration retrieved from EO-1/hyperion data were obtained. It shows that the derivative spectral method is an alternative approach for detection of water quality in coastal waters.

In this paper, a method of assessing water quality from satellite data is introduced. The composite pollution index (CPI) was calculated from measured chemical oxygen demand (COD) and nutrient concentration. The relationships between CPI and 240 band combinations of SeaWiFS water-leaving radiance were analyzed and the optimal band combination for estimating CPI was chosen from the 240 band combinations. An algorithm for retrieval of CPI was developed using the optimal band combination, (L-443 x L-510)/ (L-412 + L-490). The CPI was estimated from atmospherically corrected SeaWiFS data by employing the algorithm. Furthermore, the CPI value range for each water quality level was determined based on data obtained from 850 samples taken in the Pearl River Estuary. The remotely sensed CPIs were then transferred to water quality levels and appropriate maps were derived. The remotely sensed water quality level maps displayed a similar distribution of levels based on in situ investigation issued by the State Ocean Administration, China. This study demonstrates that remote sensing can play an important role in water quality assessment. (C) 2007 Elsevier Ltd. All rights reserved.

The Pearl River system is mainly located in the Guangdong Province in southern China, with the length of 2214 km. and total area of 453,690 km(2). The Pearl River estuary is the largest estuary in the South China Sea (SCS), with a mean annual discharge of 326 billion m(3), of which are about 30 million tons of dissolved matters annually discharged into the estuary. The high concentration of suspended sediments and dissolved matters makes the optical properties of the coastal waters very complex. The spectral absorption coefficient of yellow substance (A(y)(lambda) is one of the inherent optical properties that influence the reflectance (or water-leaving radiance) of the water body. It is essential to measure A(y)(lambda) and to quantify its contributions to the total absorption of the water body. In this study, the Gelbstoff Optical Analyse Laboratory System (GOALS), with spectral range from 200 to 850 nm and with spectral resolution of 0.37 nm per pixel, was used to measure A(y)(lambda) in the Pearl River estuary and in the adjacent coastal waters in July 2002. A(y)(400) was around 1.5 m(-1) near the river mouth (zero salinity). It decreases with increasing salinity following an apparent non-linear mixing line. There is no apparent relationship between A(y)(400) and dissolved organic carbon (DOC) concentration, indicating that the estuary is a complex, non-point source environment. This presents a great challenge to remote sensing study in this area.