State Key Laboratory of Tropical Oceanography

Abstract An unusual positive Indian Ocean Dipole (IOD) event occurred in 2015 associated with the 2015/2016 extreme El Niño. Unlike the canonical IOD, sea surface temperature (SST) warming in the west central tropical Indian Ocean (TIO) dominated the strong zonal SST gradient as cooling off Sumatra‐Java was weak. Over the southeastern TIO, deeper thermocline has suppressed the upwelling cooling since 2012. Such deepened thermocline related to a low‐frequency adjustment and curtailed cool anomalies in the 2015 positive IOD but favored warm anomalies in the 2016 negative IOD. Based on statistical analyses, ocean assimilation data confirm that an IOD‐like pattern exists in the TIO on decadal timescale. During a negative decadal IOD‐like phase, thermocline is deeper in the southeastern TIO; the thermocline‐SST feedback is unfavorable for positive IOD occurrence and intensity, but conducive to negative IOD events. Thus, we propose that the 2015–2016 IOD events are modulated by the low‐frequency variability of thermocline.

Abstract A differentiable function whose contours are orthogonal to potential density ( σ ) contours does not exist. However, such a function, called potential spicity ( π ), can be defined in the least square sense; these two functions form a practically orthogonal coordinate system in potential temperature‐salinity ( θ ‐S) space. Thus, in addition to the classical potential temperature‐salinity ( θ ‐S) diagram, seawater properties can be studied in the potential density‐potential spicity ( σ − π ) diagram.

Abstract Absolute geostrophic currents in the North Pacific Ocean are calculated from the newly gridded Argo profiling float data using the P-vector method for the period of 2004–11. The zonal geostrophic currents based on the Argo profile data are found to be stronger than those based on the traditional World Ocean Atlas 2009 (WOA09) data. A westward mean geostrophic flow underneath the North Equatorial Countercurrent is identified using the Argo data, which is evidenced by sporadic direct current measurements and geostrophic calculations in history. This current originates east of the date line and transports more than 4 × 106 m3 s−1 of water westward in the subsurface northwestern tropical Pacific Ocean. The authors name this current the North Equatorial Subsurface Current. The transport in the geostrophic currents is compared with the Sverdrup theory and found to differ significantly in several locations. Analyses have shown that errors of wind stress estimation cannot account for all of the differences. The largest differences are found in the area immediately north and south of the bifurcation latitude of the North Equatorial Current west of the date line and in the recirculation area of the Kuroshio and its extension, where nonlinear activities are vigorous. It is, therefore, suggested that the linear dynamics of the Sverdrup theory is deficient in explaining the geostrophic transport of the tropical northwestern Pacific Ocean.

Part of climate changes on decadal time scales can be interpreted as the result of adiabatic motions associated with the adjustment of wind-driven circulation, i.e., the heaving of the isopycnal surfaces. Heat content changes in the ocean, including hiatus of global surface temperature and other phenomena, can be interpreted in terms of heaving associated with adjustment of wind-driven circulation induced by decadal variability of wind. A simple reduced gravity model is used to examine the consequence of adiabatic adjustment of the wind-driven circulation. Decadal changes in wind stress forcing can induce three-dimensional redistribution of warm water in the upper ocean. In particular, wind stress change can generate baroclinic modes of heat content anomaly in the vertical direction; in fact, changes in stratification observed in the ocean may be induced by wind stress change at local or in the remote parts of the world oceans. Intensification of the equatorial easterly can induce cooling in the upper layer and warming in the subsurface layer. The combination of this kind of heat content anomaly with the general trend of warming of the whole water column under the increasing greenhouse effect may offer an explanation for the hiatus of global surface temperature and the accelerating subsurface warming over the past 10–15 years. Furthermore, the meridional transport of warm water in the upper ocean can lead to sizeable transient meridional overturning circulation, poleward heat flux and vertical heat flux. Thus, heaving plays a key role in the oceanic circulation and climate.

Using multiple satellite observations, Argo floats profiles, and one-dimensional (1-D) ocean mixed layer model, this study systematically investigated the impacts of the binary typhoons Hagibis and Mitag [which coexisted respectively in the South China Sea (SCS) and western North Pacific (WNP) during November, 22 to 26, 2007] on upper ocean environments. It was observed that intense Ekman pumping and two mesoscale cold, cyclonic eddies, which, induced by long forcing time of strong wind stress curls, appeared respectively in two certain areas instead of after the binary typhoons' trails. Both cyclonic eddies retained for similar to 39 days, accompanied with maximum sea surface height anomaly (SSHA) reduction of similar to 25 cm induced by Hagibis and of similar to 44 cm induced by Mitag, respectively. The largest sea surface temperature (SST) drop of 7 degrees C and 2 degrees C, the maximum chlorophyll a (Chl-a) enhancement respectively was >20 times and similar to 3 times in these two eddies' regions induced by Typhoon Hagibis and Mitag, respectively. The results of the 1-D ocean mixed layer model showed that, given its 84 h forcing time, the simulated MLT cooling and mixed layer deepening induced by Hagibis were similar to-2.8 degrees C and 45 m, respectively, similar to-0.5 degrees C and 25 m for Mitag at its 66 h forcing time. This work provides convincing evidences that typhoons, which appear frequently in the SCS and the WNP, play a notable role in the activities of mesoscale eddies in these areas. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.JRS.6.063583]

Using the hydrographic data collected during August 19 to September 12, 2011 and the altimetry data, we studied the characteristics and distribution of water masses in the northern South China Sea(SCS). In this study, fuzzy cluster analysis of temperature and salinity data was employed to categorize the water in the northern SCS vertically in terms of five groups: the coastal mixing water mass(M), the surface water mass(S), the subsurface water mass(U), the intermediate water mass(I), and the deep water mass(D). Results show that there is Kuroshio water intrusion into the SCS in summer 2011, and that the intrusion could reach 119°E. The geostrophic currents derived from the altimetry data show several meso-scale eddies, including two anticyclonic eddies east of Dongsha Island and east of the Luzon Strait, respectively, and a cyclonic eddy south of Dongsha Island. This indicates distinct meso-scale structures of the circulation in the northern SCS in summer 2011, which would influence the vertical distribution of water mass and the Kuroshio intrusion.

In this study, a large amount of data from precipitation radar (PR) and National Data Buoy Center (NDBC) buoys are collocated for the development and validation of a Geometrical Optics Model, in order to retrieve wind speed at small incidence angles. The omni-directional model is developed based on the combination of the quasi-specular scattering theory and non-Gaussian probability density distribution of ocean surface slope, and can be applied at incidence angles as high as 15°. There are four parameters included in the proposed model: the effective Fresnel reflection coefficient, the mean square slope, and the two coefficients associated with the kurtosis of the sea surface slope distribution. Using one half of the collocated data, the dependence of the four parameters on the in situ wind speed is acquired. The results show that the effective Fresnel reflection coefficient has a decrease relative to that obtained in previous studies. We combine the proposed model with the maximum-likelihood estimation (MLE) technique to retrieve the ocean surface wind speed at the 10 m height. The retrieved wind speeds are then validated against those measured by the NDBC buoys. The comparison shows that the root mean square error (RMSE) and bias between the model retrievals and buoy observations are 1.54 m s–1 and 0.1 m s–1, respectively, revealing high agreements in the wind speed estimations. The results of this study indicate that the proposed model and the PR measurements at low incidence angles can provide reasonably accurate estimates of the surface wind speeds within the range of 0–20 m s–1.

Abstract The Indian Ocean dipole (IOD) is a remarkable interannual variability in the tropical Indian Ocean. The improved prediction of IOD is of a great value because of its large socioeconomic impacts. Previous studies reported that both El Niño-Southern Oscillation (ENSO) and South China Sea summer monsoon (SM) play a dominant role in the western and eastern pole of the IOD, respectively. They can be used as predictors of the IOD at 3 month lead beyond self-persistence. Here, we develop an empirical model of multi-factors in which the western pole is predicted by ENSO and persistence and the eastern pole is predicted by SM and persistence. This new empirical model outperforms largely the average level of the dynamical models from the North American multi-model ensemble (NMME) project in predicting the peak IOD in boreal autumn, with a correlation coefficient of ∼0.86 and a root mean square error of ∼0.24 °C. Furthermore, the hit rate of positive culminated IOD in this new empirical model is equivalent to that in current NMME models (above 65%), much higher than that for negative culminated IOD. This improvement of skill using the empirical model suggests a perspective for better understanding and predicting the IOD.

The Pearl River Estuary is affected by river discharge,tidal currents and the near-shore circulation in the South China Sea.Thus,its hydrodynamic condition is very complicated.The tide at the Pearl River Estuary is mainly irregular semidiurnal type,its tidal amplitude increases from south to north,and its tidal flow reciprocates obviously along the coastline.The tidal front is related to the tidal dynamics and river discharge.The surface and bottom salinity fronts are mainly parallel to the shoreline.In winter,the surface front is apparently near the west coastline of the estuary,whilst in summer,the front spreads away from the estuary because of river discharge.The bottom front is not affected obviously by the season,and in both summer and winter seasons,the bottom front is stronger than the surface front.The tidal dynamics could affect the saline water intrusion.When the river discharge is weak,the tidal dynamics become predominant; therefore,the strength of the saline water intrusion becomes stronger,and the saline water intrusion could influence the strength and position of the front.Furthermore,because the tide and upwelling could destroy the water stratification occasionally,the direction and the strength of vertical convection of dissolved oxygen could change periodically with tides.The hydrodynamics of the Pearl River Estuary obviously influence the bottom hypoxia of the estuary.This paper summarizes the progress on the hydrodynamic characteristics and the hypoxia,and discusses some issues that are worth studying in the future.

Mapping bathymetry with satellite-based imagery for optically shallow waters is important for the management of coastal areas. However, mapping ultra-high-spatial-resolution bathymetry (spatial-resolution < 5 m) for a wide range of coastal optically shallow waters is limited by high cost and the absence of in situ data. Therefore, in this study, a new downscaled bathymetric mapping approach (DBMA-RGB) was established using freely accessed Landsat-8 (spatial-resolution = 30 m) and cost-effective Google Earth Pro-exported ultra-high-spatial-resolution red-green-blue (RGB) imagery. The new approach introduced the scale-invariance assumption that the log-ratio model (LRM) which is calibrated at a high scale is valid at a low scale. To reduce the inversion errors from Landsat-8 imagery, a theoretical maximum detection depth (MDD) model was proposed for the optimization-based inversion method, which is the foundation of DBMA-RGB for working without in situ bathymetric data. The theoretical MDDs overall matched the true MDDs except for the abnormal values, with root mean square error and correlation coefficient values of 3.30 m and 0.68, respectively. Additionally, a set of correction coefficients was obtained to improve the accuracy of the water depth derived from Landsat-8 imagery. Finally, the DBMA-RGB was applied to the RGB imagery of sixteen coastal areas around the world, incorporating the bathymetric results from Landsat-8 imagery. The comparison results indicated that the DBMA-RGB yielded similar results to the LRM calibrated using in situ bathymetric data. In summary, DBMA-RGB demonstrated its feature in accurately mapping ultra-high-spatial-resolution bathymetry for a wide range of coastal optically shallow waters without in situ bathymetric data.

Space-borne observations of primary production (PP) are essential for understanding the role of phytoplankton in the biogeochemical cycles on a global or regional scale. In this study, the vertically generalized production model (VGPM) and two size-fractionated PP algorithms (namely U10 and B17) were evaluated in the SCS. Comparison between estimated and in situ measured total PP showed the best performance of U10 with an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 0.65 and mean absolute percentage deviation (MAPD) of 31.11%. B17 produced better accuracy than U10 for PP from pico-phytoplankton (PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pico</sub> ) and micro-phytoplankton (PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">micro</sub> ), whereas U10-derived PP from nano-phytoplankton (PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nano</sub> ) agreed better with in situ measurements than B17-derived PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nano</sub> . Sensitivity analysis showed that PP estimation was most sensitive to chlorophyll-a (Chla), followed by euphotic zone depth (Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eu</sub> ), and photosynthetically available radiation (PAR), and physiological parameters. With regional optimization of Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eu</sub> , phytoplankton size class (PSC), photosynthesis-irradiance curve parameters, and Chla profile modelling, B17 was tuned for the SCS. Its accuracy was greatly improved, as indicated by slopes close to 1, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> s > 0.55, and MAPD < 145%, for all size classes and total PP. Application of the tuned algorithm to satellite produced data demonstrated a decreasing trend for the total PP, PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pico</sub> , and PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nano</sub> while no apparent trend for PP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">micro</sub> . This study represents the feasibility of improving PP estimation from satellite observation for regional applications through retuning to local data. Our findings are useful for understanding the ecological response to climate change in the region and unveil the role of size-fractionated phytoplankton in biogeochemical and carbon cycles on a basin scale.

Based on the in situ investigations on primary production and secondary production in the Daya Bay,the potential fishery production and the maximum sustainable yield in this region were estimated.The results showed that the average primary production in the Daya Bay were 765.23 mgC.m-2.d-1 and 1786.33 mgC.m-2.d-1 in spring and summer respectively,and the average secondary production were 175.23 mgC.m-2.d-1 and 678.95 mgC.m-2.d-1 in spring and summer respectively.The potential fishery production based on the Tait’s model and the Cushing’s model were 3.30×104 ton and 4.78×104 ton respectively.Further analyzing results showed that changes of community structure in basic trophic levels may lead to overestimate the actual fishery production in the bay when basic biological productions were used to the estmiations,high community biodiversity,healthy ecosystem structure and function should be the primary basis for sustaining quantity and quality of the fishery production.

Since the 1980s,marine observation has become much more diversified,capable of delivering three-dimensional and real-time data.National and regional observing systems have been playing important roles in key regions of the oceans.Going with the development of technology and concept innovation,regional marine observation system has been widely used and gradually improved.International marine observation stations,such as the Irish Sea Coastal Observatory,the Carolinas Regional Coastal Ocean Observing System(RCOOS),and the Victoria Experimental Network Under the Sea(VENUS) are great examples,which consist of three-dimensional and real-time data,combined with marine ecosystem,physical,biological and chemical models.Some other examples,such as the American North-East Pacific Time-series Undersea Networked Experiments(NEPTUNE),the European Seafloor Observatory Network(ESONET) and the Japanese Advanced Real-time Earth monitoring Network in the Area(ARENA) are deep-sea network systems,which make the ocean observatory more comprehensive.Under these international backgrounds,the first deep-sea observation research network station in China-Xisha Marine Research Station was completed in 2008 and has started offering real-time data.The observation system mainly includes automatic weather station,mooring in the western boundary,biological traps,Xisha surface ocean observation system,and Xisha Ocean Optics observation system.Because of the complexity of marine structure,harsh working environment and resource shortages,marine observation could be a high risk task.With the knowledge of the domestic and international marine observation systems reviewed in this study,it is hoped that Chinese marine observation system could be developed and improved to achieve more rapid progress.

Abstract As an important part of the Indo-Pacific warm pool, the Indian Ocean has great significance for research on the Asian monsoon system and global climate change. From the 1960s onward, several international and regional programs have led to important new insights into the Indian Ocean. The eastern Tropical Indian Ocean Observation Network (TIOON) was established in 2010. The TIOON consists of two parts: large-scope observations and moored measurements. Large-scope observations are performed by the eastern Tropical Indian Ocean Comprehensive Experiment Cruise (TIO-CEC). Moored measurements are executed by the TIOON mooring array and the hydrological meteorological buoy. By 2019, 10 successful TIO-CEC voyages had been accomplished, making this mission the most comprehensive scientific investigation in China. The TIO-CEC voyages have collected temperature/salinity profiles, GPS radiosonde profiles, and other observations in the Indian Ocean. To supplement the existing buoy array in the Indian Ocean, an enhanced TIOON mooring array consisting of eight subthermocline acoustic Doppler current profiler (ADCP) moorings, was established since 2013. The TIOON mooring equipped with both upward-looking and downward-looking WHLS75K ADCP provide valuable current monitoring information to depth of 1,000 m in the Indian Ocean. To improve air–sea interaction monitoring, two real-time hydrological–meteorological buoys were deployed in 2019 and 2020 in the equatorial Indian Ocean. A better understanding of the Indian Ocean requires continuous and long-term observations. The TIOON program and other aspiring field investigation programs will be promoted in the future.

Abstract In 2015, the Indian Ocean exhibits an exceptionally weakened CO 2 uptake, highlighting strong interannual variability of ocean carbon sink. By utilizing multiple ocean CO 2 partial pressure ( p CO 2 ) data and a state‐of‐the‐art ocean biogeochemical model, we show that the 2015 ocean CO 2 anomaly is characterized by a basin‐wide amplification of ocean p CO 2 , differing from ocean p CO 2 responses to other Indian Ocean Dipole events (e.g., 1997 and 2019). The distinct ocean p CO 2 anomaly is attributed to an amplified warming and an unprecedented weakening Indonesian Throughflow under the influence of co‐occurrence of positive IOD and extreme El Niño in 2015. The amplified warming drives higher ocean p CO 2 in the western and central Indian Ocean, while the ITF transports anomalously high ocean p CO 2 water from the Pacific Ocean to the southeastern Indian Ocean. This newly identified ocean carbon response provides deeper insights into the Indian Ocean carbon interannual variability.

We analyzed the interannual variability of the Wyrtki Jet and its salinity transport associated with Indian Ocean Dipole(IOD) in fall season using observations and Simple Ocean Data Assimilation(SODA). During negative IOD events, the Wyrtki Jet strengthened in the equatorial Indian Ocean, forced by enhanced equatorial westerly wind, which favors a stronger eastward transport of high-salinity water. During positive IOD events, the above-mentioned processes reversed. In addition, both the Wyrtki Jet and associated salinity transport anomalies on the strength and spatial distribution displayed significant asymmetric characteristics between the positive and negative IOD events. The amplitudes of zonal velocity and salinity anomalies were stronger during the positive IOD events. The anomalies centered in the central equatorial Indian Ocean during the positive IOD events, but they moved to the east in the negative IOD events. Moreover, the velocity anomalies reached a deeper depth during the negative IOD events, even though the salinity anomalies occurred at a rather shallow depth.

Agonistic behavior is common among crustaceans, but it presents risks such as energy loss, injury, and even death in aquaculture settings. Our previous study indicated that l-tryptophan (l-TRP) inhibits agonistic behavior in Eriocheir sinensis. However, supplementing l-TRP in diets increases costs and reduces nutritional quality. This study explores the role of tryptophan hydroxylase (TPH) in l-TRP metabolism and its regulation of agonistic behavior in E. sinensis. Our results show that l-TRP supplementation significantly increases the serotonin level and TPH expression. Subcellular localization confirmed the expression of the TPH in the cytoplasm of HEK293T cells. RNA interference of TPH significantly enhanced in the contact numbers of the crabs. While overexpression of the TPH significantly inhibited agonistic behavior in E. sinensis. Specifically, the fight duration was reduced from 6.67 ± 2.03 min in the control group to 1.81 ± 0.39 min, and the fight number decreased from 17 ± 2.47 to 8.0 ± 1.27. Moreover, the concentration of serotonin in E. sinensis was increased after TPH overexpression. Additionally, fluoxetine injection also significantly inhibited the agonistic behavior. In summary, our findings suggest that TPH regulates agonistic behavior in E. sinensis by mediating the conversion of l-TRP into 5-HT.

By analyzing the temperature,salinity,dissolved oxygen(DO),chlorophyll,and river discharge data observed in the summers of 1999 and 2009 in the Pearl River Estuary(PRE),we find that the spreading range of the freshwater plume in 1999 was larger than that in 2009 due to larger runoff from the Pearl River.The salinity profiles showed a strong stratification inside the PRE in 1999,but a weak stratification in 2009,owing to the co-effect of the smaller river discharge and stronger winds associated with the tropical storm Nangka,which makes the water column well mixed in the top 5 m.The DO distribution patterns for the two years were similar near the surface,but were quite different at the bottom,especially in the western shal-low area and outside the mouth of the PRE.In 1999,the DO concentration was less than 3 mg.L-1 in the western shallow area and between 4-5 mg.L-1 outside the mouth of the PRE;but in 2009 it was greater than 5 mg.L-1 in the western shallow area and less than 3mg.L-1 outside the mouth.Strong stratification in the PRE was the main reason for the low concentration of bottom DO in the western shallow area in 1999.The intensified vertical mixing induced by Nangka facilitated the exchange of DO between the surface and bottom waters,which prevented the formation of low concentration DO in this region in 2009;however,the salinity stratification and consumption of oxygen by the phytoplankton blooms triggered by Nangka might be the reasons for the low DO content in the bottom water outside the mouth of PRE.

Shallow waters hold ecological and economic importance. Traditional reflectance forward models, such as Hydrolight and Monte Carlo (MC), are difficult to access or time-consuming. Two-stream models show great performance in radiative transfer simulation, but most of them are applied in other mediums, or ignore the asymmetry scattering characteristic of shallow water. In this paper, we propose a general multilayer analytical radiative transfer-based (GMART) model considering the realistic volume scattering function of water body, which is theoretically applicable for various shallow waters. GMART results are validated against Hydrolight and MC. The mean absolute percentage error (MAPE) of GMART and Hydrolight remote sensing reflectance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_rs</i> ) among different combinations of the bottom depth, solar zenith angle and wind speed spans in ranges of 5.37%-28.86%, 3.37%-39.28%,and 4.91%-26.73%, with root mean square error (RMSE) values from 1.73×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> -4.49×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , 2.68×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> -1.85×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> and 1.59×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> -2.92×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sr</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , respectively, for the coral, sand, and seagrass bottom. Comparisons of the bidirectional reflectance function with Hydrolight and MC indicate the capacity of GMART to compute bidirectional reflectance. Additionally, a comparison with field measurements is carried out. The minimum MAPE and RMSE between the modeled and measured normalized <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_rs</i> among several stations in the Sanya coastal area are 13.99%, and 0.061, respectively. The mean MAPE and RMSE among 6 stations are 21.38% and 0.083, respectively. The field validation underscores the feasibility of the model in shallow water radiative transfer. Compared with MC, the computational efficiency of GMART is much higher. The new model is shown to be an alternative and efficient tool capable of addressing shallow water-related challenges across diverse environmental conditions.

In this paper,the tidal current characteristics on the continental shelf of the Xisha Islands in the South China Sea are analyzed by using the current data,which are observed at a mooring site near the Xisha Islands in July,2010.The parameters,such as the elliptical elements of the barotropic and baroclinic tidal current,the current energy spectra and the kinetic energy are calculated.The results show that the current mainly flows to the east and the barotropic tidal current is significant in this area while the baroclinic tidal current is not obvious.K1 is the main component barotropic tidal current,and then O1.The current energy of diurnal frequency is very strong and the near-inertial oscillation increases significantly after the passage of typhoon.The ratio of the mean kinetic energy of the baroclinic tidal current to the observational current is very small at the depth of 20m.