Yellow And East China Seas Research Articles

Marine Dimethyl Sulfide Fluxes in the Yellow and East China Seas: Scenario Variation During the 1980s–2090s and Its Drivers

AbstractShedding light on the response of oceanic dimethyl sulfide flux (FDMS) on the sea shelf to multi‐pressures (intensified terrigenous nutrient inputs and climate change) is of great importance for regional aerosol budget. Here, we designed 4‐group experiments in scenario (the 1980s, 2010s, 2050s, and 2090s) for the Yellow and East China seas (YECS) based on climate change signals gained from CMIP6 and a 3‐dimension biophysical and geochemical model. Results show that the climatological annual mean of YECS's FDMS will rise from ∼6 μmol m−2 day−1 in the 1980s to >9 μmol m−2 day−1 in the 2090s under Shared Socioeconomic Pathway (SSP) 2−4.5/5−8.5 scenario, and with multi‐pressures, the FDMS peak in the 2050s is one season earlier when compared to that in the 1980s. The elevated terrigenous inputs affect the phytoplankton biomass and/or community on the inner shelf, leading to the rise and phenology change in the YECS's FDMS between the1980s and 2010s, while climate change has little impact. The influence of climate change on the FDMS is projected to increase in the 2050s; climate change will change seasonal pattern of the FDMS on the central part (middle and outer shelves) of East China Sea (CECS) under every SSP scenario. Thereinto, wind change exerts a crucial role, it will enhance summertime offshore transport and, accordingly, stimulate phytoplankton growth in summer changing the phenology of FDMS on the CECS.

What controls the future phytoplankton change over the Yellow and East China Seas under global warming?

The Yellow and East China Seas (YECS) are productive continental shelves where essential nutrients for phytoplankton growth are mainly supplied by the intrusion of the Kuroshio Current, riverine inputs, and atmospheric deposition. Surface temperatures in YECS are increasing due to global warming, and are projected to increase further. In this study, future changes in YECS biogeochemical processes were evaluated using Coupled Model Intercomparison Project Phase 6 (CMIP6) Earth System Models. We found a great diversity in predictions of future changes in chlorophyll-a over the YECS region. This diversity was determined to be closely related to the extent of phosphorus (P) limitation for phytoplankton growth. Models simulating positive chlorophyll changes tend to simulate increased Dissolved Inorganic Phosphate (DIP) supplies under future global warming. Our study also demonstrated that the intrusion of the Kuroshio Current into the YECS plays a critical role in future changes in DIP and chlorophyll-a by transporting relatively DIP-rich subsurface water from the Kuroshio Current into the marginal sea.

Characteristics and Mechanisms of Marine Heatwaves in the East Asian Marginal Seas: Regional and Seasonal Differences

Characteristics of marine heatwaves (MHWs) in the East Asian Marginal Seas (EAMS) were investigated using the daily Optimum Interpolation Sea Surface Temperature for 37 years (1982–2018), focusing on seasonal changes and regional differences. The summer MHWs occur 54% more frequently (2.7 events/decade) in a relatively wide area than in other seasons. The strong (up to 3.7 °C) and long-lasting (up to 38 days/event) winter MHWs are concentrated along the subpolar front (SPF) in the East/Japan Sea (EJS) where the MHWs are 20% longer (2.2 days/event) than in the Yellow and East China Seas (YECS). The summer MHWs are primarily driven by increased shortwave radiation associated with reduced cloud cover and latent cooling from the weakened wind over the western flank of developing subtropical highs. Driving mechanisms of the winter MHWs differ by region. The YECS MHWs occur mainly due to the atmospheric processes associated with weakening continental highs, while the EJS MHWs are largely driven by the northward shift of the SPF. Although large-scale atmospheric processes primarily drive the summer MHWs occurring in a wide area in the EAMS, our findings suggest that ocean processes can be major contributors to intensified MHW generation in limited areas, especially in winter.

Controlling factors of annual cycle of dimethylsulfide in the Yellow and East China seas

We developed a dimethylsulfide (DMS) module coupled to an ecological dynamics model studying the annual DMS cycle of the Yellow and East China seas (YECS). The model results showed that surface DMS concentrations ([DMS]) peaked in August along the coast, and there exhibited several DMS peaks offshore annually. In addition, surface [DMS] were higher in the Yellow Sea than that in the East China Sea. The annual mean surface [DMS] of the YECS reached to 4.55 nmol/L, and oceanic DMS emissions from this sea area was 6.78 μmol/(m2 day). Several sensitivity experiments demonstrated that phytoplankton community and sea water temperature exerted crucial effects on seasonal variations of surface [DMS]; and phytoplankton community or temperature changed the timing of surface DMS peak while photolysis affected the magnitude of [DMS]. Moreover, the effect size of phytoplankton community or water temperature varied spatially.

Different characteristics and source contributions to aerosol aminiums over a coastal city and adjacent marginal seas

Environmental context Amines in the atmosphere play important roles in atmospheric chemistry and have potential climate effects. We characterise the concentrations, size distributions and chemical pathways of aerosol aminiums over a coastal city and marginal seas, and estimated the contribution of marine biogenic sources. This study can facilitate our understanding about the interactions between human activities, biogenic emissions and the atmospheric environment. Abstract Atmospheric amines are gaining more and more attention in the field of atmospheric chemistry owing to their important roles in new particle formation and growth. In this study, aerosol aminiums over a coastal city (Shanghai) and the Yellow and East China seas (YECS) were characterised. The concentrations of NH4+, dimethylaminium (DMAH+) and trimethylaminium + diethylaminium (TMDEAH+) over Shanghai were all found to be higher in the winter of 2018 than in the summer of 2019, suggesting their non-negligible terrestrial contributions. DMAH+ and TMDEAH+ concentrations over the YECS in summer were closely correlated and linked to surface phytoplankton biomass, implying that marine biogenic sources might be a predominant contributor to aminiums at this time. Aminiums over Shanghai generally showed a bimodal distribution with a main peak in droplet mode and a secondary peak in condensation mode, suggesting the notable contribution of aqueous-phase or heterogeneous reaction to the formation of aminiums. In contrast, aminiums over the YECS often showed a unimodal distribution, which may be caused by the competition between amines and NH3 for reaction with acidic compounds. We estimated the contributions of marine biogenic sources, ~73.6 % to DMAH+ and 80.1 % to TMDEAH+ over the YECS, using methanesulfonate/non-sea-salt SO42– as an indicator. Our results suggest that marine biogenic emission of amines from China’s marginal seas may have a potential impact on coastal cities, and this source should be considered in modelling new particle formation and air quality in coastal areas.

Record‐Breaking Sea Surface Temperatures in the Yellow and East China Seas

AbstractSatellite observations of sea surface temperature (SST) show that SST in 2004, 2006, and 2016 broke the previous record in the Yellow and East China Seas (YECS). The underlying cause of the record‐breaking SSTs in the YECS is still under debate. Our analysis results demonstrate that enhanced solar radiation and weakened wind, due to a high‐pressure system over the YECS splitting from the western Pacific subtropical high, were mainly responsible for the record‐breaking SSTs in these 3 years. The enhanced solar radiation and weakened wind both depressed oceanic turbulent mixing, and more heat was concentrated in a shallower mixed layer, inducing an anomalous SST rise and resulting in the record‐breaking SSTs.

Solubilities and deposition fluxes of atmospheric Fe and Cu over the Northwest Pacific and its marginal seas

Atmospheric input is an important exogenous source of Fe and Cu to the surface ocean. Here, we investigated temporal and spatial variations, solubilities, size distributions and deposition fluxes of aerosol Fe and Cu using a unique, new dataset including 3-year observations at Huaniao Island and two cruises during the springtimes of 2015 in the Northwest Pacific (NWP) and of 2017 in the Yellow and East China Seas (YECS). The mean concentrations of soluble aerosol Fe and Cu showed a seasonal variation over Huaniao Island with the highest and lowest values in winter and summer respectively, whilst the total Fe reached the maximum in spring. Their mean concentrations decreased significantly from the coastal island to the YECS and to the NWP. The solubility of aerosol Fe was inversely and positively correlated with crustal element Al and non-sea-salt-SO42- (nss-SO42-), respectively. Moreover, the size distribution of soluble Fe demonstrated major peaks in accord with nss-SO42- and a minor peak associated with total Fe. Based on the size distributions of total and soluble Fe, anthropogenic contribution and acid-enhanced dissolution were firstly estimated to be 61% and 32% of soluble Fe over Huaniao Island, 55% and 30% over the YECS, and 34% and 47% over the NWP, respectively. Unlike the Fe, the solubility of aerosol Cu was more correlated with relative humidity (RH). Our estimates of dry deposition fluxes of soluble Fe and Cu declined greatly from the coastal island 33.3 and 2.9 μg m−2 d−1 to the open Pacific 3.6 and 0.1 μg m−2 d−1, respectively. The fluxes of soluble Fe and Cu could vary asynchronously as a result of different origins and transport paths of air masses. Our concurrent study on aerosol Fe and Cu is very helpful for understanding the atmospheric deposition of bioavailable Fe and Cu to the ocean and their interactive effect on marine phytoplankton.

Observed cross-shelf suspended sediment flux in the southern Yellow Sea in winter

The cross-shelf circulation and its transport in the Yellow and East China Seas (YECSs) are very important to global ocean material exchanges and regional environment. A field survey including a long-term mooring, 89 sample stations, 25 drifters, etc., was conducted in the YECSs in the winter of 2015 to investigate the cross-shelf transport of the sediment plume over the Changjiang Bank. The observation shows that the northern East China Sea (ECS) current carries low temperature, low salinity, and high turbidity coastal waters southeastward from the radial tidal sand ridge off the Jiangsu coast to the outer shelf south of Cheju Island. The northern ECS current with an average speed of 4.7 cm/s and in the average direction of 100° from due north is not only measured directly by the 21-day mooring, but also recorded in trajectories of 6 satellite-tracked surface drifters. The mean current of the northern ECS current flows roughly along the 30–50 m isobaths with a small cross-isobath component. The mooring data indicate that the sediment flux is dominated by the mean advection of mean sediment concentration, resulting in an average suspended sediment flux of 52.23 g s−1 m−1 in the direction of 105°. According to the suspended sediment flux decomposition, the flux due to tidal currents is calculated to be one order of magnitude smaller than the advection by subtidal currents, implying that the sediment plume is unlikely generated by the tidal pumping, but is likely maintained by the advection. The amount of the suspended sediments carried by the northern ECS current is estimated to reach 40.62 million tons assuming an average width of 100 km of the turbid plume during December through February. The transport by the northern ECS current is suggested to provide sufficient amount of sediments for the Southwestern Cheju Island Mud to grow in time.

Sedimentary mercury (Hg) in the marginal seas adjacent to Chinese high-Hg emissions: Source-to-sink, mass inventory, and accumulation history

We comprehensively investigated sedimentary Hg in Yellow and East China Seas (YECSs), which constitute potentially important depocenters for large anthropogenic Hg emissions from mainland China. A large dataset of Al-TOC-Hg concentrations led to an in-depth understanding of sedimentary Hg in the entire YECSs, including distribution and its determinants, source-to-sink, background levels, inventory in flux and budget, and accumulation history. Especially, the net atmospheric Hg flux to the sediments was estimated to be 1.3 × 10−5 g/m2/yr, which corresponded reasonably well to that calculated using a box model. About 21.2 tons of atmospheric Hg (approximately 4% of the total anthropogenic atmospheric Hg emissions from China) were buried annually in the YECS basin. This result implies that most of atmospheric Hg from China is transferred to the surface of the Pacific (including the East/Japan Sea and South China Sea) by the westerlies and, consequently, can play a critical role in open-sea aquatic ecosystems.

Recent surface cooling in the Yellow and East China Seas and the associated North Pacific climate regime shift

The Yellow and East China Seas (YECS) are widely believed to have experienced robust, basin-scale warming over the last few decades. However, the warming reached a peak in the late 1990s, followed by a significant cooling trend. In this study, we investigated the characteristics of this low-frequency sea surface temperature (SST) variance and its dynamic relationship with large-scale climate variability through cyclostationary orthogonal function analysis for the 1982–2014 period. Both regressed surface winds on the primary mode of the YECS SST and trends in air-sea heat fluxes demonstrate that the intensification of the northerly winds in winter contribute largely to the recent cooling trend by increasing heat loss to the atmosphere. As a localized oceanic response to these winds, the upwind flow seems to bring warm waters and partially counteracts the basin-scale cooling, thus contributing to a weakening of the cooling trend along the central trough of the Yellow Sea. In the context of the large-scale climate variabilities, a strong relationship between the YECS SST variability and Pacific Decadal Oscillation (PDO) became weak considerably during the recent cooling period after the late 1990s as the PDO signals appeared to be confined within the eastern basin of the North Pacific in association with the regime shift. In addition to this decoupling of the YECS SST from the PDO, the intensifying Siberian High pressure system likely caused the enhanced northerly winds, leading to the recent cooling trend. These findings highlight relative roles of the PDO and the Siberian High in shaping the YECS SST variance through the changes in the large-scale atmospheric circulation and attendant oceanic advection.

A Model Evaluation of Biological Effects on Seasonal Variation of Air–Sea CO2 Flux in the Yellow and East China Seas

ABSTRACTBased on a coupled physical-biogeochemical model of the Yellow and East China Seas (YECS), the influence of biological activity on the seasonal variation of the air–sea CO2 flux is evaluated. The solution of a sensitivity experiment that excludes biological activity is compared with that of a reference experiment that includes the full processes. The comparison reveals that biological activity results in a much stronger seasonal variation of surface dissolved inorganic carbon (DIC) and, hence, the ratio of total alkalinity to DIC in the northern parts of the YECS. The increased ratio resulting from biological DIC consumption contributes to the undersaturated partial pressure of CO2 at the sea surface with respect to the atmosphere, causing the central Yellow Sea in summer and autumn to shift from being a CO2 source to a sink; this same shift also occurs over the Changjiang Bank in summer. In the southern YECS, the biological effect is relatively weak. The comparison further reveals that low water temperature, instead of biological activity, is the dominant factor causing the YECS to become a carbon sink in spring. The biological effect on the variation of DIC (both at the surface and in the water column) differs greatly among the three representative regions of the YECS because of differences in primary production and hydrodynamic conditions. Particle-tracking simulations quantify the regional difference in horizontal advection. In the northern region, weaker horizontal advection causes the longer residence time of low DIC water induced by biological consumption. Over the entire YECS, biological activity contributes to about one-third of the total annual absorption of atmospheric CO2.

Dynamics of the Sediment Plume Over the Yangtze Bank in the Yellow and East China Seas

AbstractA distinct sediment plume exists over the Yangtze Bank in the Yellow and East China Seas (YECS) in winter, but it disappears in summer. Based on satellite color images, there are two controversial viewpoints about the formation mechanism for the sediment plume. One viewpoint is that the sediment plume forms because of cross‐shelf sediment advection of highly turbid water along the Jiangsu coast. The other viewpoint is that the formation is caused by local bottom sediment resuspension and diffused to the surface layer through vertical turbulent mixing. The dynamic mechanism of the sediment plume formation has been unclear until now. This issue was explored by using a numerical sediment model in the present paper. Observed wave, current, and sediment data from 29 December 2016 to 16 January 2017 were collected near the Jiangsu coast and used to validate the model. The results indicated that the model can reproduce the hydrodynamic and sediment processes. Numerical experiments showed that the bottom sediment could be suspended by the bottom shear stress and diffuse to the surface layer by vertical mixing in winter; however, the upward diffusion is restricted by the strong stratification in summer. The sediment plume is generated locally due to bottom sediment resuspension primarily via tide‐induced bottom shear stress rather than by cross‐shelf sediment advection over the Yangtze Bank.

Impact of sea spray on the Yellow and East China Seas thermal structure during the passage of Typhoon Rammasun (2002)

AbstractStrong winds lead to large amounts of sea spray in the lowest part of the atmospheric boundary layer. The spray droplets affect the air‐sea heat fluxes due to their evaporation and the momentum due to the change of sea surface, and in turn change the upper ocean thermal structure. In this study, impact of sea spray on upper ocean temperatures in the Yellow and East China Seas (YES) during typhoon Rammasun's passage is investigated using the POMgcs ocean model with a sea spray parameterization scheme, in which the sea spray‐induced heat fluxes are based on an improved Fairall's sea spray heat fluxes algorithm, and the sea spray‐induced momentum fluxes are derived from an improved COARE version 2.6 bulk model. The distribution of the sea spray mediated turbulent fluxes was primarily located at Rammasun eye‐wall region, in accord with the maximal wind speeds regions. When Rammasun enters the Yellow sea, the sea spray mediated latent (sensible) heat flux maximum is enhanced by 26% (13.5%) compared to that of the interfacial latent (sensible) heat flux. The maximum of the total air‐sea momentum fluxes is enhanced by 43% compared to the counterpart of the interfacial momentum flux. Furthermore, the sea spray plays a key role in enhancing the intensity of the typhoon‐induced “cold suction” and “heat pump” processes. When the effect of sea spray is considered, the maximum of the sea surface cooling in the right side of Rammasun's track is increased by 0.5°C, which is closer to the available satellite observations.

Impact of typhoons on the Changjiang plume extension in the Yellow and East China Seas

AbstractIt is well known that river discharges, winds, ocean currents, and tides are major dynamical factors that determine the distribution and extension of the Changjiang plume (CP) in the Yellow and East China Seas (YECS). Using observations and numerical experiments, this study demonstrates that, in addition to these factors, typhoons in the YECS also play a crucial role in the extension of the CP during the summer season. The hydrographic data observed at the Ieodo Ocean Research Station (IORS) and by a research vessel during the period of Typhoons Ewiniar (0603) and Dianmu (1004) showed that the typhoon‐induced strong vertical mixing modified spatial distribution of the CP significantly, resulting in the delay of the CP's extension by as much as up to 20 days. A series of numerical experiments for Typhoon Dianmu also showed that the typhoon plays a blocking role for the extension of CP for up to 17 days through the vertical mixing process and the change of background winds. In particular, it is found that the delay due to Dianmu in 2010 contributed to the avoidance of potential mass mortality of marine life by preventing the low‐salinity water from spreading to the aquaculture regions near Jeju Island.

Living coccolithophore assemblages in the Yellow and East China Seas in response to physical processes during fall 2013

Abstract Living coccolithophore assemblages collected at discrete depths (0–490 m) from eleven stations across the shelf and slope regions of the Yellow and East China Seas (YECS) during fall 2013 were analyzed using a scanning electron microscope. A total of 32 taxa were recorded, and the predominant taxa were Emiliania huxleyi, Gephyrocapsa spp., Syracosphaera spp. and Algirosphaera robusta. The body coccoliths of A. robusta exhibited an unusual morphology with incomplete hoods, which were recorded in nearly half of the samples and may represent a new variety. In addition, an agglutination relationship was observed between Gephyrocapsa coccoliths and the tintinnid Dictyocysta lepida in oligotrophic waters. Total coccolithophores reached a maximum cell abundance of 252 × 103 cells/l (on average 27.8 × 103 cells/l), with the contribution of Gephyrocapsa ericsonii, E. huxleyi and Gephyrocapsa oceanica accounting for 36.4%, 29.6% and 15.3%, respectively, of the total abundance. Coccolithophore assemblages in the YECS were a mixture of coastal, shelf and subtropical taxa, with the diversity decreasing in a radial direction from the Okinawa Trough to the inner shelves. Distinct deep-water flora existed in the Kuroshio slope waters (100–490 m), which was precisely reflected by the cluster analysis, illustrating very low percent similarity (48.1%) with the other groups. The occurrence of subtropical taxa in the coccolithophore assemblages can be used as benign warmer water signals. In the bottom turbid layers, the coccolithophore assemblages were largely composed of free coccoliths (84.3%), implying complex processes, such as cell death, resuspension and lateral advection, in the sandy and detrital waters. To clarify the relationship between the species distribution and ambient environments, a redundancy analysis (RDA) was applied to distinguish how much the variation in the taxon composition could be attributed to changes in the environmental conditions. Conclusively, salinity and temperature, which to some extent could reflect the physical properties of water stability and stratification, were key factors in driving the distribution patterns of living coccolithophores in the study areas.

Net accumulation of suspended sediment and its seasonal variability dominated by shelf circulation in the Yellow and East China Seas

The seasonal transfer and net accumulation of suspended sediment, especially the forming mechanism of the Southwestern Cheju Island Mud (SWCIM) are investigated using multi-year monthly mean suspended sediment flux to establish the linkages between sediment transport and hydrodynamic conditions and to determine the dominant long-term sediment transport process in the Yellow and East China Seas (YECSs). The more accurate suspended sediment flux, and net deposition or erosion driven by shelf circulation in the YECSs are attained using 10-year time series data on surface suspended sediment concentration and more reliable numerically simulated circulation velocity.The calculated net deposition or erosion of suspended sediment with distinct seasonal variability in the YECSs demonstrates that during the wintertime significant deposition occurs not only along the coast, but also offshore areas with water depth of about 100m, such as the SWCIM, which is acknowledged as the only mid-shelf Holocene depocenter in the YECSs. The annual cycle of net deposition or erosion verifies the widely accepted viewpoint, that riverine suspended sediment is stored in the inner shelf, especially adjacent to the estuary in summer and transported to middle or outer shelf in winter in the YECSs. Active sediment-transport process and the forming of the SWCIM mainly influenced by shelf circulation have been reproduced using the vector field analysis on suspended sediment flux. In winter, the Yellow Sea Coastal Current with high suspended sediment concentration flows southeastward along the Changjiang Bank, and interface with the Yellow Sea Warm Current to drive the East China Sea Cold Eddy at the end of the Changjiang Bank, which contributes to the convergency of suspended sediment, eventually generating the SWCIM. The circulation-driven accumulation rates in the YECSs are 0.51mma−1 in the SWCIM area, 0.45mma−1 at the cross-shelf pathway, 0.04mma−1 in the Central Yellow Sea Mud area, 3.62mma−1 in the Changjiang Estuary, and 3.83mma−1 off the Zhejiang Coast, respectively, which agree with the measured ones reasonably well, and further reveal that shelf circulation dominates long term sediment transport. Some uncertainties on the accuracy of suspended sediment flux and influence of tidal residual currents should be resolved in the future study to achieve a more quantitative picture about sediment transport in the YECSs.

Seasonal variability of air–sea CO2 fluxes in the Yellow and East China Seas: A case study of continental shelf sea carbon cycle model

An inorganic carbon system module was established and coupled with a physical–ecological model based on the concept of continental shelf sea carbon cycle. Seasonal air–sea CO2 flux (FDIC) distribution in the Yellow and East China Seas (YECS) are simulated and the model results are in good agreement with observations. The simulations suggest that the YECS serve as a strong sink (−7.1±3.6mmolm−2 day−1) of atmospheric CO2 in winter and a moderate sink (−1.6±0.8mmolm−2 day−1) in spring. In summer, sink areas occupy the Yellow Sea (YS) and the adjacent sea of the Changjiang Estuary, while the middle and outer shelves of the East China Sea (ECS) act as moderate sources of atmospheric CO2. In fall, substantial carbon sources occur over the Changjiang Bank and the Subei Shoal.Dissolved inorganic carbon (DIC) variations in the euphotic layer and sea surface temperature (SST) are the key parameters to control the FDIC. DIC concentration relates to solubility, algae consumption and physical transport. According to the topographic features and the relationship between partial pressure of CO2 in surface water and SST, the YECS are divided into three typical subregions, namely the central YS, the Changjiang Bank, and the middle shelf of the ECS, to examine the key processes in regulating the total DIC variations in the euphotic layer and study the influential factors of the seasonal pattern of FDIC. The results imply that, in the central YS and the Changjiang Bank, biological effect plays a critical role in DIC removal in the euphotic layer and facilitates the sea to be a sink in spring and summer. In fall, horizontal advection transports DIC out of the central YS area leading this area to be a sink of atmospheric CO2, meanwhile vertical mixing provides DIC for the euphotic layer over the Changjiang Bank inversing this area to be a source. In winter, the low temperature exerts an essential effect on carbon sink which strength is enhanced by the intensive wind in the YECS. In the middle shelf of ECS, seasonal cycle of air–sea CO2 flux is mainly controlled by the SST seasonality. The Kuroshio Subsurface Water intrusion behaves as a net DIC source for the euphotic layer in the shelf of the ECS. The dynamic phytoplankton production and various ocean circulations cause the YECS to form distinctive subregions and thus induce the seasonal and regional changes in air–sea CO2 fluxes.

An effect of ENSO on summer surface salinity in the Yellow and East China Seas

The Yellow and East China Seas (YECS) has been known to exhibit interannual variability in both physical and biological aspects, in relation with El Niño–Southern Oscillation (ENSO). This paper investigates the interannual variability of summer sea surface salinity (SSS) in the YECS and its linkage with ENSO, using a global ocean general circulation model (OGCM) with a regional focus on the YECS. The OGCM experiment reveals that the dominant interannual variability of the SSS in the YECS is attributed to a variability of the Changjiang river discharge (CRD). The variability of the CRD is linked to ENSO-related precipitation over the Changjiang river; when El Niño events occur in winter, precipitation over the Changjiang river increases in the rainy season of the following years. The increased precipitation in El Niño years results from enhanced southwesterly moisture flux from the South China Sea into southern China. Our finding suggests that ENSO-related precipitation in southern China contributes to the dominant interannual variability of the summer SSS in the YECS by modulating CRD.

Seasonal variation of freshwater budget in the Yellow and East China Seas simulated from an ocean general circulation model

This study investigates a freshwater budget in the Yellow and East China Seas (YECS) using a global f general circulation model with a regional focus on the YECS. A freshwater budget analysis finds that major freshwater contributors over the YECS change seasonally. In summer, freshwater inflow from Changjiang and positive precipitation minus evaporation (P-E) dominates freshwater outflow across the boundaries around the YECS, resulting in net freshwater gain in the YECS. In winter, evaporation, intensified by strong winds, dominates freshwater inflow from Changjiang and precipitation, while net freshwater transport across the boundaries around the YECS is negligible, causing freshwater loss in total over the YECS. Although P-E has often been assumed to be negligible by supposing that the annual mean of precipitation is nearly equal to that of evaporation, this study suggests that P-E needs to be included in the seasonal freshwater budget in the YECS.

Empirical ocean-color algorithms to retrieve chlorophyll-a, total suspended matter, and colored dissolved organic matter absorption coefficient in the Yellow and East China Seas

A bio-optical dataset collected during the 1998–2007 period in the Yellow and East China Seas (YECS) was used to provide alternative empirical ocean-color algorithms in the retrieval of chlorophyll-a (Chl-a), total suspended matter (TSM), and colored dissolved organic matter (CDOM) absorption coefficients at 440 nm (ag440). Assuming that remote-sensing reflectance (Rrs) could be retrieved accurately, empirical algorithms for TChl (regionally tuned Tassan’s Chl-a algorithm) in case-1 waters (TChl2i in case-2 waters), TTSM (regionally tuned Tassan’s TSM algorithm), and Tag440 or Cag440 (regionally tuned Tassan’s or Carder’s ag440 algorithm) were able to retrieve Chl-a, TSM, and ag440 with uncertainties as high as 35, 46, and 35%, respectively. Applying the standard SeaWiFS Rrs, TChl was not viable in the eastern part of the YECS, which was associated with an inaccurate SeaWiFS Rrs retrieval because of improper atmospheric correction. TChl behaved better than other algorithms in the turbid case-2 waters, although overestimation was still observed. To retrieve more reliable Chl-a estimates with standard SeaWiFS Rrs in turbid water (a proxy for case-2 waters), we modified TChl for data with SeaWiFS normalized water-leaving radiance at 555 nm (nLw555) > 2 mW cm−2 μm−1 sr−1 (TChl2s). Finally, with standard SeaWiFS Rrs, we recommend switching algorithms from TChl2s (for case-2 waters) to MOCChl (SeaWiFS-modified NASA OC4v4 standard algorithm for case-1 waters) for retrieving Chl-a, which resulted in uncertainties as high as 49%. To retrieve TSM and ag440 using SeaWiFS Rrs, we recommend empirical algorithms for TTSM (pre-SeaWiFS-modified form) and MTag440 or MCag440 (SeaWiFS Rrs-modified forms of Tag440 or Cag440). These could retrieve with uncertainties as high as 82 and 52%, respectively.