Comparison of air-sea CO2 flux and biological productivity in the South China Sea,East China Sea,and Yellow Sea:a three-dimensional physical-biogeochemical modeling study

Marginal seas play important roles in regulating the global carbon budget, but there are great uncertainties in estimating carbon sources and sinks in the continental margins. A Pacific basin-wide physical-biogeochemical model is used to estimate primary productivity and air-sea CO_2 flux in the South China Sea（SCS）, the East China Sea（ECS）, and the Yellow Sea（YS）. The model is forced with daily air-sea fluxes which are derived from the NCEP2 reanalysis from 1982 to 2005. During the period of time, the modeled monthly-mean air-sea CO_2 fluxes in these three marginal seas altered from an atmospheric carbon sink in winter to a source in summer. On annualmean basis, the SCS acts as a source of carbon to the atmosphere（16 Tg/a, calculated by carbon, released to the atmosphere）, and the ECS and the YS are sinks for atmospheric carbon（–6.73 Tg/a and –5.23 Tg/a, respectively,absorbed by the ocean）. The model results suggest that the sea surface temperature（SST） controls the spatial and temporal variations of the oceanic pCO_2 in the SCS and ECS, and biological removal of carbon plays a compensating role in modulating the variability of the oceanic pCO_2 and determining its strength in each sea,especially in the ECS and the SCS. However, the biological activity is the dominating factor for controlling the oceanic pCO_2 in the YS. The modeled depth-integrated primary production（IPP） over the euphotic zone shows seasonal variation features with annual-mean values of 293, 297, and 315 mg/（m^2·d） in the SCS, the ECS, and the YS, respectively. The model-integrated annual-mean new production（uptake of nitrate） values, as in carbon units, are 103, 109, and 139 mg/（m^2·d）, which yield the f-ratios of 0.35, 0.37, and 0.45 for the SCS, the ECS, and the YS, respectively. Compared to the productivity in the ECS and the YS, the seasonal variation of biological productivity in the SCS is rather weak. The atmospheric pCO_2 increases from 1982 to 2005, which is consistent with the anthropogenic CO_2 input to the atmosphere. The oceanic pCO_2 increases in responses to the atmospheric pCO_2 that drives air-sea CO_2 flux in the model. The modeled increase rate of oceanic pCO_2 is0.91 μatm/a in the YS, 1.04 μatm/a in the ECS, and 1.66 μatm/a in the SCS, respectively.

Rates and fluxes of centennial-scale carbon storage in the fine-grained sediments from the central South Yellow Sea and Min-Zhe belt, East China Sea

The global carbon cycle has played a key role in mitigating global warming and climate change.Long-term natural and anthropogenic processes influence the composition,sources,burial rates,and fluxes of carbon in sediments on the continental shelf of China.In this study,the rates,fluxes,and amounts of carbon storage at the centennial scale were estimated and demonstrated using the case study of three fine-grained sediment cores from the central South Yellow Sea area(SYSA) and Min-Zhe belt(MZB),East China Sea.Based on the high-resolution temporal sequences of total carbon(TC)and total organic carbon(TOC)contents,we reconstructed the annual variations of historical marine carbon storage,and explored the influence of terrestrial and marine sources on carbon burial at the centennial scale.The estimated TC storage over 100 years was 1.18×10~8 t in the SYSA and 1.45×10~9 t in the MZB.The corrected TOC storage fluxes at the centennial scale ranged from 17 to 28 t/(km^2·a)in the SYSA and from 56 to 148 t/(km^2·a)in the MZB.The decrease of terrestrial materials and the increase of marine primary production suggest that the TOC buried in the sediments in the SYSA and MZB was mainly derived from the marine autogenetic source.In the MZB,two depletion events occurred in TC and TOC storage from 1985 to 1987 and 2003 to 2006,which were coeval with the water impoundment in the Gezhouba and Three Gorges dams,respectively.The high-resolution records of the carbon storage rates and fluxes in the SYSA and MZB reflect the synchronous responses to human activities and provide an important reference for assessing the carbon sequestration capacity of the marginal seas of China.

Characteristics of Clay Minerals in the Northern South China Sea and Its Implications for Evolution of East Asian Monsoon since Miocene

Clay mineral assemblages, crystallinity, chemistry, and micromorphology of clay particles in sediments from ODP Site 1146 in the northern South China Sea （SCS） were analyzed, and used to trace sediment sources and obtain proxy records of the past changes in the East Asian monsoon climate since the Miocene, based on a multi-approach, including X-ray diffraction （XRD） and scanning electron microscopy combined with energy dispersive X-ray spectrometry （SEM-EDS）. Clay minerals consist mainly of illite and smectite, with associated chlorite and kaolinite. The illite at ODP Site 1146 has very well-to-well crystallinity, and smectite has moderate-to-poor crystallinity. In SEM the smectite particles at ODP Site 1146 often appear cauliflower-like, a typical micromorphology of volcanic smecites. The smectite at ODP Site 1146 is relatively rich in Si element, but poor in Fe, very similar to the smectite from the West Philippine Sea. In contrast, the chemical composition of illite at ODP Site 1146 has no obvious differences from those of the Loess plateau, Yellow River, Yangtze River, and Pearl River. A further study on sediment source indicates that smectite originates mainly from Luzon, kaolinite from the Pearl River, and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The clay mineral assemblages at ODP Site 1146 were not only controlled by continental eathering regimes surrounding the SCS, but also by the changing strength of the transport processes. The ratios of （illite＋chlorite）/smectite at ODP Site 1146 were adopted as proxies for the East Asian monsoon evolution. Relatively higher ratios reflect strongly intensified winter monsoon relative to summer monsoon, in contrast, lower ratios indicate a strengthened summer monsoon relative to winter monsoon. The consistent variation of this clay proxy from those of Loess plateau, eolian deposition in the North Pacific, planktonic, benthic foraminifera, and black carbon in the SCS since 20 Ma shows that three profound shifts of the East Asian winter monsoon intensity, and aridity in the Asian inland and the intensity of winter monsoon relative to summer monsoon, occurred at about 15 Ma, 8 Ma, and the younger at about 3 Ma. The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at 15 Ma, 8 Ma, and 3 Ma.

The Combined Effect of Tibetan Plateau Uplift and Glacial-Interglacial Cycles on the Quaternary Evolution of the East Asian Monsoon: Evidence from South China Sea Sediments

The siliciclastic sediments of the uppermost section of 185 mcd （meters composite depth） from ODP Site 1146 on the northern continental slope of the South China Sea （SCS） were partitioned according to their sources using end-member modeling on grain-size data.The goal was to evaluate the evolution of the East Asian monsoon over the past 2 million years.The siliciclastic sediments were described as hybrids of four end-members,EM1,EM2,EM3,and EM4,with modal grain sizes of 8-22 μm,2-8 μm,31-125 μm,and 4-11 μm,respectively.EM1 and EM3 are interpreted as eolian dust and EM2 and EM4 as fluvial mud.The ratio of eolian dust to fluvial mud （（EM1＋EM3）/（EM2＋EM4）） is regarded as an indicator of the East Asian monsoon.The variation in this ratio not only shows periodical oscillations consistent with oxygen isotope stages,but also exhibits a phased increasing trend corresponding with the phased uplifts of the Tibetan Plateau,indicating that the evolution of the East Asian Monsoon was controlled not only by glacial-interglacial cycles,but also by the phased uplifts of the Tibetan Plateau during the Quaternary.

On a new Siphonophora from the East China Sea and South China Sea

In the course of identifying the samples of Siphonophora from the East China Sea and South China Sea, a new Siphonophora, Vogtia microsticella sp. nov. , was noted. The new species is distinguished from other five species in the genus in nectophore as follows: Parahorse-shoe shaped with five bluntly rounded projections, the two projections below the ostium, i. e. the basal projections, approach each other. The dorsal facet is smooth without any gelatinous prominence. Smaller are the nectosac and the ostium.

ADI BAROTROPIC OCEAN MODEL FOR SIMULATON OF KUROSHIO INTRUSION INTO CHINA SOUTHEASTERN WATERS

In this numerical model for simulating the Kuroshio intrusion into the East and South China Seas,vertically averaged marine hydrodynamic equations governing ocean currents and long-period waves areapproximated by a set of two-time-level semi-implicit finite difference equations. The major terms in-cluding the local acceleration, sea-surface slope, Coriolis force and the bottom friction are approxi-mated with the Crank-Nicholson scheme, which is of second order accuracy. The advection terms are app-roximated with the Leith scheme. The difference equations are split into two sets of alternating directionimplicit quations, each of which has a tridiagonal matrix and can be easily solved. The model reproduces a major Kuroshio intrusion north of Luzon Island, one north of Taiwan Island, andone west of the Tokara Strait. The model shows a current system running from the Luzon Strait to the coastof Vietnam and Hainan Island, through the Taiwan Strait and then into the Tsushima Strait. The summerand winter

Sea surface temperature variations in the southwestern South China Sea over the past 160 ka

Sea surface temperatures （SSTs） in the southwestern South China Sea have been reconstructed for the past 160 ka using the U37^k paleothermometer from the core MD01 - 2392. The temperature differences between glacial times （ MISs 6 and 2） and interglacial times （ MISs 5.5 and 1） are 2.2 ～ 2.5 ℃. Younger Dryas event during the last deglaciation was documented in both the planktonic foraminiferal δ^18 and SST records. After MIS 5.5, SSTs displayed a progressive cooling from 28.6 to 24.5 ℃ culminating at the LGM. During this gradual cooling period, warm events such as MISs 5.3, 5.1 and 3 were also clearly documented. By comparison of SST between the study core and Core 17954, a pattern of low or no meridional SST gradients during the interglacial periods and high meridional SST gradients during the glacial periods was exhibited. This pattern indicates the much stronger East Asian winter monsoon at the glacial than at the interglacial periods. Spectral analysis gives two prominent cycles：41 and 23 ka, with the former more pronounced, suggesting that SSTs in the southern SCS varied in concert with high-latitude processes through the connection of East Asian winter monsoon.

Linking Monsoon Activity with River-Derived Sediments Deposition in the Northern South China Sea

The history of the East Asian monsoon(EAM)since Last Glacial Maximum is reconstructed based on records in a sediment core retrieved from the northern South China Sea.The provenance of organic carbon and the EAM’s evolution are investigated using combined organic carbon,grain size,and AMS 14 C dating analysis.Responding to the strong winter monsoon,the marine organic matter was dominated in the sediments,andδ13 C of organic matter was high during the last glacial period.During the Holocene,the primary productivity decreased and the dilution effect of riverine inorganic clastics strengthened.Accordingly,the total organic carbon contents andδ13 C values decreased,and terrestrial organic matter content increased in the core sediments.The 4μm grain size fraction,as the environmental sensitive grain size component,is determined to reconstruct the paleoclimatic records.During the last glacial period,the contents of 4μm grain size component were mainly controlled by the sea level changes.Upon the Holocene,the influence of the sea level changes weakened and the roles of current system and provenance strengthened.The correlation between the EAM and solar insolation forcing is also discussed in this paper.

Abrupt changes of radiolarian fauna at 600 and 120 ka B. P. in the southern South China Sea and their paleoceanographic implications

Abrupt changes in radiolarian composition are discovered over the last 600 and 120 ka B. P. based on quantitative analyses of radiolarians in ~ 17957 - 2 of the southern South China Sea. The distinct changes at 600 ka B. P. could correspond to the onset of the 100 ka cycle during the glacial and interglacial periods. This abrupt change in the 100 ka cyclicity at 600 ka B. P. occurred also in the magnetic susceptibility signal that is obtained from and paleosol sequences of the China Loss Plateau. The larger amplitude and stronger cyclicity in the susceptibility signal after 600 ka B. P. reflect the prominent change in the intensity of the monsoon, induced by an enhancement of the momsoon circula- tion. Stronger seasonality during the glacial period in the South China Sea, resulted from strengthening of winter monsoon, might lead to the changes in the radiolarian composition at 600 and 120 ka B. P. It can be suggested that only species adapted to a broader temperature range might have been able to live in this environment. Therefore, the abrupt changes in radiolarian composition at 600 and 120 ka B. P. could be attributed to the stronger so differences between summer and winter that were caused by the striking change in the intensity of the monsoon circulation.

Predicting sediment flux from continental shelf islands,southeastern China

Continental shelf islands are contributors of terrestrial sediment supply to shelf regions,and the sediment flux from these islands shall be quantified.We calculated the sediment flux of continental shelf islands in the southeastern China using two empirical equations under two preconditions.The first,the sediment load/yield of the islands has the same pattern as the adjacent small,mountainous rivers along the coastline;and the second,each of the islands was treated as a single catchment.The results show that the sediment supply from these islands reached an order of magnitude of 1 Mt/a,which is comparable to the supply from the local smaller rivers.A sensitivity analysis indicates that this value represents the lower limit of estimate;if the accurate amount of sub-catchments of any island is considered,then this value will be enhanced slightly.This study demonstrates that the sediment supply from continental shelf islands to oceans is an important factor affecting the regional sedimentation and,therefore,should be paid with attention.

Progress of studies in China from July 2010 to May 2015 on the influence of the Kuroshio on neighboring Chinese seas and the Ryukyu Current

The influence of the Kuroshio on neighboring Chinese seas and the Ryukyu Current is a very important subject of interest in physical oceanography. To deeply explain the research progress made by Chinese scientists from July2010 to May 2015, the following three aspects are reviewed in this paper. The first concerns the Kuroshio intrusion into the South China Sea（SCS） and its circulation around the Luzon Strait. There are two very important points to be explained： the seasonal and inter-annual variation of the Kuroshio intrusion and the mechanisms of the Kuroshio intrusion and the influence of the Kuroshio on currents in the Luzon Strait and circulation in the northern SCS. The second concerns the variability of the Kuroshio and its interaction with the East China Sea（ECS）. There are following four interesting topics to be explained： an overview of studies on the Kuroshio in the ECS; the Kuroshio intrusion into the ECS, water exchange, and dynamic impacts; the downstream increase of nutrient transport by the Kuroshio; and the application of satellite remote sensing on terrestrial material transport by the Kuroshio intrusion into the ECS. Third, the interaction between the Ryukyu Current and Kuroshio in the ECS are also discussed. Finally, the main results are summarized and areas of further study are simply discussed.

Interbasin freshwater, heat and salt transport through the boundaries of the East and South China Seas from a variable-grid global ocean circulation model

The monthly and annual mean freshwater, heat and salt transport through the openboundaries of the South and East China Seas derived from a variable-grid global ocean circulation model is reported. The model has 1/6 resolution for the seas adjacent to China and 3 resolution for the global ocean. The model results are in fairly good agreement with the existing estimates based on measurements. The computation shows that the flows passing through the South China Sea contribute volume, heat and salt transport of 5.3 Sv, 0.57 PW and 184 Ggs-1, respectively (about 1/4) to the Indonesian Throughflow, indicating that the South China Sea is an important pathway of the Pacific to Indian Ocean throughflow. The volume, heat and salt transport of the Kuroshio in the East China Sea is 25.6 Sv, 2.32 PW and 894 Ggs-1, respectively. Less than 1/4 of this transport passes through the passage between Iriomote and Okinawa. The calculation of heat balance indicates that the South China Sea absorbs net heat flux from the sun and atmosphere with a rate of 0.08 PW, while the atmosphere gains net heat flux from the Baohai, Yellow and East China Seas with a rate of 0.05 PW.

Wind energy and wave energy resources assessment in the East China Sea and South China Sea

In this paper, the third-generation wave model WAVEWATCH-Ⅲ （WW3） was used to simulate the wave field of the East China Sea and South China Sea from January 1988 to December 2009, with wind input of CCMP wind field. Then, the wind energy density and wave energy density were calculated by using the simulated 22-years＇ wave-field data and CCMP data. By synthetically considering the size of energy density, the frequency of energy level and the stability of energy density, the resources of wind energy and wave energy in the East China Sea and South China Sea were analyzed and regionalized. The result can be a guide to searching location of wind ＆ wave power plant.

Mean sea surface heights of the South and East China Seas from ocean circulation model and geodetic leveling

The mean sea surface heights (sea surface topography) of the South China, East China, Yellow and Bohai Seas are derived from an ocean general circulation model and surface air pressure. The circulation model covers the global oceans, with fine grid (1/6°)? covering the East Asian marginal seas and coarse grid (3°) covering the rest part of the global oceans. The result shows that the China 1985 Na-tional Altitude Datum is 24.7 cm above the mean sea surface height of the world oceans. The mean sea surface in the coastal ocean adjacent to China is higher in the south than in the north. Intercomparison of the model results with the geodetic leveling measurements at 28 coastal tidal stations shows a standard deviation of 4.8 cm and a fitting coefficient of 95.3%. After correction through linear regression, the standard deviation is reduced to 4.5 cm. This indicates that the accuracy of model results is sufficient for practical application. Based on the model results, the mean sea surface heights for the

Quaternary clay mineralogy in the northern South China Sea (ODP Site 1146) —— Implications for oceanic current transport and East Asian monsoon evolution

Measurement of clay mineralogy at ODP Site 1146 in the northern South China Sea (SCS) indicates that illite, chlorite, and kaolinite contents increased during glacials and smectite content increased during interglacials. The smectite/(illite+chlorite) ratio and the smectite abundance were determined as mineralogical indicators for the East Asian monsoon evolution. At a 10 ka timescale, prevailing southeasterly surface oceanic currents during interglacials transported more smectite from the south and east areas to the north, showing a strengthened summer monsoon circulation, whereas dominated counter-clockwise surface currents during glacials carried more illite and chlorite from Taiwan as well as from the Yangtze River via the Luzon Strait to the northern SCS, indicating a strongly intensified winter monsoon. Based on a 100 ka timescale, a linear correlation between the smectite/(illite+chlorite) ratio and the sedimentation rate reflects that the winter monsoon has prevailed in the northern SCS in the intervals 2000—1200 ka and 400—0 ka and the summer monsoon did the same in the interval 1200—400 ka. The evolution of the summer monsoon provides an almost linear response to the summer insolation of Northern Hemisphere, implying an astronomical forcing of the East Asian monsoon evolution.

Grain-size records at ODP Site 1146 from the northern South China Sea: Implications on the East Asian monsoon evolution since 20 Ma

273 samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea (SCS) were analyzed for grain-size distributions using grain-size class vs. standard deviation method and end-member modeling algorithm (EMMA) in order to investigate the evolution of the East Asian monsoon since about 20 Ma. 10–19 μm/1.3–2.4 μm, the ratio of two grain-size populations with the highest variability through time was used to indicate East Asian winter monsoon intensity relative to summer monsoon. The mass accumulation rate of the coarsest end member EM1 (eolian), resulting from EMMA, can be used as a proxy of winter monsoon strength and Asian inland aridity, and the ratio of EM1/(EM2+EM3) as a proxy of winter monsoon intensity relative to summer monsoon. The combined proxies show that a profound enhancement of East Asian winter monsoon strength and winter monsoon intensity relative to summer monsoon occurred at about 8 Ma, and it is possible that the summer monsoon simultaneously intensified with winter monsoon at 3 Ma. Our results are well consistent with the previous studies in loess, eolian deposion in the Pacifc, radiolarians and planktonic foraminifera in the SCS. The phased uplift of the Himalaya-Tibetan Plateau may have played a significant role in strengthening the Asian monsoon at 8 Ma and 3 Ma.

Anti-Phase Relationship Between the East Asian Winter Monsoon and Summer Monsoon During the Holocene?

The relationship between the East Asian winter monsoon(EAWM) and East Asian summer monsoon(EASM) during the Holocene is complicated and remains controversial.In this study,analysis of grain size and benthic foraminiferal oxygen isotope,as well as accelerator mass spectrometry ^(14)C dating was performed on a sediment core retrieved from the newly revealed muddy deposit on the northern South China Sea continental shelf.The history of the EAWM and EASM were reconstructed for the last 8200 a BP.Further analysis in conjunction with previously published paleo-climate proxies revealed that the relationship between the EAWM and EASM during the Holocene is more complex than a simple and strict anti-phase one-both negative and positive correlations were identified.The EAWM and EASM are negatively correlated around 7500,4800,4200,3200,and 300 a BP(cooling periods),while positively correlated around 7100,3700,and 2100 a BP(warm periods).In particular,both the EAWM and EASM intensified during the three positive correlation periods.However,we also found that the relationship between these two sub-monsoons is anti-phase during the final phase of particularly hot periods like Holocene Optimum and Medieval warm period.The possible impact from variations of solar irradiance on the relationship between the EAWM and EASM was also discussed.

Modeling of the 1998 East Asian Summer Monsoon by a Limited Area Model with p-σ Incorporated Coordinate

The 1998 East Asian Summer Monsoon is simulated by use of an improved nine-level p-σ model, the boundary forcing is the South China Sea Monsoon Experiment (SCSMEX) reanalysis data from May 1 to August 31, 1998. It is found that basic features of the atmospheric circulation (such as the South Asia high and the West Pacific subtropical high) can be simulated fairly. However the South Asia high is a little stronger than the observed, while the West Pacific subtropical high a little weaker. Seen from variations of the time correlation coefficient, this model is good for the short-time climate simulation (less than two months), while for the long-time simulation, its climate drift is a little obvious. It can be also seen from the spatial distribution of correlation coefficient that the worse simulation areas of the model are located in the Tibetan Plateau and the adjacent northwest Indo-China Peninsula. For the simulation of precipitation, the movement of rain belt from May to June can be simulated, but the simulation of July and August precipitation shifts obviously to north of the observed. It is also found from the analysis of sensitive experiment that the improvement of the nested boundary condition has a great impact on the simulation results, especially on the precipitation, so the model and the nesting technique need further improvements.

South China Sea Monsoon Experiment(SCSMEX) and the East Asian Monsoon

The SCSMEX is a joint atmospheric and oceanic experiment by international efforts, aiming at studying the onset, maintenance, and variability of the South China Sea （SCS） summer monsoon, thus improving the monsoon prediction in Southeast and East Asian regions. The field experiment carried out in May-August 1998 was fully successful, with a large amount of meteorological and oceanographic data acquired that have been used in four dimensional data assimilations by several countries, in order to improve their numerical simulations and prediction. These datasets are also widely used in the follow-up SCS and East Asian monsoon study. The present paper has summarized the main research results obtained by Chinese meteorologists which cover six aspects： （1） onset processes and mechanism of the SCS summer monsoon; （2） development of convection and mesoscale convective systems （MCSs） during the onset phase and their interaction with large-scale circulation; （3） low-frequency oscillation and teleconnection effect; （4） measurements of surface fluxes over the SCS and their relationship with the monsoon activity; （5） oceanic thermodynamic structures, circulation, and mesoscale eddies in the SCS during the summer monsoon and their relationship with ENSO events; and （6） numerical simulations of the SCS and East Asian monsoon.

Clay mineral records of East Asian monsoon evolution during late Quaternary in the southern South China Sea

High-resolution clay mineral records combined with oxygen isotopic stratigraphy over the past 190 ka during late Quaternary from core MD01-2393 off the Mekong River in the southern South China Sea are reported to reconstruct a history of East Asian monsoon evolution.The dominating clay mineral components indicate a strong glacial-interglacial cyclicity, with high glacial illite, chlorite, and kaolinite contents and high interglacial smectites content. The provenance analysis indicates the direct input of clay minerals via the Mekong River drainage basin.Illite and chlorite derived mainly from the upper reach of the Mekong River, where physical erosion of meta-sedimentary rocks is dominant. Kaolinite derived mainly from active erosion of inhered clays from reworked sediments in the middle reaches. Smectites originated mainly through bisiallitic soils in the middle to lower reaches of the Mekong River. The smectites/(illite+chlorite)and smectites/kaolinite ratios are determined as mineralogical indicators of East Asian monsoon variations. Relatively high ratios occur during interglacials and indicate strengthened summer-monsoon rainfall and weakened winter-monsoon winds; relatively lower ratios happened in glacials, indicating intensified winter monsoon and weakened summer monsoon. The evolution of the summer and winter monsoons provides an almost linear response to the summer insolation of the Northern Hemisphere, implying an astronomical forcing of the East Asian monsoon evolution.