East China Sea Continental Shelf Research Articles

Evidence for the offshore transport of terrestrial organic matter due to the rise of sea level: The case of the East China Sea Continental Shelf

Accelerator mass spectrometry (AMS) 14C dating and analyses of the stable isotope ratio of organic carbon (δ13Corg) were carried out on two piston cores obtained from the continental slope and the Okinawa Trough in the East China Sea (ECS). These cores covered the last ca. 15 14C kyr BP (17 to 18 cal kyr BP). Mass and organic carbon (org. C) accumulation rates decreased gradually after the last deglaciation period. On the other hand, δ13Corg showed distinct depletion from ca. 14 to 12 14C kyr BP (17.5 to 13.2 cal kyr BP). The depletion relates to the large supply of terrestrial org. C from the ECS shelf triggered by the sea's intrusion onto the shelf area because of the rise in sea level.

Phytoplankton distribution and community structure in the East China Sea (ECS) continental shelf

This paper deals with the distribution and community structure of phytoplankton revealed by data obtained in a cruise in April and one in Oct.–Nov., 1994. Among 140 species of phytoplankton (including varieties and formas) identified, 104 species belonged to Bacillariophyta and 32 species belonged to Pyrrhophyta. In April, the biomass of phytoplankton was 0.09×104–465×106 cells/m3, and the dense area was located in the Zhejiang coastal zone and the estuary of the Changjiang River; the density of the studied area's west part was always higher than that of the east part. In October and November, the phytoplankton biomass was 0.42×104–289.9×104 cells/m3, and the dense area was located in the upwelling zone near the Zhejiang coast. In spring and autumn, biomass was very low in the outer part of the East China Sea continental shelf area, where phytoplankton was classifiable into two communities based on the phytoplankton's ecological characteristics and environmental parameters such as water temperature and salinity, i.e. neritic community environment characterized by warm temperature and low salinity and pelagic community environment characterized by high temperature and high salinity.

Organic carbon deposition and its control on iron sulfide formation of the southern East China Sea continental shelf sediments

Sulfate reduction rates and sedimentation rates were determined in sediments at ten stations on the southern East China Sea continental shelf. The area is characterized by relatively low organic carbon concentration with fast sedimentation rate. Rapid sulfate reduction rates, ranging from 1 to 4 mmol/m 2/day, were observed. Organic carbon concentration varied from 0.3 to 0.6 wt%. Sedimentation rate varied from 0.2 to 0.7 cm/yr. In addition, normal marine S/C ratios were observed. Up to 96% of pyrite-sulfur was reoxidized before its final burial. Sulfate reduction rate and pyrite-sulfur burial rate increased linearly with increasing organic carbon burial rate, indicating that organic carbon deposition controlled pyrite formation in the East China Sea continental shelf sediments. The organic carbon utilized by the sulfate reduction and its burial represented a significant but relatively small fraction of the primary production in the studied East China Sea region.

Echo characters and sedimentary processes along a rifting continental margin, northeast of Taiwan

The northeastern offshore of Taiwan, including the southern-most East China Sea continental margin, Ilan Shelf, Ilan Ridge and the western tip of the Okinawa Trough, is characterized by active rifting and an energetically complex hydrodynamic flow regime. In this study, sedimentary processes on the sea floor were inferred from regional mapping of 3.5 kHz echo characters. Eight distinct echo types were mapped, and based on echo type distribution, analysis of sediments and regional bathymetry, these were interpreted as deposits that had been formed under the influence of various local hydrodynamic processes. Different sedimentary processes, interpreted from the lithology and distribution pattern of sediments, were found to prevail on different physiographic provinces. In the southern East China Sea continental shelf margin, it is the outflow of Taiwan Strait Water and the on-shelf intrusion, upwelling and countercurrent induced by the impinging and turning of the Kuroshio Current that largely determine the distribution of sediments. On the narrow Ilan continental shelf, the deposition is mainly influenced by subaqueous deltaic and shallow marine processes. Over the rifting tip of the Okinawa Trough, including the Okinawa Trough Basin and its nearby slopes, the primary seafloor-shaping agents have been the mass-wasting processes and turbidity currents. Since the observed sediment data is in good consistency with other hydrographic data, the studies of transportation and deposition patterns of sediment can provide good constraints for the interpretation of physical oceanographic data.

Carbon, alkalinity and nutrient budgets on the East China Sea continental shelf

The western part of the Kuroshio Intermediate Water originates from the nutrient‐rich South China Sea intermediate water which upwells onto the East China Sea (ECS) continental shelf and contributes a large amount of nutrients to the ECS. This contribution, especially for phosphorus, is far more than the inputs from the phosphorus‐deficient Yangtze and Yellow Rivers. Mass balance calculations reveal that the net denitrification rate in the ECS shelf is 95 ± 50 × 109 mol N yr−1, which is more than the total riverine supply of nitrogen. The nutrient supply allows the ECS to produce 1030 ± 310 × 109 moles dissolved organic carbon and 709 ± 280 × 109 mol particulate organic carbon for a total of 1739 ± 870 × 109 mol organic carbon per year, which translates to a new production rate of phytoplankton as 64 ± 32 mg C m−2 d−1 or 15% of the average primary production rate. The downslope transport of modern particulate carbon is 2547 ± 1250 × 109 mol yr−1, of which 695 ± 350 × 109 mol yr−1 is organic. This value is only 12% of the offshore dissolved organic carbon transport of 5563 ± 1700 × 109 mol yr−1. The alkalinity budget, never attempted before, indicates that there is a substantial amount of alkalinity generation in the sediments (3.9 ± 3.9 mmol m−2 d−1) due to anaerobic respiration such as by iron and sulfate reductions.

Geochemical and carbon isotopic characterization of particles collected in sediment traps from the East China Sea continental slope and the Okinawa Trough northeast of Taiwan

This paper reports results from various geochemical and carbon isotopic analyses of sediment particles collected at different water depths from an array of 5 sediment traps. The traps were deployed at places characteristic of distinct seafloor topography on the East China Sea continental slope and within the Okinawa Trough northeast of Taiwan during different durations from July 1993 to December 1995. Apparent sediment mass flux (ASMF) measurements show that particle fluxes are invariably high and fluctuate greatly within the canyons, as compared to those on the slope and in the Okinawa Trough, suggesting episodic sediment resuspension and a strong bottom transport from the East China Sea continental shelf to the Okinawa Trough within the canyons. The great terrigenous input thus overshadows any appreciable geochemical and isotopic changes in particles collected inside the canyons, which are otherwise seen in particles collected on the slope region where in situ biogenic input is enhanced by the intrusion of the nutrient-laden Kuroshio subsurface waters. In addition, the shipboard Acoustic Doppler Current Profiler (sb-ADCP) survey reveals that the persistent intrusion of the Kuroshio current then developed to a counter-clockwise circulation throughout all depths in the water column on the East China Sea continental slope. The countercurrent sweeps and redistributes the dispersed fine particles across the East China Sea continental slope, funnels massive sediments through the canyons, and deposits them on the northern slope of the Okinawa Trough. Our results are consistent with previous physical and hydrological observations. We thus conclude that all the spatial and temporal variability of geochemical and carbon isotopic characteristics of sediment particles collected in the region northeast of Taiwan can be attributed primarily to the nature of sediments sourced from the East China Sea continental margin, and the in situ biogenic modification in the water columns, as well as the dynamic transport of the dispersed fine particles by the counter flows developed in the region.

Response to Liu's comments on “The Kuroshio intermediate water is the major source of nutrients on the East China Sea continental shelf” by Chen (1996)

Exchanges between the East China Sea (ECS) and the Kuroshio have been recalculated by taking into consideration the intra-annual variation of salinity on the shelf. Flux through the Taiwan Strait, previously unavailable data in the Yellow Sea and in the central and northern ECS, denitrification and ground water fluxes are now also considered. The Kuroshio Intermediate Water remains the major source of nutrients on the East China Sea continental shelf, with slightly more upwelling in the dry season than in the wet season.

Comments on “the Kuroshio intermediate water is the major source of nutrients on the East China Sea continental shelf” by Chen (1996)

Chen estimated (Oceanol. Acta 19, 1996) the influxes of water and nutrients from the Kuroshio to the East China Sea shelf separately for the wet and dry periods within a year, based on a steady-state box model. This approach is demonstrated to be flawed in terms of both mathematical rigor and observational evidence. A time-dependent term must be included in the model calculation, if intra-annual variation is to be determined.

Seismic record of tectonic evolution and backarc rifting in the southern Ryukyu island arc system

The southern Ryukyu island arc system is located at a convergent plate margin where the Philippine Sea Plate is subducting under the Eurasia Plate. We have conducted multi-channel seismic reflection surveys to study tectonic evolution and backarc rifting of the southern Ryukyu island arc system using the R/V Tansei-maru of the Ocean Research Institute, University of Tokyo, in June 1993 and 1994. We describe systematically a complete cross-section from the East China Sea continental shelf to the Ryukyu trench from the viewpoint of seismic stratigraphy. Seven major seismic units and three stages in the tectonic evolution of the system are identified: (1) during stage 1 from Late Miocene to earliest Pleistocene, pre-rift deposits of the Shimajiri Group accumulated over a wide region from the East China Sea continental shelf to the forearc region; (2) stage 2 is defined by a series of tectonic processes involving crustal doming, erosion, subsidence, and sedimentation, in association with initial rifting of the southern Okinawa Trough during most of Early Pleistocene time; and (3) the backarc rifting is still in progress and syn-rift sedimentation has been under way since the Late Pleistocene (stage 3). A new significant observation lies in the fact that the Pliocene Shimajiri Group is not distributed in most of the present-day southern Okinawa Trough. This implies that the backarc rifting of the southern Okinawa Trough was probably initiated after the deposition of the Shimajiri Group, that is, during the Early Pleistocene. Crustal-scale simple shear allowing an asymmetrical half-graben structure, rather than pure shear, governed the initial rifting of the southern Okinawa Trough. The possibility, however, cannot be excluded that pure shear associated with symmetrical rifting may be predominant in the present-day rifting of the southern Okinawa Trough as a result of northwestward migration of the rifting axis. The average extension rate of the southern Okinawa Trough is estimated to be approximately 1–2 cm/year on the basis of fault geometry observed on the acoustic basement.

Spatial Variations of Heavy Metals in the East China Sea Continental Shelf Surface Sediments

Abstract Surface sediments collected from continental shelf of the East China Sea were analyzed for heavy metals (iron, manganese, copper, zinc, lead, cadmium), carbonate, organic carbon contents, and grain sizes. the range of concentrations observed were iron: 0.3-1.3 wt%, manganese: 2.3-14 μmole/g, copper: 7.1-184 μmole/g, zinc: 0.16-0.77μmiole/g, lead: 15-98 μmole/g, cadmium: 0.17-3.9 μmole/g, carbonate: 3.6-87 wt%, sand: 10-100%, silt: 0-70% and clay: 0-50%. A zonal distribution pattern of the heavy metals was found in the East China Sea Continental shelf sediments. High concentrations of most heavy metals, organic carbon and fine-grained sediments were observed in the inner shelf zone, especially those near the discharge of the Yangtze River. Concentrations of these heavy metals decreased from the inner shelf to the shelf break region. High concentrations of metals were also found in sediments near Taiwan. Iron concentrations decreased north-east of the central shelf region. High concentrations of ca...

Study on the analysis and distribution of dimethyl sulfide in the East China Sea

A method is described for determining dimethyl sulfide (DMS) in seawater. DMS was first extracted from the seawater using organic reagent, then reverse-extracted by 5% HgCl2. In the laboratory, DMS was released by concentrated HCl and finally measured by GC-FPD. The limit of detection was 0.05 ng of S. Measurements of DMS along surface transects and on vertical profiles across the East China Sea (ECS) continental shelf showed that its concentrations of S in the surface seawater ranged from 64–180 ng/L and that its vertical distribution was divided into 3 types. Model calculations of a stagnant film show a DMS flux of 10.6 μmol/m2d across the air-sea interface.

Observation of internal tides in the East China Sea with an underwater sliding vehicle

Detailed structures of internal tides in the East China Sea were observed during autumn from 1986 to 1989, using an underwater sliding vehicle that can measure temperature, conductivity, and depth continuously, sliding up and down along a faired cable. A variety of structures were observed and are classified with internal Froude numbers of the lowest two modes, which depend on the barotropic tidal current velocities and the phase speeds of internal waves (i.e., stratification). In the central East China Sea, the second‐mode waves are most strongly generated at the shelf break and then propagate shoreward onto the East China Sea continental shelf. Since the barotropic tidal current is faster than the phase speed of the second‐mode waves on the shelf, the generation mechanism is consistent with conventional models. On the other hand, in the southern East China Sea the lowest‐mode response is dominant, although the tidal current velocity is slower than the lowest‐mode phase speed. A nonlinear model is proposed for this response.

The carbon-sulfide-iron relationship and sulfate reduction rate in the East China Sea continental shelf sediments.

Carbon/sulfide/iron relationship and sulfate reduction rate were investigated in the East China Sea continental shelf sediments. The area is characterized by median to high sulfate reduction rate, and high concentrations of iron oxide minerals. Organic carbon was found to be the primary limiting factor for the pyrite formation. Sulfate reduction rate increased with increasing organic carbon concentration. C/S ratio displays a typical normal marine sediment ratio. Low DOP values and abundance of highly reactive iron oxide, ferrihydrite and lepidocrocite, indicate that iron is not limited in the East China Sea continental shelf.

The Importance of Incised Valley Abandonment and Widespread Fluvial Deposition on the High Energy and High Sediment Supply East China Sea Continental Shelf: ABSTRACT

The Importance of Incised Valley Abandonment and Widespread Fluvial Deposition on the High Energy and High Sediment Supply East China Sea Continental Shelf: ABSTRACT

The characteristic distribution of silica over the East China Sea shelf slope

The localized near-bottom water with silica content higher than that in the adjacent shelf water was observed to exist at the eastern margins of the East China Sea continental shelf. The core of the high silica water possessed the silica content corresponding to that in the Kuroshio at depths greater than on the shelf. The mixing analysis of water masses using temperature (T) and silica (Si) showed that the core water can be produced through the vertical mixing of intermediate water of the Kuroshio deeper than 100 m. This study provides us a conclusion that the intermediate water of the Kuroshio is strongly mixed on the shelf slope and then upwelled to form the ridge-like distribution of water masses with low temperature and high silica content at the shelf edge.

Physiographic Characteristics of the continental Margin, Northeast Taiwan

The continental margin off northeastern Taiwan consists of five major physiographic units which are the East China Sea continental shelf, the East China Sea continental slope, the Southern Okinawa Trough, the Ilan continental shelf and the Ilan Ridge. This physiographic framework is provisional and may be revised if better physiographic names are proposed. The East China Sea continental shelf is relatively wide with a smooth surface marked locally by low-relief features resulting from sea-level fluctuation during the late Pleistocene and by volcanic activities of the back-arc rifting. The East China Sea continental slope varies laterally in slope gradient and topography. The continental slope is marked is marked by a variety of slumping of sliding scars, erosional gullies, and debris flow deposits of turbidites. The submarine canyons are another prominent topographic feature occurring on the slope. The submarine canyons indent the continental shelf and modify the linear shelf-slope transtition region in to an irregular shape. The western end of the Southern Okinawa Trough has curvelinear bathymetric contours at the maximum depth of about 2,000m. The trough is mainly confined by the continental slope to the north and by sloper off the Ryukyu volcanic islands.

Quantity and Quality of Summer Surface Net Zooplankton in the Kuroshio Current-induced Upwelling Northeast of Taiwan

This study compares the taxa distribution and biochemical composition of zooplankton from stations in coastal upwelling caused by the intrusion of the Kuroshio Current into the East China Sea shelf. Surface zooplankton samples were taken during summer cruise of 1989 from 21 stations using a conical net with a mesh size of 330μm. In addition to zooplankton taxonomical analysis, biochemical compositions of mixed zooplankton hauls including protein, lipid, ash and lipid classes such as phospholipids, free fatty acids, wax or sterol esters, sterols and triacylglycerides were studied. The results indicate that the copepod-dominant zooplankton biomass responded to the upwelling environment. Stations around the upwelling site showed markedly reduced water temperature, increased NO3-N, chlorophyll a and zooplankton concentrations. Zooplankton samples from the upwelled water contained higher proportions of protein and lipid and lower ash content than those from non-upwelling aregs. Higher free fatty acid level and lower phospholipids level were also observed in samples from upwellde water. These results suggest an enhancement in upwelling region of zooplankton production in both quantity and quality. Principal component analysis of zooplankton taxa and biochemical composition both indicated the existence of three distinct water masses, that can be related to the Kuroshio Current, the East China Sea continental shelf, and the upwelling. The existence of detritus in the zooplankton samples, which affected the measurement of zooplankton quality and its ecological implications, are discussed.

The calculation of Kuroshio current structure in the East China Sea—early summer 1986

On the basis of hydrographic data and moored current meter records obtained during an early summer cruise (May 20–June 23) of 1986, a three dimensional diagnostic calculation of the circulation is performed in the survey area, which covers the East China Sea continental shelf, Okinawa Trough and an area east of the Ryukyu Island. The Kuroshio Current condition and structure in the East China Sea, its branches and their interrelationship as well as the eddies around the Kuroshio, are discussed. When the Kuroshio entered the area northeast of Taiwan, there were two branches. The main branch flowed northeastward along the continental slope and the other branch was at the eastern part of the Okinawa Trough. The main axis of the Kuroshio followed the continental slope above the 300 m level, but moved gradually eastward to the Okinawa Trough below the 300 m level.

SEPARATION AND ACCUMULATION OF Mn, Fe AND THE FORMATION OF Mn NODULES

The sediment samples (including various layers) obtained from 12 stations, 35 Mn nodule samples from 16 stations and water body samples were collected during Mn nodule investigation made in the Pacific Ocean in summer, 1983. The coexisting, separating and accumulating regularities and their relation concerning the formation of Mn nodules are approached through the distribution and partition characteristics of Mn and Fe combined with the data from nearshore area in the East China Sea continental shelf.

Macrobenthos and biogenic structures in s in sediments of the East China Sea continental shelf : Boesch, D.F., Zhican Tang, Fengshan Xu and K.J. Nilsen, 1986. Stud. mar. sin., 27:187–197. (In Chinese, English abstract.)

Macrobenthos and biogenic structures in s in sediments of the East China Sea continental shelf : Boesch, D.F., Zhican Tang, Fengshan Xu and K.J. Nilsen, 1986. Stud. mar. sin., 27:187–197. (In Chinese, English abstract.)