Main geochemical characteristics and key biogeochemical carbon processes in the East China Sea

Research related to carbon geochemistry and biogeochemistry in the East China Sea is reviewed in this paper. The East China Sea is an annual net sink for atmospheric CO, and a large net source of dissolved inorganic carbon to the ocean. The sea absorbs CO, from the atmosphere in spring and summer and releases it in autumn and winter. The East China Sea is a CO, sink in summer because Changjiang River freshwater flows into it. The net average sea-air interface carbon flux of the East China Sea is estimated to be about 4.3 X 10(6) t/y. Vertical carbon transport is mainly in the form of particulate organic carbon in spring; more than 98% of total carbon is transported in this form in surface water, and the number exceeds 68% in water near the bottom. In the southern East China Sea, the average particulate organic carbon inventory was about one-tenth that of the dissolved organic carbon. Research indicates that the southern Okinawa Trough is an important site for particulate organic carbon export from the shelf. The annual cross-shelf exports are estimated to be 414 and 106 Gmol/y for dissolved organic carbon and particulate organic carbon, respectively. Near-bottom transport could be the key process for shelf-to-deep sea export of biogenic and lithogenic particles.

Temporal and spatial variability in nitrogen uptake kinetics during harmful dinoflagellate blooms in the East China Sea

Temporal and spatial variability in the kinetic parameters of uptake of nitrate (NO3-), ammonium (NH4+), urea, and glycine was measured during dinoflagellate blooms in Changjiang River estuary and East China Sea coast, 2005. Karenia mikimotoi was the dominant species in the early stage of the blooms and was succeeded by Prorocentrum donghaiense. The uptake of nitrogen (N) was determined using N-15 tracer techniques. The results of comparison kinetic parameters with ambient nutrients confirmed that different N forms were preferentially taken up during different stages of the bloom. NO3- (V-max 0.044 h(-1); K-s 60.8 mu M-N) was an important N source before it was depleted. NH4+ (V-max 0.049 h(-1); K-s 2.15 mu M-N) was generally the preferred N. Between the 2 organic N sources, urea was more preferred when K. mikimotoi dominated the bloom (V-max 0.020 h(-1); K-s 1.35 mu M-N) and glycine, considered as a dominant amino acid, was more preferred when P. donghaiense dominated the bloom (V-max 0.025 h(-1); K-s 1.76 mu M-N). The change of N uptake preference by the bloom-forming algae was also related to the variation in ambient N concentrations. Published by Elsevier B.V.

Impact of microzooplankton and copepods on the growth of phytoplankton in the Yellow Sea and East China Sea

Dilution and copepod addition incubations were conducted in the Yellow Sea (June) and the East China Sea (September) in 2003. Microzooplankton grazing rates were in the range of 0.37-0.83 d(-1) stopin most of the experiments (except at Station A3). Correspondingly, 31-50% of the chlorophyll a (Chl a) stock and 81-179% of the Chl a production was grazed by microzooplankton. At the end of 24 h copepod addition incubations, Chl a concentrations were higher in the copepod-added bottles than in the control bottles. The Chl a growth rate in the bottles showed good linear relationship with added copepod abundance. The presence of copepods could enhance the Chl a growth at a rate (Z) of 0.03-0.25 (on average 0.0691) d(-1) ind(-1) l. This study, therefore parallels many others, which show that microzooplankton are the main grazers of primary production in the sea, whereas copepods appear to have little direct role in controlling phytoplankton.

Spatial variability in biomass and production of heterotrophic bacteria in the East China Sea and the Yellow Sea

The distributions of heterotrophic bacterial abundance and production were investigated in the East China Sea and the Yellow Sea during the autumn of 2000 and spring of 2001. Bacterial abundance varied in the range 3.2-15.7 (averaging 5.7) x 10(5) and 2.3-13.6 (averaging 6.2) x 10(5) cells cm(-3) in the spring and autumn, respectively. During autumn, bacterial production (BP) (0.27-7.77 mg C m(-3) day(-1)) was on average 3 fold that in spring (0.001-2.04 mg C m(-3) day(-1)). Bacterial average turnover rate (ratio of bacterial production:bacterial biomass, mu=0.21 day(-1)) in autumn was 3 times as high as in spring (0.07 day(-1)). The ratio of integrated bacterial biomass to integrated phytoplankton biomass in the euphotic zone ranged from 4 to 101% (averaging 35%) in spring and 24 to 556% (averaging 121%) in autumn. The results indicate that the distributions of heterotrophic bacteria were controlled generally by temperature in spring and additionally by substrate supply in autumn. (C) 2010 Elsevier Ltd. All rights reserved.

Autumn net copepod abundance and assemblages in relation to water masses on the continental shelf of the Yellow Sea and East China Sea

Copepod species diversity, abundance and assemblages in relation to water masses over the continental shelf of the Yellow Sea (YS) and East China Sea (ECS) were studied extensively based on the net plankton samples in autumn 2000. Multivariate analysis based on copepod assemblage resulted in recognition of five groups (Groups 1-5) corresponding to the water masses. Groups 1 and 2 delineated from inshore stations with low salinity YS Surface Water, and offshore stations with YS Cold Water in the YS. Group 3 located in the joint area of YS and ECS mainly with Mixed Water. Groups 4 and 5 in the ECS delineated two assemblages mainly from inshore and shallow stations with ECS Mixed Water in the southeastern ECS, and offshore stations along the ECS shelf edge controlled by saline Kuroshio Water. Salinity and temperature were more important in characterizing copepod assemblage of the continental shelf than chlorophyll a. (c) 2005 Elsevier B.V. All rights reserved.

The effect of the causative algae of large-scale HAB in the East China Sea on egg hatching of Argopecten irradians, and population growth of Brachionus plicatilis and Moina mongolica

The impacts of Prorocentrum donghaiense Lu and Alexandrium catenella Balech, causative species of the large-scale HAB in the East China Sea, were studied under laboratory conditions. According to bloom densities, the effects of monoculture and mixture of the two species were examined on the egg-hatching success of Argopecten irradians Lamarck, and the population growth of Brachionus plicatilis Muller and Moina mongolica Daday. The results showed that monoculture of A. catenella had a significant inhibition on the egg hatching success of A. irradians, and the population growth of B. plicatilis and M. mongolica. The median effective densities ( EDSo) inhibiting the egg hatching success of A. irradians for 24 h and the population growth of B. plicatilis and M. mongolica for 96 h were 800, 630, and 2 400 cells/cm(3), respectively. Monoculture of P. donghaiense has no such inhibitory effect on the egg hatching success of A. irradians; P. donghaiense at lower suitable densities could sustain the population growth of B. plicatilis (1 x 10(4) similar to 3 x 10(4)cells/cm(3)) and M. mongolica (2 x 10(4) similar to 5 x 10(4) cells/cm(3)); P. doaghaiense at higher densities had significantly adverse effect on the population growth of B. plicatilis (4 x 10(4) similar to 10 x 10(4) cells/cm(3)) and M. mongolica (10 x 10(4) cells/cm(3)). When the two algae were mixed according to bloom densities, P. donghaiense at suitable densities to some extent could decrease the toxicity of A. catenella to B. plicatilis and M. mongolica. The results indicated that the large-scale HAB in the East China Sea could have adverse effect on zooplankton, and might further influence the marine ecosystem, especially when there was also Alexandrium bloom.