| Coccolithophores a re i mportant calcifiers i n marine phytoplankton functional groups study and meanwhile the main sources of biogenic inorganic carbon. They play critical roles in the oceanic biogeochemical carbon cycles through their organic carbon p ump (i.e. pho tosynthesis) a nd carbonate counter p ump (i.e. c alcification) processes which transform dissolved i norganic c arbon ( DIC) i nto respectively particulate organic and inorganic matter (POC and PIC).Two cruies were carried in the coastal China Seas during winter and summer 2009. T he first crusie covered then oerthern part o fS outh China S ea (SCS) including f our transects s tudy f rom 11th to 21st Feburary. The second c ruise surveyed t he SCS, East China S ea ( ECS) a nd Y ellow Sea ( YS) with r outine investigation a nd time-series studies. Parameters that measured were the s eawater chlorophyll-a concentration, phy toplankton a bundance a nd carbon bi omass, coccolithophore abundance and biomass, standing c rop of coccolith calcium carbonate, paniculate carbon materials (Phyto-C, POC and PIC), production rates of PIC and POC, temperature, salinity and nutrients etc.For chlorophyll-a determination, the f luorescent method was used. Phytoplankton taxonomic composition and cell abundance were performed by using inverted 1 ight mi croscope and the ca rbon biomass w as ca lculated f rom the c ell biovolume and the carbon-volume relationships. Coccolithophore counts and carbon biomass convertion w ere c arried by using a m icroscope w ith p olarization optics. Coccolith calicite content was estimated by measuring the coccolith volume using the Scanning Electronic Microscope and then converted t o the calcium carbonate ma ss according to t he c alcite d ensity in the c occolith. F or particulate o rganic carbon (POC) a nd particulate i norganic c arbon ( PIC), A CHN a naly ser a nd a n I nductively Coupled Plasma O pticalE mission Spectrometer ( ICP-OES) were a pplied. Calcification and photosynthesis rates w ere m easured following t he s tandard Micro-Diffusion Technique (MDT). Temperature and salinity were monitored by the Conductivity-Temperature-Depth (CTD) e quipment. Nutrients were determined in situ by using the automatic analyser.During the s ummer c ruise, hi gh c hlorophyll-a appeared primarily u nder t he Surface Mixed Layer ( SML) of the upper seawater. Averaging chlorophyll-a in the SCS was 0.401±0.322 mg m-3, and in the ECS and YS were 0.696±0.669 mg m-3 and 0.751±0.525 mg m"3 respectively. Total phytoplankton abundance in SCS was 1.39x 104 cells/L, with the diatom Pseudo-nitzschia delicatissima being the dominated species. In ECS and YS were 7.72×103 cells/L and 8.41×103 cells/Lr espectively, and the domiant species were diatom Chaetoceros spp. a nd dinoflagellate Prorocentrum dentatum. C occolithophore r epresentative species were Emiliania huxleyi and Gephyrocapsa oceanica. Total coccolithophore abundance in SCS was 4.24±5.61×103 cells L-1 (with the abundance 40.9±37.0xl03 cellsL"1 in winter nearly t en-times 1 arger t han that o f the s ummer), and i n E CS&YS w as 8.41±7.95x 103 cells L-1. Standing crop of calcium carbonate derived from the coccolith in the SCS was 51.9±50.5 mg m-2, and in ECS&YS was 77.2±81.4 mg m-2. Standing crop of coccolithophoresin SCS was 286.0±273.2×106 cells m-2, and in ECS&YS was 506. 4±527. 4×106 cells m -2. Total c occolithophore flux i n SCS w as 9.7±9.0xl06 cellsm-2 d-1, and in ECS&YS was 20.7±15.7×106 cellsm-2 d-1. Calcite flux in SCS was 1.80±1.70 mg m-2 d-1, and in ECS&YS was 3.08±2.33 mg m-2 d-1.During the summer cruise, phytoplankton carbon (Phyto-C) in the SCS was 24.8±30.2 mmol m-2, and in the ECS&YS was 83.4±112.0 mmol m-2. Seawater POC content in SCS was 382.6±139.6 mmol m-2, and in the ECS&YS was 431.4±136.2 mmol m"2. PIC concentration in SCS was 31.9±21.6 mmol m-2, and in ECS&YS was 53.5±54.3 mmol m-2. Averaging pPIC in SCS was 6.48±3.19μmol C m-3 d-1 (5.43±1.77mgCm-2d-1), and in the ECS&YS was 9.95±5.53μmol C m-3 d-1 (6.17±2.75 mg C m-2 d-1). AveragingpPOC in SCS was 0.402±1.457 mmol C m-3 d-1 (291.7±397.1 mg C m-2 d-1), and in the ECS&YS was 0.736±0.890 mmol C m-3 d-1 (468.7±375.6 mg C m-2 d-1).During the summer cruise, //-PIC in the SCS was 0.018±0.008 d-1, and in the ECS&YS was 0.016±0.013 d-1.μ-POC in the SCS was 0.054±0.043 d-1, and in the ECS&YS was 0.093±0.074 d-1.μ-PhytoC in the SCS was 0.83±0.52 d-1, and in the ECS&YS was 0.63±0.51 d-1.τ-PIC in the SCS was 67.9±32.6 days, and in the ECS&YS was 131.1±129.9 days.τ-POC in the SCS was 31.9±26.0 days, and in the ECS&YS was 21.6±22.9 days.τ-PhytoC in the SCS was 1.37±1.20 days, and in the ECS&YS was 4.85±9.86 days. The percentage of pPIC to total carbon fixtion (pPIC + pPOC)intheSCS was 3.5±2.8%, and in the ECS&YS was 1.9±1.5%. Coccolithophore c ontributiont o total phytoplankton pa rticulate o rganic carbon production i n S CS was 5.4±4. 5%, and i n the ECS&YS was 2. 9±2.3%. The rain ratios (pPIC : pPOC) in SCS varied between 0.002 and 0.412, averaging 0.067±0.078. While it spaned from 0.003 to 0.102 in the ECS&YS, averaging 0.034±0.031.From the research that mentioned above, results showed that in summer the living coccolithophores were main distributed in the Kuroshio area of the NE Taiwan Island, the Luzon Strait where the upper stream of the Kuroshio intruded into the SCS basin, the South East Asian Tim e-series Study station ( SEATS), a nd the a dj acent a rea between the Pearl River estuary and the continental shelf of northern SCS. Although E. huxleyi was predominant in many aspects including cell abundance, standing crops of coccospheres and cell flux, the relative small cell diameter and coccolith volume decided t he m arked 1 ow v alues of estimated c arbon biomass, standing s tock o f calcium ca rbonate ma ss, ca lcite flux et c. However, two h eavy-calicified c occolith species Calcidiscus leptoporus and Umbellosphaera tennis were crucial and critical for the carbon pools as well. Although there was obvious elevating trend in the calcification rates in the ECS&YS, the relative high production rates of POC in this region caused the rain ratio decreasing dramatically in contrast to the case in the SCS. The pPIC variations in the vertical profiles were little constrained. However, the sharp decline in pPOC at depth caused the marked drawdown of rain ratios along with the increasing depth and most of the higher values appeared near the bottom of the euphotic z one. When c omparing the results o f surface pr oduction w ith deep water mass f lux d escribed in the lit eratures, results sh owed that the r emineralization (oxidation) pr ocess of o rganic matter w as s ignificant. Only ~ 0.7% o f s urface organic p roduction c an reach t he s ea floor. However, the case w as d ifferent for calcite, only ~ 42.2% of surface calcite production was dissolved when exporting to depth (even ~ 3,700 m) because of its refractory nature and around a half of calcite production could finally buried in the sendiments which constituted the ocean interior sequestration oft he a tmospheric CO2. Seen from t he q uantitative discrepancies between surface carbon production and deep water carbon flux, calcite varied within one order of magnitude in contrast with the organic matter which changed in one to two orders of magnitude. But when seeing from the carbon quota allocation, there was ba lance be tween or ganic and inorganic c arbon that reached the s ea floor, with inorganic carbon accounted ~ 54% of total carbon that buried. |
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