Particle flux through the Huanghai Sea cold water mass

Acta Oceanologica Sinica 2005, Vol. 24, No.5, p. 78~88htp://www .occanpress .com.cnE- -mail: bhyxbe@263.netParticle flux through the Huanghai Sea cold water massGUO Xuewu!", ZHANG Yansong21. Yellow Sca Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao 266071, China2. Jiaozhou Environmental Protection Bureau, Jiaozhou 266300, ChinaReceived 14 April 2005; accepted 3 July 2005AbstractSetting particulate matter (SPM) was ollected by using sediment traps at four stations in a survey section from Qingdao to Cheju-do,across the Huanghai Sea cold water mass (HSCWM), in August 2002. The sediment traps were planted in three layers: the upper layerof the thermocline (ULT) above the HSCWM, the lower layer of the thermocline (LT), and the bottom layer of water column (BL).To determine the particle flux, the contents of organic carbon (POC), organic nitrogen (PON), total carbon (PC), and total phosphorous(PP) in SPM were analyzed, and two fux models(I and II) were improved to calculate the resuspension ratio, with an assumption inModel I that the vertical fux of SPM in the LLT equals the net vertical fux of SPM in the whole water column. AnX value, i.e, thefraction of the resuspension flux originating from the surficial sediments nearby the sampling station, was deduced from Model I toestimate the contribution of lateral currents to the total resuspension flux. The results showed that inorganic particles, fecal pellets, andmisellaneous aggregates were the major types of SPM in the HSCWM, and the contents of POC, PON, PC, and PP all decreased withwater depth. A great deal of fecal pellets found in the LLT indicatcs that the main space producing biogenic SPM is the thermocline,and especially the LLT, where the CN ratio is lower than that in the ULT. The resuspension ratios, 90%~ 96% among stations, implystrong impact of resuspension on particle fux in the BL. These values were not significantly different between the two fux models,suggesting that the hypothesis in Model I that the fux in the LLT equaling the net flux to the bottom is aceptabl for shallow waterswith sratification like the HSCWM. The POC export ratio from the HSCWM ranges from 35% to 68%。It benefts fom the shortsinking distance in shallow water. The upwelling in the HSCWM enhanced the POC flux through the water mass, and the lateralcurrents provides up to being greater than 50% of resuspension fux in the BL according to evaluation of the X value.Key words: stling particulate matter, particle fux model, resuspension ratio, thermocline, Huanghai Sea Cold Water Mass1 Introductiontonic tests and carcasses. The efficiency of biologicalpump just lies on how much atmospheric carbon diox-Particle flux is a subject in the ocean flux re-ide is transported to bottom by planktonic organismssearch because of its significant function in the global(Wang, 2003). It has been proved that the flux of pri-ecosystem (SCOR, 1990). Atmospheric carbon dioxidemary particles depends on the plankton living in the e-is regulated by the ocean working as a biological pumpuphotic zone (Bishop et al, 1977), and is susbtantially(Longhurst and Hrrison, 1989), in which phytoplank-affected by stratifcation (Weyhenmeyer, 1996). Auto-ton absorb carbon dioxide and translate them, throughgem |中国煤化τε into larger ones dur-a series of biological, chemical, and physical process-CNMH(; speed (Honjo, 1997),es, partly into particulates, such as fecal pellets, plank-and panuics ural ICaul uwu can be easily driven bywind, wave, tide, and bioturbulence into resuspension* Corresponding author, E -mail: guoxw@ysfri.ac.cnmode in shallow waters (Zheng et al., 1990). The re-GUO Xuewu et al. Acta Oceanologica Sinica 2005, Vol. 24, No. 5, p. 78~8879suspended particles release nutrients back to water col-119° 120° 121° 122° 123° 124° 125’ 126" 127"Eumn due to decomposition and mineralization and pro-,ShandongPeninsuls37°mote growth of phytoplankton, but increase water tur-bidity and restrain photosynthesis on the other hand, so36°+Huanghai Sea●51-3that influence on ecosystem (Bloesch, 1995; Wainright3S*and Hopkinson, 1997). In China seas, analysis of set-4* t●S1-7tling particulate matter collected with large openingChinatime-series sediment traps employed in the northern33cheju-doSouth China Sea revealed that the particulate organicFig. 1. Survey section and sampling stations in thematter was chiefly from the synchronous planktonHuanghai Sea.(Chen et al., 1996). That is also true in the East ChinaSea (Zhan et al, 1993), where particulate matter con-Station S1-3SI-5 .S1-7 S1-8tributed the majority of carbon transportation over the|2:continental shelf, and the particle composition and flux20-225.225201s2°in the bottom layer were influenced intensively by the4010125resuspension process (Song, 1997). The purpose of our5oresearch is to realize the status of the particle flux80through the cold water mass, which leads a special en-100 20000 400vironment in the Huanghai Sea.Distance /kmFig. 2. Vertical distribution of water temperature in the survey2 Materials and methodssection with sampling stations signed above. The 10 C isothermlines line out the two cold centers of the cold water mass..1 Study areaappears when the HSCWM grows up is suggested toIn August 2002，R/V Beidou conducted a multi-be a result of interaction between the warm and coastaldisciplinary survey in the Huanghai Sea. A survey sec-currents (Mao et al, 1986).tion was set from Qingdao, China, to Cheju-do, Korea,across the HSCWM. In this section, CTD data were2.2 Sampling and analysiscollected at 10 stations, and SPM was collected at fourstations marked S1-3, S1-5, S1-7, andS1-8 (Fig. I).To collect settling materials, the sediment traps,The HSCWM is a mass of winter water that is detainedeach equipped with five Plexiglas cylinders (6.5 cm inin the central trough of the Huanghai Sea when theinner diameter, 100 cm in height)，were employed.surface water temperature begins to increase in spring.Collection efficiency of the trap with an aspect ratio ofIt conduces to the formation of thermocline, which15:1 has been proved in Bloesch and Bums (1980).lasts till the early autumn (Su, 1986). The HSCWMStation S1-5 was located between the two cold centersowns two cold centers in the middle and the westof the HSCWM, Sta. S1-7 was located at the cold cen-Slope of the trough separately (Weng et al，1988),ter in the middle of the trough, and Stas S1-3 and S1-which were still detected in our survey (Fig. 2). Be- 8 were中国煤化工wo cold centerssides the HSCWM, other physical oceanographic prc(Fig. 2).d and planted incesses, such as the warm current, the coastal current,the ULT,TYH. CNM HGsedfor 27-34hand the Changjiang diluted water, also influence the(see Table 1). To avoid touching seabed, the traps inHuanghai Sea. A large-scale surface cyclone gyre thatBLs were hung 4~6 m above the bottom. Afer the trap80GUO Xuewu et al. Acta Oceanologica Sinica 2005, Vol. 24, No. 5, p. 78~88Table I. Exposure time and planting depth of sediment traps at cach sampling station in August 2002StationDateExposure time/hWater depth/mDepth of thermocline/mPlanting depth/mS1-325~264415~3030I0SI-524-2529.521~48.488S1-722~2327.0811S~40540S1-8.20-2134.012-~3875retrieval, most of the supernatant was decanted, sedi-F=M,(1)ments of each cylinder were washed into a 500 mLiV'plastic bottle, 3% sodium azide (NaN;) was added andF=Mf,(2)the sample was stored under temperature of 0~4 Cwhere M is the dry weight of particles collected in a(Honjo, 1978). In laboratory, each sample was partial-cylinder; V is the cylinder section area; l is the expo-ly filtered with glass fiber membranes (GF/F， What-sure time of trap under water; F。is the flux of a certainman) which were burnt under 450 C temperature andcomponent of particulate matter; and F。is the percent-weighed beforehand, dried under 60 C temperature toage of this component in particulate matter.constant weight, weighed, ground, and stored in desic-cators for further analysis. The rest of sample was2.4 Calculation of resuspension ratiochecked under microscope. A multiple corer, Midicor-er Mark -II1 400，was employed to grab bottom sedi-Two particle flux models were used to calculatement samples at the trap stations. Surficial sedimentsthe resuspension ratio (a).(0~3 cm in depth) were sub-sampled and frozen in a(1) Model I . This model was proposed byrefrigerator. In laboratory, they were dried and groundBloesch (1982):for analysis. The particulate carbon (PC), organic par-R x 100%=S-A-X 100%,(3)ticulate carbon (POC), and organic particulate nitrogen(PON) in both trap and corer samples were tested withwhere R is the resuspension flux; S is the total fux toa P-E240C CHN analyzer. The particulate phosphorusbottom; and N is the net flux to bottom (see Fig. 3).(PP) was determined by means of molybdenum blueOn account of no perfect method for determiningmethod (Hu et al, 1999), in which PP was convertedthe net particle fux over the continental shelf yet, forinto active phosphate in reaction with potassium per-calculation, we assume that (1) the particulate mattersulfate (K,$2Ox) under high temperature and pressure.n￥i parts, one is autogenicfro中国煤化工!other is resuspended2.3 Calculation of particle fluxCN MH Gon, mineaiatin, ordecomposition happens to the particulate matter dur-Particle flux (F) was calculated with the formulaeing sinkage; and (3) particulate matter collected in theGUO Xuewu et al. Acta Oceanologica Sinica 2005, Vol. 24, No. 5, p. 78~8881the particles from the bottom nearby the sampling sta-tion and the particles from other far-side regions due tothermoctinelateral current transportation. Therefore fR, take POC<9as an example, can be expressed asR=R'+ R"fe RmxSr-Ns(7)R Sa,S订R'R”sedimentf&=Xfuv +(1-X)fx",(8)where Rpoc is the resuspension flux of POC; X is thefraction of resuspension flux originating from the bot-tom nearby the sampling station; and f& andf. areproportions of POC in agreement with particles fromthe bottom nearby the sampling station and that fromFig. 3. Schematic view of the particle fux models.far-side regions respectively. From Eq. (8),a. Mode! I and b. Model II.x= ferferLLT is totally autogenic from the column, in otherthen,words, the flux in this layer equals the net flux to bot-R'=RX,(10)tom.R"=R(1-X),(11)(2) Model II . This model is applied widely in re-where R' and R" are the resuspension fluxes from thecent years (Bloesch, 1995; Zhan and Song，1997;bottom nearby the sampling station and other far-sideJimenez-Montealegre et al, 2002), and it is based onregions respectively.the following assumptions: (1) chemical componentsFor calculation, based on the previous assump-of autogenic particles do not change during sinkage;tions, fe andfv are superseded by the proportions ofand (2) chemical components of sediments do notPOC in surficial sediments and in LLT particles re-change afer resuspension. Then,spectively, and N is replaced with the particle flux inR=S-N,(4)the LLT. Seeing that R" is related to advections,f