Distribution Of Suspended Particulate Matter(SPM) And Its Influence Factors In Upper Water Of The Parece Vela Basin In Winter

From the winter cruise of the research ship �Science No. 1� in Parece Vela Basin(Dec. 2003 to Feb.2004), we obtained the concentration of the suspended particulate matter(SPM) and chlorophyll concentration, light transmission, temperature, salinity with SBE9/11 CTD. The SPM distribution characteristics and its influence factors have been analyzed in this paper. The results are as follows.During the investigation, cold and warm eddy activities once appeared in the study area simultaneously, whose influence depths were both more than 200 m.The cold eddy located between 136�and 138�E, outspreading along the northeast direction. The salinity of its water was higher than the surrounding water when the depth was less than 100 m. While relatively low salinity compared with the surrounding water were observed after more than 150 m.Meanwhile, the warm eddy appeared between 138.5� and 139�E, with no obvious features at the depth no more than 50 m.The salinity of the warm eddy water below 100 m appeared to be a low-salinity center. Then it was gradually replaced by a high-salinity center after more than 150 m in depth. In addition, the upper water of the study area can be divided into three layers: the surface water(0-80m) with high temperature and low salinity, the mixing layer(80-140m) with complex thermohaline characteristics and the subsurface water(140-200m) with low temperature and high salinity, respectively.The study area exhibited the prevalent occurrence of subsurface chlorophyll maximum(SCM). And the subsurface chlorophyll maximum layer(SCML) exerted a broad range in depth(65-165m; mean: 104m), concentration(2.14-5.63?g/l; mean: 3.61?g/l) and thickness(15-65m; mean: 33m). Throughout the study area, the chlorophyll concentration was relatively low(<2.0?g/l) in the waters shallower than 50 m and even much lower(<1.5?g/l) in waters deeper than 150 m. In cyclonic eddy region, SCMLs were observed to have relatively higher concentration of chlorophyll at shallower depths. And values of chlorophyll concentration were different within and outside the cyclonic eddy zone, the former were higher. In contrast, in anticyclonic eddy region the SCMLs were located at deeper layer with lower chlorophyll concentration. In addition, the depths of SCML were consistently accompanied by the minimum of transmittance(Trmin).The distribution characteristics of the SPM are mainly affected by the following factors:(1) Material sources. The SPM in the study area are composed of inorganic components and organic components. Inorganic particles are mainly from the islands in the vicinity of the study area. And the organic particles are mainly from in situ biological debris.(2) Water Quality structure: The distributions of light, nutrients, temperature and salt in water can influence the pycnocline and distributions of chlorophyll significantly. And then they will have a great influence on the distributions of SPM.(3) Ocean current and water mass: the water column in the study area can be stratified into two layers. The upper layer is occupied by warm and low saline water and the lower layer is cold and high saline as a part of the North Pacific central water masse and the North Pacific tropical water respectively, with a sharp pycnocline located around 80 m. Different characteristics between the upper and lower layers of water lead to the specific physical and chemical conditions. And the subsurface chlorophyll maximum and light transmission are both appear around the interface between two layers.(4)Mesoscale eddy: The studied area can be divided into three regions: the cold eddy zone(136�-138�E), the warm eddy zone(138.3�-139.5�E), and the transitional zone excluding the former two. The hydrological dynamic environments of the water body in three different areas contribute to the significantly different distribution of SPM.