Study On The Characteristics Of Marine Nepheloid Layers And Their Influential Factors In The Middle Pacific Ocean And In The East China Shelf Sea

This study on the marine nepheloid layers were conducted in the Middle Pacific Ocean and the East China shelf sea, respectively.Based on the data of total suspended matter (TSM) of 132 samples taken at 12 stations during the Chinese First Around the World Cruise in 2005 and 2820 elemental data by ICP-MS analysis for the suspended matter and surface sediment samples from the same stations a systematic study on the chemical compositions and transport trace indexes of the suspended particles in the water columns in the middle Pacific Ocean was conducted.The basic characteristics of the marine nepheloid layers (MNLs) and suspended particles, and the related particle source analysis show that: 1) The concentration of suspended particles in the water columns is very low, generally less than 0.3mg/dm~3. The vertical profiles of TSM and the concentration of the main elements in the particles vary in a three sectors way along the water column. The particle concentration in the suface nephiloid layer (SNL) is lower than that in the benthic nephloid layer (BNL). The biogenic particles are dominated in the SNL, while the terrigenous particles are dominated in the BNL ;2) The content of TSM as well as the particles of volcanic origin in the MNLS in the western China Pioneer area are significant higher than that in the eastern area. The increase of the particles of volcanic origin in the western area is, probably, due to the stronger submarine volcanic activities in western area than that in the eastern area; 3) the commonly existed BNL was not found over the top and slope of the sea mountains which are covered by the multi-metal-rich crust with little sediment.Analysis of the trace indexes show that the 96% of the Ba in the suspended matter is of biogenic origin. The bio-Ba and Ti, Al was chosen as the biogenic and terrigenous source markers, respectively, in coincidence with the previous studies in the Atlantic Ocean. Bio-Ba/Ti, bio-Ba /Al were chosen as the sensitive markers to show the variation of the biogenic/terrigenous suspended particles in MNLS through the correlation analysis of 12 major elements of the suspended particles. Comparing with the overlain waters, the content of terrigenous particles in the BNL was increased significantly, but was lower than that in the surface sediment. And the content of biogenic particles was decreased in BNL, but was higher than that in the surface sediment. This situation indicates the part of the surface sediment entered into the BNL through bottom resuspension, and the bio-Ba/Ti, bio-Ba /Al are the sensitive transport trace markers for the suspended particles in the BNL.The characteristics, classification and formation mechanism of the MNLs in the East China shelf sea (ECSS) the typhoon impact on the MNLs were analyzed and base on the successive data records of water temperature, salinity, density, depth, turbidity and suspended particles sampling in 48 stations, collected in autumn, 2003. MNLs in the ECSS were identified and three basic structural types were differentiated. The nomination of MNL types was improved to meet the shallow water depth of the shelf seas. Four major MNL areas with high turbidity and separated by different water masses were found along the cross-shelf section profiles. The structural characteristic of the MNLs is corresponded with the feature of the water masses. The intrusion of the Kuroshio Current into the shelf sea, the turbid Changjiang diluted water mass and the interaction between the coastal current system and the Kuroshio Current shelf branches are responsible for the structural variety of the marine nepheloid layers in the East China Shelf Sea. The horizontal dispersion of suspended particles in the intermediate nepheloid layer at the shelf margin is the major materials transport mode from shelf to the deep sea in the shelf margin.The study of the typhoon impact on the MNLs shows that 1) the dimension and turbidity of the lower MNLs in the ECSS is drastically increased by the strong bottom sediment resuspension caused by the typhoon process. A continued lower MNL with turbidity 2 FTU and thickness more that 20m appeared along the PN cross-shelf profile, covering the whole shelf area. However, the core locations of the three major lower MNLs remain unchanged; 2) the dimention of three major lower MNL areas increased by 2times and their turbidity increased by 5 times. This drastic increase of dimension and turbidity of the MNLs indicates that the seaward transport of the particle materials from the ECS shelf to its eastern deep sea is also increased largely; 3) The Kuroshio subsurface water intrusion into the shelf is enhanced by the typhoon from the east and reached to the middle shelf in the upper water column,preventing the lower MNLs from their uplift. This is resulted in decrease of the height/thickness of the lower MNLs which was lower than that before the typhoon. The strengthen of the intrusion of the Kurioshio subsurface water in the upper water layer results the increase of water and sediment transport from the shelf towards back to the Okinawa Trough through the lower water layer.The typhoon impact study reveals that the typhoon and other extreme dynamic processes have strong effect on the particle transport and marine environment as well. This article is the first report of the typhoon impact on the MNLs.