| Dissolved aluminum (Al) in the ocean has been investigated as a useful tracer of water mass and a proxy for dust deposition due to its geochemical characteristics, and it is one of the GEOTRACES key parameters. The marginal seas of China are between Chinese mainland and northwestern Pacific Ocean. On the one hand, many major rivers (e.g. Changjiang, Huanghe, Zhujiang, etc.) and Asian dust carry huge amount of terrigenous materials directly into them. On the other hand, the incursion of Kuroshio has the important effect on the water mass exchanging between marginal seas and north Pacific. The large number of terrigenous materials can be transported into the Kuroshio, and then be taken into northwestern Pacific. These terrigenous materials supply essential nutrients for the northwestern Pacific, and may contribute to the primary productivity and carbon cycles. The dissolved Al can be used as a tracer to study this cross shelf transport. This thesis presents the distributions of dissolved Al in the marginal seas of China measured by online preconcentration flow injection analysis method, and the cross shelf fluxes of Al are calculated. The main research results are as follow:The on-line preconcentration flow injection analysis method has been developed for determination of dissolved Al in the seawater base on the lab previous fluorescence measurement (Zhang et al.,2000). The detection limit of this method is 0.18 nmol/L (3σ), and the precisions are 4.0% at 1.5 nmol/L with a 4-min load time and 1.1% at 20 nmol/L with a 2-min load time, respectively. The intercalibration results with SAFe and GEOTRACES standard samples indicate that this method can be used to determination the low concentration of dissolved Al in the seawater accurately. In addition, the intercalibration experiment of samplers between MITESS made by Professor Ed Boyle of Massachusetts Institute of Technology (MIT), Niskin and X-Vane designed by Zhang of East China Normal University (ECNU) shows that the Niskin and X-Vane water samplers can be used to collecte seawater for determination of dissolved Al in marginal seas of China.Six cruises about Yellow Sea (YS) and East China Sea (ECS) were carried out in March and Octber 2011, May, July, August, and Octber 2013, respectively. The concentrations of dissolved Al in the YS were 31 ± 11 nmol/L in March 2011,20 ±14 nmol/L in July 2013 and 41 ± 33 nmol/L in Octber 2011, respectively. And the seasonal variations of dissolved Al in the YS presents the maximum concentration of dissolved Al in autumn, lower concentrations in spring and autumn.The average concentrations of dissolved Al in the ECS were 38 ±12 nmol/L July and August and 31 ± 18 nmol/L in spring 2011 and 2013,24 ± 16 nmol/L and 31 ± 36 nmol/L in summer 2013,30 ± 22 nmol/L and 40 ± 27 nmol/L in autumn 2011 and 2013, respectively. The seasonal variations of dissolved Al in the ECS were relatively complicated, with the higher concentration being found in the coastal area in summer, the lower in autumn and the minimum in spring. High concentrations of dissolved Al (> 100 nmol/L) in the YS and ECS mainly occurred along the coast of China (especially in the Changjiang Estuary, Subei coast and Zhe-Min coast), and then decreased rapidly towards the offshore. The minimum concentrations of only< 10 nmol/L were found in the main axis of Kuroshio Current along the ECS shelf edge. The concentrations of dissolved Al in the Changjiang at Xuliujing (120 km inland of Changjiang Estuary) ranged from 150 to 550 nmol/L, with the average of 216 ± 113 nmol/L during 2012-2013, and the variations of concentrations were closely related to the water discharge and sediment load. The highest value of dissolved Al occurred in summer, lower in spring and autumn, and lowest in winter. Approximately 60% dissolved Al from Changjiang is scavenged during the initial stage of the Changjiang and sea water mixing.Water mass mixing is the most important influencing factor of the distribution of dissolved Al in the YS and ECS, especially the input of Changjiang diluted water and incursion of Kuroshio waters. In addition, phytoplankton activity and adsotption/desorption on the suspended particulate matters (SPM) also have effects on the distribution of dissloved Al. The regions afeected by the phytoplankton bloom mainly occurr in the central YS and Changjiang Estuary, while SPM focus on the Changjiang Estuary and the Zhe-Min coast with in 50 m isobath. The dissolved Al shows semi-conservative behavior in the ECS shelf, and hence can be used as a tracer to discuss the water mass mixing and the cross-shelf transport of terrestrial materials.The cruise was carried out in August-Octber 2011 to understand the distribution of dissolved Al in the South China Sea (SCS). The concentrations of dissolved Al ranged from 2 to 69 nmol/L in the northern SCS with the average of 20 ± 9 nmol/L. The concentrations ranged from 2 to 47 nmol/L in the central SCS with the average of 15 ± 8 nmol/L. The vertical profiles of dissolved Al in the SCS show typically characteristics of scavenging elements, with highest concentrations in the surface waters, and lower concentrations in the deep waters. The behavior of dissolved Al in the Zhujiang Estuary was complicated because of many influence factors, including the different fresh water end-members caused by four river mouths, the interaction between the old and fresh water masses casued by weak tidal, the transformation of dissolved Al species by organic matters, the flocculation during the dramatic variation of salinity, and the adsorption and desorption of SPM, etc. The dissolved Al in the SCS mainly derived from riverine input, dust deposition and incursion of Kuroshio, with the flux of 4.8×109 g/yr, (10.9±8.7) ×109 g/yr and (33-84) ×109g/yr, respectively. However, the removal of dissolved Al by phytoplankton can be reached 0.2x 109 g/yr in the Vietnamese upwelling area. Simple box model was used to estimate the dissolved Al budget in the SCS basing on LOICZ Biogeochemical Modelling Guidelines suggetested by Gordon et al. (1996), and the data suggested that the residence time of dissolved Al in SCS was about 16.0 ± 5.9 years.Because of the semi-conservative behaviorof dissolved Al in the ECS shelf, the dissolved Al was used as a tracer to discuss the cross-shelf transport of terrestrial materials. With the date from ECS in August 2013 and Japanese cruises in the summer 2012 and 2013, it can be concluded that there exists cross shelf transport of dissolved Al in the ESC. The cross shelf transport pathway originates from the Zhe-Min coast, and then flow northeast and southeast into the Kuroshio, respectively. The transport path is along the isopycnal surface, especially the isopycnal layer between 23 and 24 kg/m3, which is similar with the pattern of spring 2011 and indicates the persistent existence of this cross shelf transport of terrestrial material in the ECS. The net dissolved Al fluxes across 100 m and 200 m isobaths are 6.29× 1010 g/yr and 0.63×1010 g/yr in the ECS shelf, respectively, with flux of 5.61×1010 g/yr flow through Tsushima strait into the Japan Sea/East Sea. Compare with the results in spring 2011, there exist seasonal differences both in the pathway and flux. The larger net dissolved Al fluxes across 100 m in summer 2013 than spring 2011 mainly due to the increase of the terrestrial inputs (e.g. Changjiang). While the net dissolved Al fluxes across 200 m are similar between summer and spring, which means the cross shelf transport flux from ESC to Kruoshio is relatively stable, and then can be taken into northweastern Pacific by Kruoshio. |
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