The Distribution Of Dissolved Iron And Its Organic Ligands In The East China Sea And Yellow Sea

Iron is an essential element in marine ecosystem. It is reported that about thirtypercent of the open ocean are HNLC regions, with extremely low dissolved iron,which limits the growth of the marine phytoplankton.The distribution of dissolved iron and its organic complexation in the coastalwaters of the Yellow Sea and the East China Sea were investigated studied by aCompetitive Ligand Equilibration-Adsorption Cathodic Stripping Volummetric(CLE-ACSV) in spring (22March-4April,2011) and autumn (21October-2November,2011) during two cruises of the R/V “Dong Fang Hong2”, the results ofanalysis are as follows:(1) The dissolved iron was mainly bounded to dissolved organic ligands in thecostal waters, which compare well with other studies. In the spring, the proportion ofthe organic complexation of iron was on average of92.8%; While in autumn, the ironwas on average of87.7%organically complexted.(2) The average concentration of dissolved iron in surface waters in spring andautumn were24.70nmol L-1and9.29nmol L-1respectively; in the bottom water, theaverage concentrations were37.40nmol L-1and38.78nmol L-1respectively.(3) The surface averaged concentration of the organic Fe-binding ligands inspring was31.71nmol L-1, and being1.33times dissolved iron, while the bottomaveraged concentration was51.95nmol L-1, and being1.1times dissolved iron; Inautumn, the averaged dissolved ligand concentration in the surface waterswas9.29nmol L-1and3.0times dissolved iron; In bottom waters, the dissolved ligandconcentration was on averag48.88nmol L-1, and2.0times dissolved iron.(4) The seasonal variability of the complexing strength of organic ligandsbetween spring and autumn was also observed. Overall, the complexing strength ofthe organic ligands was higher in spring.The averaged logarithm of conditional stability constant (logK′FeL) in surfacewaters in spring was with12.0; in the bottom water, logK′FeLwas mean of11.84. Inautumn, logK′FeLin the surface waters and bottom waters was on averag of11.32and11.59, respectively.(5) There was distinct distribution variability of dissolved iron and its dissolved organic ligands.Seasonal variability between spring and autumn was observed, that theconcentration was higher in spring.In the aspect of horizontal distribution, the highest values were observed at thecostal waters, such as Yangtze River Estuary and Hangzhou Bay. In the aspect ofvertical distribution, the dissolved iron generally showed the nutritat distributionprofile, that the concentration of dissolved iron in surface waters was lowerThe vertical distribution of the ligands showed systematic variations with depth,indicative of processes of production and removal. In some stations, the ligandconcentrations were generally higher in upper waters and decreased with the depth,while in some station thevertical distributions of the ligand concentration generallyshowed a sub-surface maximum.