| Summary: | 碩士 === 國立臺灣大學 === 海洋研究所 === 100 === Dissolved Cu in seawater is now recognized to be dominated by complexation with naturally occurring ligands. Marine humic substances (HS) are known to be one of the main components of bio-refractory DOM which plays an important role in copper speciation, affecting its bioavailability. In this study, depth profiles of reactivity and speciation of dissolved copper in West Philippine Sea waters were investigated by cross flow ultrafiltration (1kDa), ion exchange (Chelex-100, AP MG-1), solid phase extraction(XAD-4) and differential elution (hydrochloric acid, sodium hydroxide and methanol) techniques.
Results had shown that the concentration of total dissolved Cu(≤ 0.4 um), from surface to near bottom (~3000 m) waters, ranged 0.5~3 nM. The distribution and concentration of dissolved Cationic Cu in euphotic zone were significantly affected by the phytoplankton uptake even under strong internal wave and water mass mixing conditions in West Philippine Sea. The major part of dissolved Cu was in colloidal fraction (1 kDa~0.4 um), and cationic-exchangeable which’s bio-available, mediated by colloidal compounds released from planktons and bacterial re-mineralization, as microbial mucilages.
In euphotic zone, both fulvic fluorescence and fulvic bound Cu had similar distribution as chlorophyll-a, indicated that part of the fulvic bound Cu released by photochemical oxidation and then uptake by phytoplankton. In aphotic zone, with almost unchanged fulvic concentration through out the water column, however, Cu concentration in these fulvic acid increased with depth, a metal enrichment process possible caused by re-mineralized free Cu ions re-established bounding with previously photo-altered metal depleted fulvics. In addition, as world first discover, fulvic bound Cu changed accounted only for 8~15 % of truly dissolved Cu (≤1 kDa), and 25~60 % of its refractory fraction. These evidences suggested, that majority of refractory Cu in the ocean water might be metal sulfide compounds.
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