太平洋西北海域海水中钇与稀土元素的地球化学

YTTRIUM AND RARE EARTH ELEMENT GEOCHEMISTRY IN THE SEAWATER OF THE WESTERN NORTH PACIFIC

海水样品是在东京大学海洋研究所科学考察船（淡青丸KT）93－14次航海期间，于1993年9月12日在日本伊豆-小笠原海沟海域（29°05′N，142°51′E，水深9500m）采集的。采用化学萃取-反萃取分离法并结合等离子质谱仪，对样品进行分析研究。结果表明，海水中重稀土相对于轻稀土富集，相对于重稀土和轻稀土来说，中稀土有一定程度的亏损。钇浓度从海水表面随深度的增加而逐渐增加，与稀土元素一样在海水断面上呈营养盐型分布。同时还发现Ho是稀土中与Y相关性最好的元素，并指出Ho／Y的浓度比同样可以用来示踪海洋中水团的移动。

The studied seawater samples were collected on September 12, 1993,at Izu-Ogasawara Trench (29°05′N, 142° 51′ E; water depth, 9 500 m ) during the KT93- 14 cruise (R/V Tansei-Maru of Tokyo University). Y andREEs have been measured by using a method involving solvent extraction and back-extraction and subsequent measurements on ICP - MS.REEs and Y, in general, increase in concentration with depth. Heavy REEsreach a maximum concentration at about 2 000 m and then decrease or keep constant to the bottom, while light REEs continue to increase in concentration withdepth. The shale-normalized REE patterns, as studied by previous workers,show enrichment of heavy REEs over light REEs, which is conventionally interpreted as a result of strong complexation of heavy REEs relative to light REEs inseawater. Middle REEs show slight depletion relative to both light and heavyREEs in deep water. The first detailed depth-profile of Y (III) presented here inseawater with the lanthanide in the North Pacific provides significant insights intothe comparative behaviors of Y and REEs in seawater. The concentrations of Yrange 70 - 290 pmol/kg and show the 'nutrient-like' profile best resembling thatof Ho amongst the other REEs, in agreement with an expectation based on thesimilarity in their ionic radii and hence stability constants of complexation withcarbonate ion. Yet variation of Ho/Y ratios in seawater reflects a difference incomplexation of Y and Ho with soft organic ligands on the surface of particulatematter during scavenging and the movement of water mass.