Neodymium isotopic variations in Northwest Pacific waters
Neodymium isotopic variations in Northwest Pacific waters
复制标题
DOI：
10.1016/s0016-7037(03)00501-5
复制
发表时间：
2004-02-01
影响因子：
5
通讯作者：
Nagai, H
中科院分区：
文献类型：
--
作者：
Amakawa, H;Nozaki, Y;Nagai, H
获得了西北太平洋海水中ND浓度和同位素组成的4个垂直剖面。来自黑潮流区的两个剖面一致地表明，尽管ND浓度随着深度的增加而逐渐增加，但其同位素组成随深度的变化取决于占据水柱的水团。起源于北太平洋热带水的高盐度黑潮水携带最小的辐射成因ND(epsilon(ND)=-7.4~-8.7)到该地区，距离西缘大陆架约250米，最有可能来自东中国海。北太平洋中层水(NPIW)的Nd同位素组成在epsilon(ND)=-3.7时相当均匀，分布在600~1000m之间。日本本州三里洲附近38度至40度北侧黑潮/大洋混合水区的剖面资料还表明，最新的NPIW是由各种源水混合形成的，其epsilon(ND)=-3.2，其辐射成因成分主要来自大洋水。在近1000m以下的太平洋深水(PDW)，其同位素组成既不垂直也不水平均匀，表明它也是迟缓的深水循环的有效示踪剂。伊豆-小川海沟的两个剖面在2000m处有一个最小的epsilon(ND)值，表明日本本州附近存在水平平流流。有一些来自其他化学性质的证据支持这一观察结果。4000m以下包括亚热带海沟内的水域的epsilon(ND)值约为-5，表明深水是从西部边界向南补给的，最终来自南太平洋的南极底层水(AABW)。这条线沿着日本群岛延伸到北纬40度。在亚北极地区(>；类似于北纬42度)，水中有更多的放射性成因ND，整个水柱都有埃(ND)>；-4.0，推测是由于千岛-堪察斯卡-阿留申岛链等火成岩省份的风化提供了ND。PDW中Nd同位素组成的横向不均匀性表明，北太平洋海盆可能存在不同的环流和混合机制。版权所有(C)2004爱思唯尔有限公司
Four vertical profiles of the concentration and isotopic composition of Nd in seawater were obtained in the western North Pacific. Two profiles from the Kuroshio Current regime showed congruently that although the Nd concentration increases gradually with depth, its isotopic composition varies significantly with depth depending upon the water mass occupying the water column. The high-salinity Kuroshio waters originating from the North Pacific Tropical Water (NPTW) carry the least radiogenic Nd (epsilon(Nd) = -7.4 to -8.7) to this region at similar to250 m from the western margin continental shelves, most likely from the East China Sea. The Nd isotopic compositions in the North Pacific Intermediate Water (NPIW) that occurs at 600 to 1000 m in the subtropical region are fairly uniform at epsilon(Nd) = -3.7. The profile data from the similar to38degrees to 40degreesN Kuroshio/Oyashio mixed water region off Sanriku of Honshu, Japan, also suggest that the newest NPIW with epsilon(Nd) = -3.2 is formed there by the mixing of various source waters, and the radiogenic component of Nd is derived mainly from the Oyashio waters.In the Pacific Deep Water (PDW) below similar to1000 m, the Nd isotopic composition is neither vertically nor horizontally homogeneous, suggesting that it serves as a useful tracer for sluggish deep water circulation as well. Two profiles from the Izu-Ogasawara Trench showed a minimum epsilon(Nd) value at 2000 m, suggesting that there exists a horizontal advective flow in the vicinity of Honshu, Japan. There is some evidence from other chemical properties to support this observation. The waters below 4000 m including those within the trench in the subtropical region have epsilon(Nd) values of around -5, suggesting that the deep waters are fed from the south along the western boundary, ultimately from the Antarctic Bottom Water (AABW) in the South Pacific. This extends up to similar to40degreesN along the Japanese Islands. In the subarctic region (>similar to42degreesN), the waters have more radiogenic Nd with epsilon(Nd) > -4.0 throughout the water column, presumably due to the supply of Nd by weathering in such igneous provinces as the Kuril-Kamchatska-Aleutian Island chain. The lateral inhomogeneity of the Nd isotopic composition in PDW suggests that there may be different circulation and mixing regimes in the North Pacific Basin. Copyright (C) 2004 Elsevier Ltd