Analysis of water mixing history in high latitude oceans using chemical tracers of the third generation

本次助学金资助的研究主要包括以下两个部分。一种是利用硝酸盐氮同位素比值分析海洋表层生物活动和水混合的历史，另一种是在精确测量营养盐浓度的基础上分析中深层的水平流和混合过程。前者利用日本和加拿大之间的一艘商船每年在白令海和阿拉斯加湾采集的地表水样品进行研究，后者利用俄罗斯船只在鄂霍次克海南部盆地进行的CTD/RMS观测所采集的样品进行研究。这笔赠款的大部分用于建造氮同位素分析的真空系统和营养测量的自动分析仪。硝酸盐浓度-氮同位素比值图表明，在夏季，地表水的…变化较快。与阿拉斯加湾相比，白令海与地下水的结合程度更高。根据营养盐的精确测量，通过对中、深水的分析，提出了一个新的化学量N*(=([NO_3-]-16。[PO4^3-]+2.9)0.87)，对追踪水团的起源和混合过程非常有用。这种N~*是一种准保守示踪剂，在普通水柱中不发生变化，但在底泥或某些特殊水柱中分别随反硝化作用和固氮作用而减少和增加。对鄂霍次克海南部盆地地区N~*的详细观测表明，低N~*水不仅分布在可能发生反硝化作用的海底和陆坡，而且在200~400m深度范围内沿低位涡水沿陆坡区向中层渗透。这为北太平洋中间水的发源地鄂霍次克中水是一个水团的机制提供了证据，该水团最初形成于鄂霍次克海西北部的大陆架区域(=Low N*区)，并沿中间层水平流出。较少

The research supported by this grant-in-aid mainly consists of following two parts. One is the analysis of history of the biological activity and water mixing in ocean surface layer using nitrogen isotope ratio of nitrate, and the other is the analysis of water advection and mixing processes in the intermediate and deep layers based on precise measurements of nutrient concentration. We used the surface water samples which were annually collected in Bering Sea and Alaska Bay by a merchant vessel between Japan and Canada for the former study, and the samples collected by the CTD/RMS observations which were carried out in Southern basins of the Sea of Okhotsk by Russian ship were utilized for the latter study. Most part of this grant was applied to construct the vacuum system for nitrogen isotope analysis and the auto-analyzer for nutrient measurement. The concentration & nitrogen isotopic ratio plot of nitrate suggested the possibility that, in summer, the surface water is more rapidly m … More ixed with the subsurface water in Bering Sea than in Alaska Bay. By the analysis of intermediate and deep waters based on the precise measurements of nutrients, a new chemical quantity, N* (=([NO_3-] - 16. [PO_4^3-] + 2.9) 0.87), was found to be very useful to trace the origin and mixing process of water masses. This N* is a quasi-conservative tracer which does not change in the ordinary water column, but decrease and increase by denitrification and N_2-fixation, respectively, occurring in the bottom sediment or some special water column. The detailed observation of N* in all over the Southern basin area in the Sea of Okhotsk revealed that the low N* water was not only located on the sea floor and continental slope where the denitrification probably occurs, but also penetrated from the continental slope area into the intermediate layer along the low potential vorticity water between 200 and 400m depths. This provides an evidence for the mechanism that the Okhotsk Intermediate Water, which is the origin of North Pacific Intermediate Water, is a water mass which is originally formed on the continental shelf area (= low N* region) in the northwestern of Sea of Okhotsk and horizontally flowed out along intermediate layers. Less