Kawakami Hajime, Kusakabe Masashi
Mutsu Institute for Oceanography, Japan Agency for Marine-Earth Science and Technology, 690 Aza-kitasekine Oaza-sekine, Mutsu, Aomori, Japan.
J Environ Radioact. 2008 Aug;99(8):1335-40. doi: 10.1016/j.jenvrad.2008.04.011. Epub 2008 May 23.
We investigated the horizontal distributions of (228)Ra and (226)Ra in surface waters of the northwestern North Pacific Ocean and Okhotsk Sea. Ratios of (228)Ra/(226)Ra were relatively large in the Tsugaru Current (0.6-0.8) and Okhotsk Sea (0.4-0.5), and small in the Western Subarctic Gyre (<0.2) and the Oyashio (0.25-0.3). (228)Ra/(226)Ra ratios in western Subarctic Water (SAW) rose slightly upon mixing with Okhotsk Water (OKW), before becoming the Oyashio Water (OYW). Also, ratios in the OYW increased during mixing with Tsugaru Current Water (TCW). Estimating from (228)Ra/(226)Ra ratios and (226)Ra activities with a simple two-end members-mixing model, we assumed that approximately 23% of the OYW originated from the OKW and the coastal region off northern Honshu (Japan) was strongly influenced by the TCW. From a diagram of (228)Ra activities against salinity, we could roughly divide surface seawater in the study area into the five water masses, which were SAW, OYW, OKW, TCW, and Subtropical Water (STW).
我们研究了西北太平洋和鄂霍次克海表层水中镭 - 228（(^{228}Ra)）和镭 - 226（(^{226}Ra)）的水平分布。在津轻海峡暖流（(^{228}Ra/^{226}Ra)比值为0.6 - 0.8）和鄂霍次克海（(^{228}Ra/^{226}Ra)比值为0.4 - 0.5）中，(^{228}Ra/^{226}Ra)比值相对较大；而在亚北极西部涡旋（(^{228}Ra/^{226}Ra)比值小于0.2）和亲潮（(^{228}Ra/^{226}Ra)比值为0.25 - 0.3）中该比值较小。亚北极西部水（SAW）与鄂霍次克海水（OKW）混合后，在形成亲潮水（OYW）之前，(^{228}Ra/^{226}Ra)比值略有上升。此外，在与津轻海峡暖流水（TCW）混合过程中，OYW中的比值也会增加。通过一个简单的双端元混合模型，根据(^{228}Ra/^{226}Ra)比值和(^{226}Ra)活度进行估算，我们假定大约23%的OYW起源于OKW，并且日本本州岛北部沿海地区受TCW的影响很大。根据(^{228}Ra)活度与盐度的关系图，我们可以大致将研究区域的表层海水分为五个水团，即SAW、OYW、OKW、TCW和亚热带水（STW）。
