226Ra和228Ra对南海北部陆坡水团的示踪作用

镭同位素是研究海洋水体运动及混合过程理想的示踪物质。本文基于2017年3月春季南海北部陆坡海域调查，分析了水体中226Ra和228Ra的活度分布特征。研究结果表明:表层海水中226Ra和228Ra活度范围分别为6.4～10.7 dpm/100 L和4.6～26.0 dpm/100 L。表层海水中228Ra/226Ra放射性活度比、温度以及盐度变化表明调查区域表层水主要由南海海水和黑潮分支海水两种水团组成，结合双端元混合模型估算采样区域二者所占比重范围分别为0.13～1.05和?0.05～0.87。226Ra和228Ra在垂向上活度范围分别为5.9～29.7 dpm/100 L和2.6～6.5 dpm/100 L，通过镭同位素的垂向分布结合稳态假设和226Ra和228Ra的双箱模型估算了南海北部陆坡1500 m层以下海水的滞留时间范围为14～61 a。

Water mixing in the northern slope of the South China Sea as traced by 226Ra and 228Ra

Radium isotopes were important tracers for water transport and mixing processes. We investigated the distribution of 226Ra and 228Ra in the northern slope of the South China Sea (SCS) during spring based on a cruise conducted in March 2017. The results proved that the activities of 226Ra in surface water varied from 6.4 to 10.7 dpm/100 L, and those of 228Ra varied from 4.6 to 26.0 dpm/100 L. The 226Ra and 228Ra activities, temperature and salinity in the surface seawater reflected that the surface water in the northern SCS was mainly composed of two water masses, namely the SCS water and the Kuroshio branch water. The proportion ranges of the two water masses in study area was 0.13～1.05 and ?0.05～ 0.87, respectively. The activity ranges of 226Ra and 228Ra in sea water column were 5.9～29.7 dpm/100 L and 2.6～6.5 dpm/100 L. Using a steady-state hypothesis and the two-box model of 226Ra and 228Ra, the residence time of seawater below 1500 m in the northern SCS was estimated to be approximately 14～61 years.