Surface radiocarbon (Δ14C) in the North Pacific has been monitored using a commercial volunteer observation ship since the early 2000s. Here we report the temporal and spatial variations in Δ14C in the summer surface water when the surface ocean is vertically stratified over a 13-yr period, 2004–2016. The long-term Δ14C decreasing trend after the late 1970s in the subtropical region has continued to the present and the rate of decrease of the Kuroshio and Kuroshio Extension, North Pacific and California current areas is calculated to be –3.3, –5.2 and –3.3 ‰/yr, respectively. After 2012 the Δ14C of the Kuroshio and Kuroshio Extension area, however, has remained at an approximately constant value of around 50‰. The result may indicate that subtropical surface Δ14C in the western North Pacific has reached an equilibrium with atmospheric Δ14CO2. The Δ14C in the subarctic region is markedly lower than values in the subtropical region and it seems that the decreasing tendency of surface Δ14C has changed to an increasing tendency after 2010. The results may indicate that bomb-produced 14C, which has accumulated below the mixed layer in the past few decades, has been entrained into the surface layer by deep convection.

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2004-2016年夏季北太平洋地表放射性碳变化

表面放射性碳（Δ14C) 在北太平洋，自 2000 年代初以来一直使用商业志愿者观察船进行监测。在这里，我们报告 Δ 的时间和空间变化142004-2016 年 13 年期间表层海洋垂直分层时夏季表层水中的 C。长期Δ14亚热带地区1970年代后期后的C下降趋势一直持续到现在，黑潮和黑潮延伸区、北太平洋和加利福尼亚海流区的下降速度计算为–3.3、–5.2和–3.3‰/yr，分别。2012年之后的Δ14然而，黑潮和黑潮延伸区的 C 值一直保持在 50‰ 左右的大致恒定值。结果可能表明副热带表面Δ14北太平洋西部的 C 已与大气 Δ 达到平衡14一氧化碳2. Δ14亚北极地区的 C 值明显低于亚热带地区的值，似乎表面 Δ 的下降趋势142010 年以后 C 转为增加趋势。结果可能表明，14过去几十年在混合层下方积累的 C 已通过深层对流被夹带到表层中。