The radiocarbon content (∆14C) of the large brown macroalga Undaria pinnatifida was investigated as an indicator of oceanographic conditions during algal growth in Otsuchi Bay on the Pacific coast of northeastern Japan. In this region, warm boundary currents characterized by high dissolved inorganic carbon (DIC) ∆14C and cold subarctic Oyashio Current (low ∆14C-DIC) flow into the bay seasonally. We hypothesized that ∆14C values in U. pinnatifida pinnae (leaflet-like structures arising sequentially along the vertical axis of the blade) reflect ∆14C-DIC values in bay water during photosynthetic production. During the U. pinnatifida cultivation period (November 2013–April 2014), the Oyashio intrusion occurred from early March to early April, accompanied by a decrease in bay water ∆14C-DIC, from 15.7 ± 8.6‰ to − 57.1 ± 20.7‰. The ∆14C of the pinnae reflected ∆14C-DIC, as pinnae that formed in early March had significantly higher ∆14C (3.0 ± 5.4‰) than those that formed in early April (− 23.6 ± 7.5‰). These results indicate that the ∆14C of U. pinnatifida pinnae can serve as a record of Oyashio intrusion into the bay during algal growth.

中文翻译：

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大型藻类裙带菜的位置依赖性放射性碳含量作为藻类生长过程中海洋条件的指标

在日本东北部太平洋沿岸的大槌湾，大型棕色大型藻类裙带菜的放射性碳含量 (Δ14C) 被研究作为藻类生长过程中海洋条件的指标。在该地区，以高溶解无机碳（DIC）Δ14C和冷亚北极亲潮流（低Δ14C-DIC）为特征的暖边界流季节性流入海湾。我们假设 U. pinnatifida pinnae（沿叶片垂直轴顺序出现的小叶状结构）中的 Δ14C 值反映了光合作用过程中海湾水中的 Δ14C-DIC 值。在 U. pinnatifida 栽培期间（2013 年 11 月至 2014 年 4 月），亲潮入侵发生在 3 月初至 4 月初，伴随着海湾水 ∆14C-DIC 的减少，从 15.7 ± 8.6‰ 降至 − 57.1 ± 20.7‰。耳廓的 ∆14C 反映了 ∆14C-DIC，因为 3 月初形成的耳廓的 ∆14C (3.0 ± 5.4‰) 明显高于 4 月初形成的耳廓 (- 23.6 ± 7.5‰)。这些结果表明，U. pinnatifida pinnae 的 ∆14C 可以作为藻类生长期间 Oyashio 入侵海湾的记录。