[A-CG52] [JJ] 植物プランクトン増殖に関わる海洋－大気間の生物地球化学

[ACG52-P04] 窒素・炭素安定同位体比を用いた親潮域における動物プランクトンの動態解析

*野口 真希¹、田所 和明²、兵藤 不二夫³、陀安 一郎⁴、由水 千景⁴、西岡 純⁵、原田 尚美¹ (1.国立研究開発法人海洋研究開発機構 地球環境観測研究開発センター、2.国立研究開発法人水産研究・教育機構　東北区水産研究所、3.岡山大学異分野融合先端研究コア、4.総合地球環境学研究所、5.北海道大学　低温科学研究所)

キーワード：炭素・窒素同位体比、食物連鎖、親潮、同位体分別

Carbon and nitrogen isotope ratios (δ¹⁵N and δ¹³C) of organisms are controlled by not only biological factors, such as catabolism and assimilation, but also physical environmental conditions that influence the isotope ratios of primary producers (phytoplankton). To examine how different water properties (i.e., nutrients and temperature) affect δ¹⁵N and δ¹³C in marine food webs, we measured δ¹⁵N and δ¹³C of zooplankton in three distinct water masses: coastal Oyashio (COY), Oyashio (OY) and warm-core ring (WCR) water along the A-line monitoring transect (38N-42.5N, 144.5-147.5E) in March 6- 26, 2015, cruise of the KH-15-1 of the R/V Hakuho-maru of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), and in February 28 – March 16, 2015, cruise of the WK-15-03 of the R/V Wakataka-maru of the Tohoku National Fisheries Research Institute, Japan Fisheries Research and Education Agency (FRA). Zooplankton samples were collected from 150 m depth to the surface using vertical tow of a NORPAC twin net (45cm mouth diameter, 0.355 mm mesh size). After collection, all samples were classified using a stereomicroscope into species or genus level, and only adults were used for isotopic analysis. Water samples were collected from the surface to 250m depth profiles for the measurements of δ¹⁵N (NO₃⁺ + NO₂^-). We compared the trophic fractionations of carbon and nitrogen isotopes (Δδ¹³C, Δδ¹⁵N) of zoopalankton among the three water masses. We found that δ¹⁵N of chaetognatha at COY tended to be higher than OY and WCR, but a simple relationship between Δδ¹⁵N and Δδ¹³C, regardless of species or water masses. Combined with this Δδ¹⁵N-Δδ¹³C relation, the isotopic ratios of zooplankton would allow us to predict C and N isotope ratios of higher trophic consumers, such as carnivorous fish and seabirds.