Studies on biological activity in marine euphotic layr using ^<13>C and ^<15>N of sedimentary organic matters.

稳定的碳和氮同位素组成已被用作生物活性或海水中CO2可用性的代表，尽管仍然存在许多问题和争论。本项目旨在通过对半封闭海域生物地球化学样品的化学同位素示踪，揭示这些指标与观测生物变化之间的相互关系。1994年秋季至1996年春季在北海道丰卡湾进行了生物地球化学研究和水文观测。在春华期，悬浮粒子δ ^<13>C和δ ^<15>N表现出重同位素的显著富集。然而，我们发现氮同位素变化不能用Reighley蒸馏模型所描述的^<15>N的自发富集来解释。海水中总无机碳δ ^<13>C随初级生产的进行而升高，但不能充分解释颗粒有机碳的同位素变化。我们估计与光合作用有关的同位素分馏可能随着水密度的分层而改变。我们发现夏季POC的^<13>C变轻了-28%_0，同时底层以上δ ^<15>N从5%上升到+ 10%_0。这种变化可能与近底颗粒物的分解和还原条件的进展有关。这些结果强烈表明，在底部沉积物中发现的δ ^<15>N和δ ^<13>C值应该受到这种同位素变化的影响，因此强调有必要将其作为水体生物过程重建的代表。

Stable carbon and nitrogen isotopic compositions have been used as a proxy of biological activity or CO2 availability in sea water, although still many questions and argument are retained. The purpose of this project is to reveal the interrelation between such proxies and observational biological change based on tracing chemical and isotopic components of biogeochemical samples in a semi-closed sea.Biogeochemical researches as well as hydrographic observations have been performed in the Funka Bay, Hokkaido, for 1994 fall to 1996 spring. In the period of spring bloom, the delta^<13>C and delta^<15>N of suspended particles showed significant enrichment in heavy isotopes as expected from previous model. However, we found that nitrogen isotopic change could not be interpreted by the spontaneous enrichment of ^<15>N as described by Reighley distilllation model. The delta^<13>C of total inorganic carbon in sea water risen with progress of primary production, but it was not sufficient factor to explain the isotopic change of particulate organic carbon. We estimated that isotopic fractionation associated with photosynthesis might be changed with stratification of water density.We found that ^<13>C of POC becomes light by -28%_0 and simultaneously delta^<15>N rises from 5 to + 10%_0 above bottom layr in summer. This change appears to be related with decomposition of particulate matters in near bottom and progress of reduction condition. These recults strongly suggest that delta^<15>N and delta^<13>C values found in bottom sediment should suffer from such isotopic change, accordingly emphasize that it is essential to understand the as a proxy for reconstruction of biological process in the water column.