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海水中生物活性或CO2可用性的替代物，尽管仍然存在许多问题和争论。1994年秋至1996年春，在日本北海道北海道丰加湾进行了生物地球化学研究和水文观测。在春季水华期间，悬浮颗粒物的δ ^<13>C和δ ^<15>N表现出明显的重同位素富集，这与先前模型的预测一致。然而，我们发现，氮同位素的变化不能解释为自发富集的^<15>N所描述的Reighley模型。海水<13>中总无机碳的δ ^ C随初级生产力的增加而增加，但不足以解释颗粒有机碳同位素的变化。结果表明，在夏季，底层以上<13>POC的δ ^ C变轻了-28%_0，δ ^<15>N由5%_0上升到+ 10%_0。这种变化与近底颗粒物的分解和还原条件的进展有关。这些结果强烈地表明，<15><13>在底质沉积物中发现的Δ ^ N和Δ ^ C值应遭受这种同位素变化，因此强调有必要将Δ ^ N和Δ ^ C理解为水体中生物过程重建的代用指标。

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.