Seasonal dynamics of sinking organic matter in the Pacific Arctic Ocean revealed by nitrogen isotope ratios of amino acids

The Pacific Arctic Ocean has experienced a rapidly changing climate, sea-ice retreat, and enhanced primary production over the past few decades. The export production generated by photoautotrophs and heterotrophs has been characterized in the Arctic Ocean, but their seasonal variations in relative proportion are largely unknown due to the limited access in the ice-covered season. We measured the concentration and nitrogen isotope ratio of individual amino acids from sinking particles in the northern east Siberian Sea (KAMS1), northern Chukchi Sea (KAMS2), and Northwind Ridge (KAMS4) from August 2017 to July 2019. The average trophic position, based on differences in the nitrogen isotope ratios of glutamic acid and phenylalanine, can indicate the relative proportions of biogenic organic matters derived from photoautotrophs and heterotrophs in sinking particles. Decreasing values (close to 1.0) in summer at KAMS2 in 2018 suggest that primary producers are responsible for most of the downw..., ,近数十年来，北极太平洋海域经历了气候快速变迁、海冰消退与初级生产增强的过程。北冰洋中已对光合自养生物（photoautotroph）与异养生物（heterotroph）产生的输出生产开展了相关表征，但由于冰覆盖季的通航限制，二者相对占比的季节变化在很大程度上仍未被探明。本研究于2017年8月至2019年7月期间，对东西伯利亚海北部（KAMS1）、楚科奇海北部（KAMS2）以及北风脊（Northwind Ridge）三处海域的沉降颗粒物（sinking particles）中的单体氨基酸（individual amino acids）浓度与氮同位素比值（nitrogen isotope ratio）进行了测定。基于谷氨酸（glutamic acid）与苯丙氨酸（phenylalanine）的氮同位素比值差异计算得到的平均营养级（trophic position），可反映沉降颗粒物中源自光合自养生物与异养生物的生源有机质（biogenic organic matters）相对占比。2018年KAMS2站位夏季的营养级数值呈下降趋势（接近1.0），表明初级生产者为该站位沉降颗粒物中大部分的生源物质来源……