Microplastic concentrations in the Chukchi and Beaufort Sea sediments during the cruise MR22-06C of the R/V Mirai of JAMSTEC

The distribution of microplastic in the open ocean of the Arctic Ocean is largely undocumented. Substantial numbers of studies on microplastics have been reported in the Pacific and Atlantic Oceans, yet very few data are available in the polar oceans. In the present study, we conducted microplastic surveys along the cruise track to fill gaps in the Arctic Ocean. A multiple corer system (Asyura) equipped with three aluminum tubes was used to collect microplastics in the sea floor sediment. The aluminum tube is 60 cm length and 7.4 cm inner diameter. At the beginning of multiple corer system going down, the speed of wire out was set to be 0.5 m s-1. Wire out was stopped at a depth about 10 m above the seafloor and the corer system was left stand for 1 minute to reduce any pendulum motion of the system. After the multiple corer system was stabilized, the wire was stored out at a speed of 0.5 m s-1 with carefully watching a tension meter. After confirmation of the multiple corer system touching the bottom, the wire continued out till bowing. The rewinding of the wire was started at a dead slow speed (0.3 m s-1), and then winch wire was wound up at 0.5 m s-1. Two of the three cores were used for microplastic analysis and one for paleoenvironmental analysis. In the laboratory, 100% cotton lab coats without plastic fibers were worn. Surface sediment (top ca. 5 cm of sediment core) were taken from the sediment core samples at 1 cm intervals and stored in a freezer until analysis.北冰洋开阔洋域内的微塑料（microplastic）分布状况在很大程度上仍未被系统记录。目前针对太平洋与大西洋的微塑料相关研究已有大量报道，但极地海洋中的相关监测数据却极为匮乏。本研究沿科考航次航线开展微塑料调查，以填补北冰洋领域的研究空白。 本研究采用搭载三根铝制采样管的Asyura型多管采样器（multiple corer system）采集海底沉积物中的微塑料。该铝制采样管长度为60 cm，内径7.4 cm。在多管采样器下放初始阶段，缆绳下放速度设置为0.5 m·s⁻¹。当缆绳下放至距海底约10 m处时停止下放，静置采样器1分钟以削弱系统的摆荡运动。待多管采样器稳定后，以0.5 m·s⁻¹的速度继续下放缆绳，并密切监控张力计（tension meter）读数。确认采样器触底后，继续下放缆绳直至采样管发生弯曲。随后以极慢速度（0.3 m·s⁻¹）启动缆绳回收流程，之后以0.5 m·s⁻¹的速度完成绞车缆绳回收。三根采样柱中，两根用于微塑料分析，剩余一根用于古环境分析（paleoenvironmental analysis）。 实验室操作阶段，研究人员身着不含塑料纤维的100%棉质实验服。从沉积物岩芯样品中以1 cm间隔采集表层沉积物（约沉积物岩芯顶部5 cm），并将样品冷冻保存至后续分析。