Dominance of phytoplankton and ice algae in melt pond during expedition PS122/5 (MOSAiC Leg 5) to the central Arctic Ocean@en

Samples of microalgae groups, including phytoplankton and ice algae, in melt pond were taken during September during Leg 5 of MOSAiC expedition. Melt pond water was pumped up with a peristaltic pump through a 2-m-long PTFE tube (L/S Pump Tubing, Masterflex, USA) or scooped up in the melt pond with ladle with floating algae aggregates. Ice cores from the pond bottom ice (sample ID #3–6) and melt pond surface ice (sample ID #14) were collected using an ice corer (Mark II coring system, Kovacs Enterprises, Inc., Indianapolis, USA). Also, we sampled small pieces of the bottom ice dislodged and floated to the surface of the melt pond by poking with a ruler (dislodged ice; sample ID #7–11). Ice cores from melt ponds were segmented. Dislodged ice was cut into 0.25 m × 0.25 m size. All ice samples were placed into ice melting bags (Smart bags PA, AAK 5L, GL Sciences Inc., Japan) and melted in the dark at +4°C. Pond water and melt water sample were stored in Lugol's solution (final concentration 10%). The water sample for taxonomic analysis were concentrated for 24 hours by standing the sample tube and removing the supernatant. The cell counting for microalgae community assemblage was examined using a light microscope (Olympus, BH-T, Tokyo, Japan) with 40 × objective and 10 × oculars, and the contribution of each microalgae group to the total cell abundance was calculated. Identification of the microalgae followed Tomas (1997) and Scott and Marchant (2005).本数据集采集了MOSAiC科考航次第5航段9月期间融池内的微藻群落样本，涵盖浮游植物与冰藻两类群。融池水通过蠕动泵经2米长聚四氟乙烯（PTFE）管（L/S泵管，Masterflex，美国）抽取，或直接使用带有漂浮藻团的长柄勺在融池中采集。采用Mark II冰钻系统（Kovacs Enterprises, Inc.，美国印第安纳波利斯）采集融池底部冰芯（样本编号#3–6）与融池表面冰芯（样本编号#14）。此外，通过直尺拨动使脱离并漂浮至融池表面的底部冰块碎片亦被采集（脱离冰；样本编号#7–11）。融池冰芯需进行分段处理，脱离冰则被切割为0.25 m × 0.25 m的规格。所有冰样本均装入融冰袋（Smart bags PA，AAK 5L，GL Sciences Inc.，日本），并于4℃避光环境中完成融化。融池水与融冰水样本均保存于鲁哥氏液（Lugol's solution，终浓度10%）中。用于分类学分析的水样通过静置样本管并移除上清液的方式浓缩24小时。采用配备40×物镜与10×目镜的光学显微镜（Olympus BH-T，日本东京）对微藻群落组成进行细胞计数，并计算各微藻类群在总细胞丰度中的占比。微藻的分类鉴定参考Tomas（1997）与Scott和Marchant（2005）的研究标准。