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

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).