Arctic marine bacterial diversity study

The first expedition of the R/V ARAON to the Pacific Sector of Arctic Ocean occurred during July and August 2010. Samples were obtained from nine locations at a depth of 7 m, and sea-ice station. Nine surface water samples (SW1 to SW9) were collected using the CTD rosette system (SeaBird, SBE-911plus) and immediately passed through 3-μm pore membrane filters (ADVANTEC, Japan) to separate suspended particles and eukaryotes, and then 0.2-μm pore membrane filters (ADVANTEC) to capture bacteria. Four water samples of melting ponds (MP1 to MP4) and an ice core were collected from the sea-ice station (Fig. S1). The water samples were also filtered using both 3- and 0.2-μm pore membrane filters. The sea-ice core (103 cm) was cut into two parts, ice-top (IT1+IT2: 41 cm) and ice-bottom (IB: 61 cm). Both of the ice core parts were separately melted after peeling off a thin layer from the surface of the whole ice core using a sterile knife for decontamination, and then respectively filtered. The 0.2-μm pore-sized membranes were stored in a deep-freezer (– 80°C) equipped in the ARAON and transported back to the laboratory on ice for DNA extraction.