RV Akademik Tryoshnikov left Arkhangelsk on August 17 2018, and on August 22-30 for observations in the western part of the Laptev Sea under the auspice of CATS (The Changing Arctic Transpolar System)/Transdrift program. water samples for microbial diversity from 40-60L for the big size fraction (Large particles > 100µm, denoted as 'LD') and 2L for the small size fraction (particles < 100µm, denoted as 'SD'). All samples were prefiltered through 100µm nylon mesh. For the large size fraction particles from the pre-filter were flushed onto 0.22µm Sterivex filters and filtrate was pumped for the small size fraction onto 0.22µm Sterivex filters using a Masterflex pump and silicone hoses. Samples were stored in -80° until DNA extraction. Sequencing was performed using an Illumina MiSeq at the AWI, Bremerhaven, Germany.