A novel psychrotolerant, Gram-negative, motile bacterium, designated strain 328(T), was isolated from sea-ice samples collected off the Canadian Basin of the Arctic Ocean (7 degrees 23' 14'' N 14 degrees 06' 55'' W). Strain 328(T) was able to grow at 0-37 degrees C, with optimum growth at 25-27 degrees C. It possessed phosphatidylethanolamine and phosphatidylglycerol as major phospholipids and C(10 : 0) 3-OH (31.78 %), C(18 : 1)omega7c (27.50 %) and iso-C(15 : 0) 2-OH and/or C(16 : 1)omega7c (19.22 %) as predominant cellular fatty acids. The DNA G+C content of strain 328(T) was 45.2 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain 328(T) was a member of the genus Marinomonas (92.7-96.0 % 16S rRNA gene sequence similarity). On the basis of phenotypic, chemotaxonomic and phylogenetic distinctiveness, strain 328(T) was considered to represent a novel species of the genus Marinomonas. The name Marinomonas arctica sp. nov. is proposed, with strain 328(T) (=CGMCC 1.6498(T)=JCM 14976(T)) as the type strain.