Microbial Ecology and Biogeochemical Processes in the Ulleung Basin

Abstract

Since heterotrophic bacteria rapidly respond to variations in physico-chemical conditions, monitoring the role of bacteria in C cycles is important in the East Sea where has been known as the rapid warming occurred during the last 2 decades. Major microbiological and biogeochemical processes associated with oceanographic conditions of the water column and geochemical properties of the sediment in the Ulleung Basin (UB) are covered in this chapter. Overall, bacterial parameters in the water column are largely affected by the occurrence of coastal upwelling and formation of the anticyclonic Ulleung Warm Eddy. Heterotrophic bacterial production is closely coupled to phytoplankton biomass, but the role of bacteria either as a trophic link within the microbial food web process or as a C sink for photosynthetically fixed organic carbon varies with the physico-chemical conditions of the water column. In the sediment, high organic content (>2.5 %, dry wt.) is attributed to the high C mineralization by sulfate reduction in the UB compared to that of other parts of the East Sea (i.e. Japan Basin and Yamato Basin). In addition, the observation that manganese-oxides are accumulated at high levels (>150 µmol cm−3) in the surface sediment of the UB indicates that C oxidation by manganese reduction seems to be the major C oxidation pathway in the center of the UB, as was supported by the identification of acetate-oxidizing bacteria related to Colwellia, Oceanospirillaceae and Arcobacter that potentially reduce manganese. Finally, inventories of culture-dependent and culture-independent Bacteria and Archaea, mostly reported in the UB, are summarized at the final section of this chapter.