Water masses, shelf influences and depth distributions of arctic microbial species

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Small organisms in the ocean include not only phytoplankton and bacteria, but diverse bacterial grazers and archaea. Local and global climate processes have a direct effect on the vertical stratification and circulation patterns in shelf and off shelf marine waters, which strongly influences the timing and magnitude annual phytoplankton production. Using molecular biology techniques we are now able to identify species and ecotypes of not only phytoplankton but the entire community of microorganisms and it is becoming practical to match community composition with biomass, oceanic processes and biogeochemical pathways.We show from our recent work in Arctic Seas that microbial communities change, not only with depth, but with region and that microbial species mostly track their water mass of origin. For example below the photic zone some watermasses are richer in bacterivores while others are dominated by likely parasites suggesting different fates for fixed carbon passing through these depths. We suggest that most changes in microbial community composition can be linked to the complex oceanic current patterns and advective processes. These microbial species changes may well determine the reproductive success of larger organisms and carrying capacity of an ecosystem since many marine fish and invertebrates have multiple free living life stages dependent on particular food types.