About this Research Topic
The oligotrophic North Pacific Subtropical Gyre (NPSG) is one of the largest biomes on the planet and is a physically and biogeochemically stable habitat. Throughout the annual cycle, daylength varies less than 3 hours, surface seawater temperatures fluctuate by ~3°C, and persistently low nutrient concentrations are maintained in the upper ocean. The semi-enclosed gyre circulation isolates the NPSG and restricts vertical exchange of material and energy, further enhancing the stability of the ecosystem. The result of these environmental conditions is a plankton community dominated by unicellular microorganisms less than a few micrometers in size. Despite the persistent low nutrient concentrations, phytoplankton growth rates appear near maximal, sustained by efficient nutrient regeneration with plankton population sizes regulated by processes such as zooplankton grazing and viral lysis. Seasonal pulses of particle export to the deep sea and increases in phytoplankton abundance do occur during the summer months; however, the factors that result in these imbalances in growth and loss processes are not well-understood.
The oligotrophic conditions of the NPSG and the resident microbial populations present a unique set of challenges to microbial oceanographers. Many organisms are sensitive to environmental manipulation, resisting cultivation efforts and complicating experimental manipulations. Furthermore, the low phytoplankton biomass and low nutrient concentrations necessitate highly sensitive analytical methods to quantify temporal and spatial changes in material and energy fluxes and distributions. Nonetheless, through development of sensitive methodologies we now recognize subtle yet important biogeochemical and ecological dynamics occurring over timescales ranging from diel to interannual. These temporal patterns would be more difficult to resolve in more variable, heterogeneous marine environments such as coastal habitats. The microbial oceanography research being conducted in the NPSG continues to progress rapidly and includes remote, autonomous and in situ observations; laboratory and at-sea experiments; and cultivation-dependent and -independent approaches. Such work is facilitated through a combination of shipboard expeditions, satellites, moorings, Seagliders, and free-drifting autonomous floats. Several research programs host these activities, and one of them, the Hawaii Ocean Time-series program, has sustained long-term time-series observations at its deep water site, Station ALOHA. Additional research programs have examined the pelagic ecosystem of the NPSG at greater temporal and spatial resolution than afforded by fixed-point observations at one site. For example, the Center for Microbial Oceanography: Research and Education (C-MORE) conducted more than 20 separate research expeditions in the NPSG exploring the ecology and biogeochemistry of planktonic microbes in this ecosystem.
This Research Topic welcomes submissions covering all aspects of microbial oceanography in the oligotrophic North Pacific Subtropical Gyre including identification and isolation of microorganisms, quantification of microbial biomass and turnover, metabolism and physiological activities, and microbial-mediated biogeochemical cycling. We welcome field, laboratory, and modeling studies which have a focus on the microbial oceanography in the North Pacific Subtropical Gyre.
Keywords: microbiology, phytoplankton, biogeochemical cycling, oceanography, physiology, North Pacific Ocean, Station ALOHA
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