My current research focuses on understanding the environmental factors driving the diversity, biogeography and activity of marine nitrogen-fixing microbes. Vast areas of the sunlit surface ocean have no detectable nitrogen, yet are teeming with microbial life. Life in these “ocean deserts” is made possible, in part, by microbes that are able to convert dinitrogen (N2) gas into biomass through the process of N2 fixation. This process has been known to be important in the marine environment for several decades now, yet we are still in the beginning stages of understanding the organisms responsible. Many N2-fixers have yet to be isolated in culture, so my research relies on applying cultivation independent techniques to detect and study these cryptic microbes. I am currently involved in three collaborative research projects, funded by the National Science Foundation (NSF) and The Simons Foundation (P.I. Jonathan Zehr). Broadly, these research projects are focused on: 1) Determining whether N2 fixation is occurring in the Alaskan Arctic Ocean, identifying which N2-fixers may be responsible, and determining the environmental drivers of their activity and distributions in these cold, high latitude waters; 2) Identifying the quantitative significance of a unique N2-fixer that lives in symbiosis with another single-celled algae (UCYN-A/haptophyte association) in coastally-influenced marine waters; and 3) Measuring N2-fixer growth rates and microzooplankton grazing rates on N2-fixers in oligotrophic marine waters, to gain insight into their distribution patterns in the North Pacific Subtropical Gyre.
kturk AT ucsc DOT edu
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