A team of three researchers bring CTD floats back onto a R/V
Dror Shitrit/Simons Collaboration on Ocean Processes and Ecology
Angela Boysen (left) and colleagues in July 2015 lower an instrument at the study site in the North Pacific Subtropical Gyre, north of Hawaii. This instrument collected water samples at different depths that the researchers analyzed.

Though they may be small, microorganisms are the most abundant form of life in the ocean. Marine microbes are responsible for making roughly half of the organic carbon that’s usable by life. Many marine microbes live near the surface, depending on energy from the sun for photosynthesis.

Yet between the low supply of and high competition for some key nutrients, like nitrogen, in the open ocean, scientists have puzzled over the vast diversity of microbial species found there. Researchers from the University of Washington, in collaboration with researchers from 12 other institutions, show that time of day is key, according to a study published Jan. 20 in Nature Ecology & Evolution.

The effort began in 2015, when scientists in the Simons Collaboration on Ocean Processes and Ecology, a program now co-led by UW oceanography professor Ginger Armbrust, looked at microbes in the surface of the North Pacific Subtropical Gyre, the Earth’s largest stretch of contiguous ocean.

“[We were interested in] understanding how that fluctuation of photosynthesis during the day and the absence thereof at night propagates through the microbial community [in the ocean],” explained co-first author Angela Boysen, who did the work as a doctoral student at the UW and is now a postdoctoral researcher at the University of Chicago. “That influences how the ecosystem overall functions, how much carbon is stored, where the carbon moves around, and how organisms might interact with each other.”

“Realizing that various types of microbes acquire nitrogen at different times of day helps to answer a long-standing question in oceanography: How can there be such an incredible diversity of life, all essentially in the same place at the same time?” said co-author Anitra Ingalls, a UW professor of oceanography. “Being able to explain the underlying reasons for this diversity will help oceanographers better predict how these communities may shift as the ocean changes.”

Sacha Coesel, a UW research scientist in oceanography, is also a co-author. The research was supported by grants from the Simons Foundation, the National Science Foundation, Woods Hole Oceanographic Institution and the U.S. Geological Survey.

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