Long-term study hopes to unlock secrets of Gulf of Alaska ecosystem

After more than a month apart, Gretel and Shackleton began their reunion with a slow dance. 

The autonomous underwater vehicles circled each other in the Gulf of Alaska in April, gathering data about ocean conditions: temperature, light, salinity, chlorophyll, fluorescence, and even acoustically determined densities of fish and zooplankton.

The torpedo-shaped vehicles, known informally as gliders, met after taking separate journeys to the middle of the continental shelf south of Seward, about 70 miles offshore. Seth Danielson, a University of Alaska Fairbanks oceanographer, expects it to become a spring ritual.

Shackleton and Gretel made their first transects in the gulf in 2021 and 2022, respectively, repeating the process again this year. With each new data set, Danielson’s team at the UAF College of Fisheries and Ocean Sciences expects to better understand how weather and climate are affecting crucial components of the gulf’s ecosystem.

The project, funded by the Alaska Ocean Observing System, focuses specifically on conditions that trigger the spring phytoplankton bloom, an annual explosion of oceanic microscopic life. Dormant phytoplankton begin to grow as sunlight increases each spring, reproducing rapidly until water in the Gulf of Alaska has a greenish tint. The onset of the bloom triggers a feast for the ocean food web.

A better understanding of phytoplankton will be of particular interest to fishery managers like the North Pacific Fishery Management Council, Danielson said. Both the timing and species composition of the bloom are linked to the health and size of fish populations.

Danielson said the data could eventually serve as an “early warning system” when fish populations are subject to unfavorable ocean conditions.

“We’ll be able to tell the NPFMC if the spring bloom is early or late, or strong or weak,” Danielson said. “As the technology improves we eventually will be able to assess and track measures of food quality for the fishes.”

Satellites can monitor ocean surface conditions, and equipment aboard research vessels is able to collect water and biological samples. But the battery-powered gliders operate for just a tiny fraction of the cost and can remain at sea for up to 3 months at a time, sampling across vast areas and transmitting the data back to Danielson’s lab in Fairbanks.

The use of gliders is relatively new in Alaska waters. Such surveys are fairly common in coastal areas in the Lower 48, but Gretel and Shackleton currently have the northern Gulf of Alaska to themselves. The planned glider study will be conducted each spring in coming years, providing more insight into how ocean conditions affect the timing and progression of the phytoplankton bloom.

Even with just a few datasets, researchers have already noticed significant year-to-year differences in ocean conditions and how the phytoplankton respond. With each additional spring transect, they will better reveal cause-and-effect relationships.

“It’s a lot of active piloting, but we’re learning a tremendous amount about the ocean by doing this,” said Hank Statscewich, an oceanography researcher on the project. “This is a new way to explore the ocean with a unique combination of cutting-edge instrumentation with persistent monitoring and real-time feedback.”

ADDITIONAL CONTACT: Seth Danielson, 907-474-7834, sldanielson@alaska.edu

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