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Scientists have produced the first remote sensing analysis of how water clouded by sediment in glacier meltwater moves on the surface of Kachemak Bay. The bay on Alaska’s Kenai Peninsula is home to a rich variety of marine life that can be affected by the sediment.

Work led by Lea Hartl of the Alaska Climate �鶹���� Center at the �鶹���� Fairbanks Geophysical Institute helps explain how surface turbidity, or cloudiness, from glacial meltwater spreads in the bay throughout the year.

For Hartl, a glaciologist and climatologist, the research revealed the strong connection between glaciers and marine life.

“It was really interesting to see how direct the impacts of glacial runoff are on the marine ecosystem,” she said.

The work was published Jan. 3 in .

Surface glacial turbidity affects an average of 56 to 60 square miles of Kachemak Bay — about one-quarter of the bay — in July and August, Hartl found. Plumes originating at Grewingk Creek, at the Portlock Glacier stream and at the head of the bay frequently merge and spread across the entire inner bay during peak melt season, the authors write.

Plumes classified as “very high turbidity” and showing the cloudiest water surfaces occur near freshwater outflows and can cover nearly 2 1⁄2 square miles at the height of melt season, the research shows. Hartl’s research did not look at subsurface turbidity.

The analysis results from a new remote sensing method devised by Hartl and colleagues at several institutions. That method uses hyperspectral camera imagery to complement data already being gathered by satellites for several decades.

“Plumes have been mapped using various kinds of remote sensing imagery in different regions of the world but not previously in Kachemak Bay,” Hartl said. “Hyperspectral imagery of ocean water is generally rare, especially in high-latitude waters.”

Hartl is the lead author. UAF coauthors include assistant research professor Carl Schmitt, climate center director Martin Stuefer and professor Regine Hock of the Geophysical Institute. Others are from the �鶹���� Anchorage, U.S. Geological Survey, contractor KBR Inc. and the University of Oslo.

“We wanted a fairly automatic way to map these turbidity plumes to see where they are, how big they are and what the seasonality is,” Hartl said. “Hyperspectral imagery gives us very detailed, high-resolution information, and we looked for ways to leverage that to improve how we can map turbidity plumes in remote sensing data from satellites.” 

Hyperspectral cameras image an area in hundreds of wavelengths, including in many colors not visible to the human eye. That differs from consumer-grade cameras, which typically only image in red, green and blue.

Hyperspectral imagery produces a spectral signature of an object, revealing greater detail. Spectral signatures can be used to distinguish among different minerals, plant species or tissue types. They can define the geological makeup of glacial runoff.

Kachemak Bay turbidity imagery came from nine airborne surveys by the Geophysical Institute’s and flown by Stuefer. Flights occurred in the summer and early fall from 2019 to 2021. 

“Alaska's glaciers contribute approximately 75 billion tons of freshwater to the coastal margins every year,” Stuefer said. “That’s enough to fill Lake Erie in the Great Lakes every six and a half years.”

“Coastal waters and ecosystems of Kachemak Bay are changing due to climate change, and our data offer a baseline,” he said.

Freshwater input from glacial runoff significantly affects water quality parameters like salinity, temperature and nutrient content, especially during warmer months when glacial melting is at its peak. 

Knowing more about how glacial plumes and surface turbidity spread from river mouths into Kachemak Bay can add to knowledge about the bay’s ecosystem.

Cloudy water creates challenges for species reliant on habitats they can see. The sediment-rich glacier runoff also changes the ocean’s nutrient and light availability. Those changes can alter plankton distribution and affect organisms such as kelp that are central to the marine food web, the authors write.

This glacial flour eventually falls to the seafloor. That in turn can affect creation of kelp forests, which host a variety of fish and invertebrates and are an important hunting ground for sea otters, by impacting how well kelp spores can settle and grow.

“I enjoyed learning about subjects I usually don't work with, like marine life, and collaborating with colleagues from different fields,” Hartl said of the study. “We had experts on aerial hyperspectral surveying, hydrology, satellite data analysis and glaciologists. It was cool to see these different parts come together.”

The research was funded through the National Science Foundation’s Established Program to Stimulate Competitive �鶹���� and by the state of Alaska.

ADDITIONAL CONTACTS: Lea Hartl, lbhartl@alaska.edu; Martin Stuefer, mstuefer@alaska.edu

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