A study by the University of Alaska Fairbanks (UAF) quantified carbon dioxide (CO2) emissions and uptake in two marine algae farms located in the Gulf of Alaska during the 2023–2024 growing season. The findings revealed mixed results: one of the farms contributed to a slight decrease in CO2 in its local environment, while the other caused an increase.
Seaweed farms in Alaska are considered a potential option for reducing local CO2 levels and contributing to climate action, but this research showed that their effects are ambiguous.
“It’s easy to get carried away by the idea that seaweed is going to change the world, but ultimately we want to be honest with the public,” Amanda Kelley, a professor and researcher in the UAF College of Fisheries and Ocean Sciences and a study co-author, said adding, “It’s a very complex issue, and there are many factors that affect seaweed’s ability to achieve this.”
Published in June in the journal Ocean Science, the study found that during the season studied, the farms alternated between absorbing and releasing CO₂ depending on sunlight, tidal exposure, and respiration by marine life.
The study, in detail
Researchers from the UAF quantified CO2 flux between the air and the ocean at two seaweed farms in the northern Gulf of Alaska, which had different oceanographic conditions and cultivation practices. The goal: to determine the potential for carbon sequestration during the growing season.
To do this, they installed sensors on buoys inside and outside the farms in Windy Bay, near Cordova, and in Kalsin Bay on Kodiak Island. This allowed them to collect data on ocean oxygen levels, pH, temperature, salinity, and water chemistry—a detailed, hour-by-hour record from seeding to harvest of the seaweed.
According to the study, in Windy Bay, differences in carbonate chemistry parameters were detected between the inner and outer moorings from November through March, at which point the partial pressure of CO₂ in the seawater inside the farm decreased relative to the reference site.
In Kalsin Bay, by contrast, the inner mooring showed winter values for the partial pressure of CO₂ in seawater that were 100 µatm (microatmospheres) higher than those recorded at the outer mooring.
It is estimated that this may be due to the colonization of a biofilm on the algae lines while the young sporophytes were not yet mature. However, the values at both moorings converged in the spring.
The results
A comparison of water mass movements at the inner and outer moorings confirmed that both sets of sensors detected similar water masses. This made it possible to calculate the integrated net air-to-sea CO2 flux.
“Salinity remained relatively constant during the deployment period, while the temperature at both sites decreased from winter through early spring, before warming up again,” the study explains.
Regarding warming, in Kalsin and Windy Bays, cross-correlation analyses were conducted to examine the relationship between salinity and temperature. In Kalsin Bay, a one-hour lag was observed in salinity and no lag in temperature. In Windy Bay, however, both variables showed a one-hour lag.
These findings suggest a striking similarity in water characteristics between the inner and outer mooring areas of both bays.
The Windy Bay farm recorded a modest decrease in marine atmospheric carbon dioxide levels in its vicinity, while the Kalsin Bay farm experienced an increase.
Although measurements at both farms will continue for at least two more years, the first season has revealed that the process of carbon uptake and release in algal farming is unexpectedly complex and surprising.
“The farms aren’t necessarily causing any harm, but we shouldn’t overstate the idea that they’re going to save us from climate change,” Josianne Haag, the project leader, said.
