Arctic kelp forests mapped from light on the seafloor — new method reveals hidden biomass potential

A new study has produced the first large-scale method to predict where kelp forests could grow along Arctic coasts. These underwater forests are vital to coastal food webs and carbon cycling, yet their distribution is poorly known.

The team of researchers, including Pedro Duarte from the iC3 Polar Research Hub, developed a simple but powerful way to estimate potential kelp extent and lower-depth biomass from how much light reaches the sea floor. This approach gives scientists and managers a first baseline of where kelp might grow and how much it could contribute to local ecosystems — and how these patterns might change as climate-driven light conditions shift. 

Figure: Predicted kelp presence in the upper depth range (UDR; colored green) and predicted kelp summer biomass in the lower depth range (colored yellow to red). Credit: de la Guardia et al. (2025), Limnology and Oceanography Methods.

From local measurements to regional predictions

The international team tested the method in Kongsfjorden, a fjord on the Norwegian archipelago of Svalbard. There they had detailed measurements of seafloor irradiance — the amount of sunlight that reaches the seabed — and kelp biomass across different depths. 

From this data, they built an empirical model that predicts the deepest limit of kelp and the potential biomass where light is abundant enough for photosynthesis. 

Encouragingly, when this model was applied to six other Arctic fjords, its predictions matched published estimates of kelp biomass. 

Pedro Duarte, iC3 researcher and co-author of the paper, explained why this is an important step forward: 

“We now have a method to map potential kelp habitat across vast stretches of Arctic coastlines where direct underwater surveys are lacking. This gives us a baseline to understand how these ecosystems might respond to changing light conditions as sea ice decreases, freshwater inputs from glacier melting increase, and water clarity shifts.”

The approach does not yet capture all biological and physical constraints, such as the availability of suitable seabed substrate, but it provides a valuable first estimate. 

Duarte highlighted the simplicity and utility of the approach:

“By focusing on light and depth, we can create first-order maps of potential kelp biomass across regions where we have satellite or modelled light data. It’s not a perfect picture, but it’s a huge step toward understanding these ecosystems at scale.” 

Broader implications for Arctic ecosystems and climate

Understanding where kelp forests could occur has wide ecological and climate relevance. Kelp forests provide habitat and food for a range of species, from tiny invertebrates to fish. They contribute to carbon cycling by fixing carbon through photosynthesis and transferring it into food webs and, eventually, to sediments.

This model is especially timely as with retreating sea ice and increases in freshwater inputs, the light reaching seafloor is changing. Knowing where kelp could potentially thrive helps set expectations for future ecosystem change. 

Read more

The study “Predicting potential Arctic kelp distribution and lower-depth biomass from seafloor irradiance” is available open access in Limnology and Oceanography Methods.

Lead author Laura Castro de la Guardia is a researcher at Scottish Association for Marine Science.

Pedro Duarte is a researcher at the Norwegian Polar Institute and at the Department of Geosciences at UiT The Arctic University of Norway. His research focuses on developing coupled physical-biochemical models to simulate the complex interactions between oceanic and sea ice processes.

Pedro is currently inviting expressions of interest from potential MSCA postdoctoral candidates who want to work on coupled physical-biochemical models of the interactions between glaciers and oceans, with a focus on the European Arctic. Please see here for more information.