New study: Glacier floods do not always deliver the nutrients Arctic fjords need

As Arctic glaciers melt, they release freshwater into the surrounding ocean, carrying nutrients that can support marine life. But the effects of this runoff are more complicated than scientists once thought.

New research, co-authored by Philipp Assmy and Allison Bailey from the iC3 Polar Research Hub, shows that what happens beneath a glacier can determine how much of these essential nutrients ultimately reaches the fjord. It investigates a glacier lake outburst flood in 2021, when Lake Setevatnet drained beneath Kongsvegen glacier into Kongsfjorden, on Svalbard's west coast.

Following nutrients from glacier to ocean

Marine algae need nutrients such as nitrate and silicate to grow. Glacier runoff can transport these nutrients directly into fjords, while glacial meltwater rising at the front of marine-terminating glaciers can also draw nutrient-rich deep fjord water towards the surface, potentially supporting marine productivity.

To investigate these processes, the research team combined field observations with frequent water sampling from the lake, the glacier and the fjord along with seismic data and satellite observations throughout the summer of 2021. They tracked how changes in the drainage system beneath the glacier influenced the supply of nutrients to the ocean.

Early in the summer, when water flowed through a less efficient drainage system, runoff delivered nitrate and silicate directly to the fjord. As melting increased, channels developed beneath the glacier, producing a buoyant plume that drew deeper, nutrient-rich seawater upwards.

However, the subsequent lake outburst flood did not produce the expected increase in nitrate concentrations in the fjord. This suggests that nitrogen was being transformed beneath the glacier as floodwater travelled towards the fjord.

What happens beneath the ice matters

The findings highlight the importance of processes that are difficult to observe but can influence the chemistry of Arctic coastal waters. Although glacier floods can substantially increase the amount of nitrogen transported towards a fjord, biological and chemical transformations beneath the ice may change how much remains available to marine algae.

Philipp Assmy, iC3 researcher and co-author of the study, says:

“Glacier meltwater is not simply a delivery system for nutrients. What happens beneath the ice can fundamentally change the chemistry of the water reaching the ocean, with consequences for marine productivity and the wider food web.”

As the Arctic warms and glacier melt intensifies, understanding these processes will become increasingly important. The study demonstrates that predicting how glaciers influence marine ecosystems requires more than measuring the volume of freshwater they release: scientists must also understand how subglacial drainage systems evolve and how nutrients are transformed along the way.

Find out more

The study, The Impact of Subglacial Drainage System Evolution and Glacier Lake Outburst on Arctic Fjord Macronutrient Dynamics, was published open access in Journal of Geophysical Research: Biogeosciences.

Lead author Andreas Alexander is glaciologist at the Norwegian Water Resources and Energy Directorate. 

Co-author Philipp Assmy is a researcher at the iC3 Polar Research Hub based at the Norwegian Polar Institute in Tromsø, Norway. Within iC3, he leads the Research Unit 3: Ice sheets and the oceans where he studied the consequences on ice sheet retreat on polar marine ecosystems. To find out more about his research, read his interview, or contact him by email.

Co-author Allison Bailey is a researcher at the iC3 Polar Research Hub based at the Norwegian Polar Institute in Tromsø, Norway. Within iC3, she is part of the Research Unit 3: Ice sheets and the oceans. To find out more about her research, check out her list of publications, or contact her by email.