New study: Long term monitoring data shows that Svalbard fjord is a nutrient and carbon sink

A study by researchers from the iC3 Polar Research Hub shows that Kongsfjorden — a glacial fjord on Svalbard’s west coast — acts as a significant sink for both nitrogen and carbon.

The study, led by researcher Pedro Duarte, reveals that the fjord’s ecosystem absorbs more carbon and nitrogen than it releases.

Picture: Kongsfjorden from sky (Sentinel 2 image 31 August 2025). Credit: European Union.

The study contributes to our understanding of how Arctic coastal waters may respond to rapid climate change, with implications for the ecological health of Arctic marine systems and global carbon cycles.

What the study found

The research team analysed ten years of environmental data from Kongsfjorden to investigate how nutrients and carbon move through this fjord ecosystem. 

The team focused on what scientists call Net Ecosystem Metabolism — the balance between the creation of organic matter (which requires nutrients and removes carbon dioxide) and its breakdown (which releases carbon dioxide). 

Using a combination of traditional monitoring measurements and ocean circulation models, the team was able to build a full nitrogen budget and distinguish biogeochemical changes from physical mixing of different water masses.

The results show that nutrients and dissolved inorganic carbon are taken up within the fjord. The primary sources of these elements are the adjacent continental shelf sea, rather than rivers or terrestrial runoff.

Figure: Daily average nitrogen fluxes (tonnes N d−1) and ranges calculated for the period 2011–2023. Fluxes are calculated for the whole year. Values correspond to dissolved inorganic nitrogen (DIN = nitrate + nitrite + ammonia), N2, dissolved organic nitrogen (DON), and particulate organic nitrogen (PON) from phytoplankton (Phy) and zooplankton (Zoo) or seabird prey as specified in the panels. Figure modified from Duarte et al. (2025), Sci Rep 15, 22946.

Across multiple years, Kongsfjorden consistently exhibited a net drawdown of nitrogen and carbon, indicating that biological processes — such as phytoplankton growth — dominate and give the fjord a net sink character.

Pedro Duarte, lead author of the study, says:

“We were surprised by how consistently Kongsfjorden takes up nitrogen and carbon over time. It shows that Arctic fjords can play a much stronger role in regulating biogeochemical cycles than we often assume.”

Why this matters for the Arctic and beyond

Fjords like Kongsfjorden are interfaces between glaciers, open seas, and marine ecosystems. If these fjords shift toward releasing more carbon or nutrients as they warm, regional and global environmental change could further accelerate.

Pedro Duarte adds:

“Understanding how carbon and nutrients move through this system helps us see how Arctic coastal ecosystems may change as warming alters circulation, ice cover and biological activity.”

By showing that Net Ecosystem Metabolism can be estimated using widely available environmental data, Duarte and co-workers also demonstrate a practical path forward for long-term monitoring of ecosystem function in remote and changing polar regions.

Broader implications for polar science and policy

As the Arctic continues to warm at rates far above the global average, understanding how marine ecosystems respond to change is critical. The methods and findings from this study provide a framework for assessing other fjords and coastal systems.

For scientists and policymakers, having a simple, integrative measure like Net Ecosystem Metabolism that can be tracked over time offers a powerful tool for detecting ecosystem shifts before they become pronounced.

For early career researchers, this work highlights how combining sustained field observations with thoughtful analytical approaches can yield insights into ecosystem-scale processes that would otherwise remain hidden.

About the paper and the authors

The study “Ecosystem metabolism and nitrogen budget of a glacial Fjord in the Arctic” was published in Nature Scientific Reports and is available here.

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.

Philip Assmy is a researcher at the Norwegian Polar Institute and at the Department of Geosciences at UiT The Arctic University of Norway. His work focuses on understanding the complex interactions between ice and ocean systems and their impact on marine ecosystems, particularly in the rapidly changing Arctic and Antarctic regions.