Rising Frequency and Duration of Marine Heatwaves Around Svalbard

Over the past few decades, marine heatwaves have become increasingly common in Arctic waters.

The phenomenon occurs when sea temperatures remain unusually high for several days or weeks, which can have significant impacts on vulnerable ecosystems.

For a long time, detailed studies on this in the Arctic have been lacking. However, a new study now shows that such warm periods around Svalbard are occuring both more frequently and lasting longer than before.

Dramatic increase

Using the ocean and sea ice forecasting system Topaz, researchers at the Nansen Center analysed sea temperatures in the period from 1992 to 2022.

"During the first 20 years, we didn't see particularly major changes. But over the last ten years, we saw a sharp increase," researcher and lead author of the study, Marianne Williams-Kerslake, told Science Norway.

In certain areas around Svalbard, marine heatwaves now occur multiple times a year.

Furthermore, they are not only occuring more often, but they are also lasting longer, Williams-Kerslake explains.

"The average duration increased from around 14 days to approximately 22 days," she says.

Below the surface

The changes are particularly evident west of Svalbard, where long-lasting summer heatwaves have become far more common since 2011.

Some events lasted nearly a month, and several heatwaves extended across large parts of the Barents Sea.

It is not necessarily peak temperatures that are increasing the most, but rather the total duration the ocean remains unusually warm.

The study also reveals that these heatwaves reach deeper than previously assumed.

Researchers noted that some of the prolonged warm periods extended several hundred metres below the surface.

The main driver

To identify the cause, researchers examined both atmospheric warming and heat supplied by ocean currents.

The results show that warm Atlantic water flowing northward is the primary driver behind the prolonged heatwaves west of Svalbard.

In many cases, it is precisely this inflow that sustains the elevated temperatures.

The marine areas sorrounding Svalbard are among the most productive in the Arctic, and temperature shifts can carry consequences for both ecosystems and fisheries.

What qualifies as a marine heatwave is evaluated against a 30-year reference baseline. As ocean temperatures rise, determing what actually constitutes a heatwave becomes increasingly complex.

"What was once considered an extreme event may eventually become the new normal," Williams-Kerslake explains.