Rising Frequency and Duration of Marine Heatwaves Around Svalbard

Researchers at the Nansen Center have found that marine heatwaves in the seas around Svalbard are becoming more frequent and are lasting longer. In some parts of the area they now take place several times a year. The results come from a new study, and the lead author spoke about it to Science Norway.

The team used Topaz, a forecasting system for the ocean and sea ice, to analyse sea temperatures from 1992 to 2022. Researcher Marianne Williams-Kerslake, the lead author, said the first 20 years showed no particularly large changes, but the last 10 years brought a sharp increase. She said the typical length of an event rose from around 14 days, reaching approximately 22 days.

The change is clearest west of Svalbard, where since 2011 long summer heatwaves have occurred much more often. Some lasted close to a month, and several spread across large parts of the Barents Sea. According to High North News, the biggest increase is not necessarily in peak temperatures but in the total time the ocean stays unusually warm. Some long episodes also extended several hundred metres below the surface, deeper than earlier assumed.

To find the cause, the researchers looked at warming of the atmosphere and at heat brought by ocean currents. They concluded that warm Atlantic water moving north is the main driver of the long heatwaves west of Svalbard, and that this inflow often keeps temperatures high.

A marine heatwave is a period when sea surface temperatures stay higher than usual for several days or weeks. Detecting one means setting each day's sea temperature against long-term normal values. A 30-year reference baseline is used, and High North News says that as the ocean warms, deciding what counts as a heatwave becomes more complicated. Williams-Kerslake said that events once regarded as extreme could in time turn into the normal state. High North News adds that heatwaves are expected to grow in frequency and extent because of global warming, and that rising temperatures harm marine ecosystems, with effects for fishing and aquaculture.