Marine heatwaves, periods when ocean temperatures stay unusually high for days or weeks, are becoming more common in Arctic waters. A new study shows that around the Svalbard Archipelago; these events now occur more often and last longer than they did just a decade ago.
Marine heatwaves are known to affect marine ecosystems worldwide, but detailed studies in the Arctic are still limited. This is particularly true for heatwaves below the ocean surface. The waters around Svalbard are of special interest, as they lie at the boundary between warm Atlantic currents and colder Arctic waters.
More frequent and longer-lasting events
By analysing ocean temperatures from 1991 to 2022, the researchers found a clear increase in both the frequency and duration of marine heatwaves around the Svalbard Archipelago during the last decade. In some areas, events now occur several times each year.
The strongest changes in duration were detected west of Svalbard. Since around 2011, long-lasting summer marine heatwaves have become more common in this region, with some events lasting close to a month. Several of these heatwaves covered wider areas, including large parts of the Barents Sea.
While the peak temperatures during individual events have changed little, longer duration means that the ocean remains unusually warm for extended periods of time.
Heatwaves are not just at the surface
A key contribution of the study is that it also investigates what happens below the ocean surface. Several of the long-lasting summer marine heatwaves extended deep into the water column, in some cases reaching several hundred metres below the surface.
Subsurface marine heatwaves are still poorly studied in the Arctic. By showing how both surface and subsurface events can be identified and analysed, the study provides new insight into how heatwaves develop and persist in this region.
Ocean currents are the main driver
To understand what causes marine heatwaves around Svalbard, the researchers examined both atmospheric heating and heat transported by ocean currents. Their results show that for most prolonged events west of Svalbard, heat carried by ocean currents plays a greater role than heat input from the atmosphere.
Warm Atlantic water flowing northwards brings large amounts of heat into the region, helping to trigger and maintain marine heatwaves. Atmospheric conditions still contribute, particularly at the onset of events, but ocean heat transport is the dominant driver for most of the long-lasting heatwaves identified in the study.
Why this matters
The waters around Svalbard support productive ecosystems and important fishing grounds, and commercial fishing takes place throughout much of the region. Knowing where marine heatwaves occur, how deep they reach, and how widespread they are can provide useful information for fisheries and ecosystem management.
The results are also relevant for policy makers. Svalbard is included in one of Norway’s Ocean Management Plan areas, and improved knowledge of marine heatwaves can support long-term planning in a rapidly warming Arctic ocean.
As climate change continues to affect the Arctic, marine heatwaves are expected to become more common. This study provides new insight into how these events are developing around Svalbard, and into the processes that drive them.
Key researchers: Marianne Williams-Kerslake, Helene R. Langehaug, Annette Samuelsen, Noel Keenlyside
