Transformations in Southeast Greenland’s marine ecosystem are affecting the distribution of marine species

Two major oceanographic changes have been reverberating through the marine ecosystem in Southeast Greenland: the summer sea ice has virtually disappeared, and sea temperatures have increased. MADS PETER HEIDE-JØRGENSEN describes how this regime shift has affected a number of whale and fish species in the area.

Doing fieldwork in the fjords of East Greenland in the 1980s, we had to be careful to avoid getting trapped in ice in the Greenland Sea. At that time, the ice was notably thick and moving rapidly, posing a high risk to small boats. The conditions then were starkly different from the scenario today, where minimal ice cover is observed along the coast during the summer months.

Time-series data play a vital role in helping researchers to monitor and understand changes in Arctic marine ecosystems, particularly because most of these changes are subtle and can require retrospective analysis. The sea ice that originates in the polar basin is carried from the Arctic Ocean through the Fram Strait, progressing southward along the East Greenland coast until it reaches the southern tip of Greenland. From there, it advances northward along the West Greenland region, where it can be observed in fjords and along the coastline.

Consequently, we can derive an index that quantifies the volume of ice transported through the Fram Strait by examining the presence of this specific type of ice in West Greenland. A continuous record of such observations has been diligently maintained since 1820.

The lack of pack ice in summer, together with a warming ocean, has generated cascading effects on the Southeast Greenland ecosystem that have altered fish populations.

– Mads Peter Heide-Jørgensen, Professor, Greenland Institute of Natural Resources

Unprecedented physical changes

When you analyze this sea ice time-series, a striking trend emerges: the summer sea ice in Southeast Greenland has essentially vanished since 2003. Simultaneously, the temperature of the East Greenland Current south of 73.5°N has undergone a significant upward increase, surpassing 2°C since 1980. Furthermore, the warm Irminger Current, responsible for transporting warm, saline Atlantic water into the region, has experienced a gradual rise in temperature since 1990.

These physical changes have significantly affected the delicate balance of life in the region, and they have far-reaching implications for both the ecosystem itself and the communities that depend on it.

The lack of pack ice in summer, together with a warming ocean, has generated cascading effects on the ecosystem in Southeast Greenland that have altered fish populations, with an influx of boreal species in the south and sub-Arctic capelin further north.

Food chain implications

Further up the food chain, there has been an increase in the abundance of several boreal cetaceans—such as humpback, fin, killer and pilot whales and dolphins—that are either new to the area or now present in historically larger numbers. Most boreal whale species are not well-adapted to dense, multi-year sea ice, and would not have ventured into the coastal areas of Southeast Greenland under past ice conditions. These new cetacean species in Southeast Greenland are thought to be responsible for an annual predation level of two million tonnes of biomass per year.

A key species for predation by some of the migratory marine mammals is the capelin, which in the past two decades has shifted its distribution from the Iceland Sea north of Iceland towards the East Greenland coast and shelf region. The capelin is a cold-water species known to be an important prey of humpback whales in West Greenland and Iceland. A redistribution of capelin alone could explain the increase in humpback whales in coastal areas of East Greenland.

From 2010 to 2019, there was a rapid increase in the population of mackerel in the Irminger Sea and on the East Greenland shelf. This significant growth can be attributed to various factors, including rising summer sea temperatures. But competitive interactions with other species that have also been affected by the physical transformations in the region play a role too.

Finally, the presence of bluefin tuna, which feed on schools of mackerel, was first observed in waters near East Greenland in 2012. These sightings occurred consistently until 2018, mainly as a result of incidental catches in mackerel fisheries. The increased sea temperatures and expanding area of open water have likely contributed to the expansion of thermal habitats that are suitable for both the tuna and the mackerel.

Warmth chasing other species further north

In contrast, there has been a decline in the abundance and catch of narwhals and walrus in Southeast Greenland, indicating that these species, which are not just cold-tolerant but ice-dependent, are facing challenges. Additionally, the abundance of polar cod in the East Greenland and Iceland areas has decreased as temperatures have risen. As summer ice continues to disappear, we expect that the southern range limit of this keystone species in Southeast Greenland will shift north.

The observed regime shift in Southeast Greenland’s marine ecosystem is a clear indication of the ongoing changes taking place in the Arctic. But it is likely the initial manifestation of a more widespread scenario that will increasingly characterize the region.