Of Ice and Fish

Sea ice surrounds this terminal glacier of the Greenland Ice Sheet (Source: Lorenz Meire).

Greenland is a landscape dominated by ice. The Greenland Ice Sheet flows into terminal glaciers, which calve into icebergs, which in winter are locked in by sea ice. Ice shapes the entire food web, from ocean microbes to the fish that fuel 90 percent of Greenland’s GDP.

The relationship between glaciers and Greenlandic fisheries just became clearer with the publication of a recent paper in Global Change Biology. The study found that coastal productivity in Greenlandic fjords is determined by whether the glaciers that flow into the fjords terminate on land, or in the sea.

“Many people think that there aren’t so many things happening in the Arctic,” the paper’s lead author, Lorenz Meire, told GlacierHub. “But during the three of four months of real summer, glaciers melt really fast and the fjords are very dynamic,” he said.

Brash ice before a marine-terminating glacier shows evidence of calving (Source: Lorenz Meire).

Meire and his coauthors compared Young Sound, which receives meltwater only from land-terminating glaciers, and southwest Greenland’s Godthåbsfjord, which is fed by melt from three land-terminating and three marine-terminating glaciers. They found that both were shaped by the glacial inputs, which in summer freshen the surface water and create a stratified water column.

Despite these similarities, the researchers found that Godthåbsfjord was far more productive than Young Sound. In summer, a large “bloom” of phytoplankton grows in Godthåbsfjord, supporting a dynamic food web of krill, other zooplankton, small fish, and migrating animals like whales, seals and halibut. In Young Sound, a small bloom during spring occurs. The fjord is quite unproductive during summer, and the waters cannot support such a diversity of animals.

Bottom-feeding halibut are a mainstay of Greenland’s fishing industry (Source: NOAA).

This difference is due to the upwelling of cold, deep, nutrient-rich seawater that occurs in Godthåbsfjord. Melt enters the fjord underwater at the marine-terminating glaciers. Because it is less dense than the surrounding seawater, the freshwater rises buoyantly to the surface, bringing deep seawater up with it. This seawater delivers nutrients like nitrate, a limiting factor for growth in the ocean, to the phytoplankton who live near the water’s surface.

In contrast, there is no upwelling in Young Sound, and as a result the water is nutrient-poor and 12 times less productive than Godthåbsfjord. Walruses and eider ducks, the top predators in Young Sound, feed on shellfish that live on the bottom.

Greenland’s food web is shaped by glaciers even further. Without knowing which type of glaciers flow into a given fjord, one could guess based solely on the number of fishing boats in the area. Halibut fisherman seek the productive waters fueled by marine-terminating glaciers, but this choice comes with risk. “It’s amazing how the fisherman go fishing in regions that are quite dangerous to sail in, but they keep going because there is a lot of fish,” said Meire. Between changeable weather, cold water, dense icebergs, and sea ice in the winter, many hazards threaten the halibut fisherman, who generally work solo in small dinghies. “It’s much easier in land-terminating fjords because there are no icebergs to destroy your boat,” he added.

Greenlandic halibut fishing dinghies are small and open to the elements (Source: Lorenz Meire).

Even from land, it is clear which fjords are only supplied freshwater by land-terminating glaciers and which are home to marine-terminating glaciers. The fisheries are located close to population centers, and Greenland’s big cities are located next to marine-terminating glaciers, according to Meire. “Almost every spot in Greenland where people live or have lived in the past is close to a marine-terminating glacier. People are aware that these regions are very productive, they understand that the glacier is fueling something,” he said.

As global temperatures rise, more marine-terminating glaciers will melt into land-terminating glaciers (Source: Lorenz Meire).

The question, of course, is what will happen to ecosystems, fisheries and towns as climate change turns Greenland’s marine-terminating glaciers into land-terminating glaciers. “It’s scary to see how fast glaciers are retreating,” said Meire, such as in Godthåbsfjord, where the glaciers have moved back 5-8 km in the last five years. Currently, he added, people in Greenland tend to view global warming as a positive thing, which will make winters easier and provide opportunities for more agriculture. Because the impacts for fisheries are so far in the future, the industry has not yet started to act to mitigate the eventual changes.

“For us, climate change is just a fact,” he said. “Everyone accepts what’s happening. We can make people aware that it will have large consequences on our ecosystem and try to stimulate people to take actions against it.”

 

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