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Scientists have learned that seals ride icebergs strategically to scoot around Earth’s seas. They’ve learned that seal moms in icy parts of Earth’s globe use icebergs shed by glaciers as safe platforms to give birth and care for their young. The moms prefer stable, slower-moving bergs when caring for their newborn seal pups. Then, in the molting season, the moms and the rest of the seal population appear to move to speedier ice near the best foraging grounds. So, seals opt for different types of icebergs, depending on the time of year and their purposes. That’s according to a new study presented at this week’s American Geophysical Union meeting in Washington, D.C.
Lynn Kaluzienski, a postdoctoral fellow at the University of Alaska Southeast, shared her findings about seals and icebergs on December 10, 2024.
She explained how climate change affects glaciers and, consequently, the icebergs and seals that depend on these large blocks of ice in their daily lives.
When an iceberg breaks off from a glacier, its speed and trajectory are affected by many factors, including wind, ocean currents and freshwater runoff flowing from a glacier’s base. For example, a jet of fresh water, called a plume, is more buoyant than salty ocean water in a fjord, which is a inlet to the sea with steep sides or cliffs, often created by glaciers. The freshwater plume brings plankton and fish to the water’s surface, creating a moving buffet that seals can eat while riding aboard the icebergs.
The researchers used remote sensing data to find these plumes and compared them to where icebergs and seals were found during the pupping season in June and molting season in August.
They found that during the pupping season, seals were more likely to be on slow-moving icebergs, with speeds slower than 7 to 8 inches (about 0.2 meters) per second. In contrast, during the molting season, seals were increasingly likely to be on faster-moving icebergs, in or near the plume.
The study focused on harbor seals and icebergs in Johns Hopkins Inlet and Glacier, located in Glacier Bay National Park, Alaska. Johns Hopkins is one of the few glaciers on Earth that is getting thicker and flowing into the fjord instead of retreating due to global warming.
This is due, in part, to its terminal moraine. A terminal moraine consists of crushed rock and other sediments blocking the front of the glacier from warmer ocean water, which would increase the rate of melt.
But that wall of sediment reduces the number of icebergs the glacier dumps into the fjord. Fewer icebergs means less habitat for seals, so it’s crucial for researchers to understand how seals use the icebergs they have at their disposal.
New research shows that as glaciers change with the climate, the resulting changes in size, speed and number of icebergs affect the seals’ icy habitat.
Kaluzienski, university colleagues, and collaborators from the U.S. National Park Service spent the past few years documenting variations in iceberg and seal distribution in the fjord. They used time-lapse cameras and aerial photographic surveys.
According to Kaluzienski:
Our work provides a direct link between a glacier’s advance and seals’ distribution and behavior. Interdisciplinary studies like this one coupled with long-term monitoring campaigns will be important to understand how climate change will influence tidewater glacier fjord ecosystems in the future.
Kaluzienski added:
Icebergs are found throughout the fjord in regions of fast flow, within eddies, and close to the glacier. We wanted to understand which of these areas seals were using and how this habitat is changing in response to advances at the glacier front and reduction in iceberg numbers.
Bottom line: Surfers love to ride waves, and seals prefer to ride icebergs … but not any iceberg. Depending on the time of year, they prefer steady, slow icebergs and other times fast ones.
Read more: Carnivorous wolves have a sweet tooth: Lifeform of the week
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