Seals use icebergs as essential platforms in glacier ecosystems

Seals use icebergs as essential platforms in glacier ecosystems
by Clarence Oxford
Los Angeles CA (SPX) Dec 11, 2024
Harbor seals in icy regions rely on icebergs from glaciers as safe platforms for birthing, raising pups, and molting. A new study reveals how climate-driven changes to glaciers impact these critical habitats. Researchers found that stable, slow-moving icebergs are preferred during pupping, while faster-moving icebergs near feeding areas are more suitable during `molting.

"Our work provides a direct link between a glacier's advance and seals' distribution and behavior," said Lynn Kaluzienski, a postdoctoral fellow at the University of Alaska Southeast and the study's lead author. "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 will share the findings at the AGU 2024 Annual Meeting in Washington, D.C., on Tuesday, December 10. This event, held from December 9-13, gathers over 30,000 scientists to explore advancements in Earth and space science research.

The research focused on harbor seals in Johns Hopkins Inlet and Glacier in Alaska's Glacier Bay National Park. Unlike many glaciers retreating due to global warming, Johns Hopkins Glacier is advancing, thanks in part to its terminal moraine, a natural barrier of crushed rock and sediment. This barrier protects the glacier from warmer ocean waters that would accelerate melting but also reduces the number of icebergs it sheds, limiting seal habitat.

To better understand how seals use available icebergs, Kaluzienski and collaborators from the University of Alaska Southeast and the U.S. National Park Service conducted detailed studies using time-lapse cameras and aerial surveys.

"Icebergs are found throughout the fjord in regions of fast flow, within eddies, and close to the glacier," said Kaluzienski. "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."

When icebergs break away, their movement is influenced by wind, currents, and freshwater runoff from the glacier's base. This runoff, or plume, is more buoyant than the surrounding saltwater and brings plankton and fish to the surface, creating a dynamic feeding area for seals.

By combining remote sensing data with field observations, researchers tracked the relationship between seals, icebergs, and these nutrient-rich plumes. During June's pupping season, seals preferred icebergs moving slower than 7-8 inches per second, which likely provided more stability for newborn pups. In contrast, during August's molting season, seals were more frequently found on faster-moving icebergs near the plume, where foraging opportunities were abundant.

The study highlights the importance of stable icebergs for seal survival during critical life stages and the potential challenges posed by declining iceberg availability as glaciers respond to climate change.