Although the term 'glacial' usually implies an exceedingly slow progression, researchers have discovered that ice masses can accelerate and decelerate on both daily and hourly timescales. These rapid shifts are tied to fluctuations in air temperature, rainfall, and ocean tides.
A team from Japan's Hokkaido University tracked a Greenland glacier over six summer seasons, measuring how local weather and tides influenced its speed. Their findings, now available in The Cryosphere, shed new light on dynamic factors driving glacier flow.
"Short-term speed variations are key to understanding the physical processes controlling glacial motion, but studies are sparse for Greenlandic tidewater glaciers, particularly near the calving front," says Hokkaido University's Shin Sugiyama, who led the study. "Studying glacier dynamics near the ocean boundary is crucial to understanding the current and future mass loss of the ice sheet."
To investigate, the researchers focused on Bowdoin Glacier (Kangerluarsuup Sermia), a tidewater glacier situated in northwestern Greenland. Like many others across the region, it has exhibited thinning and substantial retreat since 2008. Throughout multiple summers, GPS instruments installed at intervals ranging from 500 meters to four kilometers from the calving front measured its motion. Concurrently, nearby sensors monitored air temperature and rainfall. In total, 90 days of data were collected between 2013 and 2019.
The data showed that the glacier's pace accelerated both once and twice each day. The single daily increase largely coincided with warmer daytime air triggering greater meltwater flow, while the twice-daily surge was more obvious closer to the calving margin and appeared to correspond with tidal shifts. In fact, the glacier tended to reach top speeds just before or during low tide.
In addition to these routine changes, researchers identified one or two episodes each summer in which the glacier sped up dramatically in response to exceptionally warm conditions or intense rainfall. "The correlations between ice speed and temperature demonstrate the strong influence of meltwater production on the dynamics of a Greenlandic outlet glacier," notes Sugiyama.
Speeds rose even faster whenever air temperatures topped 10 degrees C, and the time between peak heat and maximum ice velocity was a mere two hours, indicating rapid drainage of meltwater to the glacier bed. However, the effect of rainfall on ice flow proved more complicated, likely influenced by interactions between tide levels and the subglacial drainage network. "Our results provide important insights into tidewater glacier dynamics and contribute to an accurate understanding of future evolution of the ice sheet under a changing climate and environment in Greenland," Sugiyama says.
Research Report:Ice speed of a Greenlandic tidewater glacier modulated by tide, melt, and rain
Related Links
Hokkaido University
Beyond the Ice Age
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