Beneath Greenland's icy expanse, a groundbreaking discovery challenges conventional wisdom and could significantly impact global sea-level predictions. Researchers at the University of California, San Diego (UC San Diego) have uncovered a previously unknown layer beneath the Greenland ice sheet, one that may accelerate the flow of ice towards the ocean under warmer conditions. This revelation, detailed in the study 'Seismic evidence of widespread sediments beneath the Greenland Ice Sheet,' published in the peer-reviewed journal Geology, highlights the critical role of subsurface conditions in glacier movement. The findings underscore the potential for rapid sea-level rise if these soft basal layers are prevalent and respond to warming temperatures.
The study, led by geophysicist Yan Yang, employed seismic waves from earthquakes to map the subsurface beneath the ice sheet. By measuring the time it took for these waves to travel through the Earth, the team could differentiate between hard bedrock and softer, more flexible sediments. This distinction is crucial because the ice's movement is highly dependent on the underlying terrain. The research challenges the long-held belief that surface melting is the primary cause of Greenland's ice melt, instead emphasizing the significance of conditions below the surface in determining the speed of glacier movement towards the coast.
Satellite data reveals that Greenland's ice sheet has already contributed approximately 0.43 inches (1.1 centimeters) to global sea levels from 1992 to 2018. The new findings suggest that sea levels could rise more rapidly in the future if these soft basal layers are common and respond to warming temperatures. The study's key insight is that even seemingly stable regions may be more vulnerable than previously thought, as seismic data indicates that conditions could facilitate rapid movement once specific temperature thresholds are met.
The researchers emphasize the importance of accurate forecasts for the safety of coastal communities. Knowing whether the ice bed is composed of hard rock or soft sediment is essential for refining future sea-level change predictions. The study reveals that soft sediments can act as a lubricant, enabling ice to slide more easily, and that ice movement may be more influenced by subsurface conditions than by air temperature alone. During warmer periods, meltwater can drain through vertical shafts, known as moulins, directly to the bottom of the ice sheet, further reducing friction and accelerating ice flow.
The implications of this research extend beyond Greenland, as many ice sheets worldwide rest on complex and poorly understood bases. If soft sediments are more prevalent than assumed, it may necessitate revising global sea-level rise estimates. The study underscores the importance of better subsurface mapping for both scientific understanding and practical applications, such as coastal planning, infrastructure investment, and climate adaptation strategies, all of which rely on precise predictions of future sea levels.
