Radar imagery procured deep beneath the Greenland ice sheet has revealed intriguing, stream-like structures disrupting the stratified layers that have accumulated over eons.
More than a decade after their initial detection, researchers appear to have pinpointed the genesis of these formations, and the finding is quite stunning. Calculations suggest these “plumes” bear a strong resemblance to convection—vigorous churning associated with upward heat transfer commonly linked to scorching magma “boiling” beneath the Earth’s crust. The findings from this research were published in the journal The Cryosphere.
“The possibility of heat transfer via convection within the ice sheet runs somewhat contrary to our typical intuitions. However, ice is at least a million times less rigid than the Earth’s mantle, so the pure laws of physics simply align,” explains glaciologist Robert Lowe from the University of Bergen (Norway). “It’s like uncovering a captivating secret of nature.”
The Greenland Ice Sheet, which blankets 80% of the island, serves as a colossal global reservoir of frozen water and is projected to play a significant role in rising global sea levels as it melts and flows into the ocean. Comprehending its internal physical processes is paramount for forecasting the ice sheet’s future dynamics.
It is for this very reason that scientists employ ice-penetrating radar equipment. Radio waves pass through the ice mass and reflect differently upon encountering internal stratification—snow that long ago fell and compacted into ice under the pressure of subsequent deposits. Each such layer possesses unique characteristics, such as slightly varying acidity, alongside differences in dust concentration, volcanic ash, and overall chemical makeup.
In a 2014 publication, researchers meticulously detailed the anomalous formations observed by radar deep within the ice in northern Greenland. These monumental, up-arched features lacked any direct correlation with the underlying bedrock topography, presenting an enigma that scientists have grappled with ever since.
Prior investigations had posited potential mechanisms for these structures, such as meltwater crystallization at the ice sheet’s base or the migration of shear zones. Nevertheless, one hypothesis that remained untested was the potential for thermal convection arising directly within the ice mass itself.
To verify this conjecture, Lowe and his colleagues employed computational modeling techniques. They constructed a virtual cross-section of the Greenland Ice Sheet and posed a straightforward question: if the ice base is heated from beneath, is convection capable of generating configurations comparable to those seen in the radar scans?
To simulate an ice layer spanning 2.5 kilometers in thickness, they utilized a geodynamic modeling package typically employed to simulate convective processes within the Earth’s mantle. In doing so, they calibrated parameters such as snowfall intensity, total ice depth, ice plasticity (softness), and its surface flow velocity.
Under specific input conditions, the simulation began to reveal updrafts resembling the ice plumes—columns of ice ascending and deforming the overlying layers, manifesting shapes strikingly similar to those recorded in the radar imagery.
In the model, these flows only materialized when the ice at the base was warmer and considerably softer than conventionally assumed. This suggests that if convection is indeed the cause, the actual ice at the sole of the northern Greenland Ice Sheet might possess greater malleability than previously estimated.
Significantly, the amount of thermal energy needed to initiate these convective updrafts in the model aligned with a continuous heat supply emanating from the Earth’s interior, derived from the radioactive decay of elements in the crust and residual heat from the planet’s formation during its billion-year cooling process.
Though this thermal contribution is small, over time, being insulated beneath the colossal ice mass, it can accumulate to levels sufficient to warm and soften the overlying ice.
“We typically visualize ice as a strictly rigid material, so realizing that thermal convection, akin to water boiling in a pot, is occurring in certain regions of the Greenland Ice Sheet is a phenomenon as stunning as it is exhilarating,” shares climatologist Andreas Born from the University of Bergen.
However, this does not imply the ice has reached a slushy state. It remains solid, exhibiting plasticity only on timescales of millennia. Nor does it automatically equate to an acceleration of its melting rate. Determining the consequences of this phenomenon for the future necessitates further research into ice physics and the influence of convection on the long-term dynamics of the ice cover.
“Greenland and its nature are truly unparalleled. The ice there has existed for more than a thousand millennia, and it is the only ice sheet on the planet whose borders abut an established culture and permanent human presence,” remarks Lowe. “The deeper we delve into understanding the hidden mechanisms within the ice, the better prepared we will be for the forthcoming transformations of coastlines across the globe.”
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