Beneath the vast expanse of the Greenland ice sheet, radar imaging has brought to light peculiar, plume-like formations that disrupt the layered strata accumulated over millennia.
Now, more than a decade subsequent to their initial detection, researchers posit they have elucidated the genesis of these anomalies. Computational simulations suggest these structures bear a striking resemblance to thermal convection: the turbulent upward movement of heat, a phenomenon more commonly associated with incandescent magma circulating deep within the Earth’s lithosphere.
“The realization that thermal convection can occur within an ice sheet challenges our conventional understanding and expectations. While ice is demonstrably less viscous than the Earth’s mantle, the underlying physics nevertheless permit such processes,” observes glaciologist Robert Law from the University of Bergen, Norway.
“It represents an extraordinary natural aberration.”
The Greenland ice sheet, which blankets 80 percent of the island, constitutes one of our planet’s most substantial reservoirs of frozen water. Projections indicate it will contribute significantly to escalating sea levels as it gradually liquefies into the oceanic bodies.
Consequently, comprehending the internal dynamics of this ice mass is paramount for forecasting its future transformations.
This imperative drives the application of ice-penetrating radar technology. These instruments transmit radio waves that traverse the ice, generating distinct reflections upon encountering internal strata – compressed ancient snowfall that has solidified into ice under the weight of subsequent layers. Each of these accumulated strata possesses unique characteristics, such as subtle variances in acidity, and differing concentrations of dust, volcanic ash, and chemical constituents.
In a 2014 publication, researchers detailed anomalous structures identified deep within the northern Greenland ice by these radar surveys. These substantial, upward-curving features were divorced from the underlying bedrock topography, thereby presenting an enigma that has occupied researchers ever since.
Prior investigations had proposed mechanisms such as the refreezing of glacial meltwater onto the ice sheet’s undersurface, or the migration of lubricating basal ice layers, as potential culprits for these formations. However, one theoretical avenue that remained unexplored was the possibility of thermal convection occurring within ice sheets.
To rigorously evaluate this hypothesis, Law and his collaborators employed rigorous computational modeling. They constructed a simplified digital representation of the Greenland ice sheet, posing a fundamental question: If the ice sheet’s base were subjected to elevated temperatures, could convection give rise to structures that align with radar observations?
Utilizing a geodynamics modeling package typically employed for simulating mantle convection, they simulated a section of ice 2.5 kilometers (1.6 miles) in thickness. They systematically adjusted parameters including snowfall rates, ice depth, the ice’s inherent deformability, and its surface velocity.
Under specific simulated conditions, the model generated plume-like upwellings – ascending columns of ice that contorted the overlying layers into configurations remarkably similar to those detected by radar.
Crucially, the model indicated that plumes would only materialize if the ice at the base was both warmer and considerably more deformable than conventional assumptions would suggest. This implies that if convection is indeed the driving force, the actual ice at the base of northern Greenland’s ice sheet might also possess a greater degree of plasticity than previously posited.
Concurrently, the thermal energy requisite for generating these convective upwellings in the model was consistent with the continuous geothermal heat flux emanating from the Earth’s interior. This heat originates from the radioactive decay of elements within the crust and the residual thermal energy from the planet’s formative stages, which continues to dissipate over geological epochs.
While individually a negligible factor, this persistent heat flux, amplified by the insulating effect of the immense ice mass, could accumulate sufficiently to warm and plasticize the overlying ice.
“Our prevailing perception of ice is as a rigid solid, making the discovery that sections of the Greenland ice sheet actually exhibit thermal convection, reminiscent of a vigorously boiling liquid, both astounding and profoundly intriguing,” remarks climatologist Andreas Born of the University of Bergen.
It is essential to clarify that this phenomenon does not equate to the ice becoming slushy; it remains solid, deforming over timescales of millennia. Furthermore, it does not automatically portend an accelerated rate of melting. Further in-depth research into ice physics and the implications of convection on the ice sheet’s long-term evolution is imperative to ascertain its future consequences.
“Greenland and its distinct environmental characteristics are truly exceptional. The ice sheet there is ancient, exceeding one thousand years in age, and it is the sole ice sheet globally to host a cultural presence and a permanent human population along its peripheries,” Law elucidates.
“A more profound understanding of the concealed processes within the ice will better equip us to anticipate and respond to the forthcoming alterations along coastlines worldwide.”
