The Astonishing Discovery of Giant Swirling Plumes in Greenland's Ice Sheet
Deep beneath the vast expanse of the Greenland Ice Sheet (GrIS), scientists have uncovered enormous plume-like structures that challenge long-held assumptions about ice behavior. These giant swirling formations, hidden kilometers below the surface, resemble slow-boiling eddies in a pot of pasta, driven by thermal convection—a process more commonly associated with Earth's molten mantle than solid ice. Observed through radar surveys for over a decade, the plumes disrupt the ice's annual layering, creating vertical distortions spanning more than a third of the ice thickness in some areas. This breakthrough, detailed in a recent study published in The Cryosphere, reveals how temperature differences within the ice fuel these dynamic flows, potentially reshaping our understanding of ice sheet stability amid climate change.
The Greenland Ice Sheet, spanning over 1.7 million square kilometers and holding enough water to raise global sea levels by about 7 meters if fully melted, has been losing mass at an accelerating rate—contributing roughly 1 millimeter per year to sea level rise. For the United States, with vulnerable coastlines from Miami to New York City, these internal dynamics could influence long-term flood risks and coastal planning. The discovery underscores the ice sheet's hidden complexity, far from the static monolith it once appeared.
A Decade-Long Mystery in Ice Radar Imagery
Glaciologists first spotted these enigmatic features in airborne radar data collected during surveys like NASA's Operation IceBridge and the Center for Remote Sensing of Ice Sheets (CReSIS). In northern Greenland, near sites like the NEEM deep ice core and DYE-3 borehole, internal reflectors—annual layers tracing snowfall over millennia—suddenly warp into towering plumes rising from the bed. Spaced roughly 10 kilometers apart, these structures extend upward over 800 meters in 2.5-kilometer-thick ice, defying expectations of smooth, horizontal layering.
Prior theories included basal freeze-on (refreezing meltwater folding layers), traveling 'slippery spots' (localized fast flow), or convergent ice flow creating folds. However, none fully explained the plumes' scale, ubiquity, or geometry across low-shear regions. The new research tests convection as the culprit, using cutting-edge modeling to simulate conditions inside the ice.
Thermal Convection: Ice Behaves Like Earth's Mantle
At the heart of the discovery is thermal convection, where warmer, less dense ice rises while cooler, denser ice sinks, creating self-sustaining plumes. Geothermal heat from Earth's interior (40-70 milliwatts per square meter in the region) warms basal ice to near the pressure-melting point (-2°C at depth), making it softer and more buoyant. A modest initial temperature perturbation—perhaps from past climate variations—triggers instability, quantified by the Rayleigh number (Ra), exceeding critical thresholds above 650-1700.
This mirrors mantle convection driving plate tectonics, but ice's million-fold softness allows it despite lower temperatures. Lead author Robert Law, a glaciologist at ETH Zurich, calls it a 'freak of nature,' noting, 'Ice is at least a million times softer than the Earth's mantle, so the physics just work out.' Co-author Andreas Born from the University of Bergen adds, 'It's as wild as it is fascinating—like a boiling pot of pasta deep inside the ice.'
Step-by-Step: The Physics of Ice Convection
- Geothermal Heating: Heat flux melts basal ice slightly, creating near-melting temperatures and reducing viscosity.
- Perturbation: Small temperature anomaly (e.g., Gaussian blob) forms buoyant parcel.
- Instability: If Ra exceeds critical value, parcel rises, dragging surrounding ice.
- Plume Formation: Upward velocities reach 0.4 meters per year; cooler ice sinks, sustaining circulation over millennia.
- Layer Disruption: Flow folds radiostratigraphy into plumes visible in radar.
Simulations ran for 20,000 years, matching observed plume scales and spacing.
Cutting-Edge Methods: Radar Data Meets Geodynamic Modeling
Researchers integrated decades of radar data showing plumes near NEEM (cold) and DYE-3 (warmer) sites. Using NASA's ASPECT geodynamics code, they modeled 2D (25 km long) and 3D (22x18 km) domains with 2.5 km thick ice. Key parameters: Glen's flow law (n=3), enhancement factor E=45-75 (softer ice), constant effective stress 50 kPa, no-slip base, uniform shear.
Results classified regimes: suppressed (low vertical velocity), sustained, or amplifying convection. Low shear (<1 m/yr), accumulation (<0.15 m ice eq/yr), and thickness (>2.2 km) favored plumes—precisely northern GrIS conditions. Collaborators from NASA Goddard (Joseph MacGregor) validated against real radargrams.Explore glaciology research positions to contribute to such studies.
Photo by Jason Krieger on Unsplash
Why Northern Greenland? Ideal Conditions Revealed
Plumes cluster in the north: low surface velocities (minimal shear), long ice residence times (>20 kyr), low snowfall, and thick ice. Southern GrIS lacks them due to higher accumulation (>0.35 m/yr) and faster flow (~10 kyr residence), smothering convection. Geothermal maps show compatible fluxes (40-70 mW/m²).
Enhancement factor E implies viscosity 2×10¹² to 3×10¹⁴ Pa s—10x softer than standard, possibly from impurities or fabric. Read the full open-access paper for figures mapping plumes and properties.
Softer Ice Rheology: A Game-Changer for Models
Standard ice models assume uniform viscosity, but convection requires softer deep ice. This reduces basal sliding (compensating overestimations in traction), altering flow dynamics. Northern GrIS may flow slower internally, impacting discharge at outlets like Jakobshavn Isbræ.
While not accelerating melt directly, refined rheology cuts projection uncertainties. GrIS mass loss doubled since 2000; accurate physics vital for IPCC scenarios. US researchers at NASA and NSF-funded labs are integrating similar findings.Build your glaciology CV for polar research roles.
Implications for Sea Level Rise and US Coasts
GrIS drives ~25% of observed SLR (0.8 mm/yr total). Convection insights refine mass balance: softer ice tempers sliding, potentially lowering high-end projections (up to 1 m by 2100). For the US, where 40% population lives near coasts, this means nuanced flood mapping—from Louisiana subsidence to California tides.
No 'tipping point' signaled, but highlights geothermal role amid warming. Models ignoring convection overestimate basal traction errors; updates could align simulations closer to GRACE satellite data. NASA Sea Level Change Portal tracks GrIS contributions.
Global Parallels: Antarctica and Beyond
Similar plumes possible in East Antarctica's thick, slow-flowing domes. Convection could explain layering anomalies there, informing models for the world's largest ice reservoir (58 m SLR equivalent). Broader cryosphere: insights for paleoclimate reconstructions via disrupted isochrones.
Climate feedbacks: Warmer firn might enhance convection thresholds, but basal warming dominates. Interdisciplinary links to geothermal exploration and ice core paleoclimatology.
Looking Ahead: Unanswered Questions and Next Steps
Future work: Validate with ice cores (impurities lowering viscosity?), high-res 3D radar, coupled ice-ocean models. Implement variable rheology in ISSM/Elmer for GrIS-wide simulations. Field campaigns targeting plume sites for direct temperatures.
Law notes, 'Further studies to isolate softer ice's melt impact.' Born emphasizes, 'Key to reducing SLR uncertainties.'
Expert Perspectives on a 'Freak of Nature'
- Robert Law (ETH Zurich): 'Finding thermal convection in ice goes against intuition... exciting freak of nature.'
- Andreas Born (UiB): 'Resembling a boiling pot of pasta... wild as fascinating.'
- Joseph MacGregor (NASA): Radar expert validating plume geometries.
Consensus: Paradigm shift in ice rheology, modest but vital SLR refinement.
A Dynamic Greenland Ice Sheet in Focus
This discovery paints the GrIS as alive with internal motion, urging refined models for sustainable coastal planning. For aspiring researchers, opportunities abound in cryospheric sciences. Check research jobs, higher ed jobs, or rate your professors at leading institutions. Explore career advice for glaciology paths. Stay informed on polar science shaping our future.
