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Powerful pulses of groundwater flow up from beneath Lakes Michigan and Huron, which together form one of the largest freshwater systems in the world. This groundwater flux may dramatically alter how and where ice forms, with important implications for ice-climate models. As climate change pressures the system, new research suggests that conventional models may underestimate how groundwater can destabilize lake ice along its shorelines (coasts).

When we think of lake ice formation and stability, influencing factors that often come to mind are atmospheric, such as air temperature, humidity, wind and solar radiation. But Saeed Memari, of Colorado School of Mines, and colleagues argue that groundwater flux can play an outsized role in modulating ice formation and melt in large freshwater systems.

In their work, recently in Water Resources Research, Memari and the team built coupled hydrodynamic-ice models that incorporate spatially and temporally variable groundwater discharge at the bottom of Lakes Michigan and Huron and tested how different magnitudes of flux change thermal stratification of the lake, freezing onset and ice stability. Their core finding: when groundwater flux intensifies, it acts as a weak but persistent heat source, delivering warmer water from the subsurface and delaying ice growth or promoting melt.

The authors tested a range of groundwater flux scenarios. They found that at low fluxes (10 times base flow), the impact is subtle, with slight thinning or delayed freeze in shallow zones. At moderate flux (100 times base flow), the groundwater can disrupt the thermal stratification, mixing warmer water upward, which inhibits ice from stabilizing. But in the most extreme flux regimes (1,000 times base flow), the effect becomes dramatic; in coastal and nearshore zones, ice becomes thermally destabilized, with melting encroaching much earlier and penetrating further inland than models without groundwater would predict.

Interestingly, their simulations show that the destabilizing influence is strongest near lake margins and shores due to higher groundwater input, while in deep lake interiors, the effect is dampened by volume and insulation. Thus, the weak bottom heat from groundwater disproportionately undermines ice near where people, ecosystems and infrastructure interact with the lake surface most.

Additionally, not all groundwater flux is equal. Spatial variability means a strong flux in one coastal sector can locally melt or thin ice, even when the rest of the lake remains frozen.

Temporal variability is also important as warmer summer months mean the lake surface temperature is less conducive to ice formation, while in winter, cooler surface waters can lead to slow but steady ice accumulation. This is due to a more pronounced thermal gradient in the lake's water column, where denser, warmer groundwater does not mix upwards into surface waters, maintaining a cooler surface layer. Therefore, models should allow for differentiated bottom-flux and temperature distributions, rather than uniform assumptions.

In the context of ongoing climate warming, the authors argue that rising groundwater temperatures, altered precipitation, land use changes, or changes in aquifer recharge could shift groundwater flux regimes upward. That could amplify previously subtle subsurface heat contributions and further erode ice cover in coastal zones.

By including variable groundwater fluxes in their models, the researchers aim to provide a more realistic, dynamic model of winter ice in large lakes under future climate scenarios. Moreover, since ice cover influences ecological processes, shoreline erosion, water quality and winter navigation, better predictions of ice timing and thickness have practical downstream consequences.

As with any modeling study, there are caveats. Memari and the team note that they do not explicitly include feedbacks between evolving ice cover and groundwater patterns (for example, as ice melts, water pathways may change). Also, the extreme flux cases are hypothetical upper bounds; the frequency and drivers of such pulses in real Great Lakes aquifers remain uncertain.

Another question is: what geological and hydrogeological conditions permit such intense groundwater fluxes? Permeability structure, aquifer connectivity, sediment layering and hydraulic gradients all shape how large groundwater heat injections can become possible, but such subsurface data is not always available. Ground truthing through direct measurements of groundwater discharge under ice, temperature profiles near lakebeds and ice thickness records will help constrain which groundwater flux regimes are plausible.

The idea that subtle groundwater warming can meaningfully destabilize lake ice might be surprising, but this study demonstrates that over winter lengths, even weak subsurface heat injection can accumulate effects, especially when magnified by high flux pulses. In the coastal zones of the Great Lakes, that could mean earlier melt, thinner ice and unexpectedly weak winter cover, all of which matter for ecosystems, recreation, infrastructure and regional climate feedbacks.

By integrating groundwater dynamics into ice and hydrodynamic models, the researchers underscore that no component of the water–heat budget should be simplified or omitted, especially in a warming world. As climate change proceeds, the often-overlooked subsurface could become a critical actor in how ice behaves and the wider environmental and societal impacts.

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