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The relationship between firn microstructure and water movement is complex: firn microstructure controls the routing of meltwater through the firn while continuously being altered by liquid water flow processes. Importantly, microstructural transitions within the firn column can stall vertical meltwater percolation, which creates heterogeneities in liquid water content resulting in different rates of firn metamorphism. Physics‐based firn models aim to describe these processes to accurately predict ice layer or firn aquifer formation, but require detailed observations of firn structure to validate and inform percolation schemes. Here, we present grain size measurements and ice layer stratigraphy from seven firn cores collected in western Greenland's percolation zone during the 2016 Greenland Traverse for Accumulation and Climate Studies (GreenTrACS). Grain size transitions within the cores are negatively correlated with all temperature proxies for meltwater supply. Additionally, the number of grain size transitions are strongly anticorrelated with the number of ice layers within each core, despite these transitions, particularly fine‐over‐coarse transitions, promoting meltwater ponding and potential ice layer formation. To investigate if these negative correlations can be understood with firn model physics, we simulate water movement along stratigraphic transitions using the SNOWPACK model. We find that grain size transitions diminish from rapid grain growth in wet firn where ice layers can form, suggesting these microstructural transitions are unlikely to survive repeated meltwater infiltration. Incorporating these microstructure—meltwater feedbacks in firn models could improve their ability to model processes such as ice slab formation or firn aquifer recharge that require accurate predictions of meltwater infiltration depth.

 

Globally, glaciers are shrinking in response to climate change, with implications for global sea level rise as well as downstream ecosystems and water resources. Sliding at the ice‐bed interface (basal motion) provides a mechanism for glaciers to respond rapidly to climate change. While the short‐term dynamics of glacier basal motion (<10 years) have received substantial attention, little is known about how basal motion and its sensitivity to subglacial hydrology changes over long (>50 year) timescales—this knowledge is required for accurate prediction of future glacier change. We compare historical data with modern estimates from field and satellite data at Athabasca Glacier and show that the glacier thinned by 60 m (−21%) over 1961–2020. However, a concurrent increase in surface slope results in minimal change in the average driving stress (−6 kPa and −4%). These geometric changes coincide with relatively uniform slowing (−15 m a⁻¹and −45%). Simplified ice modeling suggests that declining basal motion accounts for most of this slow down (91% on average and 46% at minimum). A decline in basal motion can be explained by increasing basal friction resulting from geometric change in addition to increasing meltwater flux through a more efficient subglacial hydrologic system. These results highlight the need to include time‐varying dynamics of basal motion in glacier models and analyses. If these findings are generalizable, they suggest that declining basal motion reduces the flux of ice to lower elevations, helping to mitigate glacier mass loss in a warming climate.

 

The geothermal flux is an important boundary condition for ice‐sheet models because it influences whether the ice is melting at the bed and able to slide. Point measurements and remotely sensed estimates vary widely for the Ross Ice Sheet. A basal temperature measurement at Roosevelt Island reveals a geothermal flux of 84 ± 13 mW/m². The presence of Raymond Arches, which form only at ice divides that are frozen at the bed, allows inferences of the maximum geothermal flux at two coastal domes along the Siple Coast: Engelhardt Ridge, 85 ± 11 mW/m²and Shabtaie Ridge, 75 ± 10 mW/m². These measurements indicate heat flows similar to measurements at Siple Dome and the Whillans grounding zone and to the continental crust average. The high values measured at Subglacial Lake Whillans and estimated from satellite observations of Curie depths are not widespread.

 

Greenland Ice Sheet surface elevation is changing as mass loss accelerates. In understanding elevation change, the magnitudes of physical processes involved are important for interpretation of altimetry and assessing changes in these processes. The four key processes are surface mass balance (SMB), firn densification, ice dynamics, and isostatic adjustment. We quantified these processes at Summit, Greenland, where monthly Global Navigation Satellite System (GNSS) snowmobile traverses measured elevation change from 2008 to 2018. We find an elevation increase of 0.019 m a⁻¹. The sum of the effects of the four processes reproduces the measured elevation time series, in linear trend and in intra‐annual variability. The short‐term variability in elevation is primarily explained by the variability in SMB. Since SMB has not changed significantly over the last century, and the other processes change over longer time scales, the elevation change likely has been ongoing for at least the last 100 years.

 

High-resolution, well-dated climate archives provide an opportunity to investigate the dynamic interactions of climate patterns relevant for future projections. Here, we present data from a new, annually dated ice core record from the eastern Ross Sea, named the Roosevelt Island Climate Evolution (RICE) ice core. Comparison of this record with climate reanalysis data for the 1979–2012 interval shows that RICE reliably captures temperature and snow precipitation variability in the region. Trends over the past 2700 years in RICE are shown to be distinct from those in West Antarctica and the western Ross Sea captured by other ice cores. For most of this interval, the eastern Ross Sea was warming (or showing isotopic enrichment for other reasons), with increased snow accumulation and perhaps decreased sea ice concentration. However, West Antarctica cooled and the western Ross Sea showed no significant isotope temperature trend. This pattern here is referred to as the Ross Sea Dipole. Notably, during the Little Ice Age, West Antarctica and the western Ross Sea experienced colder than average temperatures, while the eastern Ross Sea underwent a period of warming or increased isotopic enrichment. From the 17th century onwards, this dipole relationship changed. All three regions show current warming, with snow accumulation declining in West Antarctica and the eastern Ross Sea but increasing in the western Ross Sea. We interpret this pattern as reflecting an increase in sea ice in the eastern Ross Sea with perhaps the establishment of a modern Roosevelt Island polynya as a local moisture source for RICE.