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1. Glacial terminations or glacial interruptions?

   https://doi.org/10.1016/j.earscirev.2024.104756  

   Stott, Lowell (May 2024, Earth-Science Reviews)

   Dupont-Nivet, Guillaume (Ed.)

   In the early 20th century, after contributing major advances in calculating radiation forcing on planetary bodies, Milutin Milankovitch the Serbian mathematician took up the challenge of explaining why Earth has experienced recurrent episodes of glaciation. Influenced by the ideas of his predecessors, Milankovitch developed a theory that centered on the notion that summertime temperature at high northern latitudes is the most important influence on the advance and retreat of glaciations. The calculations revealed a periodicity in summer insolation that had a reasonable correspondence with what was then known about the occurrence of ice ages. From that was born the elemental foundation of the orbital theory of the ice ages. That theory evolved over the next three decades while retaining the fundamental tenant that summer season insolation at the higher northern latitudes determines Earth’s climate variability. Scientists of the day were skeptical, and it was not until the 1960s that new techniques became available to test the temporal predictions of Milankovitch’s theory. The orbital theory gained support in the 1950s and 60s when methods for paleoclimate reconstructions documented an orbital-like recurrence pattern of cold and warm climate conditions spanning the past 2.5 million years. Accompanying the documentation of Earth’s climate rhythmicity from marine archives have been advances in other areas, including ice core records of atmospheric CO2 that pose challenges to the original orbital theory, namely what role have variations in atmospheric CO2 played in dictating the transitions from warm to cold and, what caused orbital scale variations in greenhouse gas concentrations. In this contribution we review the current state of knowledge about the Earth’s carbon cycle on glacial/interglacial timescales and explore how new information has begun to shed light on the long-standing goal to understand Earth’s natural climate rhythmicity. The findings presented here highlight the need to expand research on Earth’s geologic processes that influence the carbon budget on glacial timescales. And with this comes a new hypothesis that incorporates geologic processes in orbital scale climate cycles. 

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2. Glacial Isostatic Adjustment Shapes Proglacial Lakes Over Glacial Cycles

   https://doi.org/10.1029/2022GL101191  

   Austermann, J.; Wickert, A. D.; Pico, T.; Kingslake, J.; Callaghan, K. L.; Creel, R. C. (December 2022, Geophysical Research Letters)

   Abstract As ice sheets load Earth's surface, they produce ice‐marginal depressions which, when filled with meltwater, become proglacial lakes. We include self‐consistently evolving proglacial lakes in a glacial isostatic adjustment (GIA) model and apply it to the Laurentide ice sheet over the last glacial cycle. We find that the locations of modeled lakes and the timing of their disappearance is consistent with the geological record. Lake loads can deflect topography by >10 m, and volumes collectively approach 30–45 cm global mean sea‐level equivalent. GIA increases deglaciation‐phase lake volume up to five‐fold and average along‐ice‐margin depth ≤90 m compared to glaciation‐phase ice volume analogs—differences driven by changes in the position and size of the peripheral bulge. Since ice‐marginal lake depth affects grounding‐line outflow, GIA‐modulated proglacial lake depths could affect ice‐sheet mass loss. Indeed, we find that Laurentide ice‐margin retreat rate sometimes correlates with proglacial lake presence, indicating that proglacial lakes aid glacial collapse. 

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3. Glacial fluctuations in tropical Africa during the last glacial termination and implications for tropical climate following the Last Glacial Maximum

   https://doi.org/10.1016/j.quascirev.2020.106455  

   Jackson, M.S.; Kelly, M.A.; Russell, J.M.; Doughty, A.M.; Howley, J.A.; Chipman, J.W.; Cavagnaro, D.A.; Baber, M.B.; Zimmerman, S.R.H.; Nakileza, B. (September 2020, Quaternary Science Reviews)
4. Glacial erosion: status and outlook

   https://doi.org/10.1017/aog.2019.38  

   Alley, R. B.; Cuffey, K. M.; Zoet, L. K. (November 2019, Annals of Glaciology)

   Abstract Glacier-erosion rates range across orders of magnitude, and much of this variation cannot be attributed to basal sliding rates. Subglacial till acts as lubricating ‘fault gouge’ or ‘sawdust’, and must be removed for rapid subglacial bedrock erosion. Such erosion occurs especially where and when moulin-fed streams access the bed and are unconstrained by supercooling or other processes. Streams also may directly erode bedrock, likely with strong time-evolution. Erosion is primarily by quarrying, aided by strong fluctuations in the water system driven by variable surface melt and by subglacial earthquakes. Debris-bed friction significantly affects abrasion, quarrying and general glacier flow. Frost heave drives cirque headwall erosion as winter cold air enters bergschrunds, creating temperature gradients to drive water flow along premelted films to growing ice lenses that fracture rock, and the glacier removes the resulting blocks. Recent subglacial bedrock erosion and sediment flux are in many cases much higher than long-term averages. Over glacial cycles, evolution of glacial-valley form feeds back strongly on erosion and deposition. Most of this is poorly quantified, with parts open to argument. Glacial erosion and interactions are important to tectonic and volcanic processes as well as climate and biogeochemical fluxes, motivating vigorous research. 

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5. Controls on glacial kettle morphology

   https://doi.org/10.1002/esp.6030  

   Prescott, Jillian_S; Zoet, Lucas_K; Hansen, Dougal_D; Penprase, Shanti_B; Rawling, III, J_Elmo (November 2024, Earth Surface Processes and Landforms)

   Abstract Glacial kettles are surficial depressions that form in formerly glaciated terrain when buried stagnant ice melts within pro‐glacial sediments, often deposited by meltwater streams. Kettles, like other glacial landforms, provide insight into the impact of climate on landscape evolution, such as the extent and timing of glaciations. The geometry of kettle features is variable, but existing theory does not explain the range of observed morphologies. Our study aims to establish a quantitative relationship between the depth of ice burial and the resulting morphology of terrain collapse in kettle depressions. To do so, we simulated kettle formation in the laboratory by burying ice spheres of four sizes in well‐sorted coarse sand at four different depths. As the spheres melt at room temperature, a glacial kettle analog forms at the surface. We scanned the resulting kettle topography with a portable LiDAR scanner to produce 3D digital elevation models of each depression, from which we measured each depression's depth and width and, in one instance, the time series of kettle formation. Using this data, we quantified the relationship between the sphere diameter, burial depth and resulting dimensions of the kettle by developing a set of equations, which we then applied to full‐scale features. Our results indicate that ice burial deeper than one sphere diameter corresponds to a decrease in depression depth and an increase in depression width. This application offers insight into the interdependence of ice burial depth and kettle geometry. 

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