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1. Change in equilibrium-line altitude (ΔELA) for 215 Alaskan glaciers from the Little Ice Age (LIA) maximum to present (2016 to 2024)

   https://doi.org/10.18739/a2np1wm3m  

   Larocca, Laura (January 2025, NSF Arctic Data Center)

   The study associated with this dataset evaluates the climatic signature of the Little Ice Age (LIA; ~1250 to 1900) relative to the present (2016–2024) by reconstructing shifts in equilibrium-line altitude (ΔELA), a climate-sensitive parameter, for 215 glaciers in Alaska and adjacent Canada (southwest Yukon and northwest British Columbia) using remote sensing and a suite of geographic information system (GIS) tools. We quantify the magnitude and spatial pattern of ΔELA across Alaska’s major glaciated regions to infer centennial-scale changes in temperature and precipitation and to examine links with synoptic-scale circulation associated with the Aleutian Low. Data were generated in 2024–2025 at Arizona State University and Northern Arizona University as part of the NSF-funded PROGLACIAL project. The dataset includes reconstructed LIA maximum ELAs, modern end-of-summer snowline altitudes (2016–2024), and LIA–present ΔELA for 215 glaciers. LIA glacier extents were compiled from published sources and additional mapping of geomorphic evidence (terminal moraines, trimlines) using the ESRI World Imagery basemap; LIA glacier surfaces and ELAs were modeled using the GlaRe and PalaeoIce GIS toolboxes; and modern snowline altitudes were manually mapped in Sentinel-2 satellite imagery (2016-2024) and associated elevation extracted from the ArcticDEM (10 meter mosaic product). 

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2. Disentangling topographic and climatic controls on glacier length: A case study in the tropical Colombian Andes

   https://doi.org/10.1016/j.epsl.2025.119511  

   Wilner, Joel A; Doughty, Alice M; Kelly, Meredith A; Morlighem, Mathieu (October 2025, Earth and Planetary Science Letters)

   Reconstructing past climate from moraine records is complicated by the influence of non-climatic factors, particularly topography, on glacier extent. Such topographic controls have been widely identified in the literature, but a systematic quantitative assessment of their effects on glacier extent is lacking. Here, we investigate the relative influence of topographic and climatic factors on tropical glacier length variability in the Sierra Nevada del Cocuy, Colombia using a coupled ice-flow–energy-balance glacier model. Employing a parameter sweep over 450 topographic scenarios and 40 climatic scenarios for a total of 18,000 unique topo-climatic scenarios, we identify a critical transition in glacier length around 5 °C to 6 °C below modern temperature where variability in inter-valley glacier length shifts from headwall elevation-controlled to valley slope-controlled. We show through a relative weights analysis that, for this particular topo-climatic parameter space, climate accounts for 84% of the modeled variability in glacier length, while topography contributes 16%. Among climatic variables, temperature plays a more dominant role than precipitation, and headwall elevation influences glacier length most of any topographic variable. After accounting for all possible combinations of parameter subsets, we find that a sizable portion of topo-climatic scenarios (22%) yields glacier lengths dominated by topographic factors rather than climatic factors. These findings highlight the complex interplay between climate and topography, demonstrating that topography, though typically secondary to climate, has a notable impact on glacier length in this particular glacier regime. As such, this study provides a framework for quantifying the relative contributions of climate and topography to glacier evolution, critical for interpreting past glacier extents and predicting future changes. 

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3. Tropical Atlantic Temperature and Hydrologic Change During the Paleocene‐Eocene Thermal Maximum

   https://doi.org/10.1029/2024PA004939  

   Howard, Chels; Penman, Donald E; Zhu, Jiang; Harper, Dustin T; Newell, Dennis L; Norris, Richard D (April 2025, Paleoceanography and Paleoclimatology)

   Abstract The Paleocene‐Eocene Thermal Maximum (PETM, ∼56 million years ago) is among the best‐studied climatic warming events in Earth history and is often compared to projected anthropogenic climate change. The PETM is characterized by a rapid negative carbon isotope excursion and global temperature increase of 4–5°C, accompanied by changes in spatial patterns of evaporation and precipitation in the global hydrologic cycle. Recent climate model reconstructions suggest a regionally complex and non‐linear response of one important aspect of global hydrology: enhanced moisture flux from the low‐latitude ocean. In this study, we use the elemental and stable isotope geochemistry of surface‐dwelling planktic foraminifera from a low‐latitude Atlantic deep‐sea sedimentary record (IODP Site 1258) to quantify changes in sea‐surface temperature (SST) and salinity. Foraminiferal Mg/Ca and δ¹⁸O values are interpreted with a Bayesian forward proxy system model to reconstruct how SST and salinity changed over the PETM at this site. These temperature and salinity reconstructions are then compared to recent climate model simulations of Eocene warming. Our reconstructions indicate °C of warming, in excellent agreement with estimates from other tropical locations and modeled PETM warmth. The regional change in salinity is not as straightforward, demonstrating a slight decrease at extremepCO₂forcing (a reversal of the modeled sense of change under moderatepCO₂forcing) in both model and proxy reconstructions. The cause of this non‐linear response is unclear but may relate to increased South American continental runoff or shifts in the Inter‐Tropical Convergence Zone. 

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4. Synchronous Tropical Andean Hydroclimate Variability During the Last Millennium

   https://doi.org/10.1029/2023JD040255  

   Bird, B W; Steinman, B A; Escobar, J; Correa‐Metrio, A; Holper, K; Gibson, D K; Mark, S; Fonseca, H (July 2024, Journal of Geophysical Research: Atmospheres)

   Abstract The impact of latitudinal variations in the Intertropical Convergence Zone (ITCZ) on northern Andean hydroclimate during the Medieval Climate Anomaly (MCA; 950–1,150 CE) and Little Ice Age (LIA; 1,300–1,850 CE) is uncertain. Synthesis of two new lacustrine paleoclimate records from the Eastern Colombian Andes with existing circum‐Andean records shows that effective moisture anomalies were synchronous and in phase across the tropical Andes during the last millennium. During the MCA, when the ITCZ was shifted northward, topographically controlled responses in the northern Andes to vigorous atmospheric convection resulted in low precipitation and high evaporation, while precipitation was also reduced in the southern tropical Andes. During the LIA, precipitation decreased in the northern Andes as the ITCZ migrated southward but was offset by cooling that lowered evaporation, establishing high effective moisture. In the southern tropical Andes, the southward ITCZ position simultaneously strengthened precipitation, increasing effective moisture. MCA‐like responses to continued warming trends could similarly reduce northern Andean precipitation while increasing evaporation, thereby lowering effective moisture and possibly reducing water resource availability. 

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5. A Tropical Cocktail of Organic Matter Sources: Variability in Supraglacial and Glacier Outflow Dissolved Organic Matter Composition and Age Across the Ecuadorian Andes

   https://doi.org/10.1029/2022JG007188  

   Holt, Amy D; Kellerman, Anne M; Battin, Tom I; McKenna, Amy M; Hood, Eran; Andino, Patricio; Crespo‐Pérez, Verónica; Peter, Hannes; Schön, Martina; De_Staercke, Vincent; et al (May 2023, Journal of Geophysical Research: Biogeosciences)

   Abstract The biogeochemistry of rapidly retreating Andean glaciers is poorly understood, and Ecuadorian glacier dissolved organic matter (DOM) composition is unknown. This study examined molecular composition and carbon isotopes of DOM from supraglacial and outflow streams (n = 5 and 14, respectively) across five ice capped volcanoes in Ecuador. Compositional metrics were paired with streamwater isotope analyses (δ¹⁸O) to assess if outflow DOM composition was associated with regional precipitation gradients and thus an atmospheric origin of glacier DOM. Ecuadorian glacier outflows exported ancient, biolabile dissolved organic carbon (DOC), and DOM contained a high relative abundance (RA) of aliphatic and peptide‐like compounds (≥27%RA). Outflows were consistently more depleted in Δ¹⁴C‐DOC (i.e., older) compared to supraglacial streams (mean −195.2 and −61.3‰ respectively), perhaps due to integration of spatially heterogenous and variably aged DOM pools across the supraglacial environment, or incorporation of aged subglacial OM as runoff was routed to the outflow. Across Ecuador, Δ¹⁴C‐DOC enrichment was associated with decreased aromaticity of DOM, due to increased contributions of organic matter (OM) from microbial processes or atmospheric deposition of recently fixed and subsequently degraded OM (e.g., biomass burning byproducts). There was a regional gradient between glacier outflow DOM composition and streamwater δ¹⁸O, suggesting covariation between regional precipitation gradients and the DOM exported from glacier outflows. Ultimately, this highlights that atmospheric deposition may exert a control on glacier outflow DOM composition, suggesting regional air circulation patterns and precipitation sources in part determine the origins and quality of OM exported from glacier environments. 

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