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1. ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century

   https://doi.org/10.5194/tc-14-3033-2020  

   Seroussi, Hélène; Nowicki, Sophie; Payne, Antony J.; Goelzer, Heiko; Lipscomb, William H.; Abe-Ouchi, Ayako; Agosta, Cécile; Albrecht, Torsten; Asay-Davis, Xylar; Barthel, Alice; et al (January 2020, The Cryosphere)

   null (Ed.)

   Abstract. Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution inresponse to different climate scenarios and assess the mass loss that would contribute tofuture sea level rise. However, there is currently no consensus on estimates of the future massbalance of the ice sheet, primarily because of differences in the representation of physicalprocesses, forcings employed and initial states of ice sheet models. This study presentsresults from ice flow model simulations from 13 international groups focusing on the evolutionof the Antarctic ice sheet during the period 2015–2100 as part of the Ice Sheet ModelIntercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from theCoupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climatemodel results. Simulations of the Antarctic ice sheet contribution to sea level rise in responseto increased warming during this period varies between −7.8 and 30.0 cm of sea level equivalent(SLE) under Representative ConcentrationPathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment withconstant climate conditions and should therefore be added to the mass loss contribution underclimate conditions similar to present-day conditions over the same period. The simulated evolution of theWest Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica mass change varies between −6.1 and8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighingthe increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelfcollapse, here assumed to be caused by large amounts of liquid water ponding at the surface ofice shelves, yields an additional simulated mass loss of 28 mm compared to simulations without iceshelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, thecalibration of these melt rates based on oceanic conditions taken outside of ice shelf cavitiesand the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario basedon two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared tosimulations done under present-day conditions for the two CMIP5 forcings used and displaylimited mass gain in East Antarctica. 

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2. Impacts of Changing Winters on Lake Ecosystems Will Increase With Latitude

   https://doi.org/10.1111/ele.70200  

   Ozersky, Ted; Poste, Amanda; Rautio, Milla; Leu, Eva (August 2025, Ecology Letters)

   ABSTRACT Climate warming is especially pronounced in winter and at high latitudes. Warming winters are leading to the loss of lake ice and changing snow cover on lakes. Historically, lake scientists have paid less attention to the ice cover period, leading to data and theory gaps about the role of winter conditions in lake ecosystem function and the consequences of changing winters. Here we use simple models to show that the latitudinal interaction between ice cover duration and light flux seasonality has profound and underappreciated implications for lakes. Our models focus on light and temperature, two key drivers of ecosystem processes. We show that the relative amount of light arriving in lakes during ice cover increases non‐linearly with latitude and that the light climate of high latitude lakes is much more sensitive to changing winter conditions than that of lower latitude lakes. We also demonstrate that the synchronicity between high light and warm temperatures may decrease with latitude, with implications for primary and secondary production. Our results suggest that ice loss may lead to greater relative change to productivity and biotic interactions in higher latitude lakes and also offer several testable predictions for understanding the consequences of climate‐induced changes across latitudinal gradients. 

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3. Laurentide ice sheet thinning and erosive regimes at Mount Washington, New Hampshire, inferred from multiple cosmogenic nuclides

   Koester, A. J. (April 2021, GSA Special Paper)

   Richard B. Waitt; Glenn D. Thackray; Alan R. Gillespie (Ed.)

   The northward retreat history of the Laurentide ice sheet through the lowlands of the northeastern United States during the last deglaciation is well constrained, but its vertical thinning history is less well known because of the lack of direct constraints on ice thickness through time and space. In addition, the highest elevations in New England are characterized by gently sloping upland surfaces and weathered block fields, features with an uncertain history. To better constrain ice-sheet history in this area and its relationship to alpine geomorphology, we present 20 new 10Be and seven in situ 14C cosmogenic nuclide measurements along an elevation transect at Mount Washington, New Hampshire, the highest mountain in the northeastern United States (1917 m above sea level [a.s.l.]). Our results suggest substantially different exposure and erosion histories on the upper and lower parts of the mountain. Above 1600 m a.s.l., 10Be and in situ 14C measurements are consistent with upper reaches of the mountain deglaciating by 18 ka. However, some 10Be ages are up to several times greater than the age of the last deglaciation, consistent with weakly erosive, cold-based ice that did not deeply erode preglacial surfaces. Below 1600 m a.s.l., 10Be ages are indistinguishable over a nearly 900 m range in elevation and imply rapid ice-surface lowering ca. 14.1 ± 1.1 ka (1 standard deviation; n = 9). This shift from slow thinning early in the deglaciation on the upper part of the mountain to abrupt thinning across the lower elevations coincided with accelerated ice-margin retreat through the region recorded by Connecticut River valley varve records during the Bølling interstadial. The Mount Washington cosmogenic nuclide vertical transect and the Connecticut River valley varve record, along with other New England cosmogenic nuclide records, suggest rapid ice-volume loss in the interior northeastern United States in response to Bølling warming. 

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4. Pacific Northwest conifer forest stand carrying capacity under future climate scenarios

   https://doi.org/10.1111/nrm.12381  

   Heiderman, Ryan R.; Kimsey, Mark J. (November 2023, Natural Resource Modeling)

   Abstract Maximum stand density index (SDI_MAX) represents the carrying capacity of a forest stand based on the relationship between the number of trees and their size. Plot‐level inventory data provided through a collaborative network of federal, state, and private forest management groups were utilized to develop SDI_MAXmodels for important Pacific Northwest conifers of western Washington and Oregon, USA. The influence of site‐specific climatic and environmental variables was explored within an ensemble learning model. Future climate projections based on global circulation models under different representative CO₂concentration pathways (RCP 4.5 and RCP 8.5) and timeframes (2050s and 2080s) were utilized in a space‐for‐time substitution to understand potential shifts in modeled SDI_MAX. A majority of the region showed decreases in carrying capacity under future climate conditions. Modeled mean SDI_MAXdecreased 5.4% and 11.4% for Douglas‐fir (Pseudotsuga menziesii(Mirb.) Franco) dominated forests and decreased 6.6% and 8.9% for western hemlock (Tsuga heterophylla(Raf.) Sarg.) and Pacific silver fir (Abies amabilis), dominated forests under the RCP 4.5 in the 2050s and RCP 8.5 in the 2080s, respectively. Projected future conditions often fall outside the range of any contemporary climate profile, resulting in what may be referred to as extramural conditions. Within the study region, 45% and 46% of climate variables included in the final model were extramural for the Douglas‐fir and hemlock models, respectively, under RCP 8.5 in the 2080s. Although extrapolating beyond the range of input data is not appropriate and many unknowns remain regarding future climate projections, these results allow for general interpretations of the direction and magnitude of potential shifts in forest carrying capacity. 

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5. Metatranscriptomic analysis reveals dissimilarity in viral community activity between an ice-free and ice-covered winter in Lake Erie

   https://doi.org/10.1128/msystems.00753-24  

   Denison, Elizabeth R; Zepernick, Brittany N; McKay, R_Michael L; Wilhelm, Steven W (July 2024, mSystems)

   Blanchard, Jeffrey Lawrence (Ed.)

   ABSTRACT Winter is a relatively under-studied season in freshwater ecology. The paucity of wintertime surveys has led to a lack of knowledge regarding microbial community activity during the winter in Lake Erie, a North American Great Lake. Viruses shape microbial communities and regulate biogeochemical cycles by acting as top-down controls, yet very few efforts have been made to examine active virus populations during the winter in Lake Erie. Furthermore, climate change-driven declines in seasonal ice cover have been shown to influence microbial community structure, but no studies have compared viral community activity between different ice cover conditions. We surveyed surface water metatranscriptomes for viral hallmark genes as a proxy for active virus populations and compared activity metrics between ice-covered and ice-free conditions from two sampled winters. Transcriptionally active viral communities were detected in both winters, spanning diverse phylogenetic clades of putative bacteriophage (Caudoviricetes), giant viruses (Nucleocytoviricota, or NCLDV), and RNA viruses (Orthornavirae). However, viral community activity metrics revealed pronounced differences between the ice-covered and ice-free winters. Viral community composition was distinct between winters and viral hallmark gene richness was reduced in the ice-covered relative to the ice-free conditions. In addition, the observed differences in viral communities correlated with microbial community activity metrics. Overall, these findings contribute to our understanding of the viral populations that are active during the winter in Lake Erie and suggest that viral community activity may be associated with ice cover extent.IMPORTANCEAs seasonal ice cover is projected to become increasingly rare on large temperate lakes, there is a need to understand how microbial communities might respond to changing ice conditions. Although it is widely recognized that viruses impact microbial community structure and function, there is little known regarding wintertime viral activity or the relationship between viral activity and ice cover extent. Our metatranscriptomic analyses indicated that viruses were transcriptionally active in the winter surface waters of Lake Erie. These findings also expanded the known diversity of viral lineages in the Great Lakes. Notably, viral community activity metrics were significantly different between the two sampled winters. The pronounced differences we observed in active viral communities between the ice-covered and ice-free samples merit further research regarding how viral communities will function in future, potentially ice-free, freshwater systems. 

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