Boreas最新文献

{"title":"The morphosedimentary record of glacial to postglacial environmental changes in West Wiyâshâkimî impact crater lake and adjacent areas, northern Québec, Canada","authors":"Etienne Brouard,&nbsp;Patrick Lajeunesse","doi":"10.1111/bor.70008","DOIUrl":"https://doi.org/10.1111/bor.70008","url":null,"abstract":"<p>Crater lakes in core regions of former ice sheets have the potential to preserve long-term sedimentary archives that are otherwise rare in glaciated landscapes due to pervasive glacial erosion. Lake Wiyâshâkimî, an impact crater lake located in the inner core of the Québec-Labrador Dome of the Laurentide Ice Sheet, provides a rare example of such a setting. The lake was therefore investigated along the region surrounding it through remotely sensed mapping and acoustic sub-bottom profiling to reconstruct its glacial to postglacial environmental evolution from its morphosedimentary record. Mapping of ice-flow landforms suggests three distinct glacial flowsets in the region, indicating a transition from external ice-stream influences to local topographical controls during deglaciation. Contrary to previous hypotheses, mapping evidence suggests that the Tyrrell Sea deglacial marine transgression did not reach Lake Wiyâshâkimî, with surrounding strandlines likely of glaciolacustrine origin. Five acoustic facies were identified from the analysis and interpretation of the acoustic sub-bottom profiles: AF1, bedrock, till and/or glacifluvial sands forming the acoustic basement; AF2, an acoustically transparent deposit filling the deeper basins of the lake, a fine-grained diamicton either associated with mass-movements or full glacial conditions (till); AF3A and AF3B, glaciolacustrine sediments deposited proximally and distally from the ice margin, respectively; and AF4, paraglacial and postglacial deposits that have been partly, at least in the upper tens of metres of the water column, remobilized by bottom currents induced by strong winds prevailing in the large lake. While our analysis shows it is unlikely that sediments pre-dating the last glaciation were preserved in the lake basin, the findings provide new insights into the lateglacial and deglacial history of the central Québec-Labrador region and highlight the role of postglacial processes in shaping the lake-bottom morphosedimentary archives.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":"55 1","pages":"110-133"},"PeriodicalIF":2.9,"publicationDate":"2025-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.70008","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146154867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Automated delineation and morphometry of unclassified subglacial bedforms","authors":"Sofyane Hesni,&nbsp;Paul Bessin,&nbsp;Edouard Ravier,&nbsp;Olivier Bourgeois,&nbsp;Jean Vérité,&nbsp;Jean-François Buoncristiani","doi":"10.1111/bor.70003","DOIUrl":"https://doi.org/10.1111/bor.70003","url":null,"abstract":"<p>We designed an automated tool to delineate and analyse the shape of subglacial bedforms using a recently defined land surface parameter, the volumetric obscurance. The tool is based on the assumption that the diversity of subglacial bedform shapes reflects a continuum; therefore, unlike traditional methods, no pre- or post-mapping classification of bedforms is performed. It uses digital elevation models and optical satellite images to generate regional morphological maps (bedform outlines and crestlines) and regional morphometric maps (spatialized statistical analysis of bedform morphometrics). We tested the tool on the ArcticDEM, over a portion of the former Laurentide Ice Sheet bed that displays a wide diversity of bedform shapes (Keewatin Ice Dome, northern Canada). The produced morphological maps are consistent, with a correspondence of approximately 75% on individual bedform outlines, with two reference maps digitized manually by two different glacial geomorphologists. Despite the 25% difference between individual bedform outlines generated automatically and manually, the derived morphometric maps are similar. They can be interpreted in the context of subglacial deformation and hydrology, providing a new potential for palaeoglaciological reconstructions at the ice-sheet scale. The tool was developed in Python and is freely accessible.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":"54 4","pages":"506-526"},"PeriodicalIF":2.9,"publicationDate":"2025-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.70003","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145341585","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Relative sea-level trends in southern Norway during the last millennium","authors":"Max Holthuis,&nbsp;F. Chantel Nixon,&nbsp;Malin E. Kylander,&nbsp;Willem G. M. van der Bilt,&nbsp;Isabel Hong,&nbsp;Kristen M. Joyse,&nbsp;Thomas R. Lakeman,&nbsp;Jake Martin,&nbsp;Maria Peter,&nbsp;Simon Solheim Holme,&nbsp;Benjamin P. Horton","doi":"10.1111/bor.70006","DOIUrl":"https://doi.org/10.1111/bor.70006","url":null,"abstract":"<p>Geological reconstructions of relative sea level (RSL) from southern Norway show falling RSL during the last 7000 cal. a BP, but tide gauge measurements document a slow RSL rise since at least 1960 CE. With an age gap of <i>c.</i> 1400 years between the youngest geologically reconstructed sea-level index point (SLIP) and the installation of the Tregde tide gauge in southernmost Norway, the exact nature and timing of the onset of RSL rise in southern Norway remain unknown. To fill this gap, we collected peat cores from a salt marsh to reconstruct RSL trends over the past 1000 years using a multiproxy approach, including ²¹⁰Pb and ¹⁴C dating, grain-size analysis, loss-on-ignition (LOI), geochemistry (stable carbon isotopes, carbon to nitrogen ratios and XRF) and diatoms. Our data suggest decreasing tidal current strength and salinity over most of the last millennium, suggesting falling RSL. Sediment geochemistry also appears to vary with wetter and drier climatic periods. An increase in marine-brackish diatoms in combination with an acceleration in sedimentation rates after 1930 CE (1899–1954 CE) suggest that the onset of RSL rise began around this time in southernmost Norway. While most of the proxy data appear to have delayed sensitivity to RSL changes and may be linked to other causal processes, they, nonetheless, provide valuable insight into the environmental response of high-latitude temperate salt marshes to slow rates of RSL change.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":"54 3","pages":"414-430"},"PeriodicalIF":2.4,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.70006","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144647852","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Response to Comment on ‘Automatic identification of streamlined subglacial bedforms using machine learning: an open-source Python approach’","authors":"Marion McKenzie,&nbsp;Ellianna Abrahams,&nbsp;Fernando Pérez,&nbsp;Ryan Venturelli","doi":"10.1111/bor.70004","DOIUrl":"https://doi.org/10.1111/bor.70004","url":null,"abstract":"&lt;p&gt;Li &lt;i&gt;et al&lt;/i&gt;. (&lt;span&gt;2025&lt;/span&gt; this issue) state that they identify areas for improvement to our development of bedfinder through including more data sets at training, evaluating our filtering methods, and exploring modular approaches of the tool. Here we respond to these Comments by highlighting where we have already addressed each of these areas within our work and notably, our supporting information (Abrahams &lt;i&gt;et al&lt;/i&gt;. &lt;span&gt;2024&lt;/span&gt;). In our paper, we describe that bedfinder is an inherently modular tool, allowing a user to choose which components of the pipeline might be useful to them. Furthermore, bedfinder already allows a user to customize the choice to over- or under-predict a glacially derived bedform assignment. In Abrahams &lt;i&gt;et al&lt;/i&gt;. (&lt;span&gt;2024&lt;/span&gt;) we previously justified why we made the choice to over-predict, emphasizing the need for manual post-processing, which we reiterate here. Finally, we reshare statements from the ‘Model limitations’ section of Abrahams &lt;i&gt;et al&lt;/i&gt;. (&lt;span&gt;2024&lt;/span&gt;) where we also recommend incorporating additional data in future tool creation to strengthen our approach.&lt;/p&gt;&lt;p&gt;The objective of Abrahams &lt;i&gt;et al&lt;/i&gt;. (&lt;span&gt;2024&lt;/span&gt;) was to build an open-source tool that would allow for the automatic detection of glacially derived streamlined subglacial bedforms, based on the previous successes of manual approaches (e.g. Clark &lt;span&gt;1993&lt;/span&gt;; Greenwood &amp; Clark &lt;span&gt;2008&lt;/span&gt;; Spagnolo &lt;i&gt;et al&lt;/i&gt;. &lt;span&gt;2014&lt;/span&gt;; Ely &lt;i&gt;et al&lt;/i&gt;. &lt;span&gt;2016&lt;/span&gt;; Principato &lt;i&gt;et al&lt;/i&gt;. &lt;span&gt;2016&lt;/span&gt;; Clark &lt;i&gt;et al&lt;/i&gt;. &lt;span&gt;2018&lt;/span&gt;). To develop this tool, we used Random Forest (Breiman &lt;span&gt;2001&lt;/span&gt;), XGBoost (Chen &amp; Guestrin &lt;span&gt;2016&lt;/span&gt;), and an ensemble average of these two model fits on a publicly available training data set of nearly 600 000 data points across the deglaciated Northern Hemisphere (McKenzie &lt;i&gt;et al&lt;/i&gt;. &lt;span&gt;2022&lt;/span&gt;). Li &lt;i&gt;et al&lt;/i&gt;. (&lt;span&gt;2025&lt;/span&gt;) suggest a constructive critique to our approach stating our work should include more data sets at training, further evaluate our filtering methods, and explore better modularizing bedfinder. However, these suggestions have either already been implemented as existing features of bedfinder (i.e. modularity of pipeline components and tunability of bedform predictions to the needs of the user) or we have already named them in our study as known limitations of the tool that will require wider community participation (the creation of larger, more nuanced machine learning data sets for model training).&lt;/p&gt;&lt;p&gt;Abrahams &lt;i&gt;et al&lt;/i&gt;. (&lt;span&gt;2024&lt;/span&gt;) outlined the limitations of the presented approach in the section ‘Model limitations’. There, we state that the ‘TPI tool used to compile our training set performs most poorly in regions with highly elongate bedforms with low surface relief (McKenzie &lt;i&gt;et al&lt;/i&gt;. &lt;span&gt;2022&lt;/span&gt;)’ (i.e. bedforms across crystalline bedrock surfaces) (Abrah","PeriodicalId":9184,"journal":{"name":"Boreas","volume":"54 2","pages":"277-280"},"PeriodicalIF":2.4,"publicationDate":"2025-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.70004","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143809968","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Subglacial landscape formation and sediment discharge: relating basal conditions to bedform dimensions and properties at Rutford Ice Stream, West Antarctica","authors":"Rebecca Schlegel,&nbsp;Lucas K. Zoet,&nbsp;Adam D. Booth,&nbsp;Andrew M. Smith,&nbsp;Roger A. Clark,&nbsp;Alex M. Brisbourne","doi":"10.1111/bor.70002","DOIUrl":"https://doi.org/10.1111/bor.70002","url":null,"abstract":"<p>Basal conditions that facilitate fast ice flow are still poorly understood and their parameterization in ice-flow models results in high uncertainties in ice-flow and consequent sea-level rise projections. Direct observations of basal conditions beneath modern ice streams are limited due to the inaccessibility of the bed. One approach to understanding basal conditions is through investigating the basal landscape of ice streams and glaciers, which has been shaped by ice flow over the underlying substrate. Bedform variation together with observations of ice-flow properties can reveal glaciological and geological conditions present during bedform formation. Here we map the subglacial landscape and identify basal conditions of Rutford Ice Stream (West Antarctica) using different visualization techniques on novel high-resolution 3D radar data. This novel approach highlights small-scale features and details of bedforms that would otherwise be invisible in conventional radar grids. Our data reveal bedforms of &lt;300 m in length, surrounded by bedforms of &gt;10 km in length. We correlate variations in bedform dimensions and spacing to different glaciological and geological factors. We find no significant correlation between local (&lt;3 × 3 km) variations in bedform dimensions and variations in ice-flow speed and (surface or basal) topography. We present a new model of subglacial sediment discharge, which proposes that variations in bedform dimensions are primarily driven by spatial variation in sediment properties and effective pressure. This work highlights the small-scale spatial variability of basal conditions and its implications for basal slip. This is critical for more reliable parameterization of basal friction of ice streams in numerical models.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":"54 4","pages":"672-686"},"PeriodicalIF":2.9,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.70002","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145341612","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reassessing the predictive power of bedfinder: insights into machine learning for subglacial bedform detection – Comments on ‘Automatic identification of streamlined subglacial bedforms using machine learning: an open-source Python approach’","authors":"Ming Li,&nbsp;Huanyu Zhao,&nbsp;Tianfei Yu","doi":"10.1111/bor.70005","DOIUrl":"https://doi.org/10.1111/bor.70005","url":null,"abstract":"&lt;p&gt;The integration of machine learning (ML) into geomorphological research presents significant opportunities for automating the identification of streamlined subglacial bedforms. In their study, Abrahams &lt;i&gt;et al&lt;/i&gt;. (&lt;span&gt;2024&lt;/span&gt;) introduce bedfinder, an open-source Python tool designed to detect subglacial features with high efficiency. While the tool demonstrates promise, this discussion highlights critical challenges and areas for refinement. The representativeness of the training data set, dominated by sedimentary bed conditions, limits the model's generalizability to regions with diverse bedrock compositions. Additionally, the reliance on binary classifications oversimplifies complex geomorphic settings, reducing the model's adaptability. Performance metrics such as F1 scores, though favourable, warrant cautious interpretation due to class imbalances that may skew predictions. Furthermore, the integration of filtering techniques, while enhancing precision, raises concerns about potential biases from manual data curation. To enhance scientific rigour, future efforts should incorporate diverse data sets, conduct comprehensive evaluations of filtering methods, and explore modular approaches for greater applicability. Addressing these challenges will not only strengthen bedfinder but also contribute to the evolving role of ML in advancing glacial and geomorphological research. This contribution provides a constructive critique to guide future improvements and interdisciplinary applications of this innovative tool.&lt;/p&gt;&lt;p&gt;Abrahams &lt;i&gt;et al&lt;/i&gt;. (&lt;span&gt;2024&lt;/span&gt;) present a cutting-edge approach to the identification of streamlined subglacial bedforms, which are crucial in understanding past glacial dynamics and their impact on geomorphology. The authors have developed an open-source Python tool, bedfinder, that employs supervised ML algorithms – Random Forest and XGBoost – to automate the identification of these features across deglaciated landscapes. This tool is an ambitious attempt to enhance efficiency and accuracy in a domain traditionally burdened by labour-intensive, subjective, and time-consuming manual processes. The authors also provide a thorough validation of the model using an extensive data set of known subglacial bedforms from various regions in the Northern Hemisphere.&lt;/p&gt;&lt;p&gt;While the study contributes valuable insights into how ML can automate the mapping of complex glacial features, several critical issues arise from the selection of data, the application of ML methods, and the interpretation of results. Here, we will highlight some of these issues and offer suggestions to enhance the scientific robustness of the study and its potential applications. The concerns outlined here include the representativeness of the training data, the challenges in interpreting the performance metrics, and the potential over-simplifications in model design and validation.&lt;/p&gt;&lt;p&gt;A central issue in Abrahams &lt;i&gt;et al&lt;/i&gt;. (&lt;span&gt;2024&lt;/span&gt;) ","PeriodicalId":9184,"journal":{"name":"Boreas","volume":"54 2","pages":"273-276"},"PeriodicalIF":2.4,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.70005","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143809833","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cladocera assemblages indicate environmental gradients of lake productivity and morphometry in central Europe","authors":"Izabela Zawiska,&nbsp;Alex Correa-Metrio,&nbsp;Monika Rzodkiewicz,&nbsp;Jacek Wolski","doi":"10.1111/bor.70001","DOIUrl":"https://doi.org/10.1111/bor.70001","url":null,"abstract":"<p>Lakes play a vital role in numerous human activities, yet extensive economic development has led to significant pollution and nutrient enrichment, resulting in widespread eutrophication and ecological disruption. To accurately assess the current state of lakes, it is essential to understand their historical, pre-impact conditions. Palaeolimnological methods, including the analysis of subfossil Cladocera, offer a valuable tool for studying lake ecosystems over extended timeframes that go beyond modern instrumental records. Our research aims to identify the primary environmental factors that influence the distribution of individual Cladocera species and evaluate the systematic patterns within species assemblages to enhance their use as ecological indicators. This study presents an analysis of Cladocera assemblages based on environmental surveys conducted in 64 lakes across northeastern Poland. Principal component analysis revealed that the two dominant factors driving variability in the dataset are lake trophic state, indicated by total phosphorus (TP) levels, and lake depth. Species distributions across these gradients showed a turnover, reflecting distinct environmental preferences. Further, end member (EM) analysis identified five distinct assemblages of Cladocera, each associated with specific combinations of trophic status and lake size. EM1 is associated with higher trophic states, while EM2, EM3 and EM4 are indicative of medium to low trophic states. EM5 is independent of trophic status, associated with large and deep-water bodies.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":"54 2","pages":"258-272"},"PeriodicalIF":2.4,"publicationDate":"2025-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.70001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143809761","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The role of inland ice dynamics in controlling the variable maximum extent of the Laurentide Ice Sheet off southeastern Baffin Island","authors":"Alexis P. Belko,&nbsp;Patrick Lajeunesse,&nbsp;Alexandre Normandeau,&nbsp;Pierre-Olivier Couette,&nbsp;Etienne Brouard","doi":"10.1111/bor.70000","DOIUrl":"https://doi.org/10.1111/bor.70000","url":null,"abstract":"<p>Reconstructions of the maximum extent and dynamics of the Laurentide Ice Sheet (LIS) during the Last Glacial Maximum (LGM) are needed for understanding how marine-based ice sheets will respond to modern climate change. The partitioning of ice masses and the location of dominant ice flows within the LIS are broadly known at regional scales, but their influence on the marine-based maximum extent of the ice sheet remains poorly constrained. Here, we provide evidence for the maximal extent of the LIS margin during the LGM in the Broughton and Merchants cross-shelf troughs off southeastern Baffin Island based on newly acquired sea floor geomorphology data. Grounding-zone wedges (GZWs), moraines and ice-stream bedforms within the Merchants cross-shelf trough delimit the maximum extent of the LIS in this sector to near the mouth of the modern fjords. Two lateral moraines, mega-scale glacial lineations (MSGLs), and iceberg scours also indicate the presence of an ice shelf extending beyond the former grounding line. In Broughton Trough, the maximum extent of the LIS is interpreted from the distribution of MSGLs and iceberg scours. The presence of sticky spots near the shelf edge may have played a role in subglacial flow and thus glacier behaviour. The difference in ice extent between the two nearby troughs is attributed to partitioning of the LIS between ice flowing from the Penny Ice Cap into Broughton Trough and ice from local alpine glaciers flowing into Merchants Trough. In addition, the presence of a dominant ice flow south of the Cumberland Peninsula may have drained ice masses of Cumberland Peninsula towards the south and caused minimal expansion in Merchants Trough to the north. These results provide a clearer understanding of the relationship between ice-sheet extent along continental margins and inland ice dynamics.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":"54 3","pages":"468-479"},"PeriodicalIF":2.4,"publicationDate":"2025-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.70000","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144647769","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Subglacial processes at the fringe of the last Scandinavian Ice Sheet in central Poland derived from macro- and micro-sedimentological proxies","authors":"Piotr Hermanowski,&nbsp;Jan A. Piotrowski","doi":"10.1111/bor.12698","DOIUrl":"https://doi.org/10.1111/bor.12698","url":null,"abstract":"<p>Geological information contained in tills is important for deciphering processes that operated under past ice sheets and helps to constrain the fundamentals of glacial erosion, transport and deposition. Despite the progress in understanding glacial systems, interpretation of ancient tills and related deposits remains fragmentary, mostly because of the inaccessibility of ice–beds under present glaciers as modern analogues of the ancient systems. Here we report on the properties of a glacial sediment succession including various till facies and subglacial meltwater deposits from a site in central Poland close to the outermost extent of the Scandinavian Ice Sheet during the last glaciation. We use outcrop-scale and micromorphological proxies to interpret the processes of till formation and deformation, and to infer the ice movement mechanisms. A combination of macro-scale sedimentological and micromorphological data (till fabric signatures, grain-size patterns, glaciotectonic structures, features of channelized and distributed subglacial drainage) indicates time-transgressive succession of ice-marginal deposition, subglacial deposition and deformation, pressurized meltwater flows at the ice–bed interface, and material release from stagnant ice. The investigated tills are to a large extent hybrid products of multiple superposed processes involving lodgement, deformation, and material cannibalization that mostly fall into the category of subglacial traction tills. Ample field and micromorphological evidence of basal decoupling suggests that the basal water pressure fluctuated around the ice flotation point. Ice movement was by a combination of enhanced basal sliding and very shallow (millimetre-thick) bed deformation. Drainage of basal meltwater was facilitated by channelized flows in conduits subsequently filled by glacifluvial outwash. Our data indicate a mosaic of (sub)glacial processes that generated a complex deposit bearing evidence of overlapping accretion and deformation modulated by hydrological conditions at the ice–bed interface.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":"54 4","pages":"711-728"},"PeriodicalIF":2.9,"publicationDate":"2025-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.12698","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145341544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lateglacial and Holocene glacier variations in an active volcanic area, northern Jan Mayen (Nord-Jan), Norway","authors":"Astrid Lyså,&nbsp;Eiliv A. Larsen,&nbsp;Johanna Anjar,&nbsp;Naki Akçar,&nbsp;Asbjørn Hiksdal,&nbsp;Georgios Tassis","doi":"10.1111/bor.12697","DOIUrl":"https://doi.org/10.1111/bor.12697","url":null,"abstract":"<p>Jan Mayen is a volcanic island situated 550 km NE of Iceland. It has been shown previously that the island and probably also shallow shelf areas around it were covered by a contiguous ice cap during the last glaciation. Today, active glaciers exist only in the northern part of the island around the Beerenberg volcano. Until now, information on Lateglacial and Holocene glacier and environmental variations has been sparse. We focus on the northern part (Nord-Jan), discussing glacier evolution and environmental changes from the Lateglacial to the Holocene. Widespread volcanic activity during the postglacial era resulted in lava flows and volcanic craters amidst glaciogenic deposits, complicating glacial and environmental reconstructions. We suggest that the ice cap covering Jan Mayen separated into two (northern and southern) approximately 20 ka ago, based on observations from glacial striae and terrestrial cosmogenic nuclide exposure dating. Deglaciation of the southern flank of the Beerenberg ice cap was accelerated by initial subglacial volcanic activity, which probably rapidly evolved to protrude above the glacier surface. Subsequently, around 18.9 ka, vertical melting and ice-marginal recession intensified in Nord-Jan. A relatively warm period followed thereafter, evidenced by organic material giving a calibrated age of 17 to 16 cal. ka BP. The extent of deglaciation during this period is unknown as the dated material was found redeposited in lake sediments. Several cosmogenic exposure ages from bedrock and glacial erratics correspond to the Lateglacial period. The interpretation of these ages is not obvious, but we favour a hypothesis involving a Lateglacial readvance of the glaciers when lateral moraines were also deposited. Mild conditions, characterized by plant growth and soil formation, prevailed during the Early Holocene. During this period, the lateral moraines formed during the Lateglacial probably disintegrated, leaving only the remnants visible today.</p>","PeriodicalId":9184,"journal":{"name":"Boreas","volume":"54 3","pages":"305-327"},"PeriodicalIF":2.4,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/bor.12697","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144646909","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}