Boreas最新文献

Glaciers, corals, speleothems, peatlands, trees and other natural proxy archives are essential for global climate change research, but their scarcity and fragility are not equally recognised. Here, we introduce a rapidly disappearing source of palaeoclimatic, environmental and archaeological evidence from some 5000 years ago in the Fenland of eastern England to argue for the protection of natural proxy archives. We describe the region's exceptional, yet neglected subfossil wood sources, discuss its multifaceted value for scholarship and society, and outline a prototype for sustainable proxy preservation. Finally, we emphasise the urgency and complexity of conservation strategies that must balance academic, public and economic interests across different spatiotemporal scales.

We, the editors, are grateful to all reviewers for their help in processing volume 54 of Boreas.

Jan A. Piotrowski

Nicolaj Krog Larsen

The Ural Mountains are of fundamental importance for studying early human migrations along the geographical limits between Europe and Asia. Geological processes and past climates gave rise to numerous caves, mostly in Palaeozoic carbonate formations. Thirty-two caves, among the ~120 investigated sites (karst overhangs, grottos and large caverns), provided evidence of a Late Pleistocene occupation mostly as temporary habitation places or refuge shelters. Sikiyaz-Tamak 7 Cave demonstrates so far the earliest (>57 300 cal. a BP) occupancy by pre-modern (Neanderthal) people. The initial Upper Palaeolithic is recorded just at one site (Smelovskaya II/4; 49 223–42 137 cal. a BP) with formally indistinct cultural inventories. The later mid-last glacial (MIS 3) occupation (35 000–24 000 years ago) mirrors a progressing cultural development all through the Last Glacial Maximum (LGM), culminating in the major cave complexes (20 000–16 000 cal. a BP) – Shulgan-Tash, Kul'yurt-Tamak in the Southern Ural, and Medvezhya Cave in the Northern Ural. Spectacular parietal art galleries and utilitarian art objects point to religious practices. A marked increase in the number of occupied cave sites along with casual shelters and campsites suggests a post-LGM demography rise within the mountain taiga and foothill parkland habitats. The final phase of the Ice Age peopling (14 500–12 000 years ago) is less distinct, following a presumed settlement drop ~15 000 years ago. Chronostratigraphical records and palaeoecological proxies stored in the caves' geoarchaeological contexts enable reconstructions of environs and adaptations of the Urals Pleistocene hunter-gatherers.

This study presents the discovery and detailed analysis of the first confirmed beachrock occurrence on the northern coast of the Gelibolu (Gallipoli) Peninsula in the Gulf of Saros, Northeastern Aegean Sea. Despite the dynamic sandy beaches and rugged coastlines along the southern shores of the gulf, clear evidence of historical co-seismic deformation is preserved in both exposed and submerged beachrock formations. The sedimentary fabric and structural characteristics of these deposits provide critical insights into Late Holocene coastal evolution, including relative sea-level (RSL) fluctuations and tectonic activity. By integrating UAV-based aerial mapping, petrographic and multianalytical microspectroscopic techniques, and radiocarbon dating, this study reconstructs distinct phases of shoreline development shaped by both gradual uplift and episodic seismic events. Radiometric dating of undeformed beachrock indicates ages between 1.1 and 13.6 cal. ka BP, whereas younger, seaward-tilted deposits date to 385 cal. a BP, which is consistent with historical records of the AD 1756 earthquake. After correcting for the local uplift rate (0.76 mm a⁻¹), the data reveal that the RSL decreases by around −0.30 m, aligning with regional Holocene sea-level trends and reinforcing the tectonic context of the Gelibolu Peninsula within a transform-dominated setting. UAV mapping also revealed fracture patterns orthogonal to the North Anatolian Fault (NAF) stress field, supporting links to past seismic events, including the AD 1766 doublet. This study highlights the value of beachrocks as precise geological archives of coastal deformation and sea-level change. Their structural and chronological characteristics refine regional palaeoseismic models and offer a valuable framework for interpreting older or undocumented seismic events along the NAF in the Northeastern Aegean.

Examination of a streamlined flow tract in southern Ontario, Canada using LiDAR-based terrain mapping reveals a landscape that was extensively scoured by ice-constrained subglacial meltwater. Multiple scours and channels without related sediment fans/deltas are eroded into carbonate uplands at the Shield-Palaeozoic margin. Erosion extended across the highest uplands, flanks and lowlands with inset eskers, resulting in a streamlined landscape covered with rounded boulders. Palaeozoic carbonate escarpments reveal rock quarrying on stoss and lee sides, likely indicating ice plucking, load deformation and hydraulic fracture. Meltwater overtopping uplands implies ice lifting off the bed, then re-grounding as flow waned. The widespread erosion, overtopping and presence of boulder lags are indicative of vigorous meltwater scouring of ~10 m of till from carbonate uplands, leaving smooth drumlinized surfaces, scoured by sheetflow and possible ice drag. Rough terrain is inferred to have been meltwater scoured into a series of remnant landforms: poorly defined irregular ridges, scour pits and hummocks, which alternatively possibly resulted from ice deformation and melt-out. We speculate that rough terrain resulted from pressurized, turbulent flow during progressive, rapid ice sheet closure and ice contact. Erosional landscapes upflow near the Palaeozoic margin can be correlated downflow through the Peterborough drumlin field to well-documented channel incision and infill sediments beneath Oak Ridges Moraine (ORM), linked by a regional unconformity. A plausible sequence of events includes erosion of a regional unconformity and a complex series of related events that include meltwater flow, ice floatation, then closure, with combined pressurized scour, deformation, ice/hydraulic erosion and later stagnation. Similar to Icelandic jökulhlaups, flooding likely lasted days/weeks such that eroded uplands formed rapidly (<1-year) followed by matching <1 year deposition (~10–50 m gravel-sand-rhythmite fining upward sequence), documented downflow in subglacial channels beneath ORM. Our results suggest a model of sheet flow progressing to channelized flow for meltwater discharge could be considered elsewhere.

Clast-fabric analysis is a widely used method for investigating depositional and deformation processes in glacial sediments. However, traditional field-based approaches lack standardization, are time consuming and introduce sampling bias. This study aimed to develop a novel approach to automate clast-fabric analysis using machine learning-based image segmentation applied on X-ray computed tomography scanned drill-cores. By retraining a deep neural network and integrating it into state-of-the-art image-segmentation software, we establish a scalable and adaptable workflow for the analysis of sedimentary samples. This included the following: (i) clast segmentation, (ii) object-based analysis, and (iii) fabric analysis. We demonstrate this on drill-core samples of glacial diamicts (tills), achieving performance comparable to leading segmentation models used in geological sciences. We further use this automated workflow to identify grain size-dependent small-scale fabric variations, demonstrating the advantages of deep learning over conventional methods. This workflow provides a foundation for future applications, such as long, continuous drilled sections and field samples, including fluvial and colluvial sediments.

Collared lemmings (genus Dicrostonyx) are an emblematic group of Arctic-tundra mammalian communities, comprising six different species in North America. As other northern fauna, most of their diversity is impacted by Pleistocene glacial–interglacial cycles. While D. hudsonius and D. richardsoni have a restricted distribution area on both sides of the Hudson Bay, D. groenlandicus is widespread in all Nearctic northernmost regions, from Alaska and Canadian mainland to the High Arctic Archipelago and Greenland, occupying a highly fragmented area. Using extensive data, this paper investigates the morphological variability of the molar of Nearctic Dicrostonyx using geometric morphometrics. Our results show weak interspecific differences among Nearctic Dicrostonyx, while demonstrating the existence of a clear geographical structure: a north–south gradient that structures collared lemming's phenotype, surpassing interspecific differences. The possible causes of such patterns are explored, whether they are environmental (e.g. due to local to regional climatic conditions) or phylogeographic (e.g. isolation of the populations during the glacial periods) using ERA5-Land reconstruction climatic data, and a reconstruction of the Laurentide Ice Sheet extent with isometric variations. The peculiar status of several populations, including Greenland and Victoria Island specimens, can be linked with their survival and isolation in Pleistocene ice-free refugia in the High Arctic in agreement with both genetic and morphological signals. We argue that studying present-day morphological variability can provide meaningful information on the Quaternary biogeography of modern species.

The postglacial relative sea level history is reconstructed in four areas of mid- and inner Oslofjorden in southeast Norway. The reconstructions are based on radiocarbon-dated raised shoreline levels from 42 sites, mainly isolation basins, and limiting ages from four lakes above the marine limit. All localities are located inside the Younger Dryas Ra moraine and experienced high rates of glacio-isostatic crustal uplift since deglaciation, by far outpacing the eustatic sea level rise and resulting in continuous regional shoreline regression up until today. A postglacial shoreline diagram is constructed, which can be used to derive relative sea-level curves and to date raised shoreline elevations along the fjord. Reconstruction of shoreline isobases within the study area show that their orientation has shifted more than 60° from the deglaciation until present. The shift has been accounted for in the shoreline reconstructions and is likely showing that the initial postglacial uplift was largely influenced by the geometry and load of the Younger Dryas ice sheet in south Norway. We use the tilt of the oldest, well-dated shoreline levels to date a series of substages during northwards ice margin recession in southeast Norway. The results show that the ice margin retreated from the Ra moraine around 11.6 ka and provide the following ages for subsequent substages: Ås 11.45 ka, Ski 11.4 ka, Aker 11.25 ka, Hauerseter 10.9 ka, Dal 10.8 ka and Minnesund 10.6 ka. The deglaciation and shoreline chronologies are combined to produce regional palaeogeographical maps covering stages of deglaciation and land emergence.

Recent public releases of Light Detection and Ranging (LiDAR) data in south central British Columbia (BC), Canada have revealed several landforms resembling ‘murtoos’, previously identified across portions of Scandinavia. In this study, we investigate the morphology and sedimentology of these landforms, the first report of their kind associated with the Cordilleran Ice Sheet (CIS). From remote observations using LiDAR data, we determined that these landforms do not fit the classification scheme of murtoos used by previous authors, and based on our own observations, we use the term ‘murtooized terrain’, due to their superficial similarities with Scandinavian murtoos. Murtooized terrain consists of 1–8 m high, distinctly steep slopes that can continue laterally up to 2 km, changing in orientation along their lateral lengths, creating angular, zig-zag patterns. It can present as dense, subparallel groupings of slopes giving a washboard appearance. Murtooized terrain occurs in several landscape associations including till plains, ribbed terrain, isolated plateaus and near meltwater corridors. Murtooized terrain in association with till plains and ribbed terrains exhibits distinct hill-hole pairs. It typically consists of diamicton interpreted as a regional till sheet winnowed by persistent subglacial groundwater flow, sometimes overlain by melt-out till and covered with a surface veneer of silt and very fine sand interpreted as loess. Massive sand deposited by postglacial overland flows can fill small troughs at the foot of murtooized terrain slopes. The following event sequence explains the formation of murtooized terrain. The concentration of subglacial groundwater flow through very broad topographic troughs winnowed till and resulted in strong ice-bed coupling through basal ice regelation. Following channelized subglacial floods (underbursts) associated with the formation of large (Chasm and Green Lake) meltwater corridors, the CIS underwent collapse and ice surface slopes were reorganized in the adjacent region. Murtooized terrain formed due to widespread, short-term, glaciotectonism associated with this reorganization where the ice and bed were well coupled. Zig-zag slopes and hill-hole pairs are attributed to spatial variations in coupling. Stagnation followed forming melt-out till and crevasse fill ridges. This hypothesis is distinctly different from those developed for the Scandinavian murtoos, suggesting either that the superficial similarities between BC murtooized terrain and Scandinavian murtoos are the products of formational equifinality or that the BC murtooized terrain is a distinct landform.