Post-glacial Landscape Research Articles

Slip slidin' away: A post-glacial environmental history of the Waipaoa River basin

The dramatic changes that occurred to the post-glacial landscape in the headwaters of the Waipaoa River basin are a consequence of perturbations about the equilibrium that exists between the rate of tectonic uplift and fluvial incision. At times when the amount of coarse sediment delivered to channels exceeds the capacity of streams to remove it, the channel bed rises at the rate of tectonic uplift. Once bedload overcapacity is replaced by undercapacity and the alluvial cover is depleted, streams reestablish contact with bedrock and recuperate the time lost to fluvial incision. The first major perturbation occurred during the final phase of the last glaciation (ca. 33–17.5cal.ka), when aggradation was driven by a climate-forced variation in the relative supplies of sediment and water. We suggest that the subsequent transformation of channels in the headwaters of the Waipaoa River basin, from alluvial to bedrock, occurred as the atmospheric and oceanic circulation converged on their contemporary patterns ca. 12cal.ka. A second major perturbation that continues to the present began ca. 1910–1912CE, when a massive increase in sediment load was accompanied by a modest increase in water discharge after the native vegetation cover in the headwaters was replaced by pasture. The processes of terrace creation and incision are inherently unsteady, and in five interim cases incision was arrested by a transient increase in the thickness of the alluvial cover that was a response to climatic forcing. Events that disrupted the native vegetation cover in the headwaters also modulated patterns of sediment dispersal and accumulation in other parts of the fluvial system and caused rapid, storm-driven infilling of the Poverty Bay Flats. Tectonic subsidence dictates the course of the Waipaoa River across Poverty Bay Flats which, because the modern rate of floodplain construction by vertical accretion is rapid relative to the amount of destruction by lateral channel migration, has remained virtually unchanged for the past 100 years. During this time the channel assumed a narrower, deeper form that is in equilibrium with the contemporary supply of sediment and hydraulic regime.

Climate-driven thaw of permafrost preserved glacial landscapes, northwestern Canada

Abstract Ice-marginal glaciated landscapes demarcate former boundaries of the continental ice sheets. Throughout circumpolar regions, permafrost has preserved relict ground ice and glacigenic sediments, delaying the sequence of postglacial landscape change that transformed temperate environments millennia earlier. Here we show that within 7 × 106 km2 of glaciated permafrost terrain, extensive landscapes remain poised for major climate-driven change. Across northwestern Canada, 60–100-km-wide concentric swaths of thaw slump–affected terrain delineate the maximum and recessional positions of the Laurentide Ice Sheet. These landscapes comprise ∼17% of continuous permafrost terrain in a 1.27 × 106 km2 study area, indicating widespread preservation of late Pleistocene ground ice. These thaw slump, relict ground ice, and glacigenic terrain associations are also evident at the circumpolar scale. Recent intensification of thaw slumping across northwestern Canada has mobilized primary glacial sediments, triggering a cascade of fluvial, lacustrine, and coastal effects. These geologically significant processes, highlighted by the spatial distribution of thaw slumps and patterns of fluvial sediment mobilization, signal the climate-driven renewal of deglaciation and postglacial permafrost landscape evolution.

Spatial characterization of glacial and periglacial landforms in the highlands of Sierra Nevada (Spain).

Sierra Nevada constitutes the southernmost and highest massif in the Iberian Peninsula, with elevations exceeding 3000m. Two large glacial advances were recorded during the Last Glaciation and several minor advances occurred until the Early Holocene. Since then, periglacial activity has prevailed above 2500m. Here, we present a new and more accurate geomorphological map of the highlands of Sierra Nevada, integrating in a GIS environment i) high resolution satellite imagery, ii) topographic data, and iii) field observations. This approach has allowed a better characterization of the spatial extent of cold-climate morphogenic processes and associated landforms formed during the Last Glaciation and subsequent deglaciation. Despite its extension and high altitude, the steep relief of Sierra Nevada and its southern location conditioned a significantly lower glaciated surface (104.6km2) with respect to other Iberian massifs. We have also inferred the paleoclimatic conditions of the study area through the calculation of Equilibrium Line Altitudes (ELAs). The distribution of the lowest moraines suggests an ELA for the maximum glacial extent at 2525m in the northern slope and 2650m in the southern side, increasing towards the east. Local ELA differences are related to: (i) the influence of the warmer Mediterranean Sea in contrast to the cooler Atlantic Ocean, (ii) the climate with more continental characteristics on the northern slope, and (iii) the microscale control of the local topography. Mean annual air temperatures in the ice-free summit plateaus were between -4/-6°C during the maximum local glacial extent, determining permafrost conditions with intense periglacial dynamics. Rock glaciers and protalus lobes developed until 2500m, the lowest boundary for permafrost regime. The distribution of other glacial and periglacial landforms within the limits of the maximum ice extent provides evidence to better understand the extent of subsequent glacial stages and post-glacial landscape evolution in Sierra Nevada.

Postglacial morpholineaments as an indicator of ice sheet dynamics during the Saale Glaciation in the Białystok Plateau and Sokółka Hills (NE Poland)

The palaeogeographical reconstruction of the deglaciation process in NE Poland during the Odranian Glaciation Wartanian Stadial (Saale MIS 6) is based mainly on the analysis of glacial morpholineaments, performed using the GIS programs that provide us with better understanding of the glacial landscape evolution, spatial reconstruction of glacial processes, and postglacial landscape development. Analysis of postglacial morpholineaments was carried out based on the Digital Elevation Model (DEM) as well as geological, geomorphological and topographic maps. It resulted in the delimitation of visible linear postglacial landforms, their identification and classification, and the determination of their genetic and chronological relations. Directions of the lineaments were determined through quantitative analysis. Qualitative analysis was applied to determine the spatial and temporal sequence of events, directions of ice movement and its range. Two glacial lobes, Biebrza and Neman, existed in the north-western part of the Bialystok Plateau and Sokolka Hills during the last glacial advance. The lobed nature of the ice sheet can be confirmed by field data collected from, e.g., sites in Knyszewicze, and by topographic analysis of Quaternary sediments, combined with their thickness and genesis. The obtained reconstruction of the last glacial advance and retreat in the study area can be used in further regional discussions on the character and dynamics of the last glaciation in this region.

Rareness starts early for disturbance-dependent grassland plant species

Ecological communities always contain a few common species and an abundance of uncommon species. Given that most plant mortality occurs in seeds and seedlings, recruitment success often predicts plant community assemblage and patterning, but observational patterns do not reveal whether plant populations are seed or habitat limited. Grassland plant species make up a sizable portion of the overall native flora in northeastern North America (N.A.), but approximately 30 % of the area’s threatened and endangered flora are grassland species, possibly leftovers from the post-glacial landscape. Yet, close relatives of many rare grassland species thrive in the same range. We investigated whether seed or habitat limitation explained rarity and commonness in remnant grassland species. We used seed addition experiments coupled with microhabitat manipulations (burning and herbivore exclusion) in three different habitat types to evaluate recruitment (germination and seedling survival) limitation for three rare and three common grassland species. Rare grassland species successfully recruited where burning reduced initial competitor density, but seedling survival suggested they were severely limited by interspecific competition. Both the rare and common plant species survived equally well in forest habitats where herbaceous density was low whereas neither survived in the edge habitats. Only the common plants thrived in the high-competition meadow habitat, further suggesting that the rare grassland species are poor competitors. Commonness and rarity are temporal designations that can change as disturbance alters the landscape. Glacial retreat and low precipitation in northeastern N.A. created a landscape suitable for poor competitors that tolerated poor conditions. Our results suggest that rare remnant grassland plants, unlike their close relatives, display more biotic than abiotic limitation as they do not compete well with other plants. These results suggest that suitable habitat is not a spatial location but a temporally transient assemblage of species requirements.

Chemostratigraphy of the Ordovician Sarah Formation, North West Saudi Arabia: An integrated approach to reservoir correlation

Late Ordovician pre-glacial and syn-glacial deposits form economically important hydrocarbon reservoirs throughout North Africa and the Arabian Peninsula. Internal subdivision of the unit is difficult due to the short time span of deposition resulting in coarse biostratigraphic control. The arenaceous character of the sediments has also contributed to poor biostratigraphic recovery. The present study focuses on the chemostratigraphic correlation of this interval encountered in ten wells across a complex, multi-phased pro-glacial outwash fan dominated by hyperpycnal (jet-efflux) turbidites fed by glacial outburst floods. The high resolution reservoir layering scheme presented here utilizes detailed sedimentological core descriptions, borehole image-derived palaeoflow indicators, 3D seismic attributes and chemostratigraphy.The Inductively Coupled Plasma – Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) techniques were used to acquire data for 50 elements, with the chemostratigraphic scheme based on changes in the following ‘key’ element ratios: Zr/Y, Zr/Lu, Th/Nb, Th/P, Ta/P, Cr/P, P/Lu, Th/Ti, Cr/Yb and Th/Ta. G may give the impression that there are two principal aims are defined by distinct values of key element ratios, with variations in these mainly reflecting changes in source/provenance. In order to avoid complications relating to changes in grain size/lithology, separate schemes were proposed for sandstone and mudrock lithologies, with the former comprising a hierarchical order of two zones, three subzones and seven divisions. Owing to the lower number of analyzed mudrocks, the scheme produced for this dataset is less detailed but, nevertheless, consists of three principal zones and five subzones.At the formation level, chemical stratigraphy allowed for consistent identification and correlation of the pre-glacial Qasim, syn-glacial Sarah and post-glacial Qalibah formations. The earliest post-glacial unit referred to as the Uqlah Formation has an inherited signature from the syn-glacial chemozone (i.e. uppermost Sarah Formation) below, and represents initial reworking of the post-glacial landscape following isostatic rebound. Evidence for glacial isostasy is recorded in a regional deformed zone at the top of the Sarah Formation and immediately beneath an isostatic rebound unconformity at the base of the Uqlah Formation. Chemical zonation of this unit clearly illustrates significant local truncation in wells located close to NW-SE trending lineaments. It is proposed that chemozones are missing across reactivated fault block highs as a result of increased erosion on the shallow marine post glacial shelf.High resolution reservoir layering of the hydrocarbon-bearing syn-glacial Sarah Formation highlights a complex depositional system characterized by an initial phase of deeply entrenched pro-glacial turbidite channels and younger sheet-like depositional lobes. Cores and image logs from both elements of the outwash fan system record extensive climbing dune cross-bedding, an unusual sedimentary structure described from many Upper Ordovician glacial successions in North Africa, and considered indicative of quasi-steady sediment-charged flows initiated by glacial outburst floods. There is no shared chemical link between the lowest channels and overlying lobes, suggesting a large fan system may be found downdip of this deeper channel system. Integration of the zonation scheme with 3D seismic attribute analysis clearly illustrates a second and even third phase of small channels cross cutting the lower larger vintage that fed the sheet-like younger lobe system. This is substantiated by a shared chemical signature and provenance between these small channels and their attached lobes.

Biogeochemical Stoichiometry Reveals P and N Limitation Across the Post-glacial Landscape of Denali National Park, Alaska

Global warming has accelerated glacial retreat in high-elevation and high-latitude ecosystems, exposing new terrain that can undergo predictable patterns of ecosystem succession, especially in coastal areas with relatively mild climates. However, little work has been done in harsher high-elevation and inland areas where the rate of plant and microbial succession may be greatly slowed by dryness and low temperatures. The present study is the first to address microbial succession at a major glacial foreland (the Middle Fork Toklat Glacier) in the interior of Alaska. We used a spatially nested sampling regime to reveal the landscape patterns in microbial activity and biogeochemical pools during the pre-plant stage of primary succession along this high-elevation and high-latitude chronosequence. Recently deglaciated soils (0–10 years) were colonized by a diverse microbial community that included many chemoautotrophs that likely subsist on high levels of un-weathered minerals (for example, pyrite) found at this site. Rates of N-fixation and extracellular enzyme activities were very low in the youngest soils sampled, but increased during the first 20 years of succession coinciding with a decrease in TOC and C:N levels. In older soils (20–54 years), TOC and TON increased and IN became undetectable perhaps indicating N limitation. Indicators of microbial activity stopped increasing 20 years post de-glaciation and remained at levels well below those seen at lower elevation and lower latitude sites, perhaps indicating severe nutrient limitations. Stoichiometric analyses also indicated phosphorus and nitrogen limitation across the entire chronosequence, with no indication of carbon limitation of microbial activity. These results indicate that nutrient limitation, rather than the constraints of a severe climate, may be the dominant factor slowing the rate of succession at high-latitude and high-altitude glacial forelands.

Geodiversity and Biodiversity of the Postglacial Landscape (Dębnica River Catchment, Poland)

Abstract The preparation of a proper zoning plan or landscape-ecological plan requires taking into account recognition of the natural values of an area covered by the plan and evaluating its abiotic and biotic diversities. The aim of the paper is to present the new approach to the procedure of geodiversity and biodiversity assessment. This procedure is used to characterise abiotic and biotic heterogeneity of the postglacial landscape modified by a man, tested on Dębnica River catchment (Western Pomerania, Poland). This catchment is a representative example illustrating the landscape of Central European Plain. The analytical algorithm of the geodiversity assessment is based on appropriate selection of the evaluation criteria: lithological, relative heights, landform fragmentation, hydrographical elements and mesoclimatic conditions. Biodiversity was assessed on the basis of real vegetation, potential natural vegetation and the degree of anthropisation of the natural vegetation with respect to syngenesis of plant associations. Seven factor maps were obtained: five for the diversity of abiotic elements, and two for the diversity of biotic elements, which became the basis for the creation of total geodiversity and biodiversity maps. Maps produced in accordance with given methodology may find a wide range of applications.

Small water ponds as reservoirs of algae biodiversity

Abstract The areas of northern Poland are typical examples of recently formed post-glacial landscapes with a very large number of small ponds. Phycology of these ponds has been seldom studied, especially when compared to data collected from lager post-glacial lakes. The aim of our study was to determine the importance of small ponds to the biodiversity of algae. In 1996-2002 and 2012-13, we carried out phycological studies in 20 small ponds located in fields and forests. During the study period, we recorded the presence of 503 taxa of algae. The flora of algae was unique in each pond. Another important and frequent observation was the total and rapid “rebuilding” of algal flora. Statistical analyses revealed some other important facts, including the importance of small ponds to algal biodiversity. The average number of taxa recorded during the studies of individual water reservoirs was 56, thus much less than usually recorded in typical large lakes. But when we take the large number of small ponds into consideration, it appears that they represent more than 97% of the populations of algae and for this reason they are important to the biodiversity of algae.

Bedload transport in a formerly glaciated mountain catchment constrained by particle tracking

Abstract. In formerly glaciated mountain settings, Pleistocene glaciations are responsible for profound spatial reorganization of the landscape structure. By imposing local channel slope and the degree of hillslope–channel connectivity, glacial macro-forms can exert first-order controls on the downstream strength and continuity of the coarse sediment cascade. To estimate quantitatively these controls we trace bedload transport for 3 years along Strimm Creek, Eastern Italian Alps. Specifically, we monitor the travel distance of 490 PIT-tagged particles (b axis: 23–229 mm; weight: 83–6525 g) at two contrasting sites: Upper Strimm Creek (US; 4 km2), which flows through a fluvially dominated hanging valley, and Lower Strimm Creek (LS; 7.5 km2), located downstream, in a relict glacial trough where it experiences periodic colluvial sediment inputs from lateral tributaries. Tracer positioning within the streambed is periodically tracked in the field with a portable antenna in order to assess progressive travel distances, as well as the extent of the channel active layer, in relation to snowmelt and rainfall-driven peak flows. Interestingly, we show that tracer virtual velocities for selected inter-survey periods are independent of tracer weight at both study sites. Cumulatively, tracers in US have travelled across distances (i.e. inner quartiles) shorter than 2 m, which correspond to over 2 orders of magnitude less than what was observed in LS. These figures translate, after calculations of tracer inter-survey virtual velocities, into estimated bedload volumes equal to about 3 m3 in US and 600 m3 in LS, with most of the transport (75 % in US, and 93 % in LS) occurring during snowmelt. A similar contrast in bedload transport rates, even without considering the additional volumes of material mobilized by mass-wasting processes in LS, testifies the extent to which the glacial imprinting can still affect contemporary sediment transfer, and thus postglacial landscape evolution, in mountain drainage basins.

Ranunculus schmalhausenii (section Batrachium, Ranunculaceae), a neglected water crowfoot endemic to Fennoscandia—a case of rapid hybrid speciation in postglacial environment of North Europe

The taxa of Ranunculus section Batrachium (Ranunculaceae) have been variably and unsatisfactorily treated in North Europe. Since the description of Ranunculus schmalhausenii (Batrachium dichotomum), probably the most common species in the area, its taxonomic status and identity have been unclear and differently implied. In the majority of treatments, individuals of R. schmalhausenii were ascribed to R. peltatus but sometimes also to the other morphologically similar, heterophyllous taxa. Based on detailed morphological study combined with geographical, ecological and biological evaluation the separate species status of this taxon was finally evidenced. The additive ITS polymorphism pattern of R. schmalhausenii confirmed its hybridogenous origin, however identification of the parental species was impeded by the heterogeneous character of the polymorphism detected. Genetic variation expressed by R. schmalhausenii samples may provide evidence of its multiple origin and suggests sexual reproduction of the taxon. Analysis of a sequence variation of two noncoding cpDNA regions, namely psbE-petL and rpl32-trnL, showed that individuals of R. schmalhausenii inherited cpDNA from two lineages of Batrachium, indicating that this taxon was created at least in two separate hybridization events. Ranunculus schmalhausenii may have originated from sexual ancestral species as multiple created hybrids which have been stabilized by polyploidisation. Genetic structure of R. schmalhausenii is somehow similar to also hybridogenous R. penicillatus. In this study, a detailed morphological, geographical, ecological, and biological description of R. schmalhausenii was presented and the differences between this species and similar taxa were outlined. The name was lectotypified and its synonymy was provided. In contrast to many other heterophyllous species of Ranunculus section Batrachium, R. schmalhausenii occurs mainly in young, postglacial landscapes of Fennoscandia, prefering deep and clear waters with current or wave action and a hard bottom, which perfectly corresponds with a relict, postglacial nature of the species. The species probably presents an example of rapid hybrid speciation (less than 10 000 years) in postglacial environment of North Europe and may be considered as endemic to Fennoscandia. Moreover, R. schmalhausenii, as a weak competitor and pollution sensitive taxon, can be regarded as an indicator of clean waters. Phylogenetic relations within section Batrachium indicates convergent evolution of some species and two cases of possible cpDNA capture.

Old Melioration Systems: The Influence Onto Functioning Of Geoecosystems Of River Valleys In The Parsęta (NW Poland)

Abstract Meliorations and their specific forms – irrigations – are one of the forms of anthropopressure within geoecosystems. The research studies conducted within the Parsęta basin focused on the sub-irrigation (seepage irrigation) systems formed in the 19th century. Query of archive materials and maps, hydrochemical and phytosociological terrain mapping and laboratory testing of water samples collected were used in the studies. In the study area were found the remains of the thirty old irrigation systems, which together occupy 2% of the Parsęta basin area. For many years most of them have not fulfilled their primary economic functions. Still, these systems have an impact on the cycle of waters and have become an important factor in increasing the geo- and biodiversity within the postglacial landscape. By expanding a range of wetland riparian areas, they fulfil relevant functions to protect surface waters against the supply of biogenic components. Some of them could be used to enlarge wetlands and floodplains within river valleys.

Ecosystem development following deglaciation: A new sedimentary record from Devils Lake, Wisconsin, USA

Processes and rates of ecosystem development can be reconstructed using lacustrine sedimentary sequences, but this approach often requires records that contain the start of primary succession. Most lakes in the upper Midwestern U.S. were formed by glaciers at the end of the last Ice Age approximately 11,700 cal yr BP. Devils Lake, Wisconsin is a rare example of a lake from this region whose sediments extend into the Pleistocene and may include the Last Glacial Maximum. Sediment magnetic, geochemical, pollen, and charcoal records were generated from a 10 m core whose basal sediments may be 28,000 years old. Together with a previously published pollen record, these proxies combine to reveal a history of long-term climatic, vegetative and geologic change during the late Pleistocene to Holocene. We identify six sedimentary units that indicate a series of consecutive events rather than a predictable trajectory of ecosystem development at the site. Productivity in the lake was low during the late Pleistocene and increased during the Holocene, as reflected by the sediment lithology, which shows a sudden shift from glacial vivianite-rich and organic-poor clastic-dominated sediments to Holocene diatomaceous sapropels. Several important processes initiated around 17,000 cal yr BP, including the onset of organic matter accumulation and fire in the terrestrial ecosystem. However, the post-glacial landscape was not devoid of vegetation because pollen assemblages indicate that terrestrial vegetation, likely a spruce tundra, survived near the site. A switch to a hardwood forest period during the Holocene also led to a change in the fire regime, with increased frequency of burning. Aquatic ecosystem productivity lagged terrestrial ecosystem productivity throughout the record. Nutrient cycling (as recorded by sedimentary δ15N) was variable but not directional, and appeared to be correlated with climate conditions early in the record, and terrestrial ecosystem processes later in the record. Throughout the Holocene magnetic mineral concentration decreased as productivity increased, and the source of magnetic material shifted from almost exclusively lithogenic to approximately 50% derived from soil or biogenic sources. Magnetic grain size, Ambrosia pollen percentages, and charcoal concentration increased and δ15N decreased in the most recent part of the record, due to anthropogenic influence in the region including agricultural activities.

Postglacial Landscape Changes and Cryogenic Processes in the Picos de Europa (Northern Spain) Reconstructed from Geomorphological Mapping and Microstructures on Quartz Grains

AbstractA 5.4 m long sediment core was collected from Belbín, a karstic depression dammed by a moraine in a mid‐altitude environment in the Western Massif of the Picos de Europa of the Cantabrian Mountains, northern Spain. 14C AMS dating of the basal sediments in the core suggests that the maximum glacier advance during the last glacial cycle preceded the global Last Glacial Maximum and occurred prior to 37.2 ka cal BP. Four environmental stages are reconstructed from analysis of the sediment core and in particular the surface microstructures on quartz sand grains: (1) 37.2–29.4 ka was characterised by intense periglacial activity with deposition of slope deposits; (2) 29.4–22.6 ka saw the gradual infilling of the depression with sediment; (3) 22.6–8.1 ka was associated with a palaeolake; and (4) since 8.1 ka, terrestrialisation of the palaeolake commenced, and human impact related to fire activity started around 4.9 ka. Microstructures on the surface of quartz grains suggest different intensity patterns of frost weathering processes in response to Late Quaternary climate oscillations. Copyright © 2015 John Wiley & Sons, Ltd.

Toward a luminescence chronology for coastal dune and beach deposits on Calvert Island, British Columbia central coast, Canada

The Quaternary geology of the central coast of British Columbia contains a rich and complex record of glacial activity, post-glacial sea level and landscape change, and early human occupation spanning the last ∼10,000 years. At present, however, this region remains a largely understudied portion of coastal North America. This study describes the luminescence characteristics of quartz and K-feldspar from coastal dune and beach sands on Calvert Island and develops a suitable optical dating protocol that will allow for a more rigorous chronology for post-glacial landscape evolution and human occupation on British Columbia's central coast. Luminescence signals from Calvert Island quartz are dim, and appear to lack the so-called “fast” component that is most desirable for optical dating. K-feldspar signals are sufficiently bright for optical dating. We test and refine a single-aliquot regenerative-dose (SAR) protocol for K-feldspar specific to Calvert Island samples through a series of dose recovery and preheat plateau tests. Two approaches for correcting a sample age for anomalous fading are compared and a correction for phototransfer is introduced and applied. Measured fading rates vary from sample to sample implying that, in this region, it is not sufficient to rely on two or three representative fading rates as has sometimes been done elsewhere. Refined age estimates show consistency with independent radiocarbon dating control and help identify radiocarbon-dated organic-rich sediments that have been reworked.

The Younger Dryas Main Line on Leka, Norway, as determined from a high resolution digital elevation model derived from airborne LiDAR data

The Main Line is a conspicuous late glacial erosive feature along parts of the Norwegian coastline. Although the shoreline has been much studied, the genesis of the ancient raised sea-level is still somewhat unaccounted for. In this study, the Main Line on Leka, Norway, is illuminated through a high resolution (1mpixel size) digital elevation model (DEM) derived from airborne LiDAR data. The DEM allows a detailed mapping of the shoreline's dimensions and actual distribution and hence provides an improved foundation for interpreting the pronounced features. A new method for estimating cliff degradation during shoreline formation is presented. The Main Line is found from 106–112masl on Leka. Varying platform morphology across the island points to different shore-eroding mechanisms. The shoreline is thought to be developed through the interaction of sea–ice processes and freeze–thaw mechanisms, where the former agent is considered to be of particular importance where the platforms are most levelled. A bulge on the outermost part of the shoreline features is described for the first time and interpreted as a consequence of freeze-on plucking. Mean platform widths range from 9–29m, while mean cliff degradation is estimated to be 140m3m−1. By adapting the age span of Main Line formation reported elsewhere, maximum erosion rates over 1Ma totals to 58km. The study sheds light on the Main Line's potential as a reference level when assessing postglacial landscape development and highlights the significance of episodic erosional events in cold climate regimes.

Age and Land Use as Factors Differentiating Hydrochemistry and Plant Cover of Astatic Ponds in Post-Agricultural Landscape

Abstract Small, astatic ponds are important features of post-glacial landscape, which support heterogeneity and biodiversity of agricultural areas. In the presented research we explored differences in hydrochemistry and plant cover of 20 small ponds located in Northeastern Poland, characterized by diverse age and developed in differently managed areas. According to our research, though changes in water level are under direct influence of water balance in the catchment, to which belonged the ponds, their hydrochemistry seemed to be shaped by processes at the level lower than the catchment scale. Age of the ponds appeared to be an important factor influencing density and species composition of vegetation developed on the studied ponds.

Late Holocene temporal constraints for human occupation levels at the Bodo archaeological locality, east-central Alberta, Canada using radiocarbon and luminescence chronologies

The Bodo Archaeological Locality in east-central Alberta is one of the largest precontact (prehistoric) archaeological sites in the Canadian Prairie Ecozone. Situated at the transition between the aspen parkland and fescue grassland regions within a postglacial eolian dune landscape, the site has the potential to add to existing understandings of cultural–environmental dynamics as they relate to late Holocene hunter-gatherer settlement and subsistence patterns in the region. To that end, we present a composite stratigraphy for the locality constructed from five separate sampling pits, obtaining chronological control using accelerator mass spectrometry radiocarbon and luminescence ages. We identify three main periods of landscape stability and associated human occupation during the late Holocene: 750 to 400 cal B.C., 750 to 1000 cal A.D., and 1450 to 1750 cal A.D. Early Holocene eolian activity is documented, but the mid-Holocene stratigraphic record is absent, suggesting extensive sediment reworking. Evidence also exists of major cultural landscape changes that coincide with the arrival of Euro-Canadians.

How glaciers grow

A state-of-the-art numerical model shows that the advance of glaciers in a cooling climate depends strongly on the pre-existing landscape, and that glacial erosion paves the way for greater glacial extent in the future. See Letter p.206 Large parts of the Earth's surface were glaciated during the Quaternary cold periods of the past 2.5 million years, and these events have left their mark on the mountain topography we see today. Post-glacial landscapes tend to feature large areas concentrated at the same elevation, but the effect of this on subsequent glaciations was unknown. Vivi Pedersen and David Egholm use numerical simulation of glaciation and case studies of alpine topography of the Sierra Nevada, Spain, where there was little glacial activity in the Quaternary, and the Bitterroot Range in Idaho, which was significantly modified by glaciers during the Quaternary. The results show that prior glaciations transform a system from one in which climate exerts a near-linear influence on glacial extent to one in which a small change in climate can result in massive glacial expansion. This helps to explain the long-term patterns of erosion in the Quaternary period.

The Vale of Pickering in the Mesolithic: uncovering the early post-glacial landscape

Since 1954, when Grahame Clark published the results of his excavations at Star Carr in northeast Yorkshire, the site has been recognized as a key to understanding early Mesolithic huntergatherer settlement and subsistence in northwest Europe. In 1976, archaeological and palaeoenvironmental research in the area was resumed - since 1986 under the auspices of the Vale of Pickering Research Trust - and it is now possible to set Star Carr and nearby Mesolithic sites in the wider context of the early postglacial landscape.