Early Holocene Times Research Articles

Holocene gigascale rock avalanches in Vaigat strait, West Greenland—Implications for geohazard

Abstract Rock avalanche–triggered displacement waves (also termed tsunamis) have recently occurred in Greenland and Alaska, and they illustrate the presence of such hazards in polar regions. To improve understanding of the magnitude of this hazard for these areas, we investigated gigascale subaerial rock avalanches impacting a partially confined water body within the Vaigat strait (western Greenland). We present a new combined subaerial to subaqueous digital elevation model, alongside a new compilation of seismic data, which revealed nine deglacial to Holocene rock avalanche complexes that are between one and two orders of magnitude larger than nearby historical rock avalanches. The three largest complexes have deposit thicknesses up to 300 m, runout distances reaching 19 km, and best-estimate volumes from 1.7 to 8.4 km3. Based on the morphology and the volume–angle of reach relations, it is likely that each complex represents a single or few events, thus making them among the largest displacement wave–generating subaerial to submarine rock avalanches on Earth. We estimated displacement wave magnitude up to 280 m on the opposite shore. The ages of the deposits are poorly constrained but the main rock avalanche activity is referable to early Holocene times. With significant climatic changes predicted in the Arctic, we recommend that hazard assessments account for events not only from the historical record but also those from the recent geological past.

Studia porównawcze kultur łowiecko-zbierackich Europy i Północnej Ameryki

This paper presents the results of a Polish-American research project lasting ten years comparing the widely separated hunting gathering societies that experienced similar changing environments in the Old and New World during the final Pleistocene and the early Holocene times. The study intended to compare the technological and economic histories of this societies living in the same time on the North European plain and the North Central United States. Over the period of time in question, they experienced the same changes of climate and environment. The results of the project permit us to say that the hunter gatherers adaptation process was often only slightly, and over time hardly at all dependent on environmental changes.

Analysis of the Potential Range of Mountain Pine-Broadleaf Ecotone Forests and Its Changes under Moderate and Strong Climate Change in the 21st Century.

Climatic changes have a significant impact on the composition and distribution of forests, especially on ecotone ones. In the Southern Ural, pine-broadleaf ecotone forests were widespread during the early Holocene time, but now have persisted as relic plant communities. This study aimed to analyze the current potential range and to model changes in habitat suitability of relic pine-broadleaf ecotone forests of the suballiance Tilio-Pinenion under scenarios of moderate (RCP4.5) and strong (RCP8.5) climate change. For modelling, we used MaxEnt software with the predictors being climate variables from CHELSA Bioclim, the global digital soil mapping system SoilGrids and the digital elevation model. In the Southern and Middle Urals, climate change is expected to increase the areas with suitable habitat conditions of these forests by the middle of the 21st century and decrease them in the second half of the century. By the middle of the 21st century, the eastern range boundary of these forests will shift eastward due to the penetration of broad-leaved tree species into coniferous forests of the Southern Ural. In the second half of the century, on the contrary, it is expected that climate aridization will again shift the potential range border of these forests to the west due to their gradual replacement by hemiboreal coniferous forests. The relationship between the floristic composition of pine-broadleaf forests and habitat suitability was identified. In low and medium habitat suitability, pine-broadleaf forests contain more nemoral species characteristic of deciduous forests of the temperate zone, and can be replaced by broadleaf forests after thinning and removal of pine. In the Volga Upland, suitable habitats are occupied by pine-broadleaf forests of the vicariant suballiance Querco robori-Tilienion cordatae. Projected climatic changes will have a significant impact on these ecotone forests, which remained completely unaltered for a long time.

Sedimentary characteristics of baer knolls deposits in the volga river delta

Baer knolls (BK) are elongated ridges often close to the sub-latitudinal orientation sometimes spatially isometric that are widespread in the entire Northern Caspian Region up to 0 m a.s.l. (the upper limit of the Late Khvalynian sea transgression). The goal of this study was to establish the genesis of BK based on interpretation of textural and lithologic characteristics of sediments and dating the material composing these landforms. Research has led to the following conclusions that BK have been formed during the transition of Late Khvalynian and Early Holocene time. Sediments of BK consists of three lithofacies (LF1, LF2, LF3). Chocolate clay (CC) and Volga alluvium were significant sources of material for knolls formation. Nonetheless, for lithofacies 1, it was also sandy material lying below the CC. The BK material cannot be attributed to the aeolian genesis because of its lithological, faunal and geochemical characteristics. The knolls formed in brackish subaquatic conditions of the lagoon floor, where a low-energy currents occurred due to the descent of Late Khvalynian basin waters through the Manych Strait. Thus, BK are analogues of river bedforms appearing as the result of turbulent flow, like ripples and river dunes, where, in concordance with the accumulation of sandy material and detritus of redeposited shells, clay particles were deposited under the mixing of the brackish water of the lagoon and the fresh water of the rivers flowing into it.

Did the Younger Dryas to Holocene climate transition favour high seismicity rates in the north‐western Alps?

ABSTRACTIn the French north‐western Alps, several lakes of glacial origin, such as Aiguebelette and La Thuile, present some mass‐transport deposits within their sedimentary sequences. These event layers can result from lake sediment destabilization eventually triggered by earthquakes. On Lake Aiguebelette, based on sedimentological, geochemical and magnetic analyses, and high‐resolution seismic and bathymetric surveys a ca 1 m thick event layer was identified in the deepest lake basin and a synchronous ca 2 cm thick deposit in the shallow basin. Age‐depth models based on radiocarbon ages reveal that both mass‐transport deposits in Lake Aiguebelette occurred around the Younger Dryas – Early Holocene climatic transition (i.e. 11 700 cal bp) time range. In Lake La Thuile, located 30 km away, unique mass‐transport deposits (translational slide type) were recorded at the same time range in sedimentary records. Additionally, high‐resolution seismic profiles previously acquired in Lake Annecy and Lake Bourget support the hypothesis of significant mass‐transport deposits occurring at the Younger Dryas – Early Holocene time range. These outcomes on four north‐western peri‐Alpine and Alpine lakes highlight the regional occurrence of mass‐transport deposits in the Younger Dryas – Early Holocene time range. Seismic and rockfall events are discussed as potential sources of these significant and similarly aged mass‐transport deposits. Based on this study and a literature review, the authors suggest that mechanisms induced by rapid climate change and glacial retreat, such as crustal rebound and erosional unloading, could favour the triggering of earthquakes and rockfall events. In the case of mass‐transport deposits archived in north‐western Alpine lakes during this time period, this study favours the hypothesis of increased seismicity as the primary source driving process involved.

Lateglacial to Mid-Holocene Vegetation History in the Eastern Vale of Pickering, Northeast Yorkshire, UK: Pollen Diagrams from Palaeolake Flixton

Palaeolake Flixton, in the eastern Vale of Pickering in northeast Yorkshire, UK, existed as open water during the Lateglacial and early to mid-Holocene, until hydroseral succession and gradual terrestrialisation changed it to an area of fen and basin peatland by the later mid-Holocene. The environs of the lake were occupied by Late Palaeolithic and Mesolithic people over thousands of years and many Early Mesolithic sites, in particular, have been found located along the ancient lake edge, including the paradigm site for the British Early Mesolithic at Star Carr, where occupation occurred over several centuries. We have analysed eleven sediment cores, distributed in most parts of the palaeolake area, for pollen and stratigraphic data with which to reconstruct lake development and vegetation history. These new diagrams augment earlier pollen studies from the western part of the lake, particularly in the Star Carr area and near other major Mesolithic sites around Seamer Carr. Especially informative are a long core from the deepest part of the lake; cores that document the Lateglacial as well as early Holocene times, and evidence for the later Mesolithic that helps to balance the high density of Late Mesolithic sites known from research in the adjacent uplands of the North York Moors. There are many records of charcoal in the deposits but, especially for the earliest examples, it is not always possible to tie them firmly to either human activity or natural causes. Overall, the new and previously existing diagrams provide evidence for the spatial reconstruction of vegetation history across this important wetland system, including (a) for the progression of natural community successions within the wetland and on the surrounding dryland (b) the influence of climate change in bringing about changes in woodland composition and (c) for discussion of the possibility of human manipulation of the vegetation in the Late Upper Palaeolithic, Early and Late Mesolithic. Results show that climate was the main driver of longer-term vegetation change. Centennial-scale, abrupt climate events caused significant vegetation reversals in the Lateglacial Interstadial. The Lateglacial vegetation was very similar throughout the lake hinterland, although some areas supported some scrubby shrub rather than being completely open. Immigration and spread of Holocene woodland taxa comprised the familiar tree succession common in northern England but the timings of the establishment and the abundance of some individual tree types varied considerably around the lake margins because of edaphic factors and the effects of fire, probably of human origin. Woodland successions away from proximity to the lake were similar to those recorded in the wider landscape of northern England and produced a dense, homogenous forest cover occasionally affected by fire.

Pollen-based biome reconstruction on the Qinghai-Tibetan Plateau during the past 15,000 years

Reconstruction of past vegetation change is critical for better understanding the potential impact of future global change on the fragile alpine ecosystems of the Qinghai-Tibetan Plateau (QTP). In this paper, pollen assemblages comprising 58 records from the QTP, spanning the past 15 kyrs, were collected to reconstruct biome compositions using a standard approach. Six forest biomes were identified mainly on the southeastern plateau, exhibiting a pattern of gradual expansion along the eastern margin during early to mid-Holocene times. The alpine meadow biome was separately identified based on an updated scheme, and showed notable westward expansions towards lower latitudes and higher altitudes during early Holocene times. Consistent patterns of migration could also be identified for the alpine steppe biome, which moved eastward during the late Holocene after 4 ka. As the dominant biome type, temperate steppe was distributed widely over the QTP with minor migration patterns, except for a progressive expansion to lower altitudes in the late Holocene times. The desert biome was inferred mainly as covering the northwestern plateau and the Qaidam Basin, in relatively restricted areas. The spatial distribution of the reconstructed biomes represent the large-scale vegetation gradient on the QTP. Monsoonal precipitation expressed predominant controls on the development of alpine ecosystems, while the variations in desert vegetation responded to regional moisture brought by the mid-latitude Westerlies. Temperature changes played relatively minor roles in the variations of alpine vegetation, but exerted more significant impacts on the forest biomes.

Luminescence ages and new interpretations of the timing and deposition of Quaternary sediments at Natural Trap Cave, Wyoming

Natural Trap Cave, located in the Big Horn Mountains of north-central Wyoming, has a history of trapping and preserving a range of North American fauna that plummeted into the deep vertical entrance. These animal remains were buried and preserved within sediments of the main chamber and, in turn, have helped elucidate the procession of faunal dynamics during the latest glacial cycle. The cave location, south of the Laurentide and Cordilleran Ice Sheets, and proximal to Yellowstone, is at an ideal geographical juncture to provide insights to ecological changes in North America. The sediments that the animals are buried in inform us about transport and deposition both inside and outside of the cave that relate to catchment dynamics. We report on a series of optically stimulated luminescence (OSL) ages derived from samples obtained within the cave during excavation work in 2014 and in 2018. We also examine chronology produced by argon, tephrochronology, fission track, and luminescence techniques that have been used for understanding the infilling of the cave. The cave sediment ages and in situ measured gamma spectroscopy as measured in this study helped resolve an improved chronological age model when combined with previous data.The suite of OSL ages is interpreted through the stratigraphic relationships (and vertebrates contained within) which requires the use of an adequate age model; we use either the central age model or minimum age model where appropriate and with justification. Lowest sediments are dated to ∼150 ka with a hiatus at ∼130 to 52 ka. Above this, sediment deposition and entrainment of paleontological materials are representative of Pleistocene and early Holocene times, between 37 ± 6 ka and 7.6 ± 0.5 ka. The stratigraphic architecture suggests that deposition of materials into the cave is episodic and rapid, followed by quiescent periods where hydrologic scour, heavy overland flow, or possibly a cryo-hydrologic process may have altered unit relationships. Thus, the complementary geochronometers and the characteristics of quartz versus feldspar luminescence signals improve temporal interpretations of these complex deposits. This adapted understanding of mixing also sets the stage for future work with the aim to improve our understanding of ages and sources for ash units within these cave deposits. The three ash units recognized in the cave may represent an in-situ reworking of the same ash or may be representative of previously undocumented eruptions from the Yellowstone Caldera.

Extra-large grains in Late Glacial – Early Holocene aeolian inland dune deposits of cold climate, European Sand Belt, Poland: An evidence of hurricane-speed frontal winds

Only exceptionally, grains larger than 2–3 mm are involved in dune-forming processes. In 16 Late Glacial – Early Holocene inland dunes deposits from three regions of the northern and central Poland, beds, layers, laminae and lenses containing extra-large grains, up to 20.5 × 12.5 × 11 mm in the longest axes, are present. Occurrences of the extra-large grains are documented in the dunes dispersed in three distinct physiographic regions, Biebrza Basin, Central Poland Lowlands, Przedbórz Upland and the adjacent part of the Włoszczowa - Nida Basin. An aeolian genesis of these deposits is proven by sedimentary features and morphology of the landforms, including simple forms of parabolic, longitudinal and transverse dunes, as well as large, complex depositional forms. The extra-large grains occur at various depths in the sandpit sections, ranging from a few tens of centimetres just the above contact of dune deposits with the substrate up to a few tens of centimetres below the top of the dune section. Outcrops with the extra-large grains are located on both lee and stoss sides in the dune landforms. Deposits bearing extra-large grains show nearly horizontal and low angle lamination, which is typical of the dune stoss sides, to high angle foresets, which are typical of lee sides of dune landforms. Several sites display up to seven layers of the extra-large grains, indicating a few episodes of extremely strong and relatively steady wind during the dune-forming period. Estimation of the wind velocity threshold for such coarse material shows values between 23 and 82 m s−1, for speeds 1 m above the surface. On the basis of measured dimensions and volumes of particular pebbles, a principal component analysis demonstrates that the distribution of grain dimensions is clearly heterogeneous between the three physiographic regions of northern and central Poland. The concentration of values from the Central Poland Lowlands dataset is significantly higher than in the other two regions. This might have been caused by the lack of wind-flow terrain constraints in the mostly flat area of the Central Poland Lowlands. In contrast, the relatively high variance of grain dimension parameters could have been caused by the inconstancy of wind velocity and direction over the undulated morphology of the other two regions. The prevailing western direction of transportation points to frontal, episodically hurricane-speed winds (>20–40 m s−1), which were able to transport the extra-large grains during Late Glacial – Early Holocene times, in the area south of the Scandinavian ice sheet. The relatively rare occurrence of layers and laminae with extra-large grains in the investigated dune deposits suggests specific processes leading to their formation. However, reports of 16 outcrops with the extra-large grains imply that aeolian transport of very coarse material is not only a scientific curiosity, but a process occurring on a broader scale.

Dynamics of vegetation cover and quantitative palaeoclimatic reconstructions in the Western Sayan Mountains from the Late Glacial period to the present time according to a palynological study of the Yuzhno-Buybinskoe mire

The aim of this research is an investigation of long-term palaeoclimatic changes. In this paper we present results of a palaeopalynological study of a high mountain peat-lake sediment core from the Yuzhno-Buibynskoe Mire in the Western Sayan Mountains covering the last 13000 cal yrs BP. In addition to qualitative palaeopalynological reconstructions we have performed quantitative reconstructions of T January, T July, and Annual precipitations using our own transfer functions constructed on 118 surface pollen spectra by a method developed by ter Braak and coauthors [16]. The results of the quantitative palaeclimatic reconstructions have demonstrated three types of climate changes in the study area from the Late Glacial period to the present time: cryo-arid climate in the Late Glacial period from 13000 cal yr BP to 11000 cal yr BP (I), humid moderate cool climate in the Middle Holocene (II) and humid cool climate in the Late Holocene after 5000 cal yr BP (III). The cold climate during the Late Glacial period was caused mostly by low winter temperatures combined with low annual precipitation, while the summer temperatures were equal or even higher than modern ones. This is characteristic for the anticyclone influenced areas. The winter temperatures and annual amount of precipitation considerably increased in all areas of the Altai-Sayan region during the early and middle Holocene times, when Atlantic cyclones reached this area. In the Late Holocene period we observe a gradual return to the climatic parameters of the pre-Holocene time.

A first reconstruction of the evolution of Cubilche Volcanic Complex, Imbabura Province, Ecuador

Cubilche Volcanic Complex (Imbabura Province, Ecuador) includes three morphologically well-preserved eruptive centers: in increasing size, Cunrru Dome Complex (3300 m above sea level, m asl), Panga Ladera (3420 m asl) and Cubilche (3836 m asl). As this complex is poorly known, we conducted a volcanological study of its evolution by combining geomorphological, lithostratigraphic, radiocarbon (14C), and petrological analyses, along with eruption size determinations. Cunrru Dome Complex shows an eastward-opening scarp formed during a dome collapse event that emplaced a small-volume debris avalanche deposit and a pumice-rich layer from an accompanying directed explosion. The higher Panga Ladera edifice is breached towards the north, and the emplacement of the resulting debris avalanche deposit was also accompanied by a blast-forming eruption of ash and pumice. The post-collapse vent subsequently produced dilute pyroclastic density currents (PDCs) that built a low cone. The Cubilche eruptive center comprises old and young edifices. The Old Cubilche edifice emitted lavas from a summit crater and flank vents before being partly destroyed during a flank failure event associated with an explosive eruption that produced a widespread pyroclastic density current deposit dated at ca 44 ka and an associated pyroclastic fall deposit. The Young Cubilche cone grew inside the Old Cubilche avalanche crater during ~14–19 ka over five eruptive episodes that included early effusive eruptions, a dome growth period that terminated with a PDC that emplaced scoria flow deposits at ca 29.6 ka, an explosive eruption at ca 26.3 ka, and final Strombolian activity emitting more mafic products. As the adjacent Imbabura Volcanic Complex erupted in early Holocene times and the two complexes seem to share common reservoirs and plumbing systems, we cannot fully discard a possible reactivation at Cubilche. Other more short-term hazards are debris flows and landslides potentially triggered by heavy rain fall and/or seismic events.

Aquatic fauna from the Takarkori rock shelter reveals the Holocene central Saharan climate and palaeohydrography.

The abundant faunal remains from the Takarkori rock shelter in the Tadrart Acacus region of southwestern Libya are described. The material that covers the period between 10,200 to 4650 years cal BP illustrates the more humid environmental conditions in the Central Sahara during early and middle Holocene times. Particular attention is focussed on the aquatic fauna that shows marked diachronic changes related to increasing aridification. This is reflected in the decreasing amount of fish remains compared to mammals and, within the fish fauna, by changes through time in the proportion of the species and by a reduction of fish size. The aquatic fauna can, in addition, be used to formulate hypotheses about the former palaeohydrographical network. This is done by considering the possible location of pre-Holocene relic populations combined with observations on the topography and palaeohydrological settings of the Central Sahara.

Holocene glacier fluctuations on the northern flank of Cordillera Darwin, southernmost South America

Records of past variability afford context for evaluating present-day glacier behavior and for testing hypotheses of climate change. Here, we use 69 radiocarbon dates of wood and other organic materials in association with glacial deposits to document the behavior of Ventisqueros Marinelli and Brooks in Cordillera Darwin over the past ∼17,000 years. Recession from the last glacial maximum was early, with most occurring prior to 17,000 yr BP. Any glacial resurgence during the Antarctic Cold Reversal must have terminated within the bounds of Holocene ice fluctuations. By early Holocene time, Ventisquero Marinelli had retreated such that it was no more extensive than it was in AD 1992. We identify several subsequent glacier readvances, but also note long periods of restricted ice extent, particularly in the mid-Holocene. There were times when Holocene glaciers must have been smaller than at present. Our new record from Marinelli shows similarities to other reconstructions of Holocene glacier variation from southern South America, such as at Mt. Sarmiento and the South Patagonian Icefield, suggesting an underlying climate signal. The overall implication is of substantial early Holocene deglaciation followed by repeated advances interspersed with periods of recession when ice extent was smaller than at present. This general pattern of glacier behavior appears to differ from that of New Zealand's Southern Alps and points to the value of a geographic spread of datasets to elucidate the pattern of Southern Hemisphere climate during the Holocene.

Unravelling the Holocene environmental history of south-western Iberia through a palynological study of Lake Medina sediments

Lake Medina is a small, shallow and endorheic salt lake sensitive to climate variation in south-western Spain, close to Cádiz in western Andalusia. It is located in an evaporitic and karstic environment, and a saline lake affected by highly seasonal precipitation and evaporation. Geochemical and mineralogical data of core CO1313 combined with a robust age model show variation that contributes to the understanding of palaeoenvironmental and palaeoclimatic change. This study shows a pollen record that has been conducted on core CO1313, together with charcoal and non-pollen palynomorph analyses. The environmental and climatological history reconstruction of Lake Medina starts in early Holocene times (at 9.5 cal. ka BP) and shows intensified pasture and land use during middle-Holocene times as well as the 8.2 and 4.2 cal. ka BP abrupt climate events. Oxidation of plant remnants and resulting non-preservation at certain times reinforces the hypothesis of intense climate effects on vegetation during the 4.2 cal. ka BP climate event. Yet, oxidation of plant residues during other episodes shows other periods that were also affected by reduced precipitation. From around 2 cal. ka BP onwards, a recent trend towards aridification and enforced seasonality was detected.

Mobilization of fine detritus to the Dead Sea Basin during the late glacial and early Holocene

The mineralogical, grain size and geochemical properties (e.g., Nd and Sr isotopes, Mg/Al ratios) of fine detritus that accumulated in the Dead Sea during the late Glacial to early Holocene time (∼22–7 ka) are used to identify its sources and modes of transport and to reconstruct the hydroclimate conditions in the Dead Sea watershed. Samples were retrieved from the DSDDP -5017-1A core that was drilled in the deep floor of the lake, and from various exposures of surface cover in the lake's watershed. The data show that during most of the late glacial, detrital particles were either directly blown mostly from the north Sahara Desert or were washed from the surface cover (loessial soils) of the north Negev Desert and Judea Desert. This picture changed during the end of the last glacial to the early Holocene (∼14 - 7 ka) when the fine detritus showed evidence for contribution from surface cover that contained basaltic soils. The contribution of basaltic soils to the fine detritus inventory of the Dead Sea and to terraces in the Jordan Valley, indicates a period of intense erosion in the northern highlands of the Dead Sea watershed, at an interval that partly coincides with Sapropel S1. In contrast, during the last interglacial Sapropel S5, fine detritus was mostly mobilized to the lake from southern and eastern region of the watershed. The formation and accumulation of terraces from this basaltic-derived material could be an important factor in the establishment of early agriculture settlements in the Jordan Valley.

Degradation of cystatin C, an endogenous cathepsin inhibitor, stabilizes cathepsin B activity within pancreatic zymogen granules

The mineralogical, grain size and geochemical properties (e.g., Nd and Sr isotopes, Mg/Al ratios) of fine detritus that accumulated in the Dead Sea during the late Glacial to early Holocene time (∼22–7 ka) are used to identify its sources and modes of transport and to reconstruct the hydroclimate conditions in the Dead Sea watershed. Samples were retrieved from the DSDDP -5017-1A core that was drilled in the deep floor of the lake, and from various exposures of surface cover in the lake's watershed. The data show that during most of the late glacial, detrital particles were either directly blown mostly from the north Sahara Desert or were washed from the surface cover (loessial soils) of the north Negev Desert and Judea Desert. This picture changed during the end of the last glacial to the early Holocene (∼14 - 7 ka) when the fine detritus showed evidence for contribution from surface cover that contained basaltic soils. The contribution of basaltic soils to the fine detritus inventory of the Dead Sea and to terraces in the Jordan Valley, indicates a period of intense erosion in the northern highlands of the Dead Sea watershed, at an interval that partly coincides with Sapropel S1. In contrast, during the last interglacial Sapropel S5, fine detritus was mostly mobilized to the lake from southern and eastern region of the watershed. The formation and accumulation of terraces from this basaltic-derived material could be an important factor in the establishment of early agriculture settlements in the Jordan Valley.

Using a new database of plant macrofossils of the Czech and Slovak Republics to compare past and present distribution of hypothetically relict fen mosses

Modern databases containing large amounts of botanical data are a promising source of new results based on large data analyses. We used a new database of plant macrofossils of the Czech and Slovak Republics to compare the recent distributions of putative relict species of fen bryophytes with their past distributions since the late glacial. All the species studied occur in late-glacial sediments, but mostly in regions where they are recently recorded (19–21st centuries). There are specific regions rich in putative relict species of fen bryophytes both in late glacial / early Holocene times and recently. In some cases the target species were, however, found outside the recent distribution range where environmental conditions are no longer suitable for their occurrence. We further found that the total number of the glacial and early-Holocene records greatly exceeds the total number of records for the middle Holocene, when succession to woodlands or bogs resulted in a reduction in species of bryophytes that are specific to open rich fens. The observed patterns may imply a relict status of the target species. We especially documented a substantial decline in the abundance of species requiring a high and stable water level (Drepanocladus trifarius, Meesia triquetra and Scorpidium scorpioides), both throughout the Holocene and during the most recent transformations of the landscape. In contrast, those species that tolerate transient decreases in water level persisted into recent times at more localities (Calliergon giganteum, Hamatocaulis vernicosus, Paludella squarrosa). Macrofossil data cannot, however, provide a quantitative analysis of the distribution of a species, because the number of recent data usually greatly exceeds the number of fossil records. The reason is that the area sampled in palaeoecological research is very small as it is time-consuming and expensive; cores or excavations usually are of only a few square centimetres. Despite this shortcoming, macrofossil data are an important, but not the only, source of evidence for the identification of the relict status of a species.

Postglacial to Holocene landscape evolution and process rates in steep alpine catchments

AbstractClimate change and high magnitude mass wasting events pose adverse societal effects and hazards, especially in alpine regions. Quantification of such geomorphic processes and their rates is therefore critical but is often hampered by the lack of appropriate techniques and the various spatiotemporal scales involved in these studies. Here we exploit both in situ cosmogenic beryllium‐10 (10Be) and carbon‐14 (14C) nuclide concentrations for deducing exposure ages and tracing of sediment through small alpine debris flow catchments in central Switzerland. The sediment cascade and modern processes we track from the source areas, through debris flow torrents to their final export out into sink regions with cosmogenic nuclides over an unprecedented five‐year time series with seasonal resolution. Data from a seismic survey and a 90 m core revealed a glacially overdeepened basin, filled with glacial and paraglacial sediments. Surface exposure dating of fan boulders and radiocarbon ages constrain the valley fill from the last deglaciation until the Holocene and show that most of the fan existed in early Holocene times already. Current fan processes are controlled by episodic debris flow activity, snow (firn) and rock avalanches.Field investigations, digital elevation models (DEMs) of difference and geomorphic analysis agree with sediment fingerprinting with cosmogenic nuclides, highlighting that the bulk of material exported today at the outlet of the subcatchments derives from the lower fans. Cosmogenic nuclide concentrations steadily decrease from headwater sources to distal fan channels due to the incorporation of material with lower nuclide concentrations. Further downstream the admixture of sediment from catchments with less frequent debris flow activity can dilute the cosmogenic nuclide signals from debris flow dominated catchments but may also reach thresholds where buffering is limited. Consequently, careful assessment of boundary conditions and driving forces is required when apparent denudation rates derived from cosmogenic nuclide analysis are upscaled to larger regions. © 2018 John Wiley & Sons, Ltd.

Hunting in yellow waters: an ethnoarchaeological perspective on selective fishing on Lake Turkana

As riverine and lacustrine environments expanded across north tropical Africa during early Holocene times, certain characteristic fishing or “aquatic hunting” strategies became widespread. This paper investigates one such strategy and an associated technology: selective fishing and barbed bone “harpoon” points in the Turkana Basin, northwest Kenya. These tools have a geographically widespread distribution across Africa, primarily north of the equator, and can shed light on hunter-gatherer technology and resource acquisition in the face of environmental and social change. Interviews with contemporary Turkana fishers highlight near-shore fishing practices analogous to those of early Holocene hunter-gatherers. For example, Turkana fishers exploiting deltaic “yellow waters” have traditionally employed selective harpoon-like tools to acquire large aquatic fauna like Lates niloticus (Nile perch) and Synodontis sp. (catfish), while using non-selective traps, hooks and nets to catch smaller and deeper-water species. These practices have changed over several decades in response to local socioeconomic and environmental shifts. Today these selective strategies show a marked seasonality and regional variability that the archaeological record of this region has thus far been ill-equipped to investigate. Through carefully constructed analogy, this preliminary work contributes to a better understanding of human technological and behavioral responses to shifting lakeshore environments today and during early Holocene times.

A 13 000 year multi‐proxy climate record from central Utah (western USA), emphasizing conditions leading to large mass movements

Younger Dryas to earliest Holocene mega‐landslides (>10 km2) in the eastern Fish Lake Plateau of central Utah required unusually wet conditions to drive movement. The sediment from abundant small lakes, ponds and especially fens that formed in swales between hummocks on the landslide surfaces are excellent archives of past climate. An integrated geophysical, geochemical and micro‐palaeontological investigation characterized fen deposits, determining the timing of mass movement and establishing the subsequent climate history of the region. High‐resolution P‐(compressional) wave surveys of fen deposits were conducted to image fen‐landslide contacts. Past climate states were assessed through loss on ignition, pollen and diatom abundances. Diatoms, in particular, record large variations in precipitation as the present‐day wetland switched from fen (intermittent standing water) to pond states in response to variable precipitation. One core was analysed for detailed climate proxies. A wet episode (pond) prevailed from 11.5 to 10 ka after which the climate became much drier (fen) until 6 ka due to weakening of the North American Monsoon. After 2.5–2.0 ka, reduced insolation produced cooler summers and wet winters (pond). Only recently (<500 years) has a fen re‐emerged based on direct observation and the disappearance of diatoms that require standing water. 14C ages of basal sediment from four cores show two episodes of movement: 12.8–12.5 and 10.5 ka. The earlier ages indicate that Younger Dryas high effective precipitation caused mass wasting. Later, during early Holocene times, colder winters followed by warmer summers and vigorous monsoons drove movement as rapid spring snow‐melt was followed by wet summers. In broad terms, this work highlights variable climate conditions that can drive mass movement, as well as the sensitivity of diatom records in fens to effective precipitation.