Neoglacial Period Research Articles

Single grain pIRIR dating of glacigenic deposits in the Yuzhu Peak area of Kunlun Mountains of Tibetan Plateau revealed the glaciations during Holocene period

The variations of glaciers in the Kunlun Mountains of the northern Tibetan Plateau are influenced by the complex interaction of the East Asia summer monsoon (EASM), Indian summer monsoon (ISM) and Westerlies, as well as human activity during the Holocene period. Consequently there is ongoing debates regarding the evolution of glaciers and the factors driving their changes. The reconstruction of glacial evolutions in these regions has been hindered by insufficient chronological data for moraines and other glacial landforms. In this study, glacial sediment samples were collected from five moraine sequences located on the southern and northern slopes of the Yuzhu Peak in the Kunlun Mountains. These poorly bleached moraine samples were dated using the single-grain quartz optically stimulated luminescence (OSL) and K-feldspar post-infrared infrared stimulated luminescence (pIRIR) dating methods. The luminescence characteristics analysis of quartz grains shows that single grain quartz OSL dating cannot be used to date Holocene moraine samples due to the low brightness of quartz OSL signals. Various tests were conducted to assess the reliability of K-feldspar pIR50IR170 dating, including anomalous fading tests, dose recovery, and residual dose tests. The K-feldspar pIR50IR170 ages, determined using the Minimum Age Model (MAM), indicate that during the early Holocene, glaciations have expanded by ∼800 m in length at ∼ 8 ka, and during the end of the Neoglacial period, they extended by ∼200 m in length at ∼ 1 ka. The strengthened ISM precipitation and northward movement of ISM boundary likely contributed to the glacial expansion in the early Holocene. During the end of the Neoglacial period, the increase in westerlies precipitation and cold events may have played a role in the advancement of glaciers.

Radiocarbon dating of naturally shed reindeer antlers melted out of retreating and down-wasting ice patches and ice caps in western Norway

A rise in summer temperatures, especially since the turn of the 21st century, has caused negative mass balance and marginal retreat of ice caps and ice patches in western Norway. Twentytwo naturally shed reindeer antlers found at retreating and down-melting margins of fourteen retreating ice patches and ice caps on mountain summits in western Norway during the recent decades have been radiocarbon dated. The reindeer antlers show no evidence of being sawed or cut off the skull or any engravings/scrape marks if the antlers had been handled by humans. The oldest reindeer antler in this study dates at 2201-2132 cal. yr BCE. Four dated antlers fall within the age range 2300-2000 cal. yr BCE. Single dates fall within the time ranges 1100 to 1000, 900 to 800, and 500 to 300 cal. yr BCE. Four dated antlers are within the time range 200 BCE to 100 cal. yr CE and two dated antlers fall within the time range 600 to 800 cal. yr CE. Finally, fifteen dates fall within the time range 1300-1900 cal. yr CE, the highest number (n=11) between 1300 and 1600 cal. yr CE. The temperature decline and increased precipitation causing advancing glaciers and ice caps, accompanied by growing ice patches during the Neoglacial period, including the early phase of the Little Ice Age, provided good preservation conditions for the reindeer antlers during the Little Ice Age, with extensive ice and snow cover in the high mountains in western Norway.

A high-resolution record of Mid- to Late-Holocene environmental changes from a land-locked lake in Schirmacher Oasis, East Antarctica

We present a high-resolution record of environmental changes during the Mid-Late Holocene obtained from a lake sediment core covering the past 4.87 cal kyr BP in the Schirmacher Oasis, East Antarctica. The magnetic signal of Lake L6 was found to be primarily controlled by catchment-derived ferrimagnetic minerals. The period between 4.87 and 3.35 cal kyr BP is marked by several episodes of cold and warm conditions. Warm and wet conditions prevailed in the region from 3.35 to 2.43 cal kyr BP. Magnetic susceptibility values remained generally low indicating the pedogenic formation of fine magnetic grains. The high values of the chemical weathering indices reflected the warm and wet conditions conducive to chemical weathering. A transition to cold and dry conditions was observed at around 2.43 cal kyr BP, representing the Neoglacial cooling, with high values of magnetic concentration-dependent parameters. Following the Neoglacial period, a return to warm and wet conditions was observed at 1.63 cal kyr BP, coeval with the Medieval Climate Anomaly. Our record shows a Late-Holocene cooling marked by a sudden increase in magnetic susceptibility values, which could represent the Little Ice Age, followed by a shift to warmer conditions near the core top.

Palaeoglacier and palaeoclimate reconstruction since the Neoglacial of the central Gangdise Mountains, southern Tibetan Plateau

Palaeoglacier modelling is a crucial approach for reconstructing palaeoclimate. Although the timing of glaciations during the Little Ice Age (LIA) and Neoglacial in the central Gangdise Mountains has been partially determined, there are still undated fresh-looking moraines. This study utilized coupled mass balance and ice flow models to simulate the palaeoclimate during the five LIA glacial events (LIA-1 to LIA-5) and two Neoglacial glacial events (Neo-1 and Neo-2). The results revealed that the glacial volumes in the Gangdise Mountains during the LIA and Neoglacial periods ranged from ∼1.10 to 1.57 km3. Comparing the reconstructed climate with other proxies, it was found that Neo-2 and Neo-1 exhibited temperatures 0.54 to 0.82 °C and 0.7 to 1.0 °C lower than the present, respectively, with precipitation levels at 110–140% of the present. The temperatures during the LIA periods were 0.36 to 1 °C lower than the present, with precipitation levels at 80–120% of the present. The interannual variability of climate at decadal or centennial scales may have played a significant role in the formation of the LIA moraines.

Décalage temporel dans l’établissement des érables en forêt boréale révélé par une population marginale à la limite nordique de l’érable à sucre

ABSTRACT Given their position at the limit of a species’ bioclimatic tolerance envelope, range-edge populations are particularly sensitive to variations in environmental conditions. Understanding ecological history of such peripheral populations provides key insights about ecosystem responses and resilience to global change. Here, we rely on soil macrofossil charcoal analysis to infer the origin and dynamics of a marginal sugar maple stand located within the boreal forest, at the leading edge of the species range. Radiocarbon dating of sugar maple and red maple charcoal particles indicates a late origin of the sugar maple stand at c. 600 cal yr BP, compared to red maple, which was established in the early Neoglacial period c. 4000 years ago. The earlier presence of red maple may have facilitated a later establishment of sugar maple in the boreal environment, most likely by altering edaphic conditions. The relatively recent establishment of a disjunct stand of maple at its current leading edge suggests that models predicting a northward migration of temperate species to the boreal biome in response to contemporary climate change are empirically plausible.

An 8500-year history of climate-fire-vegetation interactions in the eastern maritime black spruce–moss bioclimatic domain, Québec, Canada

ABSTRACT The eastern, maritime portion of the black spruce – moss bioclimatic domain in Québec (Canada) is characterized by large wildfires with low occurrence. However, it is still poorly understood how climate–fire interactions influenced long-term vegetation dynamics in the boreal forest of eastern Québec. The long-term historical climate–fire–vegetation interactions in this region were investigated using a multiproxy (chironomids, charcoal, and pollen) paleoecological analysis of an 8500-year sediment core. Chironomid-inferred August air temperatures suggest that the warm Holocene Thermal Maximum (HTM; between ca. 7000–4000 cal yr BP) shifted to the cooler Neoglacial period (4000 cal yr BP to present), consistent with other temperature reconstructions across Québec. The shift to spruce-moss forest dominance around 4800 cal yr BP occurred nearly a thousand years before the climatic shift to the Neoglacial period and rather coincided with a shift from frequent low-severity small fires to infrequent but large and severe fire events. Our results suggest that long-term changes in the summer temperature are probably not the main factor controlling fire and vegetation dynamics in eastern Québec. It seems that, throughout the postglacial period, summer temperatures never fell below a threshold that could have induced a significant vegetation response.

The impact of the Neoglacial and other environmental changes on the raised beaches of Joinville Island, Antarctica

AbstractIn order to reconstruct past environmental conditions along the north-eastern Antarctic Peninsula, we documented changes in grain size, grain roundness, onlap as seen in ground-penetrating radar reflection profiles and ice-rafted debris on a set of 36 raised beaches developed over the last ~7.7 ± 0.9 ka on Joinville Island. The most pronounced changes in beach character occur at ~2.7–3.0 ka. At this time, there appears to have been a reintroduction of less rounded material, the development of stratification within individual beach ridges, an introduction of seaweed and limpets to the beach deposits, a change in clast provenance (although slightly earlier than the change in cobble roundness) and a shallowing of the overall beach plain slope. Prolonged cooling associated with the Neoglacial period may have contributed to these changes, as the readvance of glaciers could have changed the provenance of the beach deposits and introduced more material, leading to the change in roundness of the beach cobbles and the overall slope of the beach plain. This study suggests that late Holocene environmental change left a measurable impact on the coastal zone of Antarctica.

Climatic and vegetational controls of Holocene wildfire regimes in the boreal forest of northern Fennoscandia

Abstract Climate change is expected to increase wildfire activity in boreal ecosystems, thus threatening the carbon stocks of these forests, which are currently the largest terrestrial carbon sink in the world. Describing the ecological processes involved in fire regimes in terms of frequency, size, type (surface vs. crown) and severity (biomass burned) would allow better anticipation of the impact of climate change on these forests. In Fennoscandia, this objective is currently difficult to achieve due to the lack of knowledge of long‐term (centuries to millennia) relationships between climate, fire and vegetation. We investigated the causes and consequences of changes in fire regimes during the Holocene (last ~11,000 years) on vegetation trajectories in the boreal forest of northern Finland. We reconstructed fire histories from sedimentary charcoal at three sites, as well as vegetation dynamics from pollen, moisture changes from Sphagnum spore abundance at two sites, and complemented these analyses with published regional chironomid‐inferred July temperature reconstructions. Low‐frequency, large fires were recorded during the warm and dry mid‐Holocene period (8500–4500 cal. year BP), whereas high‐frequency, small fires were more characteristic of the cool and wet Neoglacial period (4500 cal. year BP onward). A higher proportion of charcoal particles with a woody aspect—characterizing crown fires—was recorded at one of the two sites at times of significant climatic and vegetational changes, when the abundance of Picea abies was higher. Synthesis. Our results show both a direct and an indirect effect of climate on fire regimes in northern Fennoscandia. Warm and dry periods are conducive to large surface fires, whereas cool and moist periods are associated with small fires, either crown or surface. Climate‐induced shifts in forest composition also affect fire regimes. Climatic instability can alter vegetation composition and structure and lead to fuel accumulation favouring stand‐replacing crown fires. Considering the ongoing climate warming and the projected increase in extreme climatic events, Fennoscandian forests could experience a return to a regime of large surface fires, but stand‐replacing crown fires will likely remain a key ecosystem process in areas affected by climatic and/or vegetational instability.

Postglacial fluctuations of western outlet glaciers of the Southern Patagonian Icefield reconstructed from fjord sediments (Chile, 50°S)

Postglacial fluctuations of Southern Patagonian Icefield (SPI) glaciers are well constrained on the leeward side of the Andes, but they remain mostly unknown on the windward side of the icefield, where most glaciers are marine-terminating. Here, we reconstruct the postglacial fluctuations of the HPS19, Penguin, and Europa glaciers along the hyperhumid western side of the SPI using a multi-proxy sedimentological and geochemical analysis of a 12.2 m long sediment core from Wide Channel (50°S). Results show that the glaciers retreated into Penguin and Europa fjords by 11.2 cal kyr BP and that they were relatively stable and marine-terminating between 11.2 and 5.8 cal kyr BP. Thereafter, they fluctuated rapidly, with four marked episodes of glacier shrinkage at 5.8–4.8, 3.9–2.4, 1.0–0.2 cal kyr BP, and during the 20th century. Although the HPS19, Penguin, and Europa glaciers were calving into Penguin and Europa fjords during most of the Holocene, our data suggest that they retreated to land-based positions between 5.8 and 4.8 cal kyr BP. The comparison of our sediment record with geological archives from both sides of the Patagonian icefields (46°–56°S) suggests synchronous glacier variability on multi-centennial timescales during the Neoglacial period, which is particularly clear after 2.5 cal kyr BP. We conclude that western SPI outlet glaciers remained relatively stable during the first half of the Holocene but fluctuated considerably during the Neoglacial period, and that they retreated to locations further inland than today during the first retreat of the Neoglacial period between 5.8 and 4.8 cal kyr BP.

Recent and Past Arboreal Change: Observational and Retrospective Studies Within a Subalpine, Birch-Dominated (Betula Pubescens Ssp. Czerepanovii) Mountain Valley in the Southern Swedish Scandes-Responses to Climate Change and Land Use

Multi-scale observations and reconstructions of treeline and associated plant cover changes are reviewed in this study. The main focus is on the dynamics of the treeline ecotone within a mountain valley in the southern Swedish Scandes. This area is well-researched for more than 100 years, with a background of historical studies covering the entire Holocene epoch. Trees were present on ice-free nunataks already during the Late-Glacial, 17 000-13 000 cal. a BP. Mountain birch (Betula pubescens ssp. czerepanovii), Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) then grew 400-700 m higher than their current treelines, indicative of summer temperatures 3 °C higher than present. In addition, the tree flora contained Siberian larch (Larix sibirica) and broad-leaf thermophilic and deciduous species, Quercus robur, Corylus avellana, Ulmus glabra and Alnus glutinosa. Eventually, the climate turned cooler, particularly enhanced around 5000 cal. a BP. This course of change initiated the Neoglacial period, when thermophilic species were extirpated. Concomitantly, mountain birch forest and spruce benefitted from this course of change. Pine, on the other hand was disfavored and regressed in the treeline elevation and general abundance on the landscape. These trends continued until the Mediaeval period AD 1000-1300, when temperature raised above present-day standards and the pine treeline locally shifted upslope by at least 100 m. This favourable epoch was discontinued quite abruptly by resurgence of Neoglacial cooling; the “Little Ice Age”, which prevailed until the late 19th century. Widespread glacier expansion, high-elevation arboreal decline and treeline retraction then occurred. With a gentle onset in the late 19th century or somewhat earlier, a modern and still prevailing warming period was accentuated by the late 1930s. Subsequently, slight cooling prevailed for 3-4 decades, whereupon warming was resumed with short interruptions until the present day. One distinct short-term cooling-conditioned setback occurred during the 1980s. Transient permafrost formed close to the treeline, and locally some treeline recession took place. Thereafter, warming has re-occurred and glaciers and permafrost have receded. Treeline rise and densification of the treeline ecotone are once again active processes in the mountainscape. Currently, most conspicuous is a process of pine reclamation of local ground lost during the Little Ice Age. Hereabouts, seed regeneration, still virtually without winter injuries, is taking place at an unprecedented rate and abundance. Mountain birch is gaining ground in snow rich depressions in the birch belt and is currently regressing in exposed and snow-poor sections of the local topography. Current biotic changes within the treeline ecotone are well within the ranges of inferred natural variabilty during the postglacial period.

Increased North Atlantic dust deposition linked to Holocene Icelandic glacier fluctuations

Mineral dust concentrations are coupled to climate over glacial-interglacial cycles with increased dust deposition occurring during major cold phases over the last ~100 ka. Holocene records suggest considerable spatial and temporal variability in the magnitude, frequency and timing of dust peaks that reflects regional or local drivers of dust emissions and transport. Here, we present stratigraphical, geochemical and isotopic evidence for dust deposition from two high-resolution peat sequences 200 km apart in northern Scotland spanning the last c. 8200 years. εNd isotope data suggest the dominant minerogenic dust source switches between a low latitude (likely Saharan) and a high latitude, Icelandic source. Marked peaks in increased minerogenic dust deposition at: c. 5.4–5.1, 4.0–3.9, 2.8–2.6, 1.0 and 0.3 ka BP occur against a backdrop of low dust deposition during the mid-Holocene (c. 5.0–4.0 ka BP) and increased background levels of dust during the neoglacial period (<4.0 ka BP). These dust peaks coincide with periods of glacial advance in Iceland and heightened storminess in the North Atlantic. Isotope data for additional dust peaks at c. 1.0 and 0.7 ka BP and the last ~50 years suggest these reflect increased dust from the Sahara associated with aridity and land-use change in North Africa during the Late-Holocene, and modern anthropogenic sources. This work highlights the complexity of Holocene records of dust deposition in the North Atlantic and emphasises the role of dynamic sub-Polar glaciers and their meltwater systems as a significant dust source.

Lateglacial and Holocene sedimentary dynamics in northwestern Baffin Bay as recorded in sediment cores from Cape Norton Shaw Inlet (Nunavut, Canada)

The physical, sedimentological, mineralogical and elemental geochemical properties of sediment cores AMD1803‐02BC and 01PC from the Cape Norton Shaw Inlet were investigated to reconstruct glacial sediment discharges from southeastern Manson Icefield and document the impact of ice–ocean interactions on the sediment dynamics and opening of the North Water Polynya (NOW) in northwestern Baffin Bay since the last deglaciation. Laminated glaciomarine sediments rich in quartz and feldspar are observed prior to 11 cal. ka BP and were probably deposited by hyperpycnal currents triggered by the local retreat of the southern margin of the Innuitian Ice. Detrital proxies suggest that Early Holocene sediment dynamics were mainly influenced by sea ice and iceberg rafting and meltwater discharges related to the deglaciation of eastern Smith (~11 to 10.65 cal. ka BP) and Jones (~10.7 cal. ka BP) sounds. This also provides an upper limit to the timing of formation of the NOW. The high detrital carbonate contents during 8.8 to 6.6 cal. ka BP confirm that enhanced carbonate‐rich sediment export from Nares Strait to northern Baffin Bay occurred during and after the deglaciation of Kennedy Channel (8.8 to 8.2 cal. ka BP). Canadian Shield sediment inputs have dominated since 6.6 cal. ka BP, indicating that sedimentation is mainly influenced by Cape Norton Shaw glacier discharges. The lower level of sedimentation recorded in core 01PC during the Middle to Late Holocene suggests an accelerated landward retreat of the Cape Norton Shaw glaciers in response to warmer marine conditions. During the Neoglacial period, higher sedimentation rates and detrital proxies in the cores suggest increased glacial erosional processes, probably associated with the long‐term declines in boreal summer insolation and glacier growth. Finally, mineralogical and grain‐size data in core 02BC support the idea that increased Arctic atmospheric temperatures have had an important influence on the glacial dynamics during the industrial period.

Atlantic Ocean Circulation as the Driving Force for the Holocene Thermal Maximum and Millennial Scale Climatic Variability

The aim of this meta-study is to provide an understanding of the Atlantic Ocean Circulation as the driving force for the Holocene Thermal Maximum (HTM) and Millennial Scale Climatic Variability. In addition to continental ice sheets, during the Great Ice Age (GIA) there was also a 900-m thick floating ice shelf (FIS) in the Arctic Ocean. Below the FIS, it was likely freshwater. It is plausible that around 11,700 BP the Gulf Stream established the present flow route. Until around 10,800 BP the Grand Banks of Newfoundland (GBN) diverted part of the Gulf Stream flow west towards the north-eastern American coast, where the HTM existed between ca. 11,600 and 10,800 BP. Soon after the Gulf Stream was able to flow over the GBN, the HTM started in Ireland ca. 10,700 BP. By ca. 10,000 BP, the Gulf Stream arrived on the coast of Norway, which diverted the outflow south through the English Channel for approximately 2,000 years. In Northern and Central Europe, the HTM existed between ca. 9,500 and 7,000 BP. Due to the melting of ice, the outflow turned brackish, and was mainly surface currents, having a temperature of around 0℃. The formation of descending salty water (DSW), which creates the suction of the Gulf Stream, was low. Between ca. 6,000 and 4,500 BP, there was Mid-Holocene cooling. Then the Arctic Ocean water was salinated by double diffusive convection (DDC). When DSW formation increased to its present-day volume, the Neoglacial period started ca. 4,500 BP. Since then, outflow has taken place mainly through cold (approximately –2℃) undercurrents. At this time, the intensive millennial scale cycling of warmer and colder periods also started. When increasingly larger areas in Arctic Ocean are covered by insulating multi-year ice (MYI), DSW formation and the suction of the Gulf Stream decrease, and vice versa. The amplitude of the cycle is approximately 750 to 800 years.

A 5000‐year paleoclimate record from Nettilling Lake (Baffin Island) based on diatom assemblages and oxygen isotope composition

ABSTRACTSedimentary diatoms have been used to quantitatively reconstruct climate‐related variables, such as temperature at different timescales. Even though temperature is often less of a key driver of diatom ecology than other environmental parameters (water chemistry), diatom inference models have been shown to be reliable in deducing past temperature trends. In addition, the oxygen isotope composition (δ18Odiatom) preserved in buried diatom frustules has demonstrated its potential to reflect climatic and hydrological conditions at the time of frustule formation. This study combines results from both diatom‐based climate proxies to reconstruct summer water and mean annual air temperatures, and hydrological trends in Nettilling Lake, Baffin Island, from ca. 5000 to 500 cal a bp. Diatom‐inferred temperatures revealed an overall ca. 2 °C cooling throughout the Late‐Holocene. The δ18Odiatom values showed an increasing trend up to ca. 1900 cal a bp, where they reached their highest values (+24.8‰ at 15 cm) and thereafter decreased to their lowest values (+21.4‰ at 4 cm). These trends were linked to meltwater inflows associated with Penny Ice Cap thaw rate that was in turn controlled by regional climatic conditions which went from intensified cooling during the Neoglacial period to slight warming thereafter. Our results suggest that diatom‐ and diatom‐isotope‐based temperature and hydrological reconstructions can identify trends related to the natural climate system variability. The diatom oxygen isotopes are useful for paleoenvironmental studies of terrestrial aquatic ecosystems, but not for all hydrological systems are the ideal temperature proxy. Hence, the combination of proxies helps to disentangle temperature and hydrological effects for paleoclimatic reconstructions and may support future studies of postglacial environmental change in northern lakes.

Last Glacial Maximum to Holocene paleoceanography of the northwestern Ross Sea inferred from sediment core geochemistry and micropaleontology at Hallett Ridge

Abstract. During the Late Pleistocene–Holocene, the Ross Sea Ice Shelf exhibited strong spatial variability in relation to the atmospheric and oceanographic climatic variations. Despite being thoroughly investigated, the timing of the ice sheet retreat from the outer continental shelf since the Last Glacial Maximum (LGM) still remains controversial, mainly due to a lack of sediment cores with a robust chronostratigraphy. For this reason, the recent recovery of sediments containing a continuous occurrence of calcareous foraminifera provides the important opportunity to create a reliable age model and document the early deglacial phase in particular. Here we present a multiproxy study from a sediment core collected at the Hallett Ridge (1800 m of depth), where significant occurrences of calcareous planktonic and benthic foraminifera allow us to document the first evidence of the deglaciation after the LGM at about 20.2 ka. Our results suggest that the co-occurrence of large Neogloboquadrina pachyderma tests and abundant juvenile forms reflects the beginning of open-water conditions and coverage of seasonal sea ice. Our multiproxy approach based on diatoms, silicoflagellates, carbon and oxygen stable isotopes on N. pachyderma, sediment texture, and geochemistry indicates that abrupt warming occurred at approximately 17.8 ka, followed by a period of increasing biological productivity. During the Holocene, the exclusive dominance of agglutinated benthic foraminifera suggests that dissolution was the main controlling factor on calcareous test accumulation and preservation. Diatoms and silicoflagellates show that ocean conditions were variable during the middle Holocene and the beginning of the Neoglacial period at around 4 ka. In the Neoglacial, an increase in sand content testifies to a strengthening of bottom-water currents, supported by an increase in the abundance of the tycopelagic fossil diatom Paralia sulcata transported from the coastal regions, while an increase in ice-rafted debris suggests more glacial transport by icebergs.

Processes controlling the development of talus slopes in SW Spitsbergen: The role of deglaciation and periglacial conditions

AbstractThe location of Svalbard at the interface between the warm Atlantic and cold Arctic oceans causes the terrestrial environment to be highly sensitive to contemporary climate warming. Talus slopes provide a component of glaciated areas that has been registering these changes on a scale of several thousand years. However, knowledge about their development during glacial recession is still limited. This paper fills this gap by providing unique data obtained by geophysical methods: electrical resistivity tomography (ERT) and ground‐penetrating radar (GPR), regarding the talus slopes in Revdalen (SW Spitsbergen), which was last glaciated in the Neoglacial period. The results indicate that the thickness of talus slopes depends first of all on the size of the sediment supply area and only secondarily on the stage of development. The initial content of buried glacial ice in the talus deposits is differential and depends on both the rate of deglaciation and the local intensity of rock wall denudation. Over time, as a result of creep, the presence of massive ice is limited to ever lower parts of the slope. Above, there is aggradation of pore ice in delivered debris material. At the end of this stage, the buried glacial ice can form, or co‐create together with pore ice, the core of subslope rock glaciers. The relatively long period since the beginning of the Revdalen deglaciation allowed a general model of the development of talus slopes in the polar environment to be prepared.

Constraints on the timing of debris-covered and rock glaciers: An exploratory case study in the Hólar area, northern Iceland

Eighteen samples for 36Cl Cosmic-Ray Exposure (CRE) dating were taken from glacially polished bedrocks, moraine boulders, fossil/active rock glaciers and debris-covered glaciers in Fremri-Grjótárdalur and Hóladalur cirques in the Víðinesdalur, Hofsdalur and Héðinsdalur valleys, close to Hólar village, in the Tröllaskagi peninsula, northern Iceland. Boulder sampling was preceded by a study of the boulder stability with the twofold aim of: ensuring that the surfaces to be sampled were stable enough for the reliable application of CRE dating, and to better understand the relation between the glacier dynamics and exposition history. The results show that the glaciers which occupy the valleys in Tröllaskagi began their retreat around 16 ka. Later, the glaciers advanced again around 11 ka within the cirques, and small moraines were formed. Thereafter, these small glaciers retreated and evolved into rock glaciers as debris from paraglacial processes accumulated on the glacier surface. The fronts of these rock glaciers stabilized definitively shortly after their formation and became eventually fossil after the melting of their internal ice. New rock glaciers and debris-covered glaciers formed afterwards, which still have internal ice at present, although their current dynamics are mostly related to subsidence. The stabilization of these rock glaciers and debris-covered glaciers is dated to the period between 7 and 3 ka, although they may have been reactivated during cold neoglacial periods. This research demonstrates the potential interest in applying CRE dating methods to debris-covered glaciers and rock glaciers to determine their origin, evolution and phase of cessation of internal movement until they finally lost their internal ice and became fossil.

Neoglaciation in the Spanish Pyrenees: a multiproxy challenge

Following the Holocene Thermal Maximum, dated between 11 and 6 ka, the Neoglacial period was one of the progressive, fluctuating cooling that peaked during the Little Ice Age (LIA). The almost total absence of glacial tills prior to the LIA in the Pyrenees forces recourse to a high variety of proxies, including lacustrine sediments, palynological records, dendroclimatology, ice cores from glaciers and caves, speleothems, historical documentation and glacial records. This has enabled us to identify several colder periods during the mid- and late-Holocene: (i) the first phase of the Neoglacial period occurred at some time around 6 ka; (ii) a glacial pulse immediately before 3.4 ka; (iii) a glacial re-advance during the Dark Ages, i.e., immediately before the Medieval Climate Anomaly, between the fourth and ninth centuries; and (iv) the Little Ice Age, which started at the beginning of the fourteenth century and finished in the mid-nineteenth century. During the LIA, there was remarkable climate variability, with two, and probably three, glacial pulses, mainly between 1620 and 1715 and in the first half of the nineteenth century. Of all of the Holocene cold periods, most of the European paleoclimatic records coincide on the occurrence of the LIA. For the remaining Holocene cold periods, European records show high variability and uncertainty, particularly for the onset of the Neoglacial, although the phases of glacial pulses in the Pyrenees broadly coincide with those identified in the Alps and northern Europe.

Holocene fire and vegetation dynamics in the Central Pyrenees (Spain)

Fire-vegetation relationships are critical to understand transient mountain ecosystems and their long-term landscape dynamics, which is essential for alpine forest conservation. In this paper we aim to (1) reconstruct the Holocene fire history at high altitudes of the southern Central Pyrenees, (2) add evidence to the debate on fire origin, naturally or anthropogenically produced, (3) determine the importance of fire as a disturbance agent for sub-alpine and alpine vegetation, in comparison with the plant community internal dynamics applying conditional inference trees. We present and compare microcharcoal and pollen data series, from two lacustrine sedimentary sequences in the Central Pyrenees: Basa de la Mora (BSM), within the treeline ecotone at the sub-alpine belt (1914 m a.s.l.) and Marboré Lake, above the treeline at the alpine belt (2612 m a.s.l.).We evidence that, fire activity was not the most important factor in driving vegetation dynamics regionally. Our results suggest that spatially, the fire signal might be site-dependent while over time, climate exerted a strong influence on fire activity during the early-to-mid Holocene, showing more fires during the Holocene Thermal Maximum (HTM) (ca. 7000–6000 cal yr BP) whereas fire activity decreased with the cold Neoglacial period. At ca. 3700 cal yr BP, fire activity increased coinciding with a regional landscape opening, suggesting that human activities may have strengthened the importance of fire. Fire activity remained low over the last two millennia but a remarkable Holocene maximum for the last centuries in both sequences is observed, likely related to increasing human pressure.

From Climatic to Anthropogenic Drivers: A Multi-Proxy Reconstruction of Vegetation and Peatland Development in the French Jura Mountains

A 4 m core was extracted from the center of a peatland located in the Drugeon valley (France). Thirteen radiocarbon dates were used to build a robust age model. Testate amoebae were used for reconstructing mire surface wetness. High-resolution pollen analysis of the sequence reconstructed 9 millennia of development of the peatland and its surrounding vegetation. During the early/middle Holocene (9500 to 5800 cal BP), warm conditions led to high evapotranspiration and low water levels. The vegetation history is characterized by the development of a Pinus and a mixed Quercus forest. From 5800 cal BP, testate amoebae show wetter conditions, indicating the onset of the cooler Neoglacial period. The cooling is also evidenced by the development of Abies and Fagus trees, replacing the oak forest. The first indicators of human impact appear at about 4800 cal BP, and indicators of farming activity remains very rare until ca. 2600 cal BP, at the beginning of the Iron Age. The development of the peatland responded to climatic fluctuation until 2600 cal BP, after which human impact became the main driver. The last millennium has been characterized by sudden drying and the spread of pine on the peatland.