Late Glacial Period Research Articles

Holocene vegetation change at Grosssee, eastern Swiss Alps: effects of climate and human impact

AbstractPollen, spores, and microscopic charcoal from the sediments of Grosssee (1,619 m a.s.l.), a small lake in the lower subalpine vegetation zone of the Glarus Alps, Switzerland, were analysed to reconstruct vegetation patterns and land use over the past ca. 12,300 calibrated 14C years bp (cal bp). Pollen data revealed an open landscape covered with grasses and herbs such as Artemisia during the Late Glacial Period. The catchment was likely initially afforested with Betula and Pinus cembra or Pinus sylvestris during the Early Holocene. Thermophilous taxa such as Ulmus, Tilia, and Alnus glutinosa-type expanded from ca. 11,000–9,200 cal bp, and mesophyllic Picea abies and Fagus sylvatica followed, and expanded beginning from ca. 8,000–7,600 cal bp. Interestingly, Alnus viridis (synonym: A. alnobetula) expanded about 2,000 years earlier than at comparable sites in the northern Swiss Alps. Its expansion was profound and persistent, and percentages > 15% were already achieved by ca. 7,000 cal bp. Local erosion events that followed are well explained by vegetation changes and inferred human land use activities at Grosssee. In particular, this led to a more open landscape, and land uses (e.g. grazing) intensified from the Mid- to Late Holocene. Indicators of environmental disturbance including persistently high levels of A. viridis, monolete fern spores, and microscopic charcoal were pronounced after ca. 4,000 cal bp. At that time, high influxes of spores from coprophilous fungi and the consistent presence of cultural indicators (Cerealia-type, Plantago lanceolata) indicate increased grazing and high levels of human impact. Land use and grazing activities seemed to have been particularly pronounced and to have promoted diversity in the vegetation over the past 1,000 years.

Increase in Paleoproductivity Driven by Strengthening of Indian Summer Monsoon During Past ~14kyrs: Evidenced by Biogenic Silica Accumulation Rates at Southeastern Arabian Sea

We analysed the BSi (Biogenic Silica) contents of the marine core SK-313/1 from the southeastern Arabian Sea which is dated up to ~14.5 kyr BP. Results show that the maximum and minimum BSi contents are 2.5 and 0.5%, respectively. This is because of the low supply of silica skeleton and the high dissolution and dilution of terrigenous materials. The BSi mass accumulation rates indicate a trend of reduced paleoproductivity during the late Glacial period and increase during the Holocene, with global climatic shifts. Insolation changes at low latitudes, which regulate temperatures, may affect nutrient availability and, consequently productivity variations on a glacial–interglacial timescale. Notably, millennial events like the Younger Dryas (YD) periods, exhibited lower paleoproductivity, in contrast to the Bølling/Allerød (B-A) period and the middle Holocene, which displayed elevated levels of paleoproductivity. These millennial-scale fluctuations in siliceous productivity may be due to the changes in nutrient supply caused by the Indian summer monsoon (ISM). The period of increased paleoproductivity could be influenced by intensified chemical weathering and a boosted nutrient supply, which are consequences of the strengthened ISM during periods of relatively higher temperature.

Cold mountain stream chironomids (Diptera) of the genus Diamesa indicate both historical and recent climate change.

Chironomids of the genus Diamesa (Meigen, 1835, Diptera: Chironomidae) inhabit cold, oxygen-rich running waters. We have investigated the presence of Diamesa and other freshwater macroinvertebrates at 22 stream sampling sites in 3 European high mountain regions (the Central Pyrenees, the Ötztal Alps, and the Tatra Mountains) to establish suitable temperature conditions for Diamesa dominance. It has been generally accepted that their high abundance was linked to the presence of glaciers; however, we have shown that in the Tatra Mountains, where there are no glaciers, the conditions for the dominance of Diamesa species are created due to permanent snowfields, the geographical orientation of the valley and shading by the surrounding high peaks. The historical connection of Diamesa to glaciers was investigated from the paleolimnological records of subfossil chironomid assemblages from the Bohemian Forest, where glaciers disappeared before or during the Late Glacial period. As expected, water temperature seems to be the main driver of Diamesa distribution, and we determined that the relative abundance of Diamesa species was significantly higher at the sites with a mean July water temperature below 6.5 °C. The Diamesa-dominated stream communities seems to be endangered due to ongoing climate warming and this assumption is supported by our paleolimnological results from the Bohemian Forest lakes, where Diamesa has disappeared due to warming of lake inflows at the beginning of the Holocene. These findings strengthen the former suggestions that some Diamesa species could be used as an indicator for tracking recent environmental changes in vulnerable ecosystems of cold mountain streams.

A comparison of plant macrofossil-based quantitative climate reconstruction methods: A case study of the lateglacial Baltic States

The recent advancements of new quantitative tools compatible with plant macrofossil proxy data have revived its potential for paleoclimate research. Plant macrofossils are commonly used in so-called indicator-species approaches, using methodologies that are typically built on known observations linking modern plant distributions with climate. This allows complementary paleoclimate reconstructions using an approach that is not limited by the spatial availability of calibration samples obtained from surface sediments (e.g., pollen or chironomids).We aim to evaluate the impact that various methodological choices have on the plant-macrofossil based reconstructions of January and July temperature patterns for the Lateglacial (14–11 ka BP) period. We use a variety of classic and novel quantitative climate reconstruction algorithms with plant macrofossil assemblages from 13 sites of the Baltic States. We use unfiltered plant data to evaluate the ability of each method to also handle the presence of plants that might have a weak sensitivity to temperature. Additionally, we test the influence of another methodological choice – the choice of modern calibration region – on the reconstructed climate.Our findings indicate that, with no prior filtering of summer and winter-sensitive plants, temporal temperature variations can be reconstructed with methods that implement probability density functions. Although some disparities in reconstructions are seen between the tested algorithms, we note that the choice of calibration region bears a greater influence on the results. A calibration region that best represents the past environment should be chosen rather than one representing the same spatial extent as the fossil site(s). Moreover, for long-term reconstructions, a “dynamic calibration set” approach should be considered in future studies by using a range of calibration regions and mirroring the continuously changing broadscale environmental regime of the past.

Hydrological Regime of Rivers in the Periglacial Zone of the East European Plain in the Late MIS 2

At the end of the Pleniglacial and the first half of the Late Glacial period, approximately between 18 and 14 ka BP, rivers of the central and southern parts of the East European Plain had channels up to 10 times as large as the present day channels of the same rivers. These ancient channels, called large meandering palaeochannels, are widespread in river floodplains and low terraces. The hydrological regime of these large rivers is of great interest in terms of the palaeoclimatology of the late Marine Isotope Stage 2 (MIS 2). In this study, we aimed at quantitative estimation of maximum flood discharges of rivers in the Dnepr, Don and Volga basins in the late MIS 2. To approach this, we used massive measurements of the morphometric characteristics of large palaeochannels on topographic maps and remote sensing data—palaeochannel width, meander wavelength and their relationships with river flow parameters. The runoff depth of the maximum flood, which corresponds to the maximum depth of daily snow thaw during the snowmelt period, was obtained for unit basins with an area of <1000 km2. The mean value for the southern megaslope of the East European Plain was 44.2 mm/day (6 times the modern value), with 46 mm/day for the Volga River (5.5 times), 45 mm/day (6.3 times) for the Don River and 39 mm/day (8 times the modern value) for the Dnepr River basins. In general, the Dnepr basin was drier than the Don and Volga basins, which corresponds well to the modern distribution of humidity. At the same time, the westernmost part of the Dnepr River basin was relatively wet in the past, and the decrease in humidity from the past to the modern situation was greater there than in the eastern and central regions. The obtained results contradict the prevailing ideas, based mainly on climatic modeling and palynological data, that the climate of Europe was cold and dry during MIS 2. The reason is that palaeoclimatic reconstructions were made predominantly for the LGM epoch (23–20 ka BP). On the East European Plain, the interval 18–14 ka BP is rather poorly studied. Our results of paleoclimatological and palaeohydrological reconstructions showed that the Late Pleniglacial and the first half of the Late Glacial period was characterized by a dramatic increase in precipitation and river discharge relative to the present day.

Postglacial vegetation and climate change in the Lake Onega region of eastern Fennoscandia derived from a radiocarbon-dated pollen record

With its numerous environmental archives stored in lake and peat sediments and relatively low human pressure, the Lake Onega region in eastern Fennoscandia is regarded as a particularly promising area for studying past changes in vegetation and climate since the Lateglacial period. The 885-cm-long sediment core RZ19 (62°27′53″N, 34°26′4″E) was collected from Razlomnoe Peat on the northern shore of Lake Onega in 2019, radiocarbon-dated and analysed for pollen and cryptogam spores. The age-depth model suggests continuous sedimentation since ca. 11,800 a BP (all ages given in years (a) or kiloyears (ka) before present (BP) with BP referring to 1950 CE). The results of pollen analysis and pollen-based biome reconstruction show rapid afforestation of the area in the Early Holocene, although the scores of the tundra biome remain relatively high prior to ca. 11,450 a BP, suggesting that the vegetation was likely more open than today. Between 8300 and 8000 a BP, Betula sect. Albae shows a marked increase in pollen percentage, while Pinus sylvestris experiences a marked decrease. These changes coinciding with the 8.2 ka BP cooling event indicate less favourable conditions for Scots pine while being beneficial for fast-growing birch. The transition from the Early to Middle Holocene (i.e. from Greenlandian to Northgrippian) is marked by an increase in pollen productivity, spread of Picea and further afforestation of the area. The decrease in arboreal and Picea pollen percentages and the abrupt increase in landscape openness after ca. 4000 a BP mark the onset of the Late Holocene (i.e. Northgrippian-Meghalayan transition) and likely reflect the combined effect of insolation-induced temperature decrease and associated paludification and forest retreat rather than a decrease in atmospheric precipitation and/or spread of Late Neolithic agriculture.

Early Beringian Traditions: Functioning and Economy of the Stone Toolkit from Swan Point CZ4b, Alaska

AbstractThe pressure knapping technique develops circa 25,000 cal BP in Northeast Asia and excels at producing highly standardized microblades. Microblade pressure knapping spreads throughout most of Northeast Asia up to the Russian Arctic, and Alaska, in areas where the human presence was unknown. Swan Point CZ4b is the earliest uncontested evidence of human occupation of Alaska, at around 14,000 cal BP. It yields a pressure microblade component produced with the Yubetsu method, which is widespread in Northeast Asia during the Late Glacial period. Through the techno-functional analysis of 634 lithic pieces from this site, this study seeks to identify the techno-economical purposes for which the Yubetsu method was implemented. Data show that the microblade production system is related to an economy based on the planning of future needs, which is visible through blanks standardization, their overproduction, their functional versatility, and the segmentation of part of the chaîne opératoire. This expresses the efficiency and economic value of the microblade production system. The flexible use of pressure microblades identified at Swan Point CZ4b is also found in Japan, Korea, Kamchatka, and the North Baikal region, suggesting that their modes of use accompany the spread of early microblade pressure knapping over an immense territory across Beringia.

Balkan Neanderthals: The Late Pleistocene palaeoecological sequence of Pešturina Cave (Niš, Serbia)

The Central Balkans are a key biogeographical region in Southern Europe, influenced by a central European-Mediterranean climate, which acted as a refugium for flora and fauna, and favored the dispersion of Neanderthals and migration of modern human populations during Late Glacial Period. This study presents pollen analyses of sediment and hyaena coprolites from Pešturina Cave in Serbia to reconstruct the vegetation landscapes faced by Balkan Neanderthals and early Anatomically Modern Humans between MIS 5e-3. Between MIS 5e-5c (archaeological layers 4c and 4b) and MIS 5b-5a (layer 4a), semi-forested environments prevailed, characterized by Pinus, deciduous Quercus, Tilia and other angiosperm woody taxa, accompanied by heliophytes such as Artemisia and Poaceae. During MIS 4-3 (layers 3-2), the vegetation was dominated by Artemisia-Poaceae steppes with Quercus patches, conifers and legumes. Overall across the sequence, pollen assemblages are highly diverse and include a number of deciduous trees and sclerophylls. In addition, the occurrence of several herbaceous taxa reinforces the view that the Balkans were outstanding for endemicity. Neanderthals and early Upper Palaeolithic hominins lived in a highly diverse refugium, offering multiple opportunities for survival during the warm interstadials and, more critically, the cold stadials of the Pleistocene.

Holocene vegetation dynamics of the Yamal Peninsula based on palaeobotanical data from relict peat bog deposits

We have performed a comprehensive paleoecological study of the peat bog deposits from six localities of the Seyakha, Yuribey and Khadytayakha rivers in the subarctic tundra zone on the Yamal Peninsula. Radiocarbon dating, as well as pollen and plant macrofossil analyses were used to track the chronological changes of the plant communities on the peninsula along the North-South transect in the Late Glacial and Postglacial periods. It was found that open woodland with tree birch and spruce existed in the Yuribey river valley during the Bölling-Allerød interstadial (between 14.7 and 12.7 cal. ka BP). Shrub tundra with Betula nana was widespread in this area during the Younger Dryas, between 12.6 and 11.7 cal. ka BP, under climatic conditions similar to modern ones. The spread of arboreal species (Betula sect. Betula, Picea obovata, Larix sibirica) and associated boreal herbaceous plants began later (between 10.2 and 9.7 cal. ka BP) as climatic conditions improved. The most favorable conditions for tree birch and larch existed in the Seyakha river valley between 10.2 and 8.7 cal. ka BP, whereas the best conditions for the same species and spruce in the Yuribey river valley were observed between 10.2 and 4.4 cal. ka BP. It was much warmer than it is today, and open woodland or even closed forests were widespread. Forest degradation and spread of open landscapes with tundra communities occurred in the Seyakha river valley after 8.7–8.5 cal. ka BP and in the Yuribey river valley after 4.7–4.3 cal. ka BP. Climatic conditions became similar to modern ones. Today, arboreal species grow in the Khadytayakha river valley, forming extrazonal forest communities in the subarctic tundra zones.

Late Gravettian lithic finds from Felsőtárkány-Peskő Cave, Northern Hungary

Peskő Cave near Felsőtárkány (North Hungarian Mountains) is known for its Early Upper Palaeolithic bone industry found in the lower layer of its sediments in the early 20th century. Besides the points, a small amount of lithics were found in the Pleistocene stratum. Two archaeological horizons were identified. The lower two layers were classified as Aurignacian and the upper two ones Magdalénian. The Aurignacian included a few retouched blades, while the Magdalénian was never published. In the second half of the 20th century, the Magdalénian was reclassified as ‘Pilisszántó culture’ or ‘Cave Gravettian’, dated to the Late Glacial period. After the replacement of ‘Pilisszántó culture’ with the term Epigravettian in the 1980s the ‘Magdalénian’ layer of Peskő Cave fell out of research focus. Our research found that the automatic conversion of Pilisszántó culture finds to Epigravettian did not work and the finds at Peskő belong to the Late Gravettian.

Lake level dynamics in the centre of the East European Plain during the Holocene

Based on the lithostratigraphic and geomorphological approach, the study of lake level fluctuations in Nero and Seliger over the past 15,000 years was conducted. Common features of level changes were revealed: deep regression at the end of the late glacial period and early Holocene, intensive rise in level in the early-middle Holocene, stabilization (with a slight upward trend) in the late Holocene. Similar features in level changes were revealed in the history of a number of lakes in Germany and Scandinavia. A connection was found between lake level fluctuations and the intensity of fluvial processes in the center of the East European Plain.

Palaeoecological reconstruction of the Late Glacial and Early Holocene based on pollen data from lake Novozhilovo (Perm region, Russia)

This paper provides the first paleolimnological studies performed in the upper Kama basin (Perm region). These yielded a detailed pollen record characterizing the changes in the natural conditions of the transition from the periglacial environment of the Late Glacial period to the interglacial conditions of the Holocene between 14.15 and 10.0 cal ka BP. It was found that open birch woodland with larch existed in the Allerød period (14.15–12.7 сal ka BP) and was replaced by larch forest-steppe during the Younger Dryas (12.7–11.5 cal ka BP). The spread of spruce began in the early Holocene between 11.5 and 10.7 cal ka BP, whereas open larch and spruce woodlands became dominant between 10.7 and 10.0 cal ka BP. Quantitative palaeoclimatic reconstruction reveals that the average temperature of the warmest month (July) and the annual precipitation were considerably lower than modern values. The average July temperature increased from 10 to 16ºС between 14.15 and 12.7 cal ka BP. Then, small fluctuations within 1ºС occurred between 12.7 and 10.0 cal ka BP. The average annual precipitation was 200-300 mm below modern values between 14.15 and 10.7 cal ka BP and reached them only after 10.7 cal ka BP.

Forest mosaics, not savanna corridors, dominated in Southeast Asia during the Last Glacial Maximum.

The dominant paradigm is that large tracts of Southeast Asia's lowland rainforests were replaced with a "savanna corridor" during the cooler, more seasonal climates of the Last Glacial Maximum (LGM) (23,000 to 19,000 y ago). This interpretation has implications for understanding the resilience of Asia's tropical forests to projected climate change, implying a vulnerability to "savannization". A savanna corridor is also an important foundation for archaeological interpretations of how humans moved through and settled insular Southeast Asia and Australia. Yet an up-to-date, multiproxy, and empirical examination of the palaeoecological evidence for this corridor is lacking. We conducted qualitative and statistical analyses of 59 palaeoecological records across Southeast Asia to test the evidence for LGM savannization and clarify the relationships between methods, biogeography, and ecological change in the region from the start of Late Glacial Period (119,000 y ago) to the present. The pollen records typically show montane forest persistence during the LGM, while δ13C biomarker proxies indicate the expansion of C4-rich grasslands. We reconcile this discrepancy by hypothesizing the expansion of montane forest in the uplands and replacement of rainforest with seasonally dry tropical forest in the lowlands. We also find that smooth forest transitions between 34,000 and 2,000 y ago point to the capacity of Southeast Asia's ecosystems both to resist and recover from climate stressors, suggesting resilience to savannization. Finally, the timing of ecological change observed in our combined datasets indicates an 'early' onset of the LGM in Southeast Asia from ~30,000 y ago.

Late Palaeolithic to Early Mesolithic transition in the Carpathian Basin

Szekszárd-Palánk is one of the handful in situ excavated sites from the Late Glacial period of East-Central Europe which is also supported by radiometric dating. However, the considerable time that has passed since its discovery necessitates a revision, the topic of this paper. The technotypological analogues of the assemblage are Late Epigravettian – Early Mesolithic sites of the Northern Balkans to the south, and Epimagdalenian sites of the Moravian Basin to the north. These analogues, the southern location and northern raw materials of the site support two previous hypotheses: the regional survival of the Epigravettian traditions, and the pivotal role of the Danube in the communication between East-Central Europe and the Balkans in the Late Glacial – Early Postglacial. The site is thus identified as a Final Epigravettan, Late Palaeolithic – Early Mesolithic transitional industry.

Human impact leads to unexpected oligotrophication and deepwater oxygen increase in a Swiss mountain lake

Human impacts on lakes can lead to nutrient release, increased algal productivity and consequently low oxygen concentrations in deepwater environments. Here we report the unexpected and contrasting finding of a pronounced shift to chironomid and invertebrate assemblages suggesting oligotrophication and oxygen increase in Lac de Champex, a Swiss mountain lake, due to human activities during the Mediaeval period. Chironomid assemblages in the lower part of the lake sediment record show changes that agree with known climatic shifts during the Lateglacial period and early Holocene and a progressively stronger influence of peat development, and possibly humic conditions, from ca. 8500 calibrated 14C years BP (cal. BP) onwards. This resulted in low chironomid influx and assemblages with high abundances of Procladius and Chaoborus ca. 2000–3000 cal. BP. These assemblages resemble those found in relatively nutrient-rich, oxygen-poor lakes and may have developed due to natural, long-term development to more nutrient-rich and possibly humic conditions, and from the Bronze Age (ca. 4000 cal. BP) onwards, due to human activities such as pasturing. Ca. 1000 cal. BP, an abrupt increase in sediment accumulation, chironomid influx and distinct changes in the chironomid assemblage composition were observed, coinciding with evidence for local human activities from pollen data. A major transition in chironomid and invertebrate assemblages followed ca. 500 cal. BP with the disappearance of Chaoborus, a decrease in Procladius, and the increase or appearance of several chironomid taxa, including several rheophilous groups. We conclude that Late-Holocene human impact led to re-oligotrophication and increased oxygen availability for invertebrates in the lake. This reversal of the long-term Holocene trend was possibly promoted by increased erosion from the Mediaeval period onwards and from ca. 500 cal. BP likely by the construction of an irrigation canal (bisse), leading to inflow of clear, cool water which changed the lake’s hydrological characteristics.

Identification of modern meteoric water, glacial meteoric water, and fossil seawater in a deep borehole at the coastal area of Horonobe, north Japan, using groundwater dating and paleoclimatic proxy methods

Groundwater flow in deep areas of coastal regions has attracted significant attention for geological radioactive waste disposal or geological CO2 storage. To investigate groundwater flow in coastal areas, groundwater dating methods with the potential to assess slow groundwater flow were used at depths of up to 1200 m at Hamasato, Horonobe, northern Japan. Multiple groundwater dating methods were applied using pore water in drilling core and pumping groundwater. This study shows that modern meteoric water, glacial meteoric water, and fossil seawater are distributed in sand and silt layers at 300–360 and 90–300 m in depth and in silt and mud layers below 800 m in depth, respectively. Modern meteoric water infiltrated after and glacial meteoric water infiltrated during the latest glacial period were identified using δD and δ18O values, estimated recharge temperature from noble gas concentrations, and 14C concentrations. The estimated recharge temperatures of modern and glacial meteoric waters were 8.1 ± 2.0 and 2.1 ± 2.0 °C, respectively, whereas the δD and δ18O values were −68 ± 3‰ and −10.3 ± 0.2‰, −81 ± 2‰ and −11.4 ± 0.3‰, respectively. The 14C age of modern meteoric water was 10–16 ka. However, the 14C age of glacial meteoric water could not be estimated because it was highly diluted by 14C-free CO2 from methanogenesis and marine carbonate dissolution. Fossil seawater was identified using δD, δ18O, 36Cl, and 4He. δD and δ18O values underwent water-rock interaction and approached inland fossil seawater with increasing depth. 36Cl/Cl values did not reach secular equilibrium in situ in the Yuchi Formation due to its relatively short geological age and consolidation-induced porosity changes. However, the Yuchi Formation seawater is considered extremely old because its 36Cl/Cl ratio is higher than that of modern seawater as a result of 36Cl production, which also explains the observed 36Cl/Cl increases with depth toward the secular equilibrium ratio (36Cl/Clse). 4He concentrations were in the order of 10−6 ccSTP/gw, corresponding to an in situ accumulation age of 1–2 Ma, neglecting the external flux. The contribution of external flux could be negligible for the short geological age and rapid sedimentation rates. 4He ages were equivalent to the geological age of the Yuchi Formation. Core investigations can interpolate groundwater investigations because cores, particularly those from low-hydraulic conductivity layers, can be collected continuously. In addition, stable and radioactive isotopes and noble gases can help identify modern meteoric water, glacial meteoric water, and fossil seawater, assisting in understanding the groundwater flow velocity.

Was the Late Glacial human occupation of northernmost Europe facilitated by whales? New data and perspectives on lithic technology and the paleoecology of the Vendsyssel area, Northern Jutland, Denmark

The archaeology of the Vendsyssel area in Northern Jutland suggests that early human foragers reached the northernmost tip of continental Europe during the middle part of the Late Glacial Period. This occupation presents a paleoecological conundrum, however, as Vendsyssel was likely characterized by low terrestrial productivity and mammalian biodiversity. Why did human foragers disperse so far north, and what sustained them there? We here report an updated inventory of Late Glacial lithic surface material recovered from the Hollendskær region in north-western Jutland. Based on our discussion of the lithic assemblages, we recontextualize human settlement in the European far north vis-à-vis highly productive marine ecosystems in the circum-Kattegat. We suggest that beached whales may have been a previously overlooked ecological attractor as persistent terrestrial biases impede our understanding of the role of land–sea interfaces in facilitating the earliest northward human expansions.

Evolution of the alpine Critical Zone since the Last Glacial Period using Li isotopes from lake sediments

Comprehending and predicting the way humans affect the Earth's Critical Zone remains a challenge. An understanding of the past changes resulting from human and non-human influences in the dynamics of the Critical Zone is crucial. Here, we use a retrospective approach to address this question based on a new lithium (Li) isotope record from the Late Glacial Period to the present from a pre-Alpine lake sediment sequence (Lake La Thuile, France). Coupled with the lake sediment archive, the investigation of present-day soils in the lake catchment suggests that lake sediments are not necessarily recording the erosoin of topsoil in the catchment. Our findings indicate that soil particles can be sorted during transportation to the lake, with finer particles being preferentially mobilized, highlighting the influence of fine particle transport on the Li isotope signature of soils and lake sediments. Characterized by low Li isotope signatures, changes in weathering signatures in lake sediments can be amplified by the combined effect of soil development and selective transport. In the La Thuile catchment, soil development was limited during the Late Glacial Period, whereas it became a dominant process during the Holocene climatic optimum together with enhanced selective transport of fine particles. Human activities since 3,000–4,000 yr cal BP induced a strong perturbation hindering both soil formation and selective transport by reinforcing erosion rates. After a period of topsoil destruction caused by intense deforestation and agriculture, lake Li isotopes record the evolution of soil profiles associated with changes in agricultural practices.

Late glacial–Younger Dryas climate in interior Alaska as inferred from the isotope values of land snail shells

AbstractThe isotope values of fossil snail shells can be important archives of climate. Here, we present the first carbon (δ13C) and oxygen (δ18O) isotope values of snail shells in interior Alaska to explore changes in vegetation and humidity through the late-glacial period. Snail shell δ13C values were relatively consistent through the late glacial. However, late-glacial shell δ13C values are 2.8‰ higher than those of modern shells. This offset is best explained by the Suess effect and changes in the δ13C values of snail diet. Snail shell δ18O values varied through the late glacial, which can be partially explained by changes in relative humidity (RH). RH during the snail growing period was modeled based on a published flux balance model. Results suggest a dry period toward the beginning of the Bølling–Allerød (~14 ka) followed by two distinct stages of the Younger Dryas, a wetter stage in the early Younger Dryas from 12.9 to 12.3 ka, and subsequent drier stage in the late Younger Dryas between 12.3 and 11.7 ka. The results show that land snail isotopes in high-latitude regions may be used as a supplementary paleoclimate proxy to help clarify complex climate histories, such as those of interior Alaska during the Younger Dryas.

A radiocarbon spike at 14 300 cal yr BP in subfossil trees provides the impulse response function of the global carbon cycle during the Late Glacial.

We present new 14C results measured on subfossil Scots Pines recovered in the eroded banks of the Drouzet watercourse in the Southern French Alps. About 400 new 14C ages have been analysed on 15 trees sampled at annual resolution. The resulting Δ14C record exhibits an abrupt spike occurring in a single year at 14 300-14 299 cal yr BP and a century-long event between 14 and 13.9 cal kyr BP. In order to identify the causes of these events, we compare the Drouzet Δ14C record with simulations of Δ14C based on the 10Be record in Greenland ice used as an input of a carbon cycle model. The correspondence with 10Be anomalies allows us to propose the 14.3 cal kyr BP event as a solar energetic particle event. By contrast, the 14 cal kyr BP event lasted about a century and is most probably a common Maunder-type solar minimum linked to the modulation of galactic cosmic particles by the heliomagnetic field. We also discuss and speculate about the synchroneity and the possible causes of the 14 cal kyr BP event with the brief cold phase called Older Dryas, which separates the Bølling and Allerød millennium-long warm phases of the Late Glacial period. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.