Lateglacial Holocene Transition Research Articles

Environment and Plant Use at La Tourasse (South-West France) at the Late Glacial–Holocene Transition

Abstract The aim of this study is to present new data on vegetation dynamics and plant collecting practices during the Late Glacial and the Early Holocene in southwestern France. La Tourasse cave is located in the Pyrenean piedmont plain, where the Azilian cultural complex was initially defined. The last excavations of the site took place in the 1980s and 1990s and the recovered materials are currently being studied or revisited from a multidisciplinary perspective. We present here the results of the charcoal analysis performed on La Tourasse’s Azilian (ca. 13000–11500 cal. BP) and Mesolithic (ca. 10500–9000 cal. BP) levels, complemented by the study of a small seed assemblage. Our results document the shift from an open landscape towards a forested environment, with the gradual passage from open vegetation dominated by shrubs of the Rose family (Prunus spp.) to the mixed oak forest, which speaks in favor of the biochronological coherence of this sequence. However, marked differences in taxonomic richness and state of the wood from one level to another, unrelated to the prevailing environmental conditions, suggest variable behavior of humans toward wood that could be the result of differing mobility strategies, hearth functionalities, or taxonomic preferences.

Holocene environmental changes in the fuegian forest and steppe, Argentina

Environmental changes were reconstructed from a multiproxy synthesis of over 30 localities from the Isla Grande de Tierra del Fuego and Isla de los Estados, southernmost South America. At a local scale, the results from the mountain forest and gently undulating steppe areas were integrated as well as those from the marine environments of the Beagle Channel and the Atlantic coasts. At a regional scale, the results were integrated with those published for the southernmost Andean and Extra-Andean Patagonia and the Antarctic Peninsula. This study focuses on the environmental evolution during the Late Glacial-Holocene transition, the Middle to Late Holocene transgressive-regressive hemicycle and wet-dry oscillations, the Medieval Climate Anomaly, the Little Ice Age, the tephra inputs from the Patagonian Andes, and the recent climatic warming. Most paleoenvironmental changes are related to variations in the latitudinal position and intensity of the Southern Westerly Winds (SWW) while others are associated with astronomical or endogenous forcings. At a strong intensity of the SWW, a greater contribution of humidity to the forest areas and an increase in the rainfall gradient create windy and arid conditions in the steppe. At a weak intensity of the SWW, lower humidity input in the forest areas and the advection of air masses from the Atlantic Ocean promoted humid and slightly windy conditions in the steppe. Similar environmental trends are observed between terrestrial and marine environments in the center and south of Tierra del Fuego, Isla de los Estados and the Antarctic Peninsula, and between the Fuegian steppe and Extra-Andean Patagonia. The paleoclimatic evidence reveal high environmental variability in the last 10,000 years for this sector of the Southern Hemisphere.

Past vegetation reconstruction maps and paleoclimatic variability inferred by pollen records in southern Patagonia Argentina since the Late Glacial-Holocene transition

Palaeoecological reconstructions document past vegetation distribution with estimates of the communities boundaries shifts. This work presents a compilation of palaeoecological studies from southern Patagonia Argentina as a contribution to a better understanding of the composition and distribution of Andean and extra-Andean plant communities. Paleoenvironmental reconstructions are based on pollen sequences from different types of deposits located in the forest, forest-steppe ecotone and steppes between 46° and 51°S. The comprehension of modern pollen and its relation with the actual vegetation is a critical component of palaeoecological research. Models of the current relationship pollen-vegetation-climate were applied to interpret these sequences. Their integration made it possible to reconstruct the spatio-temporal patterns of vegetation and past climatic changes since the Late Glacial-Holocene transition. Four areas were selected to map past vegetation communities; three lake basins: Pueyrredón, San Martín and Argentino, and the Deseado Massif. The local conditions given by the geomorphology of each site were also taken into account. The vegetation reconstruction during the Pleistocene-Holocene transition came from records located in the Deseado Massif only, and indicated steppes, without modern analogues, linked to arid and cold conditions. During the Holocene, plant communities were sensitive to moisture conditions related to westerly winds or Atlantic-derived precipitation events. Taxa related to the anthropogenic impact of the past centuries were found at all sites, both in Andean and extra-Andean Patagonia.

Environmental changes since 14 ka BP in the southernmost Kuril islands (North-Western Pacific) and regional correlation of events

• New data on climatic changes at the late Pleistocene-Holocene boundary for Kurils. • Climate fluctuations and volcanic ash-falls were mail drivers in lake-mire evolution. • The lake level was highest during warmer and humid climate of the Allerød. • Younger Dryas cooling in the Kuril Islands was less distinct than on the continent. • Pollen record vegetation changes on the land bridge at Late Glacial–early Holocene. Despite considerable progress in understanding Late Pleistocene and Holocene palaeoenvironmental changes worldwide, there are still very few such data for the Far East, and Kuril islands, in particular. Here, the sea level rise during the Late Glacial–Holocene transition was accompanied by a loss of the land connectivity culminating into the development of isolated islands. The ecosystems evolution and importance of isolation for vegetation dynamics on islands are still insufficiently understood. We investigated a unique natural record of environmental change since 14 ka has been recently discovered in lake–mire complex on Kunashir Island. The sediments include 12 tephra layers from Kunashir and Hokkaido volcanoes. The lake level was highest during warmer and humid climate of the Allerød. Diatom assemblages indicated the higher lake level between 12 730–12 160 cal yr BP. The first half of Younger Dryas was characterized by heavy snowfalls. Cooling attributed to the Younger Dryas in the Southern Kurils was less distinct than on the continent. The pollen assemblages recorded changes in vegetation on the land bridge. At the end of the Pleistocene large areas were occupied by birch forests and shrub pine. The broadleaf species first appeared at the end of Allerød. Starting from the Pleistocene-Holocene transition and during the early Holocene , the role of conifers sharply increased. In the middle Holocene the proportion of broadleaf trees in forests increased. Coniferous forests became abundant during the Little Ice Age. Short-tern climatic fluctuations correlate well with regional pattern, particularly with fluctuations of the moisture supply.

Food availability and temperature optima shaped functional composition of chironomid assemblages during the Late Glacial–Holocene transition in Northern Europe

Non-biting midges (Chironomidae) are the most diverse and abundant invertebrate group in boreal lakes and are strongly responsive to climate change, thus they are a valuable palaeoecological proxy for studying aquatic biodiversity response in the face of climate change. Here, we aim to decipher the influence of climate-induced changes on temporal patterns in chironomid assemblages. We apply a novel approach combining traditional taxon-based analysis and species-trait framework to subfossil chironomid assemblages in a sediment core covering the Late Glacial–Holocene transition in Northern Europe. We produce pollen-based July and January temperature reconstructions to characterize past climate fluctuations that show a distinct Early Holocene warming for continuous 1700 years with considerably greater warming in winter (ca. 10 °C) than summer (ca. 4 °C) temperature. Overall, chironomid taxonomic changes were mainly induced by the temperature tolerances and optima of species, as temporal dynamics showed agreement with temperature reconstructions. Our results suggest that vegetation dynamics could also play a role in structuring chironomid assemblages by selecting taxa with the highest ability to exploit available food resources, thus potentially confounding chironomid-based summer climate reconstructions. We demonstrate that the study of the hidden chironomid functional composition could help to identify secondary drivers and thus strengthen the reliability of climate reconstruction based on subfossil chironomids.

Low-topography deep-seated gravitational slope deformation: Slope instability of flysch thrust fronts (Outer Western Carpathians)

Unlike high-relief mountain areas, low-relief hilly landscapes are usually rarely affected by deep-seated gravitational slope deformations (DSGSDs). However, low-topography flysch thrust fronts can create suitable structural conditions for DSGSDs. The study area of the Kavalčanky ridge represents a relatively low-lying (<120 m of local relief) DSGSD-affected ridge situated at the thrust front in the flysch Outer Western Carpathians (Czech Republic). With the aim of revealing the main controlling factors and temporal constraints of mass-movement activity, a multidisciplinary investigation of DSGSDs was performed. Typical DSGSD landforms were mapped using high-resolution LiDAR-based mapping. Structural analysis revealed the presence of specific flysch thrust structural conditions with competent sandstone units overthrusted on a weak tectonically disrupted claystone basement. Geophysical measurement with the use of electrical resistivity tomography (ERT) and ground penetrating radar (GPR) profiling confirmed the deep reach (>50 m) of the studied DSGSD. Together with slope stability finite element modelling, geophysics suggests that the shear zone of DSGSDs is represented by one of the thrust faults, whereas lateral limits are formed by a set of conjugate strike-slip faults. Radiocarbon dating of bogs within the DSGSD body showed two phases of mass-movement activity corresponding to the Late Glacial-Holocene transition and Middle Holocene. The recent activity was excluded by dendrogeomorphic analysis. We concluded that the structural conditions involving high lithological complexity, tectonic weakening and the presence of major tectonic contacts might create conditions prone to DSGSDs even in relatively low-topography settings with mass movement activity, especially during humid and warmer Late Quaternary periods.

Late Quaternary vegetation and climate of SE Europe–NW Asia according to pollen records in three offshore cores from the Black and Marmara seas

High-resolution pollen analyses were performed on two cores from the western Black Sea and one core from the Marmara Sea, covering the Late Glacial-Holocene transition using 14C chronology. Particular effort was invested in the botanical identification of pollen grains thereby significantly improving our knowledge of regional flora. When interpreted with respect to modern vegetation, pollen records revealed all the major changes caused by climatic fluctuations over the last 20,000 years. The results of this study provide evidence for the occurrence of relict thermophilous-hygrophilous trees (papillate Cupressaceae, Carya, Liquidambar, Zelkova) in certain refugia up to the Holocene. Vegetation dynamics is specified for some taxa (e.g. Cupressus–Juniperus, Fagus, Cedrus) and some ecosystems (e.g. mesophilous forests, Mediterranean sclerophyllous populations, steppes). Pollen data enabled palaeoclimatic reconstructions which were compared with available estimates in the region. The use of a powerful pollen ratio between ‘thermophilous and steppe taxa’ led to fruitful climatostratigraphic relationships with the oxygen isotope curve from the NGRIP core. The Younger Dryas and cooling at 8.2 ka are among the most obvious climatic phases identified in the three cores studied here.

Geomorphic response to the Lateglacial–Holocene transition in high Alpine regions (Sanetsch Pass, Swiss Alps)

Several palaeoclimatic archives have documented the pronounced climatic and environmental change associated with the Lateglacial–Holocene transition in the European Alps. However, the geomorphic response to this major environmental transition has only been punctually investigated. In this study, we propose a detailed reconstruction of post‐Last Glacial Maximum palaeoenvironmental conditions and geomorphic connectivity in the Sanetsch Pass area (2252 m a.s.l., western Swiss Alps) based on a multi‐method approach combining geomorphological and sedimentological field investigations with quantitative sedimentology and geochronology. Samples for sediment characterization (grain size, micromorphology and X‐ray diffraction) and geochronology (optically stimulated luminescence and 10Be surface exposure dating) were collected from three representative landforms of the study area: a high‐elevation silty deposit covered by patterned ground, an alluvial fan, and a hummocky moraine covered by rockfall deposits. Our results reveal the geomorphic history of the three deposits and their connectivity through sediment cascade. These results highlight the development of rapid and most probably transient landscape changes in high Alpine regions during the Lateglacial–Holocene transition, with an increase in sediment flux and the establishment of paraglacial and periglacial geomorphic processes.

The end of the Epigravettian and the beginnings of the Sauveterrian in Tuscany (Italy): Essay based on a typological re-interpretation of the lithic assemblage

The Late Glacial-Holocene transition is characterized by the onset of warmer Holocene temperatures in the Tuscany, Liguria and Latium regions (Italy) which were occupied by humans between 15,000 and 8000 CalBP. The stone tools associations and the regional and chrono-cultural impact they reflect are assessed. Principal components analysis (PCA) is applied for the investigation. Results show that the lithic tools were structured in groups that do not exactly match those originally proposed by Laplace in 1964. There are in fact unexpected situations of association-repulsion between the lithic tool groups that clearly differentiate samples according to regions and chrono-cultural origin. This study highlights the characteristics of Tuscany's final Epigravettian in its evolution towards the Sauveterrian, allowing to distinguish it from the bordering sites of the Liguria and Latium regions.

Keep your feet warm? A cryptic refugium of trees linked to a geothermal spring in an ocean of glaciers.

Up to now, the most widely accepted idea of the periglacial environment is that of treeless ecosystems such as the arctic or the alpine tundra, also called the tabula rasa paradigm. However, several palaeoecological studies have recently challenged this idea, that is, treeless environments in periglacial areas where all organisms would have been exterminated near the glacier formed during the Last Glacial Maximum, notably in the Scandinavian mountains. In the Alps, the issue of glacial refugia of trees remains unanswered. Advances in glacier reconstructions show that ice domes did not cover all upper massifs, but glaciers filled valleys. Here, we used fossils of plant and malacofauna from a travertine formation located in a high mountain region to demonstrate that trees (Pinus, Betula) grew with grasses during the Lateglacial-Holocene transition, while the glacier fronts were 200-300m lower. The geothermal travertine started to accumulate more than 14,500years ago, but became progressively more meteogene about 11,500years ago due to a change in groundwater circulation. With trees, land snails (gastropods) associated to woody or open habitats and aquatic mollusc were also present at the onset of the current interglacial, namely the Holocene. The geothermal spring, due to warm water and soil, probably favoured woody glacial ecosystems. This new finding of early tree growth, combined with other scattered proofs of the tree presence before 11,000years ago in the western Alps, changes our view of the tree distribution in periglacial environments, supporting the notion of tree refugia on nunataks in an ocean of glaciers. Therefore, the tabula rasa paradigm must be revisited because it has important consequences on the global changes, including postglacial plant migrations and biogeochemical cycles.

Double response of glaciers in the Upper Peio Valley (Rhaetian Alps, Italy) to the Younger Dryas climatic deterioration

A pronounced climate reorganization characterized the Lateglacial–Holocene transition in the Northern Hemisphere. Glaciers in the Alps reacted to the last climate deterioration at the end of the Late Pleistocene leaving landscape features suitable for reconstructing Lateglacial and early Holocene history. In this context, the Upper Peio Valley in the Ortles‐Cevedale Group (Rhaetian Alps, Italy) has well‐preserved moraines of La Mare Glacier and Careser Glacier, which we used to reconstruct the glaciers' behaviour and to investigate the Lateglacial–Holocene transition. Detailed glacier reconstructions combined with 11 new 10Be exposure ages allow dating of the response of these glaciers to the Younger Dryas (YD) cold event. La Mare and Careser glaciers reacted to the YD with a double response, building two clear moraine sets. Data from La Mare Glacier indicate the first advance occurred prior to 12.3±0.7 ka (before 10.0±0.7 ka at Careser Glacier). Both glaciers then re‐advanced before 11.2±0.8 ka as dated at La Mare Glacier. This phase can be interpreted as the Egesen stadial glaciers' expression of the end of the YD. Morphometric parameters of the reconstructed phases allowed the estimation of areal and volumetric variations of the studied glaciers as well as equilibrium line altitude (ELA). ΔELA with respect to the Little Ice Age (LIA) maximum position are −225 m for La Mare Glacier and −180 m for the Careser Glacier. Although the behaviour of the two glaciers showed coherence during the Egesen stadial and the LIA, they have behaved individually since then. La Mare has lost 60% of its area, while Careser has lost 85% since the latest Pleistocene. We attribute this to the greater proportion of ice at high elevation of the La Mare Glacier, underlining the importance of bed hypsometry in glacier response.

Lakes ecosystem response to Holocene climate changes and human impact in the Southern Urals: Diatom and geochemical proxies

Major changes in the Holocene were identified based on a diatom and geochemical analysis of sediment cores from Lakes Ufimskoe and Syrytkul (the Southern Urals). The Lake Ufimskoe ecosystem in the Central mountain area is identified to be highly sensitive to variations in temperature. Meanwhile, Lake Syrytkul is more responsive to climate aridization because of its limnological characteristics and less precipitation in the piedmont area. Climate events were the main drivers for lake ecosystems dynamics throughout almost the whole history of the lakes. The records of lake sediments reflect several climate events noted elsewhere in the Northern Hemisphere: Lateglacial–Holocene transition (~12,000–11,600), Preboreal oscillation (~11,200–11,000 cal. BP), climate warming and aridization (~9700–9600 cal. BP), warming and increase in precipitation since 9000 cal. BP, climate aridization at ~5800 cal. BP, cooling since 4000 cal. BP, and warming at ~2500 cal. BP. Climate warming of the last hundred years was not reflected in lake sediment records because of the significant human impact on the lake ecosystem. The upper sediments of both lakes are enriched in As, Bi, Sb, Te, Sn, Cd, Cu, Zn and Pb because of the influence of the Karabash copper smelter. However, the significant changes of the Lake Syrytkul ecosystem are not related to the technogenic impact and explained mainly by the dam construction. The changes in diatom communities identified in Lake Ufimskoe, which is located in an area geologically sensitive to acidification, are related to the acidification and heavy metal loading on the water area.

A varved lake sediment record of the 10Be solar activity proxy for the Lateglacial-Holocene transition

Solar modulated variations in cosmogenic radionuclide production provide both information on past changes in the activity of the Sun and a global synchronization tool. However, to date the use of cosmogenic radionuclides for these applications is almost exclusively based on 10Be records from ice cores and 14C time-series from tree rings, all including archive-specific limitations. We present the first 10Be record from annually laminated (varved) lake sediments for the Lateglacial-Holocene transition from Meerfelder Maar. We quantify environmental influences on the catchment and, consequently, 10Be deposition using a new approach based on regression analyses between our 10Be record and environmental proxy time-series from the same archive. Our analyses suggest that environmental influences contribute to up to 37% of the variability in our 10Be record, but cannot be the main explanation for major 10Be excursions. Corrected for these environmental influences, our 10Be record is interpreted to dominantly reflect changes in solar modulated cosmogenic radionuclide production. The preservation of a solar production signal in 10Be from varved lake sediments highlights the largely unexplored potential of these archives for solar activity reconstruction, as global synchronization tool and, thus, for more robust paleoclimate studies.

A lake-bog succession vs. climate changes from 13,300 to 5900 cal. BP in NE Poland in the light of palaeobotanical and geochemical proxies

This paper presents and discusses the influence of climatic and edaphic factors on vegetation succession of the postglacial Lake Czarne (LC) located in NE Poland. On the basis of pollen, macroscopic plant remains, non-pollen palynomorphs (NPPs), and geochemical analyses, we reconstructed the transition from a clear oligotrophic lake to an ombrotrophic mire from 13,300 to 5900cal. BP. Climatic events/periods that may have affected the lake/mire succession were as follows: (i) relatively warm conditions in the younger part of the Younger Dryas (ca. 12,220cal. BP) that led to water eutrophication recorded as blooms of Scenedesmus ellipticus, whose response preceded that of woodland vegetation by ca. 200years, (ii) the warming of the Late Glacial–Holocene transition and early Holocene that caused the final melting of dead ice block(s) and led to the deepening of the water body and/or an increase in the water level, the retreat of submerged macrophytes, and the enrichment of waters with sulphur, (iii) the global cold period between 8600 and 8000cal. BP that contributed to a rise in the water level during the phase of sedge swamp and enabled the reappearance of Nymphaeaceae and blooms of S. ellipticus (ca. 8570–8500cal. BP), and (iv) the global climate cooling 6500–5900cal. BP that still remains enigmatic in terms of palaeobotanical patterns; however, geochemical markers point to an increase in the water level and enhanced erosion in the LC catchment ca. 6200–6000cal. BP. Lake terrestrialization resulted in the concurrent appearance of microhabitats suitable for mosses with contrasting ecological preferences, e.g., Warnstorfia exannulata (acidic) and Scorpidium revolvens (alkaline), or Straminergon stramineum (acidic), Meesia triquetra (alkaline) and S. revolvens (alkaline).

Reviewing the Lateglacial–Holocene transition in NW Iberia: A palaeoecological approach based on the comparison between dissimilar regions

Isotopic records from Greenland ice cores have revealed a number of centennial to millennial-scale climatic fluctuations affecting the eastern North Atlantic during the Lateglacial/Holocene transition. Most of them appear directly correlated with quantitative temperature changes reconstructed for a very climate-sensitive locality in NW Iberia, Laguna de La Roya (LR). The chironomid-inferred LR temperature record was used as a reference to update the chronologies and improve the interpretations of 16 different key pollen sites from NW Iberia. Botanical and zoological macroremains from archaeological sites and natural deposits were also reviewed in order to check if they support the changing environments predicted by pollen data. Pollen evidence corresponding to the less intense Lateglacial and Early Holocene cold phases identified in LR was found at all sites. Nevertheless, only minor vegetation changes occurred during the Older Dryas, La Roya-I (13,600–13,350 cal BP), La Roya-II (13,300–12,900 cal BP), the 11.4 ka and the 9.3 ka event at very sensitive sites located close to ecotonal situations. We conclude that the LR chironomid inferred-temperature curve is able to explain the main tree-line oscillations and also the major local/regional vegetation changes that occurred over the whole of NW Iberia during the Lateglacial and Early Holocene. During this period, the most relevant landscape modifications occurred at the onset of the Lateglacial, at the transition to the YD, and at the onset of the Holocene. However, noticeable changes also occurred during the 8.2 ka event, which mostly affected the hyperoceanic coastal mountain ranges and some continental depressions inland. The rapid succession of changes registered during the Early Holocene affected the different co-existing biocoenoses in an unequal way and resulted in a diversity of plant and animal resources available for human populations. This may explain that the hunter–gatherer groups even persisted in some areas of NW Iberia until the Mid Holocene.

Lateglacial and Holocene environmental changes in the Southern Urals reflected in palynological, geochemical and diatom records from the Lake Syrytkul sediments

A multi-proxy study including lithology, geochemistry, diatom analysis and palynology of the Lake Syrytkul sediments provides continuous environmental reconstruction of the Lateglacial and Holocene in the Southern Urals and make it possible to compare the role of natural and anthropogenic factors in lake history. The Lake Syrytkul sediment records reflect the main Lateglacial and Holocene paleoclimate changes. The Lateglacial–Holocene Transition (11,600–11,500 cal BP) expressed in all palaeorecords was followed by great limnological and vegetation changes. The climatic changes of ∼7400 and ∼4300 cal BP were fixed in all lake sediment records. Vegetation and lake ecosystem were less affected by global climate events: the Preboreal Oscillation (11,200–11,000 cal BP), 8.2 ka event and regional climate events: ∼10,350 cal BP, ∼9750 cal BP, ∼9000 cal BP and ∼2000 cal BP. As follows from lake sediment records, the environment deterioration after the Holocene climatic optimum started in different time in the range of 6300–5100 cal BP due to various sensitivities of different proxies to paleoclimate parameters. The climate events were the main drivers for the dynamics of the Southern Urals lake ecosystems during almost the entire lake history. The role of the human factor in the change of the lake ecosystem was critical since the beginning of the twentieth century. Despite the adjacent Karabash copper smelter as the source of considerable technogenic contamination, it was a dam constructed ∼100 years ago that had the greatest impact on the lake system. This event is reflected in all sediment records, especially diatom and geochemical. Changes in the diatom species composition and sediments geochemistry of the shortest human impact period are comparable in magnitude to the response of the lake ecosystem to the Lateglacial–Holocene Transition.

A high-resolution Late Glacial to Holocene record of environmental change in the Mediterranean from Lake Ohrid (Macedonia/Albania)

Abstract Lake Ohrid (Macedonia/Albania) is the oldest extant lake in Europe and exhibits an outstanding degree of endemic biodiversity. Here, we provide new high-resolution stable isotope and geochemical data from a 10 m core (Co1262) through the Late Glacial to Holocene and discuss past climate and lake hydrology (TIC, δ13Ccalcite, δ18Ocalcite) as well as the terrestrial and aquatic vegetation response to climate (TOC, TOC/N, δ13Corganic, Rock Eval pyrolysis). The data identifies 3 main zones: (1) the Late Glacial–Holocene transition represented by low TIC and TOC contents, (2) the early to mid-Holocene characterised by high TOC and increasing TOC/N and (3) the Late Holocene–Present which shows a marked decrease in TIC and TOC. In general, an overall trend of increasing δ18Ocalcite from 9 ka to present suggests progressive aridification through the Holocene, consistent with previous records from Lake Ohrid and the wider Mediterranean region. Several proxies show commensurate excursions that imply the impact of short-term climate oscillations, such as the 8.2 ka event and the Little Ice Age. This is the best-dated and highest resolution archive of past Late Glacial and Holocene climate from Lake Ohrid and confirms the overriding influence of the North Atlantic in the north-eastern Mediterranean. The data presented set the context for the International Continental scientific Drilling Program Scientific Collaboration On Past Speciation Conditions in Lake Ohrid project cores recovered in spring–summer 2013, potentially dating back into the Lower Pleistocene, and will act as a recent calibration to reconstruct climate and hydrology over the entire lake history.

Initial results from a new Lake Elsinore sediment core reveal evidence for hydrologic change during the late Glacial-Holocene transition

Initial results from a new Lake Elsinore sediment core reveal evidence for hydrologic change during the late Glacial-Holocene transition

Natural and human-induced environmental changes in Eastern Europe during the Holocene: a multi-proxy palaeolimnological study of a small Latvian lake in a humid temperate zone

This study uses the Holocene lake sediment of Lake Ķūži (Latvia, Vidzeme Heights) for environmental reconstruction with multi-proxy records including lithology, computerised axial tomography scan, grain-size analysis, geochemistry, diatoms and macrofossils, supported by AMS radiocarbon dating. Numerical analyses (PCA; CONISS) reveal three main phases in the development of the lake. Response to the Lateglacial–Holocene transition in Lake Ķūži took place around 11,300 cal. BP. Organogenic sedimentation started with distinctive 5-cm-thick peat layer and was followed by lacustrine sedimentation of carbonaceous gyttja. Several findings of the peat layer with similar dated age and position at different absolute altitudes indicate that lake basin was formed by glaciokarstic processes. In the Early Holocene (until around 8,500 cal. BP), the lake was shallow and holomictic, surrounded by unstable catchment with erosion and inflow events. Predominance of diatom species of Cyclotella and Tabellaria, large numbers of respiratory horns of phantom midge pupae (Chaoboridae), high Fe/Mn ratio, as well as the presence of laminated sediments indicates the transition to a dimictic and oligo-mesotrophic lake conditions with high water level, anoxia in the near-bottom and stable catchment in the Middle Holocene (8,500–2,000 cal. BP). This contrasts with many hydrologically sensitive lakes in Northern and Eastern Europe in which the water level fell several meters during this period. During the Late Holocene (from 2,000 cal. BP to the present), the lithological and biotic variables reveal major changes, such as the increase in erosion (coarser grain-size fraction) and eutrophication [diatoms Aulacoseira ambigua (Grun.) Sim., Stephanodiscus spp., Cyclostephanos dubius (Fricke) Round]. Characteristics of lake-catchment system during the Late Holocene reflect anthropogenic signal superimposed on the natural forcing factors. To date, the Late Quaternary palaeolimnological reconstructions using lake sediment has been limited in the Baltic region. Therefore, findings from Lake Ķūži provide important information about environmental and climatic changes that took place in this part of Eastern Europe. This study shows that the relative importance of climate and local factors has varied over the time and it is essential to consider the lake basin topography, catchment size and land cover as potential dominant forcing factors for changes in sedimentary signal.

The Younger Dryas in the Neotropics: paleoecological evidence from Venezuela

A continuous lacustrine sequence from the western part of Lama Lake (69°32′N, 90°12′E), complemented by a peat sequence from the lake catchment provides the first detailed environmental reconstruction for the Late Glacial and Holocene on the Taymyr Peninsula. Scarce steppe-like communities with Artemisia, Poaceae, and Cyperaceae dominated during the Late Glacial. Tundra-like communities with Betula nana, Dryas, and Salix grew on more mesic sites. There are distinct climatic signals, which may be correlated with the Bølling and Allerød warming and Middle and Younger Dryas cooling. The Late Glacial/Preboreal transition, at about 10,000 14C yr BP, was characterized by changes from predominantly open herb communities to shrub tundra ones. Larch forest might have been established as early as 9700–9600 14C yr BP, whilst shrub alder came to the area ca 9500–9400 14C yr BP, and spruce did not reach area before ca 9200 14C yr BP. Spruce-larch forests with shrub alder and tree birch dominated the vegetation around the Lama Lake from ca 9000 14C yr BP. Dwarf birch communities were also broadly distributed. The role of spruce in the forest gradually decreased after 4500 14C yr BP. The vegetation cover in the Lama Lake area became similar to the modern larch-spruce forest ca 2500 14C yr BP. A pollen-based biome reconstruction supports a quantitative interpretation of the pollen spectra. Climate reconstructions obtained with information-statistical and plan-functional-type methods show very similar trends in reconstructed July temperature since ca 12,300 14C yr BP, while precipitation anomalies are less coherent, especially during the Late Glacial–Holocene transition.