Younger Dryas Research Articles

Fire, volcanism and climate change: the main factors controlling mercury (Hg) accumulation rates in Tropical Lake Lantoa, Sulawesi, Indonesia (∼16,500–540 cal yr BP)

The effects of climate change on long-term mercury (Hg) cycling are still not well understood, as climate changes are usually gradual and can only be assessed using high-resolution archives. Our study site (a small, lowland tectonic lake in Sulawesi, Indonesia) provides a unique opportunity to further understanding of Hg cycling in the Southeast Asian (SEA) tropics during the transition from the Pleistocene to the Holocene, a period of significant climate variability. We present a high-resolution record of Late Glacial and Holocene Hg deposition within the sediments of tropical Lake Lantoa, Sulawesi. Using a multi-proxy framework (including pollen, charcoal, carbon:nitrogen ratio and high-resolution geochemistry records) we investigate the response of Hg accumulation rates (HgAR) in sediments to shifts in climate between ∼16,488 and 538 cal BP. This period encompasses the Bølling-Allerød (BA) warming, Younger Dryas (YD) cooling and Holocene warming events, providing new insights into the effects of global climatic transitions on HgAR in SEA sediments. The Pleistocene Termination had the highest HgAR and substantial variability (µ = 11.32, 5.38–33.91 μg m−2 yr−1), when drier conditions and high charcoal accumulation rates suggest that fire activity was the main source of Hg to the lake. The Holocene Transition was marked by a decrease in HgAR (µ = 8, 3.50–18.84 μg m−2 yr−1) as humid conditions precluded forest burning, followed by high HgAR (µ = 11.35, 3.30–158.32 μg m−2 yr−1) in the Early Holocene. Mercury accumulation rate in the Late Holocene (µ = 3.80, 1,67–43.65 μg m−2 yr−1) was the lowest in the Lake Lantoa record, marked by the lowest fire events and a stable catchment. An increase in carbon:nitrogen ratios during the Late Holocene, coupled with a decrease in HgAR, suggests that the establishment of lowland forest resulted in suppressed Hg erosion/leaching. Our results demonstrate that forest fires, vegetation change and volcanism are important drivers of Hg inputs to Lake Lantoa, a relationship which is strongly mediated by climate and lake-catchment dynamics.

A Continuous Centennial Late Glacial-Early Holocene (15-10 cal kyr BP) Palynological Record from the Iberian Pyrenees and Regional Comparisons.

This paper presents the first continuous (gap-free) Late Glacial-Early Holocene (LGEH) pollen record for the Iberian Pyrenees resolved at centennial resolution. The main aims are (i) to provide a standard chronostratigraphic correlation framework, (ii) to unravel the relationships between vegetation shifts, climatic changes and fire, and (iii) to obtain a regional picture of LGEH vegetation for the Pyrenees and the surrounding lowlands. Seven pollen assemblage zones were obtained and correlated with the stadial/interstadial phases of the Greenland ice cores that serve as a global reference. Several well-dated datums were also derived for keystone individual taxa that are useful for correlation purposes. Four vegetation types were identified, two of them corresponding to conifer and deciduous forests (Cf, Df) and two representing open vegetation types (O1, O2) with no modern analogs, dominated by Artemisia-Poaceae and Saxifraga-Cichorioideae, respectively. Forests dominated during interstadial phases (Bølling/Allerød and Early Holocene), whereas O1 dominated during stadials (Oldest Dryas and Younger Dryas), with O2 being important only in the first half of the Younger Dryas. The use of pollen-independent proxies for temperature and moisture allowed the reconstruction of paleoclimatic trends and the responses of the four vegetation types defined. The most relevant observation in this sense was the finding of wet climates during the Younger Dryas, which challenges the traditional view of arid conditions for this phase on the basis of former pollen records. Fire incidence was low until the Early Holocene, when regional fires were exacerbated, probably due to the combination of higher temperatures and forest biomass accumulation. These results are compared with the pollen records available for the whole Pyrenean range and the surrounding lowlands within the framework of elevational, climatic and biogeographical gradients. Some potential future developments are suggested on the basis of the obtained results, with an emphasis on the reconsideration of the LGEH spatiotemporal moisture patterns and the comparison of the Pyrenees with other European ranges from different climatic and biogeographical regions.

From tundra to tree-birch; late-glacial and early Holocene environment and vegetation oscillations at the ecotonal positioned Bjerkreim, Dalane, SW Norway

Basin sediments from Bjerkreim, SW Norway, have been analyzed regarding pollen, plant macrofossils, chironomids, palaeomagnetism, elements, volcanic ash, and loss-on-ignition. The chronology is based on the Vedde Ash and Saksunarvatn ash layers and radiocarbon dates of plant and insect macrofossils. The records spanning the period from local deglaciation around 16 ka BP to the early Holocene ca 10.2 ka BP, have given new detailed information of the late-glacial environments. In the cold pre-Bølling (prior to 14.6 ka BP), open pioneer vegetation on unstable mineral soils was dominant. After the Bølling warming, climate became moister and reached the late-glacial thermal maximum (July mean of 12–13 °C), and dominant dwarf shrubs and snow beds established. Shallow soils, strong winds, and drought may have restricted vegetation development. Despite colder summers (July mean of 9.5–11 °C) in Allerød 13.9–12.8 ka BP, fertile humus-soils developed, and shrub vegetation and open birch-forests established. Snow beds regained dominance in Younger Dryas (July mean of 6.5–9 °C). The early Holocene warming initiated rapid establishment of early Betula/Populus-forests and the later Corylus forests around 10.7 ka BP. Three cooling events in the Bølling-Allerød interstadial (Older Dryas/GI-1d, G1-1c2, GI-1b/Gerzensee) temporarily increased open-ground vegetation showing the ecotonal position of Bjerkreim with low resistance to these changes. The Empetrum expansion was delayed (from 14.5 to 13.7 ka BP) towards the east along the coast of Rogaland. This could point to a precipitation/outwash gradient decreasing towards the east and developing the acid soils necessary for Empetrum to expand. For the first time, macrofossils show the late-glacial presence of tree-birch in Norway. Tree-birch were sparse in Bølling and formed patches of open-forests in Allerød. Several pollen taxa previously thought to reflect long-distance dispersal, such as Populus, Hippohaë, Jasione, and Sanguisorba ssp., most probably were present in Rogaland during Late-glacial. Doggerland seem to have been important for the late-glacial northwards migration of plants into South Norway.

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.

Late-Weichselian (Vistulian) environmental changes in NE Poland – Evidence from Lake Suchar Wielki

By applying pollen and subfossil Cladocera analyses to the Late-Weichselian section of the sediment profile from Lake Suchar Wielki, we aimed to track paleoenvironmental changes in NE Poland, locally (lake formation and its early development) and regionally (terrestrial plant succession). The article aims to indicate how not only stadial-interstadial changes were noticeable in the study area, but above all even short-term climatic fluctuations.The obtained record covers the period of ca. 13,400–11,500 cal. BP, i.e. the part of the Allerød interstadial (GI-1c1 to GI-1a), the Younger Dryas stadial (GS-1), and the very beginning of the Holocene. During the Allerød, a short-lasting cooling was recognized (the Gerzensee oscillation, GI-1b). It is the first study for this part of Poland evidencing the inter-Allerød cooling by the Cladocera-based mean July temperature reconstruction. In the palynological record it was reflected in an increased temporary share of Betula alba t. pollen, while in the Cladocera record in the appearance of cold-water taxa and low total abundance. At the transition to the Younger Dryas further cooling took place that was evidenced by the increase in the proportion of herbaceous plants together with a distinct decrease of tree pollen concentration in sediments as well as by important changes in Cladocera communities including reduced species diversity, disappearance of more demanding temperate taxa and the expansion of cold-tolerant species. The palaeobotanical record revealed that the proportion of juniper pollen in the studied area was lower than in other regions of NE Poland. A case study demonstrated this was mainly due to local conditions. Moreover, it is noteworthy that, at the end of the Younger Dryas, spruce appeared temporarily in local forest stands. The results of the study suggest climate change, which has also been recorded in ice cores from Greenland as cooling ca. 11,800–11,600 cal. BP.

Late Quaternary glacier advances in the Andes of Santiago, central Chile, and paleoclimatic implications

Andean mountain glaciers in central Chile are in a transitional zone between the seasonal influence of the mid-latitude westerlies and subtropical semiarid conditions to the north. Long-term glacial dynamics for these glaciers and their relationship with the paleoclimate during the late Quaternary are poorly known despite their relevancy. We estimate here the timing and extent of late Pleistocene–early Holocene glaciers in the Andes of Santiago (33°50′S) from geomorphological and geochronological analyses. Our observations evidence that a glacial stage occurred before the Last Glacial Maximum (ELGM) at the San Gabriel drift (1,300 m a.s.l.), dated as ∼46–36 ka. Glacial stages during the latest Pleistocene–early Holocene transition period, partially concomitant with the Antarctic Cold Reversal (ACR) and with the Younger Dryas (YD) chronozones, were identified and dated at La Engorda drift (2,450–2,570 m a.s.l.) at ∼15–10 ka. We propose that the San Gabriel drift represents a prolonged glacial advance driven by increased precipitation and cold conditions off central Chile during glacial times. In La Engorda drift, late glacial advances occurred associated with increased regional precipitation, in the context of a transition from humid to arid climate in central Chile, concomitantly with a general warming trend of sea surface temperatures offshore in the southeastern Pacific and with reduced austral summer insolation. The results support the sensitivity of the Andean mountain glaciers to precipitation and paleoclimate conditions, most possibly associated with periods of increased northward influence of the mid-latitude westerlies during glacial and late glacial times, in addition to the El Niño/Southern Oscillation (ENSO) impact since the mid-Holocene, driving late Quaternary glacier advances in central Chile. We estimate a maximum variation of ∼1,200 m in the position of the late Quaternary Equilibrium Line Altitude (ELA), inferred at ∼3,400 m and ∼3,600 m a.s.l. at the time of the San Gabriel and La Engorda drifts, respectively, with respect to its modern location close to 4,600 m a.s.l.

Changes in Kuroshio Current dynamics and East Asian monsoon variability during the last 26 kyr

The Kuroshio Current flows northward along the east coast of Taiwan toward the Okinawa Trough and the East China Sea, but its dynamics and trajectory were probably different during the Last Glacial Maximum (LGM) due to the globally lower sea level that could have caused a (debated) deflection of the current along the eastern edge of the Ryukyu Arc.Core MD18–3532 has been recovered in an intra-slope basin of the Ryukyu accretionary prism, currently disconnected from the Kuroshio Current, but would have been on its trajectory in case of a NE deflection. Measurements of clay mineral assemblages and illite crystallinity revealed that Taiwan has been the main sediment source at this site over the last 26 kyr. The significantly higher sedimentation rate from the Last Glacial Maximum to the Bølling–Allerød compared with the period from the Younger Dryas to the Holocene, coupled with very low δ15Nsed during LGM and Heinrich Stadial 1, provide evidence for the transport of sediments and Trichodesmium spp. cyanobacteria by the partially deflected Kuroshio Current toward the eastern edge of the Ryukyu Arc. Combined with δ13Corg, TOC, TN, and XRF analyses, an increase in primary productivity has been observed during LGM and Heinrich Stadial 1. This would have been caused by an enhanced East Asian Winter monsoon winds resulting in the deepening of the mixed layer that would have led to the upwelling of the Kuroshio Current nutrient-enriched subsurface waters to the oligotrophic surface waters, and the supply of dust-borne iron from the Chinese Loess Plateau.

Laguna Seca sediments reveal environmental and climate change during the latest Pleistocene and Holocene in Sierra Nevada, southern Iberian Peninsula

Sedimentation in most glacial lakes and wetlands in the Sierra Nevada (southern Iberian Peninsula) began after the last deglaciation and since the Younger Dryas (YD)-Early Holocene (EH) transition. Therefore, until now, studies on older sedimentary records were lacking in this alpine area, which limits the paleoenvironmental and paleoclimatic information to the Holocene. In this study, we studied palynomorphs from the alpine record from Laguna Seca (LS), the longest and oldest (∼18,000 cal yr BP = 18 kyr) sedimentary record in the Sierra Nevada to investigate the response of forests and lake environments in the western Mediterranean area to climate changes and human impact during the latest Pleistocene and Holocene. The deepest lake conditions occurred during the last deglaciation, indicated by the occurrence of Pediastrum algae, which showed highest abundances during the Heinrich Stadial 1 (HS1) and Bølling-Allerød (B-A) transition. Xerophyte herbs such as Artemisia, Ephedra, and Amaranthaceae were highest during the late B-A and YD indicating regional aridity. Poaceae (grasses) were maxima in the B-A and EH, probably indicating expansion in the barren areas after deglaciation. Maximum in temperature and humidity during the EH and cooling and aridification in the Middle (MH) and Late Holocene (LH) are indicated by the changes in the abundance of deciduous Quercus and Pinus forest species. Botryococcus algae increased during the Early Holocene, while the rest of the algae almost vanished, which could indicate that the lake became very productive but shallower until 8.2 kyr. The lake level lowered and became seasonal in the Middle-Late Holocene transition, coinciding with the regional climate aridification. Microcharcoal analysis done on the palynological preparations agrees with the vegetation changes, showing maxima in the EH and MH, related with the maximum in regional forest occurrence, and a decrease in the LH when the Mediterranean vegetation, and thus fuel availability, diminished. This record shows evidence of anthropogenic impact in the last centuries by cultivation, reforestation, cattle grazing, enhanced erosion and eutrophication.

Human occupations of upland and cold environments in inland Spain during the Last Glacial Maximum and Heinrich Stadial 1: The new Magdalenian sequence of Charco Verde II.

The settlement of cold and arid environments by Pleistocene hunter-gatherers has been a heated topic in Paleolithic Archaeology and the Quaternary Sciences for years. In the Iberian Peninsula, a key area for studying human adaptations to such environments is composed by the large interior and upland regions of the northern and southern plateaus (Mesetas) and bordering areas. As, traditionally, these regions have been relatively under-investigated compared to the ecologically more favored coastal areas of the peninsula, our knowledge of the human settlement of the whole Iberian hinterland remains scarce for the Last Glacial. In this paper we present the discovery and first geoarcheological, paleoenvironmental and chronometric evidence obtained at Charco Verde II, a new site close to the southwestern foothills of the Iberian system range (Guadalajara province, Spain), bearing a sequence of Magdalenian human occupations starting at least at 20.8-21.4 ka cal BP during the Last Glacial Maximum, and covering Greenland Stadial 2 until ∼15.1-16.6 ka cal BP, including Heinrich stadial 1. As this site is located in an upland region which today faces one of the harshest climates in Iberia, such occupation sequence, occurred during some of the coldest and most arid phases of the Last Glacial, has relevant implications for our understanding of human-environment-climate interactions and population dynamics in Iberia and Western Europe. These findings support the hypothesis that the Iberian hinterland was not avoided by Upper Paleolithic hunter-gatherers due to ecological constraints, but it hosted a complex and relatively dense settlement at least in some areas, even during cold periods. This suggest, one more time, that the historical scarcity of Upper Paleolithic sites in inland Iberia is, to a significant extent, an artifact of research bias.

Late Pleistocene paleoenvironments and megafauna from the Sierra Madre del Sur flanks and the Central Depression of Chiapas (Southern México)

Pleistocene fluvial sequences have been recognised in some regions of México as an important source of information on past environmental change using a wide range of proxies. However, this has not been attempted in Mexico's southernmost state of Chiapas until the current paper, where the main aim is to describe and date five new Late Pleistocene fossil rich sequences and to interpret their paleoenvironmental record and changes that they indicate. This interpretation is based on the sedimentology, pollen record and stable isotopes from vertebrate fossils together with the radiocarbon dating of the fluvial sediments. At Los Mangos and El Bajión fossil sites the fluvial sediment record reported here includes a conspicuous layer with aerodynamic Fe magnetic microspherules associated with the Younger Dryas (YD) meteorite impact which adds to the type of paleoenvironments in which such meteorite impacts have been recognised. The sediment dating indicates that the fossiliferous sites are Late Pleistocene in age, and they add new locations and information for México for this climatic phase.

Late Devensian to Holocene environmental change, Loch Lomond, UK: A seismic sedimentary record of deglaciation, paraglacial and postglacial landscape evolution

We present an interpretation of two-dimensional sub-bottom profiling data from Loch Lomond, Scotland, UK. Sediments deposited during and following the last glacier advance have been investigated for decades around the shores of Loch Lomond. For the first time, this study presents an interpretation of the subsurface providing a window into the late Quaternary and Holocene history of Loch Lomond and its surrounding. The seismic stratigraphy records the infill of the loch during the final stages of the Loch Lomond Stadial (LLS, 12.9–11.7 ka BP), through the Holocene and into the present day. Results reveal the presence of distinct seismic facies (SF) identifying four principal seismic horizons; SF-I, SF-II, SF-III, and SF-IV. The SF-I horizon represents the glaciated surface, interpreted as subglacial till (locally forming drumlins), glacial moraines or bedrock. Ice retreat was accompanied by glaciolacustrine sedimentation in a proglacial lake setting, depositing up to 44 m of laminated sediments and ice marginal fans (SF-IIa, b). A period of landscape instability followed with extensive deposition of mass transport deposits (SF-III). These deposits, characterised by chaotic seismic facies with an erosional basal surface, are up to 43 m thick and may represent up to 50 % of the sediment fill. SF-IV comprises finely laminated sediments deposited during the Holocene and highlights slower sedimentation rates in comparison to earlier phases of sedimentation. This study reveals new insights into the deglaciation of Loch Lomond, including previously unrecognised extensive mass transport deposits buried in the subsurface, associated with a period of paraglacial adjustment.

Palaeoecological and palaeoenvironmental responses to abrupt climate changes during the Late Glacial: The unique archive recorded at the Osinki site (NE Poland) and its regional importance

The reconstruction of environmental changes at the termination of the Last Glaciation range in NE Europe during the Late Glacial is hampered by the multiplicity of processes underway at that time and during the Holocene that dynamically modified the Young Glacial landscape. In lake sediments, these changes are recorded in a manner that is almost always incomplete or disturbed. For this reason, the succession that was successfully reconstructed in two profiles from the Osinki site in NE Poland is extremely valuable. Palynological, Cladocera and geochemical analyses, as well as fragmentary malacofauna and diatom analyses, made it possible to trace the changes in the environment that took place in two differently functioning parts of a single lake, in not interrupted periods from the Oldest Dryas to the Younger Dryas. Detailed research results show that despite the proximity of natural environment components, their developments in both cases were conducted in different ways, what they prove to the changes in pollen record, Cladocera, and geochemical composition of sediments. Climate changes affected the changes in the vegetation, the composition of malacofauna, Cladocera and diatoms. They also influenced the erosion processes within the catchment and the oxidation-reduction conditions. On the basis of the research results, changes in water trophy, from oligotrophic to eutrophic, were also observed. In this case, we also observe significant differences between the two analysed profiles. These changes first occurred in Allerød in the shallow part of the lake, and then in its deeper zone in Young Dryas.In addition, Late Weichselian profiles from the Poland–Belarus–Lithuania borderland area were analysed in detail, and the age of the bottom of sediments is usually estimated to the Allerød, and the Bølling. The results of analyses from Osinki and Osinki2 profiles (beginning of sedimentation in the Oldest Dryas) indicate that the reason for this discrepancy is to be found in, among other things, the methodological limitations of the palynological analysis for most of the sites. The above-standard amount of mineral sediment allows the age of the sediment to be established as being much older than if determined using only pollen analysis of organic sediments.

Sediment Record of the Earliest Stage of the Evolution of Lake Kanozero (Sw Kola Peninsula): New Data for Regional Deglaciation Reconstructions and Relative Sea-Level Studies

The multi-proxy study of the lowermost part of the sediment sequence of Lake Kanozero (south-western part of the Kola Peninsula, ca. 53 m a.s.l.) revealed the evidences for marine waters penetration into the basin during the earliest stage of its evolution. The diatom analysis inferred the conditions of a large brackish-water basin. Sediments composition and very low organic content also supported large-basin and low-productivity environments. Based on the pollen study, this stage covers a cooling period preceding the Allerød (tentatively assigned to the Older Dryas) and the onset of the Allerød. Periglacial vegetation typical of the cold and dry climate prevailed in the area for the most of the period. The subsequent transition to the freshwater conditions inferred from the diatom study took place in the Allerød, according to the pollen data. Except for a minor decrease in the fine sand fraction, no other corresponding changes were observed in the sediment record suggesting no major shifts in sedimentary environments. In the late Allerød and throughout the Younger Dryas, Lake Kanozero remained a large, low-productive freshwater basin. Our results indicate that ice-free conditions with aquatic sedimentation in the Kanozero depression had already existed in the Older Dryas. This assumes earlier deglaciation of the study area than it was previously thought. The study also suggests that brackish conditions in the White Sea basin established earlier than reported before. While the previous studies found no signals of marine transgression above ca. 41 m a.s.l., our results indicate that the local marine limit in the study area exceeds ca. 53 m a.s.l.

RELATIVE SEA-LEVEL CHANGE OF THE WHITE SEA IN THE LATE GLACIAL AND HOLOCENE: CASE STUDY OF THE SREDNYAYA TRET’ LAKE, EASTERN COAST OF THE GORLO STRAIT<a href="#FN4"><sup>4</sup></a>

The relative sea-level changes for the time interval of ~12.1–9.1 ka cal BP were reconstructed on the eastern coast of the Gorlo Strait using the results of paleolimnological, GPR and geomorphological analyses conducted in the basin of the Srednyaya Tret’ Lake (7.3 m a.s.l., 66.014009° N, 41.086294° E), as well as UAV surveying of the lake surroundings. Bottom sediments of the lake were studied from the four core sections and correlated with each other according to the results of GPR data interpretation. Lithostratigraphic descriptions of bottom sediment cores, grain-size and diatom analyses, radiocarbon dating (AMS), determination of LOI, Corg content and Corg /Norg ratio were performed. We present the reconstruction of the coastlines at heights of 4–5 and 12–15 m formed by currents and/or wave processes within the lower Ruch’i River valley and Srednyaya Tret’ Lake according to field observations and interpretation of space images. As a result, the position of the relative sea-level and the chronology of the Late Glacial (Younger Dryas) transgression and the early stages of the Holocene (Tapes) transgression were refined. Late glacial transgression finished earlier than ~12.1 ka cal BP, and its relative level was probably no higher than 15 m a.s.l. After a deep regression, the relative sea-level approached the modern again ~9.5 ka cal BP, and at the Tapes transgression maximum (~9.1 ka cal BP) it was near the lake runoff threshold (∼5 m). Though the coastline was near the lake basin, sea waters never entered the lake. Sands, carried by the wind, accumulated in the part of the basin facing the coast. The the Srednyaya Tret’ Lake basin was gradually filled by fresh water according to the results of diatom analysis.

VEGETATION AND CLIMATE CHANGES IN THE SOUTHERN URALS IN THE LATE GLACIAL AND HOLOCENE DERIVED FROM POLLEN RECORD OF LAKE BOLSHOE MIASSOVO<a href="#FN1"><sup>1</sup></a>

A spore-pollen analysis of a 526 cm sediment core retrieved from Lake Bolshoe Miassovo, Southern Urals, was carried out. The obtained data made it possible to reconstruct the vegetation cover in the lake’s catchment area and the climatic situation of the region for 13 400 cal yr BP, which significantly expands and complements the paleogeographic chronicle of the Southern Urals. It was found that in the range of 13 400–12 700 cal yr BP in the conditions of a relatively warm and dry climate of Allerød, periglacial forest-steppe formations were widespread in the studied region. Steppe herb communities and birch-pine sparse woodlands with spruce grew on open landscapes. The pine degradation and replacement of spruce with more cold-resistant larch was most likely caused by a cooling in the period of 12 700–11 700 cal yr BP, which corresponds to the Younger Dryas. The periglacial forest-steppe formations are replaced by birch forests since 11 700 cal yr BP. The significant changes in the vegetation cover of the lake’s catchment area indicate warming and humidification of the climate at the beginning of the Holocene. The dominance of birch forests in the interval of 11 300–10 300 cal yr BP, probably, corresponds to the second half of the Pre-Boreal period. The distribution of pine and spruce in the range of 10 300–8300 cal yr BP indicates a warming of climatic conditions in the Boreal period. Since 8400 cal yr BP the proportion of broad-leaved species in the tree stand increases. The broad-leaved species cover reached its peak between 6000–4500 cal yr BP at the end of the Atlantic - the beginning of the Sub-Boreal period (Holocene climatic optimum). Some cooling of the climate was observed in the range of 4500–2000 cal yr BP, which presumably corresponds to the Sub-Boreal and the beginning of the Sub-Atlantic period. The birch forest with spruce and broad-leaved species grew in the lake’s catchment area. Some aridization and warming of the climate in the Sub-Atlantic period in the range of 1800–1000 cal. yr BP led to an increase in the role of pine and a reduction of spruce in the area around the lake. Since 1800 cal yr BP the vegetation of the territory adjacent to Lake Bolshoe Miassovo was similar to the modern one: pine-birch forests with an admixture of dark coniferous and broad-leaved species prevailed on the territory.

LATE GLACIAL PALAEOENVIRONMENT AND DEVELOPMENT OF PROGLACIAL LAKES ON THE NORTHERN COAST OF THE SAMBIAN (KALININGRAD) PENINSULA<a href="#FN1"><sup>1</sup></a>

Comprehensive investigations of the northern coast of the Sambian (Kaliningrad) Peninsula, that included geomorphological survey, lithostratigraphic description of the section logs, diatom, botanical and LOI analyses, radiocarbon dating, and GNSS survey relating lithological boundaries and sampling levels to the sea level and determining terrace elevations, were performed. New data on the regional palaeogeographic settings of the Late Glacial period and the stages of development of the large proglacial basin, the Baltic Ice Lake (BIL) were obtained. It has been established that after the degradation of the last glaciation, erosional (subaquatic) processes prevailed in the coastal area, while in the interval of 14–13 cal kyr BP subaerial conditions established at the study site, and tree-moss phytocenoses formed during the Allerød warming. At the end of the warming period there was a shallow, isolated lake, with decreasing depth. During the Younger Dryas oscillation, ca. 12 000 cal kyr BP, the area was flooded by waters of a vast freshwater, ultra-oligotrophic basin with high content of suspended fine mineral particles. The conditions of a shallow bay of the BIL sheltered from the main basin by a moraine ridge at least 4–5 m high, are suggested for this period. The lake drainage took place around 11 660 cal kyr BP. Since then, no accumulation or alternating accumulation and erosion conditions prevailed in the study site until the late Holocene. The obtained results allow us to speak about two stages of flooding of the northern coast of the Sambia Peninsula during the Late Glacial, possibly caused by the BIL transgressions. The occurrence of BIL deposits in the northern part of the Sambia Peninsula above sea level suggests that the Late Glacial basin level in the study area may have exceeded the present sea level.

Изменение окружающей среды северо-западного сектора Японского моря в период последней дегляциации

Environment changes in the northwestern part of the Sea of Japan and adjacent land during last 21.0 kyr was reconstructed based on the analysis of pollen and diatom data with a high temporal resolution. Relatively dry climate caused a wide distribution of forest-steppe landscapes in the region between 21.0 to 16.6 ka. Boreal forests covered mountain slopes. Broad-leaved trees survived in refugia located in lower mountain belts. The low sea level during the Last Glacial Maximum (LGM) changed the general patterns in the sea circulation and longshore current directions, which transported the waters formed in the shallow areas of the northwestern and northern parts of the Sea of Japan. A slight increase in sublittoral benthic diatoms indicates the lowered sea level during the LGM. Occurrence of Betula indicates the start of warming after 18.5 ka; it was interrupted by the cold event Heinrich 1 and marked by the spread of coniferous Larix, Picea, and sphagnum bogs. The beginning of late glacial climatic amelioration Bølling-Allerød (BA) is contributed to dispersal of Quercus and Polypodiaceae ferns. The distribution of conifers Larix and Picea as well as of sphagnum bogs is correlated with the Younger Dryas (YD) cooling. Significant changes in vegetation occurred in the Holocene. The high percentage of sublittoral planktonic diatoms reflects a gradual rise in sea level during the BA and YD. A greater component of oceanic diatom species in the Holocene indicates the inflow of the Pacific waters through both the Tsushima and Tsugaru straits. Some increase in the participance and species diversity of relatively warm-water diatoms was noticed in the warming periods. The study of pollen and diatom records demonstrates a clear response to climatic fluctuations and changes in the Sea of Japan level in the Late Pleistocene and Holocene.

Contourite stratigraphic models linked to the light intermediate versus dense deep Mediterranean water flow regime variations (Alboran Sea, SW Mediterranean)

Several water masses are involved in the circulation of oceans, their bottom layers impacting on sedimentation through contourites. The majority of palaeoceanographic studies on regional contourites are performed for one water mass despite that their joint study would offer relevant clues to understand past ocean and climate interaction. This works presents for the first time a an analysis about the impact of the Light Intermediate Mediterranean (LMW) and Dense Deep Mediterranean (DMW) bottom currents on the sedimentation in the Alboran Sea (SW Mediterranean) and its paleoceanographic significance in response to climatic oscillations from the last glacial period to the Holocene. To do this, an integration of chronostratigraphical, sedimentological, and compositional data is carried out from contourites formed by those water masses. That integration enable us to define three distinct contourite stratigraphic models. (I) The contourite terrace model, characterized by coarse-grained contourites, which is an archive of the interplay between the high-energy Atlantic Water-LMW interface and glacioeustasy from the Younger Dryas (YD) to the Holocene. (II) The contourite drift models, which are archives of rapid ocean-climate coupled fluctuations since 29.5 kyr. They comprise coarse-grained contourites formed by a relatively fast LMW and fine-grained contourites formed by a relatively weak DMW, except for the Heinrich Stadials HS3 to HS1 and YD when coarse-grained contourites were deposited. (III) The contourite/turbidite mixed model represents another archive of DMW and glacioeustasy interplay from the end of the late Pleistocene to Holocene.That contourite stratigraphy allows us to infer for the first time the relative variability of the LMW versus DMW flow regimes, which records differences and similarities. The similarities indicate that the LMW and DMW fluctuations occur in parallel at millennial and centennial time scales. The differences refer to the overall higher velocity of LMW versus DMW; the magnitude changes in velocities that are lower for LMW and higher for DMW; the recognition of three short ventilation events (a, b, c) during HS1 and HS2 for only DMW; and the distinct LMW and DMW responses to the onset of glacial conditions and return to interglacial conditions during the HSs, YD and Holocene cold periods.The proposed contourite stratigraphic models can be applied for other areas in the Mediterranean margins to identify and correlate the LMW and DMW palaeoceanographic events throughout this sea. The findings suggest that the different water masses that make up the water column must be seriously considered to fully understand palaeoceanographic and palaeoclimatic studies based on contourites. This is because their distinct impact on sedimentation may provide new insights into their different palaeoceanographic responses to rapid climatic oscillations and their triggering mechanisms.

Stalagmite-based long-term and multi-centennial hydroclimatic variations in southwestern China during the Holocene and relations to global climate change

Knowing the behavior of the Asian summer monsoon (ASM) and its global correlation help understand roles of the ASM in global climate change. Here we synthesize a stalagmite δ18O record, based on a new record and an available nearby record, both covering the nearly entire Holocene. The synthesized δ18O record correlates with meridional migration of the Intertropical Convergence Zone (ITCZ), and with change in inter-subtropical insolation contrast throughout the Holocene. However, its correlation with the Atlantic meridional overturning circulation (AMOC) broken down during the period of the strongest ASM, when the AMOC weakened. This scenario points to a persistent influence of the ITCZ and subtropical insolation contrast on the change in ASM throughout the Holocene. Our record also correlates with a change in atmospheric CO2 concentration on the multi-millennial scale. These correlations of our cave record with variations in the ITCZ, subtropical insolation contrast, and CO2 level indicate that changes in low-latitude climates, including the ASM, were involved in the evolution of the Holocene CO2 concentration. These changes in the low-latitude climates were likely connected with variation in the Holocene southern westerly wind, which modulated upwelling of carbon-enriched deep ocean water around Antarctica. On the multi-centennial scale, seven weak ASM events are identified, with the magnitudes of the Younger Dryas and the events at 9.8 ka and 8.2 ka event broadly three and two times larger than the other ones. These events have a quasi-period of approximately 1.463 ka. This period in the monsoon regime probably arose from solar activity, but involving the feedback of ENSO. In summary, our study provides insights into the connection of the Holocene ASM with tropical climate, and into the involvement of the ASM in the change of the Holocene CO2 concentration.

N-Alkane and terpenoid fingerprints of modern biomass producers unveil floral changes recorded in postglacial alpine lake sediments, Tatra Mountains, Slovakia

Sediments of two alpine lakes in Tatra Mts., Slovakia, record the environmental history of their catchments from deglaciation in Late Glacial warming up to the Subboreal period. We present abiomarker-based reconstruction of changes in the surrounding biota of two contrasting lakes – a relic lake in open fen Trojrohé pleso (TROJ) and a tarn lake Batizovské pleso (BAT). Taking advantage of young unaltered sediments, well-known source area, and main biomass producers, we used an actualistic approach and interpreted sedimentary lipid distributions using fingerprints of modern plant groups. Four chemostratigraphic units were defined in TROJ lake and five units in BAT lake, with boundaries and environmental changes roughly conforming to paleoclimatic intervals of the Holocene. The dry climate was recorded in the period 13,200 BP–11,500 BP, coincident with Younger Dryas stadial. In the sediment of TROJ lake at ca. 5,200 BP asharp spike in the abundance of the aromatic terpenoid retene, decoupled from the trend of other abietane-type diterpenoids, may best be explained by episodic flooding due to the rise of the water table. Diploptene as abiomarker for bacterial activity is suggested to indicate the development of soil cover at the end of the B/A interstadial and its gradual increase in abundance in the Holocene most reflecting an extension of vegetated area and more complex development of soil cover. Based on the absence of conifer biomarkers in the sediments of BAT lake, the upper limit of the continuous Pinus mugo scrub never reached the altitude of 1880 m a.s.l. between 16,247 and 4,420 BP, whereas conifer canopy was permanently present around TROJ lake at 1611 m a.s.l. between 10,439 and 3,113 BP.