High-resolution Pollen Research Articles

Visible or not? Reflection of the 8.2 ka BP event and the Greenlandian–Northgrippian boundary in a new high-resolution pollen record from the varved sediments of Lake Mondsee, Austria

This paper presents a new pollen record from Lake Mondsee in the north-eastern European Alps and discusses changes in vegetation composition between 9000 and 7000 a BP in response to the 8.2 ka BP cooling event, which is clearly reflected in a stable oxygen isotope record from the same lake. Pollen and microcharcoal analyses performed at bi-decadal resolution provide detailed insights into the vegetation history and fire regime in the study area. The late Greenlandian and early Northgrippian between ca. 9000 and 8000 a BP were mainly characterised by the gradual expansion of spruce, accompanied by the retreat of hazel. Results of the pollen-based biome reconstruction show that the Greenlandian–Northgrippian boundary at ca. 8280 a BP was marked by a shift in the affinity scores of regional forest biomes, reflecting a decreasing role of temperate broadleaved trees and shrubs and a strengthening of boreal conifers in the study area. During the early Northgrippian between ca. 8000 and 7000 a BP, fir and beech spread around Lake Mondsee, which is in line with other pollen records from the northern Alpine Foreland, indicating cooler and moister conditions. This long-term trend is likely a response to decreasing summer insolation (i.e. decreasing summer temperatures) and the weakening of the Siberian High, which promoted westerly-driven moisture transport from the Atlantic region. Visual inspection of the Lake Mondsee pollen data does not reveal a clear signal of the 8.2 ka BP event. However, biomization results show a distinct minimum in the temperate deciduous biome scores and summed scores of plant functional types representing warm-loving tree and shrub taxa at ca. 8165–8135 a BP.

Disturbance and Succession in Early to Mid-Holocene Northern English Forests: Palaeoecological Evidence for Disturbance of Woodland Ecosystems by Mesolithic Hunter-Gatherers

Forest succession can be monitored in the present, modelled for the future, but also reconstructed in the past on the records of forest history, including through the use of palaeo-ecological techniques. Longer-term records from pollen data can show changes over centennial and millennial timescales that are impacted by climate, migration or soil development. Having knowledge of previous phases of post-disturbance seral stages of woodland regeneration however, as after fire, can provide insights regarding successional process and function over short-term decadal timescales. The aim of this paper is to test the high-resolution pollen record as a source of new insights into processes of succession, assisted by the supplementary data of microscopic charcoal analyses. On short-term timescales, multiple phases of forest disturbance and then recovery have been identified in early to mid-Holocene peat records in northern England, many from the uplands but also from lowland areas. We identify and describe a typology of recovery patterns, including the composition and rate of recovery, and then test the processes and factors that impacted on different seral trajectories, concentrating on fire disturbance which might have had a natural origin, or might have been caused by pre-agricultural Mesolithic hunter-gatherers. Factors considered include the spatial location and intensity of the fire event, the duration of the disturbance phase, the structure and dynamics of the successional regeneration vegetation communities and the pre-disturbance tree cover. Data from examples of fire disturbance of woodland have been examined from both upland and lowland sites in northern England and indicate that they had different successional pathways after disturbance. Fire disturbances in the denser lowland forests were mostly single burn events followed by natural successions and regeneration to forest, whereas fire disturbances in the upland woods usually showed continued or repetitive fire pressure after the initial burning, arresting succession so that vegetation was maintained in a shrub phase, often dominated by Corylus, for an extended period of time until disturbance ceased. This creation of a kind of prolonged, almost plagioclimax, ‘fire-coppice’ hazel stage suggests controlled rather than natural successional pathways, and strongly suggests that Mesolithic foragers were the fire starters in the upland English woodlands where hazel was naturally common and could be maintained in abundance in later-stage successions, along with other edible plants, for human use. All post-fire seral stages would have been attractive to game animals, providing a reliable food source that would have been of great benefit to hunter-gatherer populations.

Palynological data confirm the occurrence of forest on the Loess Plateau of central China during the Middle Quaternary (MIS13)

The Loess paleosol sequence S5SS1 (top layer of S5 paleosol layers; marine isotope stage (MIS) 13) has been extensively studied because it is the most developed paleosol layer among all Quaternary soils in the China loess and represents the greatest humidity since the past 2.5 Ma. The question of whether forests occurred on the Loess Plateau tablelands when these paleosols were deposited is still a controversial scientific issue. This research provides a quantitative reconstruction of the past climate and forest cover between 544 and 480 ka based on a high-resolution pollen record together with magnetic susceptibility (χfd) and L*a*b* color parameters. Results suggest that the Luochuan area (central Loess Plateau) was sparsely covered by temperate deciduous forest under warm and humid conditions with a strong East Asian summer monsoon. The precipitation and woody cover during 544 and 531 ka were similar to those today and much greater than modern from 531 to 480 ka. Our findings are supported by paleosol profile research and modern vegetation studies. This study confirms that MIS 13 was a warm and humid period and that sparse forest developed on the tablelands of the central Loess Plateau, which provides new thinking on the ecosystem restoration program of the Loess Plateau.

Climate Change, Fire and Human Activity Drive Vegetation Change during the Last Eight Millennia in the Xistral Mountains of NW Iberia

An 8500-year record of high-resolution pollen, non-pollen palynomorph, microscopic charcoal and selected geochemical data (Ti, Zr and Pb) is presented from an ombrotrophic mire from the Xistral Mountains, Galicia, North-West Iberia. The results suggest that vegetation changes over the last eight millennia are primarily the result of human disturbance, fire and climate change. Climate and fire were the main factors influencing vegetation development during the early to mid-Holocene, including a short-lived decline in forest cover c. 8.2 cal. ka BP. Changes associated with the 4.2 and 2.8 cal. Ka BP events are less well defined. Human impact on vegetation became more pronounced by the late Holocene with major periods of forest disturbance from c. 3.1 cal. ka BP onwards: during the end of Metal Ages, Roman period and culminating in the permanent decline of deciduous forests in the post-Roman period, as agriculture and metallurgy intensified, leading to the creation of a cultural landscape. Climate change appears to become less influential as human activity dominates during the Late Holocene.

Landscape Response to Dynamic Human Pressure in the Paliouras Lagoon, Halkidiki Peninsula, Macedonia, Greece

High-resolution pollen analysis of a sediment core recovered from Paliouras lagoon (Greece) allowed us to reconstruct the environmental dynamics of the Halkidiki peninsula during the last 4000 years. Palynological results have been interpreted and compared with detailed historical data, showing distinct phases of human-landscape interactions from the Bronze Age until recent times. Pollen spectra revealed an environment characterized by Mediterranean vegetation, mixed deciduous forest, and pine stands from the Late Bronze Age until the 11th century CE. The first signs of human impact were attested during the Archaic period with the cultivation of Olea, Castanea, and Vitis in the inland of the study area. An intensive land management was highlighted by arboriculture and cereal cultivation (Secale and Hordeum group) in Roman times. Late Antique-Early Medieval times coincided with less human pressure due to warfare-related crises, leading to the expansion of the forest and the abandonment of fields colonized by Amaranthaceae. A massive increase in pastoral activities, suggested by the high percentages of Cichorieae during the Ottoman period, is possibly linked to the significant demographic growth of the nearby city of Thessaloniki in the 16th century CE.

Vegetation succession, climate change and cold events during 9.2–8.0 cal kyr BP in eastern China: High-resolution pollen evidence from the Yangtze delta plain area

High resolution pollen records in the northern edge of subtropical China are crucial to understand the pattern of postglacial vegetation change and climate transition. Here we present vegetation succession and climate change during 9.2–8.0 cal kyr BP based on sub-decennial scale pollen data. Pollen spectra show that Quercus (evergreen) &Cyclobalanopsis were relatively stable during the whole period, while Quercus (deciduous) were gradually decreased. Pollen-based climate change shows gradual warming during this period, and noticeably, the rapid warming during 8610–8545 cal yr BP can be detected according to the sharp decrease of Quercus (deciduous). Our results show two cold and dry events at 8.5 ka and 8.2 ka. The 8.5 ka event is rarely reported in the East Asian Monsoon area, while the 8.2 ka event is frequently mentioned. In this study, the 8.2 ka event has two peaks, similar to the previous reports from the Yangtze delta area and Dongge Dong Cave. In the Yangtze delta area, the vegetation and climate change show a strong relationship with the high latitude area, indicating that they are not only related to solar activity, but also impacted by the high latitude climate events. However, the impacts of these events on the Asian monsoon area still need further studies to verify.

Multiple forcing on Late Miocene East Asian Summer Monsoon Precipitation Variability in NE Tibetan Plateau

Understanding how the East Asian Summer Monsoon (EASM) evolves at different time scales affords a valuable opportunity to reveal the interactions between the hydrosphere, land, oceans and atmosphere. However, the pre-Quaternary evolutionary history and the driving forces that controlled its variability in response to different boundary conditions remain enigmatic. Here, we focus on the late Miocene (∼10.8 to 6.3 Ma) – a period of profound climatic and topographic changes in Asia – and present a quantitative reconstruction of EASM precipitation using the probabilistic CREST (Climate Reconstruction Software) method with a high temporal resolution pollen record from the Tianshui Basin in NE Tibetan Plateau (TP). Our new EASM precipitation record shows a slowly decreasing long-term trend during the period of ∼ 10.8–7.6 Ma, which was followed by a strengthening period from ∼ 7.6 to 6.3 Ma with a large amplitude of precipitation variability. We argue the decrease and increase periods of EASM precipitation were primarily response to late Miocene global cooling and TP uplift after ∼ 8 Ma, respectively. These results are supported by existing climate model simulations, wherein both global climate and paleotopography play key roles in regulating the long-term evolution of late Miocene EASM. On orbital time scales, the precipitation time series exhibit a dominant ∼ 410 kyr eccentricity periodicity, with lower (higher) values intervals corresponding to eccentricity minima (maximum). The synchronous phase of the precipitation and eccentricity records indicate that the eccentricity exerts a dominant influence on the EASM precipitation cycles via its modulation of the precessional amplitude, and the period expansion and contraction of Antarctic ice sheet (AIS) also probably play an important role during that time. Our quantitative late Miocene EASM precipitation records provide new insight into late Miocene EASM precipitation evolution and its relation with global climate, paleotopography, and cryosphere.

Large-scale vegetation response to the 8.2 ka BP cooling event in East Asia

The 8.2 ka BP cooling event is the most prominent and abrupt climate event in the Holocene at mid-to-high latitudes in the Northern Hemisphere. In this paper, we conduct model simulations of vegetation responses to the 8.2 ka BP event over East Asia, and compare them with pollen-based vegetation records. Our results reveal that all major Plant Functional Types responded to the climate changes, but the magnitude, timing, and impact of their responses varied. In addition, it was found that after the 8.2 ka BP climate event the vegetation did not always recover to the state simulated before the perturbation, suggesting that different vegetation compositions may occur under similar climate conditions. Changes in temperature exerted a major influence on the vegetation dynamics in the most high latitude regions, and changes in both temperature and precipitation were responsible for the vegetation changes at mid-to-high-latitudes. Compared with pollen-based vegetation reconstructions, our model simulations generally capture the main features of vegetation responses to the 8.2 ka BP event. Notably, only a relatively small proportion of taxa were climatically sensitive during the 8.2 ka BP cooling in pollen records. Only one high-resolution pollen record indicated that the vegetation did not recover to the pre-perturbed state, showing a different vegetation composition after the 8.2 ka BP event similar to our simulations. Such different vegetation compositions could be a long-lasting effect of abrupt climate changes on vegetation through eco-physiological and ecosystem demographic processes, e.g., plant competition. Moreover, our model simulations suggest a more pronounced vegetation responses to the severe cooling in the north and weaker responses to less cooling in the south. Since significant vegetation responses during this event were only seen in few records, more high-resolution pollen records and simulations in terms of vegetation responses to different abrupt climate changes are needed in future.

Vegetation and climate changes since the Last Glacial Maximum inferred from high-resolution pollen records from the Sichuan Basin, southwest China

Reconstructing the vegetation history of southwest China since the Last Glacial Maximum is crucial for understanding the evolution of the Indian summer monsoon. In this study, we present a high-resolution palynological investigation from a 5 m core from the Ganchi peatland (southwest margin of the Sichuan Basin, southwest China) in order to reconstruct regional vegetation and climate over the last 25 kyrs. The succession, from bottom to top, comprises lake, wetland, and peat deposits, and wetland/aquatic pollen types are found to be a sensitive indicator of palaeoenvironmental change. Deciduous broad leaf forests dominated by Betula were present between 25-18 cal kyrs BP, suggesting a cold and dry climate during the Last Glacial Maximum. After 18 cal kyrs BP, temperature and summer insolation increased gradually, marking the Lateglacial transition. Thermophilous and hygrophilous species expanded between 11-8 cal kyrs BP, indicating a progressively warmer and wetter climate. From 8-4 cal kyrs BP, evergreen forests developed, while Tsuga reached its maxim abundance, implying a warm and humid climate coincided with the mid-Holocene climatic optimum. Results indicate that residual ice sheets may have impeded the northward shift of the Intertropical Convergence Zone, resulting in peak Holocene warmth lagging behind peak summer insolation forcing. Vegetation change was primarily controlled by climate, with no obvious evidence of anthropogenic disturbance until the last 1 cal kyrs BP. Our study shows that vegetation and climate in the southwest margin of the Sichuan Basin were controlled by summer insolation and ice sheet dynamics, and also influenced by sea surface temperature in the Indian Ocean.

Spatial and temporal characteristics of the precipitation response to the 4.2 ka event in the Asian summer monsoon region

The 4.2 ka event was the most abrupt climatic event during the transition between the middle and late Holocene. It had a profound influence on the regional ecological environment and human cultural development and was characterized by the rapid onset of aridification in the mid- and low-latitudes regions of the Northern Hemisphere. However, the nature, structure and spatial expression of the 4.2 ka event in the Asian summer monsoon (ASM) region are controversial. We produced a detailed record of regional vegetation change during the interval of 5000–3500 cal yr BP, based on a high-resolution (~10 yr) pollen record from Yazihai Lake, on the margin of the region influenced by the ASM. The results indicate that an interval of climatic aridification, correlative with the 4.2 ka event, occurred during 4340–3880 cal yr BP, with the duration of 460 yr. However, the structure of the event is relatively complex, with arid conditions during 4340–4280 cal yr BP, wetter conditions during 4280–4150 cal yr BP, and arid conditions during 4150–3880 cal yr BP. A comprehensive comparison of the results from Yazihai Lake with existing high-resolution and well-dated paleoclimate records from the ASM region show that the precipitation response to the 4.2 ka event was spatially and temporally synchronous, with a consistent of timing, duration, and structural characteristics in the northern and southwestern parts of the ASM region; whereas the opposite response occurred in the southeastern part, where the precipitation increased. We suggest that the driving mechanism of the 4.2 ka event was related to sea-air interactions in the low-latitude region. Sea surface temperature (SST) anomalies and the variation of the El Niño-Southern Oscillation (ENSO) in the tropical Pacific region was the main cause, which led to a weaker ASM circulation and a southward shift of the monsoon rainbelt. These changes resulted in decreased monsoonal precipitation and a dry climate in the northern and southwestern parts of the ASM region, but to increased precipitation in the southeastern part.

History of human disturbance to vegetation in the Southeast Hills of China over the last 2900 years: Evidence from a high resolution pollen record

The lower reaches of the Yangtze River have a long history of human occupation and rice cultivation, but our understanding of human activities in the mountainous region south of the lower Yangtze is still limited. In this study, we present a high-resolution vegetation record spanning the past 2900 years from the Southeast Hills of China by analyzing loss-on-ignition, pollen, charcoal, and non-pollen-palynomorphs from a lake sediment core. Combining our data with historical records, results suggest the study region was covered by dense broadleaved forests dominated by evergreen Cyclobalanopsis/Quercus from the start of the pollen record at 890 BCE until 850 CE. During this early period, colonization of the mountainous region was limited by rugged relief, closed forests, and lack of suitable land for farming. Later between 850 CE and 1180 CE, a slight decrease of evergreen trees, small rises in cereals and the ruderal herb Artemisia, and more frequent fire events point to the development of small-scale agricultural practices related to increased population. This change may reflect the shift of the economic center of China towards the lower Yangtze reaches, which happened during the Tang Dynasty (618–907 CE) and the influx of war refugees from the north especially during the Song Dynasty (960–1279 CE). From 1180 CE, a sharp decline of evergreen broadleaved trees and a peak in fire frequency was closely linked to a wave of deforestation resulting from the abrupt expansion of cereal cultivation. These changes were accompanied by the remarkable spread of pioneer secondary plants such as Pinus, Artemisia, and Dicranopteris-type ferns, which are typical indicators of human-induced deforestation in the region. It is probable that the population boom spread to the mountains and intensive agricultural activities took place involving terraced fields. Additionally, the coeval mining, smelting, and porcelain production in the mountains enlarged the scale of deforestation. Our study provides valuable information for landscape management and biodiversity conservation in the mountainous hinterland of subtropical southeast China.

Significant weak monsoon events during the early to middle Holocene transition: Pollen evidence from an alpine lake in North China

The response characteristics of East Asian summer monsoon (EASM) precipitation to abrupt climatic events during the early to middle Holocene transition may provide insights into the response of EASM precipitation to possible extreme climatic events under future global warming scenarios. We present a high-resolution (∼10 yr) pollen record from a hydrologically closed alpine lake (Yazihai Lake) in North China spanning the interval of 9000–7500 cal yr BP. The results reveal two significant weak monsoon events during 8830–8730 cal yr BP and 8100–8000 cal yr BP. Based on a comparison with the GRIP δ18O ice core record from Greenland and the stalagmite δ18O record from Dongge Cave in South China, we suggest that the second weak monsoon event (8100–8000 cal yr BP) recorded at Yazihai Lake corresponds to the 8.2 ka event that originated in the North Atlantic region, it is spatially and temporally synchronous between the northern and the southern parts of the EASM region and is characterized by a significant decrease in EASM precipitation. For the first weak monsoon event (8830–8730 cal yr BP) recorded at Yazihai Lake, it was also captured by pollen, stalagmite δ18O, and marine sedimentary records from middle to low latitudes of the Northern Hemisphere, and its nature and amplitude resemble the 8.2 ka event. We infer that the possible cause of these two significant weak monsoon events was related to the southward shift of the intertropical convergence zone (ITCZ) due to the collapse of the Atlantic Meridional Overturning Circulation (AMOC), triggered by meltwater influx to the North Atlantic Ocean, and that the abrupt climate signals were transmitted via the monsoon circulation from low latitudes to middle–high latitudes in the EASM region.

Quantitative reconstruction of the vegetation of the Qinhuangdao area, western coast of Bohai Sea, North China, during the Little Ice Age

It is widely recognized that the climate of the Little Ice Age (LIA) was generally cold. However, there are differences in the climate response of the vegetation in different regions during the LIA, and high-resolution quantitative research is lacking. Here, we present a high-resolution pollen analysis and the Landscape Reconstruction Algorithm (LRA) based on relative pollen productivity, combined with AMS 14C dating, to quantitatively reconstruct the vegetation response to climate and sea level change on the western coast of Bohai Sea. The main findings are as follows: (1) The coverage of the main plant taxa reconstructed using estimates of relative pollen productivity was closer to the actual vegetation conditions than that based on pollen percentages. (2) Since ∼1250 A.D., the study area was occupied by temperate deciduous broadleaved forest, dominated by Quercus, with a smaller proportion of Pinus forest. The regional vegetation types did not change significantly, but the forest cover decreased gradually from ∼60% in the Middle Warm Period (MWP, 1250–1310 A.D.) to ∼40% in the LIA (1310–1610 A.D.), due to the combined influences of climate and human activities. (3) The composition of herbaceous plants changed substantially during the LIA. In the early LIA (1310–1450 A.D.), the climate became cold and dry and the sea level began to fall, resulting in a substantial increase in the proportion of Poaceae (∼10%). In the middle of the LIA (1450–1610 A.D.), the climate became colder and drier, the sea level fell further, and the lagoon shrank. In response, there was an increase in drought and salt-tolerant Chenopodiaceae (∼10%) and Artemisia (∼5%), a substantial increase in Selaginella sinensis supplied by fluvial processes.

Managing wilderness? Holocene-scale, human-related disturbance dynamics as revealed in a remote, forested area in the Czech Republic

In the lowlands and uplands of Central Europe, which were inhabited continuously from the very start of the Holocene to the present times, it is difficult to find territories suitable for investigation of natural baselines. For this reason, we picked the complicated rocky terrain of one upland area in NE Bohemia called Adrspach because, based on the absence of archeological finds, it was supposed to have never been deforested or managed by people. The remote and inhospitable character of this particular area further encouraged this assumption. To our great surprise, however, high-resolution pollen analyses, supplemented by analyses of non-pollen palynomorphs and microscopic charcoals reveals that the local forest ecosystem had a dynamic development over entire Holocene. We were able to correlate this high-resolution understanding of vegetation successions with repeated fire disturbances. Was this fire disturbance dynamic natural? Subsequent archeological exploration and excavation in the area brought unexpected evidence, pointing to rather continuous human presence throughout most of the Holocene. From the Early Mesolithic to the Late Neolithic, available evidence suggests a hunter-gatherer mode of resource management. From the start of the Late-Holocene (ca 4 ka BP), the occurrence of coprophilous fungal spores and secondary anthropogenic pollen indicators suggest this area was impacted by recurrent domestic animal grazing. Testing this approach also in other remote forested areas of Central Europe, we argue, can have far-reaching implications for understanding long term human-environment agency by transforming our understanding of alternative subsistence and land use strategies during prehistory. At the same time, this can significantly alter existing concepts used in Central European nature conservation strategies, which tend to be based on an underlying assumption that our work challenges – the survival of little impacted wilderness at the Holocene scale.

Phytolith and simulation evidence for precipitation-modulated vegetation dynamics along the East Asian monsoon margin

An improved understanding of past interactions between terrestrial vegetation and various forcings, such as climate change, human impact, and paleofire, is crucial for assessing impacts of future global change on terrestrial ecosystems. This study seeks to find the key factor or factors that have driven Holocene vegetation change along the East Asian monsoon margin. Several high-resolution pollen records are reviewed and new phytolith-based paleovegetation reconstructions and physical geochemical datasets are presented from a peatland in northeastern China. Using 108 modern topsoil samples as a training set, canopy cover and vegetation composition are estimated for the period since 5100 cal. yr BP. Variation partitioning analysis (VPA) is used to determine the relative importance of climate change, human impacts, and paleofire disturbance. The generalized dynamic vegetation model LPJ-GUESS is forced with climate anomaly output from an atmospheric general circulation model to simulate vegetation dynamics during the mid-Holocene and the pre-industrial era. The proxy-based estimates are compared to modelling output. Results indicate that regional tree cover varied from 10% to 40% during the past five millennia. The single-core, phytolith-based reconstructions are generally consistent with stacked tree pollen z-scores calculated from different records along the East Asian monsoon margin, implying that mid-Holocene tree cover decrease was persistent and almost synchronous over extensive areas. VPA demonstrates that long-term monsoon marginal vegetation successions were mainly caused by climate effects. Numerical modelling suggests that since the mid-Holocene the retreat of forests along the monsoon margin was primarily associated with precipitation deficits. Our investigation highlights that the precipitation associated with the East Asian monsoon system has exerted a stronger influence than the westerlies on the monsoon margin climate and vegetation change. With ongoing global change, close attention to variations in precipitation patterns and amounts should be especially helpful in efforts aimed at ecological monitoring, change prediction, and restoration.

Intensified climate drying and cooling during the last glacial culmination (20.8–17.5 cal ka BP) in the south-eastern Asian monsoon domain inferred from a high-resolution pollen record

Recent global sea-level data indicate that a final growth of ice volume occurred towards the end of the Last Glacial Maximum (LGM). The LGM culmination, LGM-b, lasted from about 21 to 17 ka and was followed by rapid deglaciation. This finding suggests a millennial-scale state with extreme glacial conditions (at least regionally) that immediately preceded the onset of full deglaciation marked by Heinrich event 1. In order to check how regional climate and vegetation in subtropical East Asia responded to the global-scale LGM culmination and the deglaciation onset, a new high-resolution pollen record from the Lijiafang peatland (LJF: 26°36.849′N, 116°08.463′E, 270 m) in Southeast China was generated. This record demonstrates a massive expansion of herbs during LGM-b. The dominance of herbaceous pollen suggests sparse forest cover in the lowlands of the subtropical East Asian Summer Monsoon (EASM) region and indicates an approximately 3300-year-long interval of the driest climate conditions of the entire last glacial-interglacial cycle. The LJF pollen-based reconstruction is consistent with the other vegetation records from the larger region, suggesting the climate change during LGM-b significantly impacted terrestrial ecosystems. The environmental change in the EASM region is likely linked to the Sea Surface Temperatures (SSTs) decrease that weakened the Walker cell convection over the western Pacific Ocean and reduced convection and moisture content in the Intertropical Convergence Zone. The strengthened decrease in moisture supply during LGM-b seems to have resulted in extreme and widespread megadroughts in the EASM and Australian regions. Our data indicate that the cold SSTs may have also decreased air temperatures in the neighboring parts of the continents. We suggest that the widespread SSTs decline in the western Pacific may have been linked to the cooling of the Southern Ocean and the expansion of Antarctic sea ice during LGM-b.

Late Holocene vegetation history of the Western Caucasus inferred from high-resolution pollen record from Lake Karakel

Abstract. The paper presents a new paleoecological evidence for the last 2200 years based on high resolution pollen record and detail radiocarbon dating, obtained from Lake Karakel (Teberda River valley, Western Caucasus). The obtained results showed that vegetation changes from 2200 to stage 1200 cal, yr BP occurred under a climate warming and increase of humidity. The Medieval Climatic Anomaly-MCA (ca. 1200-880 cal. yr BP) was characterized in this region by the predominance of broadleaved forests. The MCA was followed by a cold interval of the Little Ice Age (ca. 880-120 cal yr BP) that marked by expansion of pine, spruce and fir forests to the lower altitude the present time.

Rapid Vegetation Evolution and Climate Change During 9.2–8.0 Cal Kyr BP in Eastern China: High-Resolution Pollen Evidence from the Yangtze Delta Plain Area

Rapid Vegetation Evolution and Climate Change During 9.2–8.0 Cal Kyr BP in Eastern China: High-Resolution Pollen Evidence from the Yangtze Delta Plain Area

Timing and drivers of local to regional scale land-cover changes in the hemiboreal forest zone during the Holocene: A pollen-based study from South Estonia

Current land use and climate change pose a threat to the continued provision of ecosystem services expected from terrestrial land cover. Studies on past land-cover responses to such changes provide valuable information for future decisions. The hemiboreal zone, situated between temperate and boreal biomes, is a natural sensitivity hotspot for land cover change: it contains a continuous distribution limit of several temperate (Quercus robur, Tilia cordata, Fraxinus excelsior, Ulmus glabra, etc.) and some boreal (e.g. Picea abies) tree species. High resolution pollen data from three lakes in South Estonia, a hemiboreal zone in Northern Europe, was used to reconstruct the climate-driven dynamics of vegetation composition, anthropogenic deforestation, species-specific responses to climate cycles, and plant related environmental variables during the Holocene at a local and regional scale. The Landscape Reconstruction Algorithm (LRA) was used to reconstruct the vegetation composition, the Ellenberg Indicator Values for environmental reconstructions, and the Wavelet analysis for detecting cyclic patterns. The major land cover and environmental changes are in good accordance with the climate-based formal tripartite subdivision of the Holocene: a quick succession of tundra, boreal, and nemoral biomes during the Early Holocene, a dominance of temperate, broad-leaved forests during the Middle Holocene, and an expansion of mixed boreal forests and anthropogenic deforestation during the Late Holocene. Several episodes of compositional turnover ranging from a century (e.g., the transition from wet to dry tundra) to several millennia (e.g., the replacement of the temperate deciduous forests with boreal mixed forests) were identified. Our results show that local community changes have a shorter duration than the regional ones. The introduction of slash-and-burn agriculture caused abrupt forest composition changes at a local scale, promoting early successional tree species, even prior to the establishment of a permanently open cultural landscape. The only late successional tree species favoured by slash-and-burn cultivation was Picea abies. However, the application of more permanent cultivation strategies reduced its representation considerably. The determined cyclic changes in the proportions of tree taxa show, that most late successional trees exhibit high frequency (ca 200–400 year) cyclicity, probably reflecting the stand scale regeneration processes. The observed 1600 ± 200 and 1200 ± 200 year cycle changes in the occurrences of Quercus robur, Ulmus glabra and U. laevis, and Picea abies have a possible connection with a 1500 ± 500 year Bond cycle. Most of the tested tree taxa also had a statistically significant correlation with the ca 2200–2500 year Bray solar forcing cycle.

Two pollen-based methods of Eemian climate reconstruction employed in the study of the Żabieniec-Jagodne palaeolakes in central Poland

The aim of the present study was to estimate the range of climate variability in Central Poland during the Eemian Interglacial (MIS 5e). High resolution pollen records are available for all seven RPAZs typical of this interglacial in Central Europe. These pollen records were used to estimate total annual precipitation and mean annual temperature, as well as the mean temperatures of the warmest and the coldest months based on the plant indicator method and the modern analogue technique. The reconstructions indicate that the combination of these two methods provides a much clearer insight into the climate changes of the Eemian optimum. The results confirmed no drastic drop in temperature in the Middle Eemian, with high total precipitation in the hazel phase, and that this was followed by a decrease in temperature in the Late Eemian (fir-spruce and pine phases). A drop in precipitation occurred during the youngest part of the Carpinus phase, while coincided with a marked lowering of the water level in lakes and their transformation into peatbogs. The last part of the Eemian is characterized by decreasing temperature, particularly during the coldest month, rising water levels due to a combination of lower evaporation and higher air humidity, and a transition to glacial conditions. Principal Component Analysis found all investigated sites to follow the same pattern of changes. Mean winter temperature, annual temperature and precipitation were found to have a strong positive correlation with the occurrence of thermophilus temperate broadleaved trees (hazel, linden, and ash) typical for the mid-Eemian optimum. These three factors also have a negative correlation with the presence of cold tolerant boreal trees (birch and pine) and open land taxa characteristic of the beginning and end of the interglacial. Mean July temperature was found to be positively correlated with the occurrence of temperate broadleaved trees (oak, ash and elm) typical for early stages of the Eemian and negatively with that of coniferous trees (fir and spruce) characteristic for later stages of the interglacial.