High-resolution Pollen Research Articles

Late holocene vegetation succession and climate change in the Central Plains of China: Evidence from a high-resolution pollen record

Changes in the East Asian summer monsoon precipitation will have a significant impact on China’s politics, economy, and social development. To explore the controls and drivers of the Late Holocene (∼3350–2560 cal. yr. BP) vegetation succession and East Asian summer monsoon precipitation changes in the Central Plains of China, we conducted pollen analysis of the Pu Tian core collected from Zhengzhou, China. The results showed three periods of vegetation and East Asian summer monsoon variation: coniferous and broad-leaved mixed forest between ∼3350–3025 cal. yr. BP, increasing forest vegetation dominated by broadleaf Betula between ∼3025–2930 cal. yr. BP, decreasing forest vegetation and increasing herbaceous plants dominated by Artemisia and Poaceae between ∼2930–2560 cal. yr. BP. Weighted Averaging Partial Least Squares Regression was used to quantitatively reconstruct the average annual precipitation variation in the Central Plains of China. Our precipitation reconstruction and its comparison to other reconstructions and forcing show that it was influenced by internal (intertropical convergence zone and El Niño-Southern Oscillation) and external (Northern Hemisphere Summer Insolation) forcing. Specifically, average annual precipitation decreased significantly between ∼2980–2680 cal. yr. BP, and tree pollen (such as Betula) also decreased significantly during this period, possibly related to the “2.8 ka” event (a weak monsoon event in the Holocene). Our comparison of the published climate and environmental records of the East Asian monsoon region suggests that the 2.8 ka event exhibiting a “W” structure of “dry-wet-dry” and may have been caused by the weakening of solar activity, which affected the climate of the East Asian monsoon region through oceanic and terrestrial atmospheric circulation such as El Niño-Southern Oscillation.

Environmental changes and human impacts over the past 1200 years: Evidence from high-resolution pollen records from peat in the Yunnan-Guizhou Plateau, Southwest China

Over the past millennium, the understanding of vegetation and climate changes in mountainous regions, driven by both natural and anthropogenic forces, remains unclear. In this study, we provide a high-resolution vegetation record spanning the past 1200 years from a subalpine peatland in the Niangniang Mountains, southwestern China. By analyzing pollen, charcoal, and loss-on-ignition from the peat sediment, we elucidate the interactions between vegetation, fire, and human impact. Our findings reveal that before 1150 CE, the mountains were covered with dense broadleaf forests and experienced minimal human activity. Natural forcings, primarily climatic conditions, drove vegetation succession and forest fires. After 1150 CE, the Human Influence Index (HII) increased sharply, coinciding with a rise in cereal-type pollen. Significant agricultural activities in the southwestern mountainous regions of China began after 1150 CE, which is later than those in the low-altitude lake basins of southwestern China. During the Medieval Climate Anomaly (MCA, 836–1400 CE), the Niangniang Mountains were characterized by warm and humid climatic conditions, a stable forested landscape, and a high peat carbon accumulation rate. Although human activities increased markedly during this period, the arbors did not undergo notable changes, and climate forcings continued to have a greater impact on vegetation than anthropogenic forcings. During the Little Ice Age (LIA, 1400–1900 CE), the regional vegetation landscape transitioned from dense forests to open grasslands as climate conditions became cold and dry, reducing peat carbon accumulation rate. This period also saw increased forest fires and significant human-driven deforestation, with anthropogenic forcings becoming dominant. After 1900 CE, vegetation changes were increasingly influenced by government policies. Comparison with major climate forcings and spectrum analysis have shown that variations in monsoon intensity, regulated by solar and volcanic activity, have influenced the climate and peat depositional environment in the Niangniang Mountains. Our research offers meaningful insights into forest conservation in the mountainous regions of the Yunnan-Guizhou Plateau.

Vegetation, temperature, and Indian Summer Monsoon evolution over the past 4400 years revealed by a pollen record from Drigo Co on the southern Qinghai-Tibet Plateau

Understanding the changes in temperature and precipitation on the southern Qinghai-Tibet Plateau (QTP), which is influenced by the Indian Summer Monsoon (ISM), is crucial for predicting possible future changes in the regional ecological environment under ongoing climate change. However, due to the lack of well-dated, high-resolution paleoclimate records, the trends of temperature and ISM precipitation on the southern QTP since the mid-Holocene are poorly understood. We present a high-resolution pollen record from Dirgo Co, on the southern QTP, spanning the past 4400 years. The decrease in the pollen ratio of Artemisia to Cyperaceae (A/Cy) indicates a downward shift of altitudinal vegetation belts in the Drigo Co area over the past 4400 years, suggesting falling temperatures; and decreases in tree pollen percentages indicate the gradual weakening of the ISM. Our pollen record also indicates five cold phases with the near-simultaneous weakening of the monsoon, during: 4300–4100 cal yr BP, 3600–3400 cal yr BP, 2800–2600 cal yr BP, 1600–1400 cal yr BP, and 700–100 cal yr BP, and these climate anomalies were also recorded elsewhere on the QTP. We suggest that the changes in temperature and ISM intensity on the southern QTP over the past 4400 years were modulated by changes in summer insolation and solar activity. These changes affected the sea surface temperature (SST) over the tropical Pacific and Indian Ocean regions, and they were linked to a positive phase of the El Niño/Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), which weakened the ISM intensity in the Drigo Co area. Additionally, due to increased evaporation related to high temperatures, combined with intensified grazing activities over the past ∼200 years, the lake level has fallen, and the vegetation cover has decreased. As global temperatures continue to rise, the alpine steppe in the Drigo Co area may increase and the vegetation density may gradually decrease, and at the same time the regional ecological environment may gradually deteriorate.

Pollen-based seasonal temperature reconstruction in Northeast China over the past 10,000 years, and its implications for understanding the Holocene Temperature Conundrum

The Holocene Temperature Conundrum refers to the mismatch between proxy-based temperature records and those based on climate model simulations. A possible reason for this mismatch is a putative proxy-based bias in reconstructed summer temperatures, and therefore, regional reconstructions of seasonal temperature are crucial for resolving the conundrum. In this paper, we reconstruct vegetation and climate changes over the last ∼10,000 years BP based on a high-resolution pollen record from Gushantun peatland, Changbai Mountains, Northeast China. Multiple quantitative reconstruction approaches were used and weighted averaging partial least squares regression (WAPLS) was found to be the most appropriate method for reconstructing Holocene temperature and precipitation. The reconstructed climate record shows that the Holocene Climate Optimum occurred between 8 ka and 6 ka and exhibited a cold month mean temperature that was 3 °C warmer than modern temperatures. Climate gradually cooled during late Holocene with a minimum cold month temperature of −19.6 °C. Four prominent cold events occurred around 8.7 ka BP, 7.8 ka BP, 5.7 ka BP, and 2.5 ka BP with an amplitude variation up to 3 °C. The synthesized seasonal temperature time series and a comparison with other proxies show that the decreasing trend in mean annual temperature is not a seasonal bias caused by summer temperature change. This study provides evidence of a Holocene seasonal temperature change at a regional scale and insights for further understanding of the Holocene Temperature Conundrum.

Holocene Vegetation Dynamics Revealed by a High-Resolution Pollen Record from Lake Yangzonghai in Central Yunnan, SW China

Long-term regional vegetation dynamics is essential for the understanding of past land cover changes. High-resolution pollen analysis of a 1020 cm core from a large lake, Lake Yangzonghai (YZH), in central Yunnan, SW China, was conducted to reveal regional vegetation dynamics in the lake catchment over the past 13,400 years. Pollen record, principal component analysis (PCA) of pollen percentages of major arboreal taxa, and plant abundances estimated from the “Regional Estimates of VEgetation Abundance from Large Sites” (REVEALS) model show five successional stages of vegetation dynamics since 13,400 cal. a BP: regional vegetation with high coverages in the lateglacial (13,400–11,400 cal. a BP) was dominated by evergreen broadleaved forest (EBF) and deciduous broadleaved forest (DBF), together with some grass meadows and marshes; pine forest and alder forest expanded in the early Holocene (11,400–9000 cal. a BP) when vegetation coverages were still high; regional vegetation with low coverages was dominated by sweetgum forest, together with some pine forest during the mid-Holocene (9000–4200 cal. a BP); more pine forest, grass meadows and marshes occupied the lake catchment during the late Holocene (4200–800 cal. a BP), when vegetation coverages were higher than the average of the past 13,400 years; regional vegetation with low coverage was dominated by grass meadows and marshes, great deforestation happened in the last 800 years. Regional vegetation dynamics over the past 13,400 years in the Lake YZH catchment was the result of regional vegetation response to climate changes during the lateglacial and early–mid Holocene, and to human activities mainly during the late Holocene.

Late Quaternary Araucaria forest and Campos (grasslands) vegetation dynamics inferred from a high-resolution pollen record from Lagoa Dourada in southern Brazil

Forest-grassland mosaics are ecosystems with sharp contrasts. Factors controlling their heterogeneity have interested researchers worldwide. To date, only few natural remains of these ecosystems exist, such as the Araucaria and Campos region in southern Brazil. Different paleoecological studies elucidate the vegetation and climate history of the region, documenting shifts between forests and grasslands since the Middle Holocene. However, uncertainty remains about whether system shifts were sudden or gradual and on the importance of driving factors and triggers such as climate, change and disturbance. We reconstruct the paleoecological history of the Araucaria forest-grassland mosaics in Paraná state in decadal to sub-decadal resolution during the Holocene. High resolution pollen analysis documents that in this region the expansion of woodlands occurred gradually while sedimentological analyses reveal stepwise shifts of the precipitation regime of the region. During the Early Holocene (10300-8300 cal yr BP), the landscape was characterized by grassland-dominated Campos vegetation, with sporadic occurrences of arboreal taxa. Araucaria angustifolia was present initially in small abundances. In the Mid-Holocene (8300-4000 cal BP), a transition to more humid conditions fostered the development of woodlands. The establishment of Araucaria angustifolia near the lake occurred around 7300 cal yr BP, together with a general expansion of woodlands. In the Late Holocene (4000-150 cal yr BP), Araucaria angustifolia became dominant within forest patches with a second stepwise expansion around 3300 cal yr BP. The onset of Euro-American land use during the last two centuries intensified erosion and altered species composition, reflected in sediment and pollen data. In addition, Lagoa Dourada documents vegetational changes that seem to coincide with the 8.2 ka event and the Little Ice Age.

Transformation of regional vegetation driven by climate change during the last deglacial–early Holocene at Chaohu Lake, eastern China: New pollen insights

Reconstructing the vegetation history of east China during the last glacial–interglacial transition is crucial for understanding the East Asian Summer Monsoon (EASM) evolution. Here, we present a new high-resolution pollen record from Chaohu Lake to determine the detailed process of regional lowland vegetation succession and its response to the EASM changes during the last glacial–Holocene transition (13.9–9.1 cal ka BP) in the lower Yangtze Valley, eastern China. During the Older Dryas (OD, 13.9–13.5 cal ka BP) period, regional forest-steppe indicative of co–dominance of Artemisia, Poaceae, and deciduous Quercus was present under a cool and dry climate. During the Allerød Interstadial (AI, 13.5–12.9 cal ka BP), significant arboreal expansions of deciduous Quercus, Hydrangea type and evergreen Quercus occurred, while herbs retreated significantly, presumably driven by the relatively warm, humid climate. Forest-steppe readvanced during the Younger Dryas (YD) interval, as indicated by increases in Poaceae and Artemisia, suggesting a cool and dry climate. During the early Holocene, extensive oak-pine forest flourished as regional vegetation, responding to pronounced climatic amelioration.Our pollen-based climatic record is closely correlated with stalagmites δ18O records from EASM region and Greenland ice cores δ18O records, indicating the teleconnection between EASM variation and North Atlantic climate during the last deglacial–early Holocene. However, our record indicates an intensified EASM during the early AI and a prolonged onset excursion during the YD, diverging from North Atlantic climate but closely correlated to sea surface temperature (SST) variations in the western tropical Pacific.

Rates of palaeoecological change can inform ecosystem restoration

Abstract. Accelerations of ecosystem transformation raise concerns, to the extent that high rates of ecological change may be regarded amongst the most important ongoing imbalances in the Earth system. Here, we used high-resolution pollen and diatom assemblages and associated ecological indicators (the sum of tree and shrub pollen and diatom-inferred total phosphorus concentrations as proxies for tree cover and lake-water eutrophication, respectively) spanning the past 150 years to emphasize that rate-of-change records based on compositional data may document transformations having substantially different causes and outcomes. To characterize rates of change also in terms of other key ecosystem features, we quantified for both ecological indicators: (i) the percentage of change per unit time, (ii) the percentage of change relative to a reference level, and (iii) the rate of percentage change per unit time relative to a reference period, taking into account the irregular spacing of palaeoecological data. These measures document how quickly specific facets of nature changed, their trajectory, as well as their status in terms of palaeoecological indicators. Ultimately, some past accelerations of community transformation may document the potential of ecosystems to rapidly recover important ecological attributes and functions. In this context, insights from palaeoecological records may be useful to accelerate ecosystem restoration.

Effects of varied modern pollen-climate calibration-set establishment approaches on quantitative climate reconstructions

A representative modern calibration dataset is an essential prerequisite for a reliable quantitative reconstruction of paleoclimate. However, there has been a notable lack of systematic research on the optimal filtering of calibration sets. Four representative high-resolution pollen records were selected to repeatedly reconstruct paleoclimate using multiple approaches such as geographical distance, analogues and climate gradient. Comparisons of pollen-based reconstructions indicate that these varied approaches exhibit significant discrepancy in model performance and reconstruction accuracy under different geographical circumstances and time scales. Generally, in terms of calibration-set selection, the geographical distance method demonstrates greater efficiency for the plain region, but exhibit limitations in areas characterized by significant topographic changes. Analogue-calibration has been found to be more suitable for the edge of the database and also has been proven superior to other two methods for reconstructions exceed Holocene. Selecting calibration sets based only on climate gradients is inappropriate for independent applications, but may act as a limitation for other methods. This preliminary research can contribute to a more precise projection of potential future climate changes by providing essential data input or validating hindcasts for Earth system models.

Low-latitude forcing on 4.2 ka event indicated by records in the Asian monsoon region

The 4.2 ka event is an important climatic event of the Holocene that is expected to considerably influence the development of human civilizations. However, the forcing mechanism of the 4.2 ka event remains unclear, with current evidence being divided between high-latitude and low-latitude forcings. The Asian climate system contains strong summer and winter monsoon circulations, and thus the region is ideal for studying high- and low-latitude climate forcings on 4.2 ka event. In this study, we present a high-resolution pollen record of the past 5000 years from Wudalianchi Crater Lake in northeastern China in the East Asian monsoon region. An evident decrease in broadleaf trees occurred during the 4.2 ka event, suggesting a decrease in summer monsoon rainfall. Well-dated high-resolution pollen, stalagmite δ18O, and winter monsoon records were collected to study the possible transportation of high- and low-latitude signals. Most of the pollen records showed significant changes during the 4.2 ka event, while no apparent change was found in winter monsoon records. Meanwhile, more obvious changes in stalagmite δ18O records were observed in lower- rather than the higher-latitude regions around 4.2 ka. Our results suggest that the signal of the 4.2 ka event might be transported by low-latitude processes, thus corresponding to a low-latitude forcing.

Millennial-scale variability of vegetation and fire activity in a northern Cerrado driven by an east-west rainfall gradient during the Holocene

This paleoecological study investigates vegetation variability and fire regimes in Northeastern Brazil (NEB)’s Cerrado. We present high-resolution pollen and charcoal records from a palm swamp located in a Cerrado in Chapada das Mesas National Park, in the southwest of Maranhão State. The Vereda do Dodó sedimentary core is 187 cm deep and covers the past 6000 years. Our results show first the presence of an open cerrado between 6000 and 5200 cal yr BP with no fire activity and a gradual expansion of the palm Mauritia and woody cerrado after 5000 cal yr BP. This is synchronous with other studies of northeastern and central Brazil. At c. 4300 cal yr BP, sterile samples suggest a strong dry event, also recorded in other eastern NEB records. Frequent burnings lasted until 2600 cal yr BP, when fires stopped and Mauritia, arboreal cerrado, and gallery forest taxa expanded under increased moisture rates. The increase of southern hemisphere summer insolation and the warmer tropical Atlantic Ocean enhanced the monsoon system over eastern Amazonia and western NEB in agreement with speleothem records. Our study reveals that northern Cerrado biodiversity was very sensitive to SASM dynamics, a different pattern from eastern NEB vegetation and climate.

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

The paper presents the new paleoecological evidence for the last 10,000 years based on high resolution pollen record supported by detail radiocarbon dating, obtained from the Khuko Lake (Western Caucasus). The obtained results showed that change of vegetation corresponding main Holocene stages. 10368-10577 – 8000-8200 cal. yr BP – Boreal period was characterized in this region by the presence of both broad-leaved (Fagus, Ulmus) and coniferous (Abies) species to an equal. 8000-4400 cal. yr BP – Atlantic period was marked by predominance of broad-leaved forests have been formed mainly by beech and a little hornbeam. 4400-2600 cal. yr BP – Subboreal period is characterized by an increase in the role of boreal vegetation (Abies, Pinus). 2600 cal. yr BP up now – Subatlantic period looked like Atlantic period, but at this time declined value of coniferous species and grew value of alder and hazel.

Palynological and sedimentological evidence for early mid-Holocene hydroclimatic variability in the Ningshao Plain, East China

The southeastern coastal areas of China represent one of the most populous and economically developed regions in China, but they are often severely affected by flood hazards. Therefore, studying the phenomenon and mechanisms behind extreme rainfall changes in this region is of great significance for economic and social development. In this study, we present high-resolution pollen and grain-size records from the Shanglin Lake located in Zhejiang, eastern China, based which changes in the frequency of paleo-flood events were reconstructed and the climatic context was inferred. Our pollen records show that the content of evergreen broadleaf trees gradually increased during 8000–7000 cal. yr BP, reflecting the gradually increasing temperature in the growing season. The content of Altingia increased substantially during the periods of 7960–7860, 7600–7500, and 7200–7100 cal. yr BP, especially in the first and last periods, indicating the prevalence of an El Niño-like condition in the study area during the early mid-Holocene warm period. Grain-size record shows that the prolonged El Niño condition facilitated a significant increase in flood frequency. Our results suggest that, similar to that of today, the early mid-Holocene warm climate was the most important factor controlling extreme hydroclimatic changes in the middle and lower reaches of the Yangtze River.

Effects of Climate Change and Fire on the Middle and Late Holocene Forest History in Yenisei Siberia

This study presents the long-term forest history in the forest–tundra ecotone of the Low Yenisei River basin. The new high-resolution pollen and macroscopic charcoal data were inferred from the 8.6 m long peat archive covering the last 6300 years. Climate reconstructions are based on the application of the best modern analogue technique using pollen data. Our findings suggest an alternation of phases of middle-taiga forests of Larix sibirica, Abies sibirica, Picea obovata, and Pinus sibirica (intervals of climate warming: 6320–6050, 5790–5370, 4480–4220, and 3600–2700 cal yr BP, respectively) and open larch woodlands with the participation of Betula, Picea, and Pinus sibirica, typical for northern taiga (intervals of climate cooling and increasing humidification: 5370–4480, 4220–3600 cal yr BP, respectively). The vegetation pattern of the region became similar to the modern one around 2700 cal yr BP. Climate warming caused a northward shift of vegetation-zone boundaries in Yenisei Siberia and an expansion of the range of Abies sibirica by about 200 km to the north compared to the present day. The increased frequency of fires and biomass burning during warm periods may promote the melting of the local permafrost, thereby enhancing the tree growth and regeneration.

The Neolithic ceremonial centre at Nowe Objezierze (NW Poland) and its biography from the perspective of the palynological record

Rondels are the oldest monumental ceremonial objects in Europe. They appeared some 200 years after the demise of the Linear Pottery culture (c. 4800BCE). They have given a new shape to the resurgent 'Danubian Neolithic World'. However, despite intensive research, it is still unclear (1) how the transition process took place after the fall of the LBK; (2) how long rondels were function; and (3) under what circumstances they were abandoned. In this paper, we present a new approach to this problem based on an analysis of the biography of a single object based on the integration of archaeological and palaeoenvironmental data. We assume that the high-resolution pollen analysis of lake sediments provides critical data on the dynamics of population change (hiatuses, sharp declines and increases in population size) and how the environment is affected (felling of specific tree species, fires, cultivation of particular crops, grazing intensity). They provide a better understanding of the sequence of settlement and construction changes as well as alterations in material culture available in the archaeological record. The subject of the analysis is a site in the Lower Oder Valley (north-west Poland), at the furthest northern periphery of the 'Danubian World'.

3000 Years of past regional and local land-use and land-cover change in the southeastern Swedish coastal area: Early human-induced increases in landscape openness as a potential nutrient source to the Baltic Sea coastal waters

Reconstructions of past land use and related land-cover changes at local and regional scales are needed to evaluate the potential long-term impacts of land use on the coastal waters of the Baltic Sea. In this purpose, we selected the Gamleby area at the Swedish Baltic Sea coast for a case study. We use a new, high resolution pollen record from a small lake (Lillsjön) located 3.6 km NNW of the bay Gamlebyviken and detailed analysis of the available archeological data to reconstruct local land-use changes over the last 3000 years. To estimate land-cover change at local (2–3 km radius area) and regional (50 km radius area) scales we use four additional, published pollen records from two small and two large lakes (25–70 km S of Lillsjön) and the Landscape Reconstruction Algorithm, a pollen-vegetation modeling scheme. Results show that regional and local (small lakes Lillsjön and Hyttegöl) land-cover changes are comparable over the last 1500 years (Late Iron Age to present), and that landscape openness was much larger locally than regionally (difference of 20–40% cover over the last 500 years). The periods of largest potential impacts on the Gamlebyviken Bay from regional and local land use are 200–950 CE (Late Iron Age) and 1450 CE to present, and of lowest potential impacts 950–1450 CE. The question on whether the large landscape openness 1150–50 BCE and significant afforestation 50 BCE–200 CE reconstructed for Lillsjön’s area are characteristic of the Gamlebyviken region will require additional pollen records in the catchment area.

Vegetation, fire and climate history in central-western Tasmania (41°S), Australia, over the last ∼21,000 years

We present high resolution pollen and macroscopic charcoal records from Basin Lake, a relatively small mid-latitude (42°S) lake located in central-western Tasmania, Australia, to examine vegetation, fire and climate change since and during the Last Glacial Maximum (LGM). We find dominance of cold-resistant alpine vegetation with buttongrass moorland and scant trees between ∼21.0-17.7 cal kyr BP, with local biomass burning and low lake levels between ∼21.0-20.0 cal kyr BP and a reduction in local biomass burning and a rise in lake levels between ∼20.0-17.7 cal kyr BP. These data suggest glacial-cold conditions during the last millennia of the LGM, with relatively humid conditions between ∼21.0-20.0 cal kyr BP and a further increase in humidity between ∼20.0-17.7 cal kyr BP. These shifts suggest an intensification of the South Westerly Winds (SWW) over the site between ∼20.0-17.7 cal kyr BP. An increase in cold-temperate rainforest taxa followed between ∼17.7-16.0 cal kyr BP along with lake-level lowering, suggesting a warm pulse and southward shift of the SWW at the beginning of the Last Glacial Termination (T1). Subsequent cold-temperate conditions and increased precipitation ensued between ∼16.0-14.9 cal kyr BP promoted by increased SWW influence. A rise in cold-resistant and hygrophilous rainforest taxa and lower biomass burning activity occurred between ∼14.9-12.8 cal kyr BP under colder conditions, enhanced precipitation and major SWW influence. A multi-millennial warm/dry interval began at ∼12.8 cal kyr BP with a decline in rainforest taxa, high fire activity and low lake levels and a further opening of the vegetation in response to elevated biomass burning between ∼11.1-8.9 cal kyr BP. We suggest a decline in the SWW influence that started at ∼12.8 cal kyr BP and accentuated between ∼11.1-8.9 cal kyr BP at the beginning of the Holocene. We detect increases in precipitation between ∼8.9-5.8, ∼3.4-1.9 cal kyr BP and the last ∼900 years, with declines in the intervening intervals. Our data indicate a pronounced and sustained fire-driven shift to a more open and shrub dominant landscape after ∼5.0 cal kyr BP, in synchronous with other pollen data from Tasmania's west, reflecting an increased efficacy of Aboriginal burning under more variable and overall reduced precipitation. Our climate inferences from Basin Lake are coherent with variations of the SWW identified in other terrestrial mid-latitudes records, suggesting synchronic changes in the SWW during and since the LGM.

The changing role of hazelnuts (Corylus avellana) in the Mesolithic diet: The Scheldt basin (W Belgium) as a case-study

Hazelnuts were an important foodstuff for Early to Mid-Holocene (Mesolithic) hunter-gatherers all over North-western and Central Europe, mainly thanks to their high fat content, the fact that they are easy to collect and process and produce high areal yields. Based on an extensive and well-dated dataset of charred hazelnut shells, collected on Mesolithic camp-sites from the western Scheldt basin (W Belgium), in this paper the availability of this food resource is studied. Unlike other North(west) European regions, the decline in the exploitation and consumption of hazelnuts in the Scheldt basin appears to start early, from the mid-Boreal period onwards. The available high-resolution pollen and anthracological records indicate that this is presumably related to the rapid and substantial expansion of oak, creating a shady environment which was less favourable for hazel. This paper further examines the impact as well as the possible response of Mesolithic hunter-gatherers to this drastic change in subsistence resources, which arose on top of other challenges during the Boreal, such as increased drought and forest fires, abrupt cooling around 9.3 ka and the possible influx of groups from the adjacent drowning North Sea basin. Human responses possibly ranged from increased mobility, over intensified exploitation of other edible plants to increased fish consumption. The paper ends with emphasizing the importance of high-resolution paleoecological studies on a local/regional level as well as the systematic fine-meshed recovery of plant remains, such as charred hazelnut shells, from archaeological sites.

Climatic variability during the 4.2 ka event: Evidence from a high-resolution pollen record in southeastern China

The 4.2 ka event was a period of global drought and climate cooling linked to the widespread disruption of Neolithic culture. However, the detailed climatic changes during this period are not completely understood. In this paper, we report a high-resolution pollen record for the Dayanghu wetland in the Zhejiang region of southeastern China, which we use to infer mean annual precipitation (MAP) fluctuations during the period spanning 4600–4000 calendar years before present (cal. yr BP). There was a long-term trend of decreasing MAP during this interval, consistent with weakening of the East Asian Summer Monsoon since the mid-Holocene. This trend was punctuated by episodes of relatively high MAP at 4350–4320, ca. 4260, and 4220–4200 cal. yr BP, and extreme droughts at 4200 and 4150 cal. yr BP. We propose that solar activity promoted El Niño events and contributed to dramatic MAP fluctuations in the Dayanghu wetland. La Niña events and negative-phase intervals of the Pacific Decadal Oscillation may have been responsible for the extreme drought at 4200–4150 cal. yr BP. In summary, we propose a close relationship between MAP and solar forcing, with short-term enhanced solar activity increasing the intensity of the East Asian Summer Monsoon and contributing to increasing decadal variability in the inner tropical Pacific, which ultimately leads to increased precipitation variability in southeast China. The results improve our understanding of the detailed climatic features of the 4.2 ka event.

Volcanic impact on terrestrial and aquatic ecosystems in the Eastern Mediterranean

Natural disturbances such as volcanic eruptions provide a unique opportunity to study past ecological dynamics. Here we illustrate the response of terrestrial and aquatic ecosystems to volcanic eruptions in connection to prevailing climate conditions. We selected five volcaniclastic depositions in the Lake Van (Turkey) sediments from different interglacial/glacial periods (Marine Isotope Stages 3 to 9e). Using high-resolution pollen data, non-pollen palynomorphs, and microscopic charcoal particles we attempted to disentangle climatic and volcanic forcing of natural environmental disturbances. Our results highlights that the thickness of subsequent volcanic deposits and the respective climatic conditions strongly influence the impact on terrestrial and aquatic ecosystems. The most common response to ash deposition is a shift towards herbaceous taxa and abrupt fire activity. The affected herbaceous vegetation recovers to pre-eruption levels in 20 to 40 varve-years. The lake water experiences intensified productivity due to subsequent nutrient input and significant increase in aquatic microfossils. Our findings pave the way for disentangling climatic and volcanic forcing of natural environmental disturbances.