Modern Analogue Technique Research Articles

Stadial and interstadial deposits of Late Nemunas (Late Weichselian/MIS 2) glaciation in south Lithuania and their interpretation

This paper presents sedimentological and paleobotanical studies of the deposits from Last Glaciation (Late Nemunas, Late Weichselian) in the middle reaches of the River Nemunas in southern Lithuania. Spores, pollen, and other palynomorphs in the intercalated sediments between the diamicton (glacial till) beds were analyzed, and the paleogeographical and paleoclimatic conditions of their sedimentation were assessed using the modern analog technique (MAT). The two till layers from the Last Glaciation, characterized by significant differences in their composition, testify to a difference in glacier movement paths in the region. The continuous sedimentation process between glacial tills provides evidence of global climate changes during the Last Glaciation and the restructuring of glacial lobes during deglaciation in the southeastern part of the Scandinavian Ice Sheet. The sedimentation process and vegetation composition bear witness to an open landscape of steppe-tundra, scattered wooded areas, and the emergence of thermophilic vegetation afterward, suggesting increased annual temperatures and higher humidity. The available data enable the identification of the Balbieriškis interstage period within the Late Nemunas Glaciation (Upper Nemunas Formation) between the Grūda and Baltija stages (Grūda and Baltija subformations) in the regional Quaternary stratigraphic scheme. This period correlates with the Marine Isotope Stage 2 (MIS 2).

Quantitative Holocene climate reconstruction and anthropogenic impact analysis based on the pollen records in peat sediment in Southern China

The quantitative reconstruction of Holocene paleoclimate is pivotal for unraveling the evolution of East Asian Monsoon (EAM). Some recent studies have highlighted the escalating human activities in the late Holocene, which could potentially pose significant challenges to the precise quantitative reconstruction of paleoclimate. In this study, we undertake a quantitative reconstruction of Holocene climate and human influence index (HII) based on pollen data from the Shiwangutian (SWGT) in Southern China. This is achieved by developing and applying a pollen-based calibration model utilizing Locally Weighted Average-Partial Least Squares Regression (LWWA-PLS) and the Modern Analogue Technique (MAT). Our findings reveal that evergreen forests experienced expansion between 11.6 and 9.0 cal ka BP, coinciding with elevated Mean Annual Precipitation (Map) and Mean Annual Temperature (Mat) levels. These patterns signify a progressively warm and wet climate during this period. Subsequently, evergreen forests achieved their maximum abundance between 9.0 and 4.0 cal ka BP, aligning with a notable increase in vegetation richness, indicating a warmer and wetter climate during the mid-Holocene. Notably, during the interval of 6.0–4.0 cal ka BP, the Map, Mat, and Precipitation of Warmest Month (Mpwa) reached the Holocene optimum, approximately 14% higher than modern. Consequently, we deduce that in the early and middle Holocene, when the monsoon was particularly strong, synchronous changes in precipitation fostered the regional expansion of evergreen broad-leaved forests. Furthermore, the record demonstrates a substantial reduction in forest cover and a noteworthy increase in the HII value since 4.0 cal ka BP, likely attributable to anthropogenic impacts. Our analysis suggests that the influence of anthropogenic activities surpassed that of natural climate factors in shaping regional vegetation cover. These findings offer insights into potential drivers of climate change. As a preliminary conclusion, we propose that the summer insolation, ice sheets, and meltwater fluxes were the primary controlling factors for climate variations during the early to mid-Holocene in Southern China.

Hydroclimatic changes in eastern China during the Holocene based on pollen data and climate modeling

The Asian monsoon system represents one of the world's most dynamic interactions of the cryosphere-continent-ocean-atmosphere system. Understanding and responding to changes in monsoonal precipitation is a major component of environmental management in this region, given its profound influence on socioeconomic activity in monsoonal Asia. In particular, characterizing the spatiotemporal variability of the East Asian summer monsoon (EASM) is critical for comprehensively understanding its dynamics and future impacts. Although substantial progress has been made in reconstructing past changes in the EASM, the spatial pattern of EASM intensity in China on the orbital-scale remains controversial. This is mainly because of uncertainties in the climatic interpretation of EASM-related proxies. Here, we present a quantitative seasonal precipitation reconstruction for monsoonal China during the Holocene, using the Modern Analog Technique (MAT) based on pollen data. The results show that during the Holocene both the annual and summer precipitation in monsoonal China increased gradually and reached a peak during the early mid-Holocene, with respective values that were ∼ 170 mm and 60 mm higher than today, followed by a decrease in the late Holocene. On the regional scale, the temporal pattern of monsoon rainfall was discrepant: a decrease from the early through late Holocene in northern China, and an increase from the early through late Holocene in southern China.To investigate the possible forcing mechanisms of these phenomena, we used the full TraCE-21 k simulation and single-forcing transient simulations to analyze spatial and temporal rainfall patterns. The results suggest that the north-south pattern is the product of orbital forcing. Intensified summer insolation during the early Holocene enhanced the land-sea thermal contrast, which strengthened the EASM along with the northward extension of the west Pacific subtropical high. Both factors caused the increased withdrawal of oceanic water vapor and the northward advance of the EASM rain belt, delivering more rainfall to northern China and less rainfall to southern China, and vice versa. Overall, our results indicate that insolation variations were the dominant factor determining the spatial pattern of EASM precipitation during the Holocene. Our findings are relevant to the calibration of palaeoclimate models and they contribute to an improved understanding of the Asian monsoon sub-systems.

Charcoal analysis for temperature reconstruction with infrared spectroscopy

The duration and maximum combustion temperature of vegetation fires are important fire properties with implications for ecology, hydrology, hazard potential, and many other processes. Directly measuring maximum combustion temperature during vegetation fires is difficult. However, chemical transformations associated with temperature are reflected in the chemical properties of charcoals (a by-product of fire). Therefore, charcoal could be used indirectly to determine the maximum combustion temperature of vegetation fires with application to palaeoecological charcoal records. To evaluate the reliability of charcoal chemistry as an indicator of maximum combustion temperature, we studied the chemical properties of charcoal formed through two laboratory methods at measured temperatures. Using a muffle furnace, we generated charcoal from the woody material of ten different tree and shrub species at seven distinct peak temperatures (from 200°C to 800°C in 100°C increments). Additionally, we simulated more natural combustion conditions by burning woody material and leaves of four tree species in a combustion facility instrumented with thermocouples, including thermocouples inside and outside of tree branches. Charcoal samples generated in these controlled settings were analyzed using Fourier Transform Infrared (FTIR) spectroscopy to characterize their chemical properties. The Modern Analogue Technique (MAT) was employed on FTIR spectra of muffle furnace charcoal to assess the accuracy of inferring maximum pyrolysis temperature. The MAT model temperature matching accuracy improved from 46% for all analogues to 81% when including ±100°C. Furthermore, we used MAT to compare charcoal created in the combustion facility with muffle furnace charcoal. Our findings indicate that the spectra of charcoals generated in a combustion facility can be accurately matched with muffle furnace-created charcoals of similar temperatures using MAT, and the accuracy improved when comparing the maximum pyrolysis temperature from muffle furnace charcoal with the maximum inner temperature of the combustion facility charcoal. This suggests that charcoal produced in a muffle furnace may be representative of the inner maximum temperatures for vegetation fire-produced charcoals.

A low-frequency summer temperature reconstruction for the United States Southwest, 3000 BC–AD 2000

Temperature variability likely played an important role in determining the spread and productive potential of North America’s key prehispanic agricultural staple, maize. The United States Southwest (SWUS) also served as the gateway for maize to reach portions of North America to the north and east. Existing temperature reconstructions for the SWUS are typically low in spatial or temporal resolution, shallow in time depth, or subject to unknown degrees of insensitivity to low-frequency variability, hindering accurate determination of temperature’s role in agricultural productivity and variability in distribution and success of prehispanic farmers. Here, we develop a model-based modern analog technique (MAT) approach applied to 29 SWUS fossil pollen sites to reconstruct July temperatures from 3000 BC to AD 2000. Temperatures were generally warmer than or similar to those of the modern (1961–1990) period until the first century AD. Our reconstruction also notes rapid warming beginning in the AD 1800s; modern conditions are unprecedented in at least the last five millennia in the SWUS. Temperature minima were reached around 1800 BC, 1000 BC, AD 400 (the global minimum in this series), the mid-to-late AD 900s, and the AD 1500s. Summer temperatures were generally depressed relative to northern hemisphere norms by a dominance of El Niño-like conditions during much of the second millenium BC and the first millenium AD, but somewhat elevated relative to those same norms in other periods, including from about AD 1300 to the present, due to the dominance of La Niña-like conditions.

Quantitative methods for reconstruction of the Holocene paleoclimatic characteristics and vegetation changes based on palynological data from lake and peat sediments

The paper presents the results of a methodological study of the quantitative reconstruction of paleoclimatic characteristics (mean January and July temperatures, mean annual temperature and precipitation) and forest cover within a 20 km radius of the study site using palynological data from lake and peat sediments. The following quantitative methods have been tested: the best modern analog technique, transfer functions as weighted averaging, weighted averaging partial least square, and the Random Forest method, a meta estimator that fits a number of decision tree classifiers on various sub-samples of the dataset. A database of subfossil pollen assemblages for northern central Siberia (north of 60°C) was used as a training data set for model construction, containing 174 pollen assemblages, climatic characteristics for the sampling area, and calculations of forest cover based on remote sensing data. Leave-one-out cross validation was appy for testing of the methods. The results showed that all models had the highest coefficients of determination (R2), the smallest errors and the lowest uncertainty for the reconstruction of the mean July temperature. The developed methods were applied to two key sites in Central Siberia, located in the vicinity of Igarka and the settlement of Tura (Krasnoyarsk Region). The results obtained showed similar trends in the changes in palaeoclimatic characteristics reconstructed by different methods, but a rather large variation in temperature and precipitation values at some time intervals.

Anthropogenic activity in prehistory on the background of Holocene climate changes in the south-eastern Baltic region

Data on natural palaeoarchives combined with archaeological materials from prehistoric sites of the south-eastern Baltic provide a picture of ancient anthropogenic activity and main stages of evolution of local communities starting from the Mesolithic. Modern Analog Technique (MAT) method applied for the Kamyshovoe lake palynological data is used to reconstruct the seasonal temperature and precipitation trends and values during the Holocene. During the Mesolithic, climate conditions changed from those close to the late Glacial through a period of warmer and wetter climate with parameters close to the present day to conditions of climatic optimum, when temperature was several degrees higher that modern ones. These climate conditions existed during the first part of the Neolithic as well, while from about 5500 cal yr BP the climate changed towards colder temperatures and a shift in seasonal moisture content: summers became wetter and winters less snowy. For the Bronze Age, relative temperature stability along with significant precipitation fluctuations are reconstructed. Since the Iron Age, temperatures remain close to modern ones and several “wetter” episods are distinguished.

Contrasting patterns of Last-deglacial and Holocene precipitation between the southern and northern portions of Arid Central Asia

The north-south migration of prevailing westerly system shapes the seasonality of modern precipitation in Arid Central Asia (ACA). The temperate continental climate with warm-season precipitation dominates the northern ACA and the Mediterranean climate with cold-season precipitation dominates the southern ACA. However, the north-south contrasts of precipitation/moisture for longer time scales remain unknown. In this study, we quantitatively reconstructed the precipitation sequence covering the past ~14.4 cal. kyr BP based on pollen data obtained from Shayan loess section in southern ACA using MAT (Modern Analogue Technique) method. Our reconstruction shows that the precipitation had an increasing trend from ~14.4 to ~8.2 cal. kyr BP and a decreasing trend from ~8.2 to ~1.5 cal. kyr BP with the past 1500 years being characterized by an averagely high precipitation. The precipitation trend in southern ACA was rather different from that in northern ACA where the precipitation has increased more or less constantly since the late deglaciation. The contrast between southern and northern ACA appears to have been associated with the south-north migration of westerlies that was accompanied with alterations of NAO (North Atlantic Oscillation) phases and also with changes in strengths of Siberian High and ENSO (El Nino-southern Oscillation).

NORWEGIAN SEA HOLOCENE ENVIRONMENTS BASED ON THE FOSSIL MICROALGAE ASSEMBLAGES

Detailed micropaleontological analysis was performed on the sediment core AMK-6142 collected in the deep-sea southwestern part of the Lofoten Basin in the Norwegian Sea. Summer sea-surface temperature for the last 7 cal. ky was reconstructed from dinocyst assemblages using the modern analogue technique (MAT). Sea-surface temperature reconstruction and dinocysts species composition indicate repeated changes in the surface environments during the Middle and Late Holocene. Episodes of cooling and probable displacement of the Arctic Front to the southwestern part of the Lofoten Basin were recorded for 5–7, 1.6–2.1, and 0.1–1.0 cal. ka BP.

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.

Reconstructing 15 000 years of southern France temperatures from coupled pollen and molecular (branched glycerol dialkyl glycerol tetraether) markers (Canroute, Massif Central)

Abstract. Climatic changes in southern Europe during the Holocene are characterized by a strong spatial and temporal heterogeneity whose patterns are still poorly understood, notably the presence or not of a Holocene thermal maximum (HTM; 10 000–6000 cal BP). The climatic patterns also differ according to the proxies used (e.g. pollen, chironomid) and the latitude of the record. Here, a multi-proxy approach combining pollen and lipid biomarkers (branched glycerol dialkyl glycerol tetraethers, brGDGTs) is applied to the Canroute sedimentological sequence (Massif Central, France) to reconstruct the climatic variation over the last 15 000 years in southern Europe. This area is poorly documented in terms of vegetation and climate change. To provide reliable climate reconstructions, we have (1) performed a multi-method approach applied to pollen (modern analogue technique, MAT; weighted averaging partial least squares regression, WA-PLS; boosted regression trees, BRT; and random forest, RF) and molecular biomarkers brGDGTs (five calibrations) and (2) investigated the role of modern databases and calibrations in climate reconstructions. Three different databases were tested for pollen data: one global database based on a Eurasian pollen database and two regional databases corresponding to Mediterranean–Temperate Europe and Temperate Europe–Scandinavian databases respectively. Five global calibrations were tested for lipid biomarkers including four for soil and one for peat. Results show that the use of different modern databases highlights the importance of considering environmental and ecological constraints when using transfer functions on pollen sequences. Pollen- and brGDGT-inferred climate trends are consistent, notably for the Late Glacial and the Early and Late Holocene. However, the reconstructions notably differ concerning the presence of a Holocene thermal maximum with the MAT pollen-based method, but no difference is apparent with the BRT pollen method nor brGDGT. The temperature reconstructions estimated from the two independent pollen and lipid proxies are then compared to regional climate signals (chironomids, pollen, molecular biomarkers) to better understand global regional climatic patterns in southern Europe. Altogether, our results from the Canroute sequence and those already available in southern Europe reveal that for the Late Glacial and Early Holocene, the regional climate trends are consistent between sites and proxies, supporting the reliability of their reconstructions despite some discrepancies. During the Holocene, the temperature signal of Canroute does not indicate the clear presence of a pronounced HTM, but rather stable temperatures.

Disentangling environmental drivers of subarctic dinocyst assemblage compositional change during the Holocene

Abstract. Analysis of compositional changes in fossil organic-walled dinoflagellate cyst (dinocysts) assemblages is a widely used tool for the quantitative reconstruction of past environmental parameters. This approach assumes that the assemblage composition is significantly related to the reconstructed environmental parameter, which requires an independent correlation between the assemblage and the variable, meaning that the variable explains a dimension of the assemblage variance that is not also explained by other parameters. Theoretically, dinocyst assemblages can be used to reconstruct multiple environmental variables. However, there is evidence that primary and subordinate drivers for assemblage compositions regionally differ, and it remains unclear whether a significant relationship to specific parameters in the present ocean always implies that this relationship is significant in fossil assemblages, questioning if past changes in these multiple parameters can be reconstructed simultaneously from fossil assemblages. Here, we analysed a local subset of the Northern Hemisphere dinocyst calibration dataset (n=1968), including samples from the Baffin Bay area (n=421), and evaluated the benefits of a local versus a more regional or global calibration for the environmental reconstruction of Baffin Bay oceanography during the Holocene. We determined the dimensionality of the dinocyst ecological response and identified environmental drivers in the Baffin Bay area for the modern dataset. We analysed four existing Holocene records along a north–south transect in the area and evaluated the statistical significance of downcore reconstructions by applying the local and global datasets with different techniques: the modern analogue technique (MAT), the weighted average partial least square (WA-PLS) and maximum likelihood (ML). We evaluated reconstructions tested as significant in light of the existing state of knowledge about West Greenland's Holocene palaeoceanography. Our analyses imply that present-day and Holocene dinocyst assemblages in the Baffin Bay area are primarily driven by salinity changes; other parameters were less important in driving assemblage compositions, and their contribution differed among the studied records. We show that the objectively occurring and temporally coherent shifts in dinocyst assemblages in the Holocene of Baffin Bay can be robustly interpreted only by transfer functions that are locally calibrated. Transfer functions based on the broad Northern Hemisphere calibration yielded many insignificant environmental reconstructions. At the same time, we show that even in the local calibration, not all parameters that appear to significantly affect dinocyst assemblages in the calibration dataset can be meaningfully reconstructed in the fossil record. A thorough evaluation of the calibration dataset and the significance of downcore applications is necessary to reveal the region-specific information contained in dinocyst assemblage composition.

LegacyClimate 1.0: a dataset of pollen-based climate reconstructions from 2594 Northern Hemisphere sites covering the last 30 kyr and beyond

Abstract. Here we describe LegacyClimate 1.0, a dataset of the reconstruction of the mean July temperature (TJuly), mean annual temperature (Tann), and annual precipitation (Pann) from 2594 fossil pollen records from the Northern Hemisphere, spanning the entire Holocene, with some records reaching back to the Last Glacial Period. Two reconstruction methods, the modern analog technique (MAT) and weighted averaging partial least squares regression (WA-PLS), reveal similar results regarding spatial and temporal patterns. To reduce the impact of precipitation on temperature reconstruction, and vice versa, we also provide reconstructions using tailored modern pollen data, limiting the range of the corresponding other climate variables. We assess the reliability of the reconstructions, using information from the spatial distributions of the root mean squared error in the prediction and reconstruction significance tests. The dataset is beneficial for synthesis studies of proxy-based reconstructions and to evaluate the output of climate models and thus help to improve the models themselves. We provide our compilation of reconstructed TJuly, Tann, and Pann as open-access datasets at PANGAEA (https://doi.org/10.1594/PANGAEA.930512; Herzschuh et al., 2023a). The R code for the reconstructions is provided at Zenodo (https://doi.org/10.5281/zenodo.7887565; Herzschuh et al., 2023b), including the harmonized open-access modern and fossil datasets used for the reconstructions, so that customized reconstructions can be easily established.

Agricultural development has not necessarily caused forest cover decline in semi-arid northern China over the past 12,000 years

Forest cover significantly affects the global carbon cycle, biodiversity, and human welfare, but is seriously threatened by human activities. Here we found that anthropogenic forces did not necessarily lead to forest cover decline in the marginal agricultural region of northern China based on a quantitative reconstruction of 12,000-years forest cover changes using modern analog technique and random forest. The forest cover was strongly affected by human activities in the core agricultural region, as indicated by the high independent effects of archeological sites (38.3%) and burning area (42.3%). In contrast, climate impacted the forest cover in the marginal agricultural region, where the annual precipitation and summer mean temperature contributed 52.4% and 27.4%, respectively. Agricultural development in the marginal agricultural region likely occurred in the river valley or sunny slopes, not overlapping with zonal forests growing on shady slopes. This study implies much less afforestation potential than previously expected in the marginal agricultural region.

Multiproxy reconstruction of late quaternary upper ocean temperature in the subtropical southwestern Atlantic

Paleoceanographic studies addressing the oceanographic variability in the western sector of the subtropical South Atlantic - especially those focused on the Brazil Current (BC) and on a time scale that reaches marine isotope stage (MIS) 5 - are still rare when compared with equivalent studies carried out in the Northern Hemisphere. In order to close the data gap prior to the last 75 ka, in an unprecedented approach in this region, we reconstructed the upper temperature variations in the Subtropical Southwestern Atlantic (SSWA) between late MIS 6 and the onset of MIS 4 from organic proxies, using a marine sediment core (GL-1090). Sea temperature records derived from alkenone-based U37K’ and isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs)-based TEX86H proxies were compared with those previously obtained from the same core via Globigerinoides ruber (G. ruber) Mg/Ca and planktonic foraminifera Modern Analog Technique (MAT). The temporal variations of the temperature estimates derived from the U37K′ and TEX86H indexes showed similar patterns, even though the absolute U37K′ temperatures were systematically lower than those derived from TEX86H. Such a difference was related to the different habitat depths of alkenones and isoGDGTs source organisms of – haptophyte algae and marine Thaumarchaeota, respectively. The temperature estimates from TEX86H match the range of Mg/Ca and MAT-derived temperatures between 0 and 10 m depth, suggesting that these proxies reflect mixed layer temperatures. In contrast, the temperature estimates derived from U37K′ were close to the MAT values at between 0 and 100 m and to those derived from TEX86H between 0 and 200 m depth, demonstrating that the U37K′ proxy recorded temperatures from the upper thermocline. During MIS 5e, the difference in temperature estimates from TEX86H and U37K′ was reduced due to more prominent warming, probably related to a change in the thermal structure of the photic zone. Comparison of our data with studies of intensity and salinity anomalies of the Agulhas Current indicates a connection between the intensification of the Agulhas Leakage and the heat storage in the upper thermocline in the SSWA during MIS 5e. Our data suggest that the joint use of TEX86H and U37K′ is a promising approach to estimating paleoceanographic changes in the upper thermocline.

A diatom-inferred water-depth transfer function from a single lake in the northern California Coast Range

This study examines the relationship between water depth and diatom assemblages from lake-sediment-surface samples at Kelly Lake, California. A total of 40 surface-sediment samples (integrated upper 5 cm) were taken at various depths within the small (~ 3.74 ha) 5.7 m-deep lake. Secchi depths, water temperature, pH, salinity, conductivity, and total dissolved solids were also measured. Some diatom species showed distinct association with depth (e.g., Fragilaria crotonensis, Nitzschia semirobusta). The relationship between the complete diatom assemblages and water depth was analyzed and assessed by depth-cluster analysis, a one-way analysis of similarity, principal components analysis and canonical correspondence analysis. Statistically significant differences were found between the assemblages associated with shallow depth (0–1.25 m), mid-depth (1.25–3.75 m), and deep-water (3.75–5.2 m) locations. The relationship between diatom assemblages and lake depth allowed two transfer models to be developed using the Modern Analogue Technique and Weighted Averaging Partial Least Squares. These models were compared and assessed by residual scatter plots. The results indicate that diatom-inferred transfer models based on surface-sediment samples from a single, relatively small and shallow lake can be a useful tool for studying past hydroclimatic variability (e.g., lake depth) from similar lakes in California and other regions where the large number of lakes required for traditional transfer-function development may not exist.

Climate changes during the Late Glacial in southern Europe: new insights based on pollen and brGDGTs of Lake Matese in Italy

Abstract. The Late Glacial (14 700–11 700 cal BP) is a key climate period marked by rapid but contrasted changes in the Northern Hemisphere. Indeed, regional climate differences have been evidenced during the Late Glacial in Europe and the northern Mediterranean. However, past climate patterns are still debated since temperature and precipitation changes are poorly investigated towards the lower European latitudes. Lake Matese in southern Italy is a key site in the central Mediterranean to investigate climate patterns during the Late Glacial. This study aims to reconstruct climate changes and their impacts at Matese using a multi-proxy approach including magnetic susceptibility, geochemistry (XRF core scanning), pollen data and molecular biomarkers like branched glycerol dialkyl glycerol tetraethers (brGDGTs). Paleotemperatures and paleo-precipitation patterns are quantitatively inferred from pollen assemblages (multi-method approach: modern analogue technique, weighted averaging partial least-squares regression, random forest and boosted regression trees) and brGDGT calibrations. The results are compared to a latitudinal selection of regional climate reconstructions in Italy to better understand climate processes in Europe and in the circum-Mediterranean region. A warm Bølling–Allerød and a marked cold Younger Dryas are revealed in all climate reconstructions inferred from various proxies (chironomids, ostracods, speleothems, pollen, brGDGTs), showing no latitudinal differences in terms of temperatures across Italy. During the Bølling–Allerød, no significant changes in terms of precipitation are recorded; however, a contrasted pattern is visible during the Younger Dryas. Slightly wetter conditions are recorded south of 42∘ N, whereas dry conditions are recorded north of 42∘ N. During the Younger Dryas, cold conditions can be attributed to the southward position of North Atlantic sea ice and of the polar frontal jet stream, whereas the increase in precipitation in southern Italy seems to be linked to relocation of Atlantic storm tracks into the Mediterranean, induced by the Fennoscandian ice sheet and the North European Plain. By contrast, warm conditions during the Bølling–Allerød can be linked to the northward position of North Atlantic sea ice and of the polar frontal jet stream.

Holocene Paleoenvironmental Implications of Diatom, Non-Pollen Palynomorph, and Organic Carbon Records from the Kandalaksha Bay of the White Sea (European Arctic)

Variations in sea surface conditions and sea level through the Holocene in the Kandalaksha Bay, the White Sea, were reconstructed based on the study of core sediments from the outer Kandalaksha Bay, using the modern analog technique applied to dinocysts in addition to diatoms, TOC, δ13Corg, CaCO3, and grain size data. The chronostratigraphy of the core sediments was defined from accelerator mass spectrometry 14C dates on mollusk shells. The results indicated an increase in water depth in the outer Kandalaksha Bay and in the central Dvina Bay until the late Holocene. From about 9.5 to 7.5 cal kyr BP, the data suggested a general trend of increasing sea surface temperatures (up to 14 °C), at least in areas with inflow of Atlantic waters. The last 2.5 kyr were characterized by increased freshwater runoff to the White Sea.

Microfossil evidence for a possible maar crater and tuff ring beneath Rangitoto Volcano, Auckland, New Zealand

ABSTRACT Distinctive low diversity foraminiferal and ostracod faunas in Holocene mud from a stratigraphic drillhole through Rangitoto Volcano (∼600 years old) indicate a highly sheltered, shallow-marine environment existed near the middle of the exposed entrance to Waitemata Harbour, Auckland, for at least 7000 years prior to Rangitoto’s eruption. Modern Analogue Technique estimates for these faunas indicate they accumulated at low tidal to shallow subtidal depths (0–11 m). The most similar analogue faunas lived subtidally in the extreme shelter inside the breached Onepoto maar lagoon, Auckland. Therefore, we infer the possible existence of a pre-7500 year-old maar crater and surrounding tuff ring buried beneath Rangitoto Volcano. This Holocene mud occurs in the drillhole 24–10 m lower than where the microfaunas indicate it accumulated. It is inferred to have slid into the adjacent harbour channel, along with 7 m of basaltic tuff and a piece of lava flow, near the start of the second phase of Rangitoto’s eruption.

Vegetation and fire history of the East-European forest-steppe over the last 14,800 years: A case study from Zamostye, Kursk region, Russia

The East-European forest-steppe extends from the Carpathian to the Ural Mountains, representing a mosaic of broadleaf deciduous forest patches and meadow-steppe, where up to 80% of the territory has been converted to croplands. Here we examine the Late Glacial and Holocene history of the forest-steppe of the East European Plain to better understand its sensitivity to climate fluctuations, fire and human impact, and also the timing of its transition into the modern agro-pastoral landscapes. We studied a radiocarbon-dated sediment core from the village of Zamostye (Kursk region, Russia), which provides a continuous record of vegetation change for the last 14,800 years. We conducted an analysis of pollen, non-pollen palynomorphs, loss-on-ignition, macro- and mirco-charcoal and macroremains, and applied a modern analogue technique to the pollen data to reconstruct forest cover. The pollen data reveal high sensitivity of the vegetation in this region to moisture availability caused by the northern hemispheric climate changes and permafrost. The region was occupied by a pine forest-steppe during Bølling/Allerød but transformed into a cold steppe during the GI 1d and Younger Dryas events. Around 11.7 cal kyr BP the climate warming triggered an expansion of birch trees into the steppe but the lack of moisture and strong fire activity hindered the development of pine and broadleaf forests for more than a millennium. Vegetation turnover occurred at ∼10.3 kyr BP, when the vegetation became dominated by pine. Pine and mixed deciduous oak forests continued to dominate through the Middle to Late Holocene reaching their maximal extension by 4.4 cal kyr BP. During the Late Holocene, human impact was detected for the Late Bronze Age, Early Iron Age, Roman period and Early Middle Ages. However, natural forests were recovering after a decrease in human activities. We demonstrate that the forest-steppe of the East European Plain has experienced a total deforestation in the 17th century and has remained open although climate conditions could have allowed the recovery of pine-broadleaf mixed forests.