Timing of the Baltic Ice Lake in the eastern Baltic

A shoreline database for the Baltic, covering the Late Weichselian and Holocene, was compiled. The database includes about 1600 sites from Estonia, Latvia, Lithuania, Finland, NW Russia, Poland, Sweden and was used to create a GIS-based palaeogeographical reconstructions on the development of the Baltic Ice Lake (BIL). The formation of thehighest shoreline of the BIL in Estonia was connected with the development of the Pandivere ice marginal zone (Estonia) and the lowest with the Salpausselkä ice-marginal formations (Finland). There was a well-accepted knowledge that the Pandivere ice marginal zone correlates with the Neva ice marginal zone in NW Russia dated to 13 300 cal yr BP. Recent studies of the late glacial sites in northern Estonia indicate that the age of the Pandivere ice marginal zone and hence the highest shoreline of the BIL A1 is about 13 800–14 000 cal yr BP. It was followed by the BIL stage A2, which formed in front ofthe Palivere ice marginal belt about 13 200–13 500 cal yr BP. The final drainage of the BIL took place about 11 650 cal yr BP. The timing of the BIL stages was derived from AMS-14C dates and correlated with varve chronology, OSL and 10Be dates

Spring onset and seasonality patterns during the Late Glacial period in the eastern Baltic region

Spring onset is an important phenological observation that is sensitive to modern climate change and can be traced back in geological time. The Late Glacial (∼ 14 500-11 700 cal yr BP) spring onset and growing season (growing degree days) dynamics in the eastern Baltic region were reconstructed using the micro-phenological approach based on the dwarf birch (Betula nana) subfossil leaf cuticles. The presented study sites, Lake Lielais Svetinu (eastern Latvia) and Lake Kosilase (central Estonia), are located ∼ 200 km apart in the region affected by the south-eastern sector of the Scandinavian Ice Sheet. During the Late Glacial period the region and its biota were influenced by the retreating glacier and the different stages of the Baltic Ice Lake. The plant macrofossil data confirm that the study sites were in different vegetation zones (arctic-to-boreal) during the Late Glacial period. The dynamics of the estimated length of the growing season and spring onset, combined with the regional collection of plant macrofossil records, suggest the importance of local settings to species migration. During the Late Glacial warming period (Bølling-Allerød), a notable spring warming and longer growing season was calculated based on micro-phenology, but the treeline did not extend beyond central Estonia. The comparison of pollen-A nd chironomid-inferred past temperature estimations with spring onset, growing degree days, and plant macrofossil data shows coherent patterns during the cooler Older Dryas and warmer Bølling-Allerød periods, while suggesting more complicated climate dynamics and possible warmer episodes during the Younger Dryas cold reversal

Holocene fire activity during low-natural flammability periods reveals scale-dependent cultural human-fire relationships in Europe

Fire is a natural component of global biogeochemical cycles and closely related to changes in human land use. Whereas climate-fuel relationships seem to drive both global and subcontinental fire regimes, human-induced fires are prominent mainly on a local scale. Furthermore, the basic assumption that relates humans and fire regimes in terms of population densities, suggesting that few human-induced fires should occur in periods and areas of low population density, is currently debated. Here, we analyze human-fire relationships throughout the Holocene and discuss how and to what extent human driven fires affected the landscape transformation in the Central European Lowlands (CEL). We present sedimentary charcoal composites on three spatial scales and compare them with climate model output and land cover reconstructions from pollen records. Our findings indicate that widespread natural fires only occurred during the early Holocene. Natural conditions (climate and vegetation) limited the extent of wildfires beginning 8500 cal. BP, and diverging subregional charcoal composites suggest that Mesolithic hunter-gatherers maintained a culturally diverse use of fire. Divergence in regional charcoal composites marks the spread of sedentary cultures in the western and eastern CEL The intensification of human land use during the last millennium drove an increase in fire activity to early-Holocene levels across the CEL Hence, humans have significantly affected natural fire regimes beyond the local scale - even in periods of low population densities - depending on diverse cultural land-use strategies. We find that humans have strongly affected land-cover- and biogeochemical cycles since Mesolithic times

Fire hazard modulation by long-term dynamics in land cover and dominant forest type in eastern and central Europe

Wildfire occurrence is influenced by climate, vegetation and human activities. A key challenge for understanding the risk of fires is quantifying the mediating effect of vegetation on fire regimes. Here, we explore the relative importance of Holocene land cover, land use, dominant functional forest type, and climate dynamics on biomass burning in temperate and boreo-nemoral regions of central and eastern Europe over the past 12 kyr. We used an extensive data set of Holocene pollen and sedimentary charcoal records, in combination with climate simulations and statistical modelling. Biomass burning was highest during the early Holocene and lowest during the mid-Holocene in all three ecoregions (Atlantic, continental and boreo-nemoral) but was more spatially variable over the past 3–4 kyr. Although climate explained a significant variance in biomass burning during the early Holocene, tree cover was consistently the highest predictor of past biomass burning over the past 8 kyr. In temperate forests, biomass burning was high at ~ 45% tree cover and decreased to a minimum at between 60% and 70% tree cover. In needleleaf-dominated forests, biomass burning was highest at ~60 %–65%tree cover and steeply declined at > 65% tree cover. Biomass burning also increased when arable lands and grasslands reached ~15 %–20 %, although this relationship was variable depending on land use practice via ignition sources, fuel type and quantities. Higher tree cover reduced the amount of solar radiation reaching the forest floor and could provide moister, more wind-protected microclimates underneath canopies, thereby decreasing fuel flammability. Tree cover at which biomass burning increased appears to be driven by warmer and drier summer conditions during the early Holocene and by increasing human influence on land cover during the late Holocene. We suggest that longterm fire hazard may be effectively reduced through land cover management, given that land cover has controlled fire regimes under the dynamic climates of the Holocene

The Reading Palaeofire Database : an expanded global resource to document changes in fire regimes from sedimentary charcoal records

Sedimentary charcoal records are widely used to reconstruct regional changes in fire regimes through time in the geological past. Existing global compilations are not geographically comprehensive and do not provide consistent metadata for all sites. Furthermore, the age models provided for these records are not harmonised and many are based on older calibrations of the radiocarbon ages. These issues limit the use of existing compilations for research into past fire regimes. Here, we present an expanded database of charcoal records, accompanied by new age models based on recalibration of radiocarbon ages using IntCal20 and Bayesian age-modelling software. We document the structure and contents of the database, the construction of the age models, and the quality control measures applied. We also record the expansion of geographical coverage relative to previous charcoal compilations and the expansion of metadata that can be used to inform analyses. This first version of the Reading Palaeofire Database contains 1676 records (entities) from 1480 sites worldwide. The database (RPDv1b - Harrison et al., 2021) is available at https://doi.org/10.17864/1947.000345.Peer reviewe

Simulating the palaeorecord of northern European lakes using a coupled lake-catchment model

A coupled lake-catchment model was developed to examine the controls on lake-level changes in currently overflowing lakes during Holocene. The lake energy-balance is simulated as the one-dimensional vertical heat transfer by eddy diffusion and convective mixing. The accumulation and ablation of lake ice, and snow cover on the ice, is simulated thermodynamically. The lake water-balance is given by the balance between precipitation over the lake, evaporation from the water surface, catchment runoff, and lake outflow. Runoff is calculated using a one-dimensional, two layer soil covered by vegetation and a snowpack. Snow accumulation and ablation are controlled by air temperature. Outflow is controlled by the outlet size and outflow velocity, using the Manning equation. The coupled model was validated for Lake Bysjön (southern Sweden) and Lakes Karujärv and Viljandi (Estonia). The simulated monthly lake level matched observations of lake-level changes between 1944-1956 at Lake Viljandi (r=0.78), between 1976-1987 at Lake Karujärv (r=0.78) and between 1973-1977 at Lake Bysjön (r=0.7). The model was used to examine lake-level sensitivity to changes in individual climatic parameters. Changes in radiation, temperature, vapour pressure and wind strength produce lake-level changes of <0.5 m. Changes in mean annual and winter precipitation produce changes an order of magnitude larger. The lake-level sensitivity to precipitation changes is greatest when winter temperatures were higher than present. The magnitude of the response to a specific climatic change is strongly affected by the ratio of the lake area to the catchment area

Palaeoenvironment and shoreline displacement on Suursaari Island, the Gulf of Finland

The island of Suursaari in the middle of the Gulf of Finland is exceptionally high (175 m a.s.l.). Sediment profiles from one mire and three lakes were investigated using diatom and pollen analysis, radiocarbon dating and levelling of the elevations of ancient shorelines. The pollen stratigraphy of the Lounatkorkiasuo Mire sediment suggests a sedimentary record dating from the late Allerød.The development of late-glacial vegetation went through the same phases as in southern Finland, however these are probably somewhat earlier on the island of Suursaari. There are differences in the Holocene vegetation history of the higher and lower areas of the island. Lake Ruokalahenjärvi was isolated around 10 000 BP during the initial phase of the Yoldia Sea and the diatom assemblage indicates that at that time brackish-water flow had not penetrated into the Gulfof Finland. Diatoms from the isolation sediments of Lake Liivalahenjärvi and Lake Veteljärvi indicate a freshwater environment for the Yoldia Sea final phase at 9500–9600 BP. Levelling of coastal formations on Suursaari Island reveals that the Late Weichselian and early Holocene ancient shorelines are 5–15 m higher than expected from the isobase data for similar land uplift areas on the mainland.The anomalous shoreline levels on Suursaari Island may be explained byirregular land uplift. By the time of the Litorina Sea differences in shoreline altitudes had disappeared

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