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In this work, we studied the course of climatic fluctuations at the beginning of the Preboreal period using multiproxy analyses (Chironomidae, pollen, diatoms, Cladocera, stable isotopes, macrocharcoal, microlithofacial) combined with varve chronology of sediments. The results showed a decrease in the mean July temperature and stronger continentalism followed by climate wetting at the start of the Preboreal period. This was reflected in the remodeling of the vegetation cover from birch forests to more open spaces with grass vegetation dominance, as well as that of the species composition of Cladocera and diatoms, and the high variability of isotopic composition. In addition, the results showed the impact of local conditions (fires and relict permafrost) on the amplification of environmental responses due to climate cooling. The environmental transformations presented here correspond temporally to the changes that are well documented in other parts of Europe as the Preboreal Oscillation. [ABSTRACT FROM AUTHOR]

The study, based on the examination of 70 published and unpublished pollen profiles from Poland and supplementary data from the surrounding regions, shows that an abrupt, episodic Alnus population decline at the end of the first millennium CE was a much more widespread event than has been previously reported, spanning large areas of the temperate and boreal zones in Europe. The data from Poland suggest that the decline was roughly synchronous and most likely occurred between the 9th and 10th centuries, with strong indications for the 10th century. The pollen data indicate that human impacts were not a major factor in the event. Instead, we hypothesize that one or a series of abrupt climatic shifts that caused floods and droughts at the end of the first millennium CE could have initiated this ecological disturbance, leading to a higher vulnerability of the alder trees to a pathogen outbreak. Following current observations of the decline of alder stands in Europe due to a Phytophthora outbreak, we suggest that a similar process may have occurred in the past. This study provides insight into long-term alder (mainly Alnus glutinosa) dynamics in a condition of climate change and illustrates its great resilience, enabling the natural, successful regeneration of alder stands after critical diebacks if environmental conditions improve. Our finding that the Alnus pollen decline reflects a roughly synchronous event indicates that the decline could be used as an over-regional chronostratigraphic marker for 800–1000 CE in pollen diagrams from a large part of the European Lowland. [ABSTRACT FROM AUTHOR]

Late glacial and Holocene environmental history of Lake Łukie and its catchment is reconstructed from the lake sediments. This shallow lake is situated in the marshy Polesie region in eastern Poland. Sediments began to accumulate in the lake in the Older Dryas. On the basis of macrofossils, pollen, and Oribatida remains, and with the use of Kohonen’s artificial neural network (self-organising map, SOM), six stages (corresponding to subclusters X 1 , X 2 , X 3 in cluster X, and Y 1 , Y 2 , Y 3 in cluster Y) of the lake history were distinguished, and indicator taxa of each stage were identified from the indicator value (IndVal) index. During the transition period corresponding to the border between X and Y, the ecosystem transformed in the broad sense from the protocratic to mesocratic phase in a 5-point scale transformation of the landscape in the glacial–interglacial cycle. All the steps involved in post-glacial history succession during interglacial cycles include changes in climate, soil, and biotic interactions. Indicator taxa for the subsequent SOM subclusters X 1 , X 2 , and X 3 are associated with the first phase of the protocratic glacial–interglacial cycle. The transformation that occurs on the level of cluster Y (subcluster Y 1 ) is the mesocratic phase (ca. 9000–5000 14 C age BP), which is characterised by high temperatures and development of closed forest (climax forest). Subcluster Y 2 corresponds to the transformation of forest cover during the oligocratic phase (ca. 5000–3000 14 C age BP), which is associated with decreasing forest share and deteriorating soils. Finally, subcluster Y 3 can be associated with the telocratic phase, characterised by the influence of a more oceanic climate (from ca. 2500 14 C age BP) with declining temperatures, higher humidity, and milder seasonal contrasts, which contributed to the development of more open vegetation and infertile soils. This stage also corresponds to an increased human activity and landscape transformation, such as from forests to cornfields and from wetlands to meadows. Interestingly, the currently strictly protected brittle naiad ( Najas minor ) was present in the lake during the Atlantic, Subboreal, and Subatlantic periods; however, this species is not listed as being part of the present vegetation and may have become extinct relatively recently. [ABSTRACT FROM AUTHOR]

ABSTRACT We report pollen-stratigraphical evidence for an abrupt, episodic and widespread population decline of alder ( Alnus), one of the most common boreal tree genera, during the medieval period in northern Europe. Decline of alder pollen values was observed both in forest hollow pollen records reflecting local vegetation of pristine forests and in pollen percentage and pollen accumulation data from lake sediments. The event began roughly at AD 600 and the recovery took place at AD 1000. Human impact is an unlikely cause because the decline is specific to alder and there is no evidence for a concurrent episode of human impact. It is possible that the decline was caused or influenced by a severe drought. Another potential cause is a sudden, widespread pathogen outbreak, especially as alder is known to be sensitive to the impacts of fungal pathogens such as the oomycete Phytophthora. [ABSTRACT FROM AUTHOR]

On the basis of macrofossil and pollen analyses, AMS 14 C-dating, and geomorphological investigations, we reconstructed the development of hydrological changes during the Lateglacial to early Holocene transition in Tuchola Pinewoods (Bory Tucholskie) in northern Poland. In this region, the Wda River flows in polygenetic valleys, typical for the young glacial landscape of the northern central European lowlands. The middle section of this river provides a suitable setting to demonstrate the environmental and hydrological changes in the Late Glacial and early Holocene, because (1) it is a small and well-defined area and (2) the existence of a morphologically preserved river valley from late glacial period. In this study, we focused on a short terrestrial sediment core (48 cm) that represents four phases of landscape evolution during the early Holocene: telmatic, lacustrine, lacustrine-fluvial and alluvial. Abrupt changes in lithology and sediment structures exhibit rapid changes and threshold processes in environmental conditions. The AMS 14 C dating of terrestrial plant remains revealed an age for the basal sediments of 11 223 ± 23 cal BP and thus falls within the Preboreal biozone. Plant macrofossil indicators provide evidence of water level and edaphic changes in the basin. The results of our study demonstrate a strong influence of melting buried ice blocks on the geomorphological development, hydrological changes in the catchment, and the biotic environment in the early Holocene. [ABSTRACT FROM AUTHOR]

Siberian peatlands provide records of past changes in the continental climate of Eurasia. We analyzed a core from Mukhrino mire in western Siberia to reconstruct environmental change in this region over the last 1300 years. The pollen analysis revealed little variation of local pine-birch forests. A testate amoebae transfer function was used to generate a quantitative water-table reconstruction; pollen, plant macrofossils, and charcoal were analyzed to reconstruct changes in vegetation and fire activity. The study revealed that Mukhrino mire was wet until the Little Ice Age (LIA), when drought was recorded. Dry conditions during the LIA are consistent with other studies from central and eastern Europe, and with the pattern of carbon accumulation across the Northern Hemisphere. A significant increase in fire activity between ca. AD 1975 and 1990 may be associated with the development of the nearby city of Khanty-Mansiysk, as well as with the prevailing positive Arctic Oscillation. [ABSTRACT FROM AUTHOR]

Sphagnum peatlands in the oceanic-continental transition zone of Poland are currently influenced by climatic and anthropogenic factors that lead to peat desiccation and susceptibility to fire. Little is known about the response of Sphagnum peatland testate amoebae (TA) to the combined effects of drought and fire. To understand the relationships between hydrology and fire dynamics, we used high-resolution multi-proxy palaeoecological data to reconstruct 2000 years of mire history in northern Poland. We employed a new approach for Polish peatlands – joint TA-based water table depth and charcoal-inferred fire activity reconstructions. In addition, the response of most abundant TA hydrological indicators to charcoal-inferred fire activity was assessed. The results show four hydrological stages of peatland development: moderately wet (from ∼35 BC to 800 AD), wet (from ∼800 to 1390 AD), dry (from ∼1390 to 1700 AD) and with an instable water table (from ∼1700 to 2012 AD). Fire activity has increased in the last millennium after constant human presence in the mire surroundings. Higher fire activity caused a rise in the water table, but later an abrupt drought appeared at the onset of the Little Ice Age. This dry phase is characterized by high ash contents and high charcoal-inferred fire activity. Fires preceded hydrological change and the response of TA to fire was indirect. Peatland drying and hydrological instability was connected with TA community changes from wet (dominance of Archerella flavum , Hyalosphenia papilio , Amphitrema wrightianum ) to dry (dominance of Cryptodifflugia oviformis , Euglypha rotunda ); however, no clear fire indicator species was found. Anthropogenic activities can increase peat fires and cause substantial hydrology changes. Our data suggest that increased human fire activity was one of the main factors that influenced peatland hydrology, though the mire response through hydrological changes towards drier conditions was delayed in relation to the surrounding vegetation changes. [ABSTRACT FROM AUTHOR]

• July temp. dropped at the YD onset, then increased up to the Holocene onset. • There were four cold and four warm summer temp. oscillations during YD. • Seasonal contrast was higher at the AL/YD and YD/Hol. transitions than in mid-YD. • Water level fluctuations, TP content and winds also drove lake biota in the lake. • Lake ecosystem transition from the YD to Holocene took place in four stages. The Younger Dryas (YD) is a roughly 1,100-year cold period marking the end of the last glaciation. Climate modelling for northern Europe indicates high summer temperatures and strong continentality. In eastern Europe, the scale of temperature variation and its influence on ecosystems is weakly recognised. Here, we present a multi-proxy reconstruction of YD conditions from Lake Gościąż (central Poland). The decadal-resolution analysis of its annually varved sediments indicates an initial decrease in Chironomidae-inferred mean July air temperature followed by steady warming. The pollen-inferred winter-to-summer temperature amplitude and annual precipitation is highest at the Allerød/YD transition and the early YD (ca. 12.7–12.4 ky cal BP) and YD/Holocene (11.7–11.4 ka cal BP) transition. Temperature and precipitation were the main reasons for lake level fluctuations as reflected in the planktonic/littoral Cladocera ratio. The lake's diatom-inferred total phosphorus decreased with increasing summer temperature from about mid YD. Windy conditions in the early YD until ∼12.3 ka cal BP caused water mixing and a short-lived/temporary increase in nutrient availability for phytoplankton. The Chironomidae-inferred summer temperature and pollen inferred summer temperature, winter temperature and annual precipitation herein are one of only a few in eastern Europe conducted with such high resolution. [ABSTRACT FROM AUTHOR]