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Long-term paleofire perspectives provide key information on natural and human-derived land cover changes. The last few millennia are crucial to understanding the future of wildfire threats, since the increasing global temperatures are expected to have an impact on regions previously assumed to not be endangered. In this study we investigate the interplay between changing climatic conditions, land cover transformation, fires, and human activity based on the first 1750-year-long macrocharcoal record derived from varved sediments of Lake Jaczno, located in northeast Poland. The study is supported by macrocharcoal morphotype analysis, pollen and historical data, and statistical analysis, which revealed that in the vicinity of the lake both low- and high-intensity fires may have occurred. Most of them were set by humans, but in some periods biomass burning was favored by droughts or even derived by natural causes (i.e. lightning). Human-induced fires are especially evident between AD 1081 and 1283. This period corresponds to the peak activity of the Jatvings tribe in the region and the related deforestation for agrarian purposes. Fire combined with human activity and deforestation in the area impacted the limnological processes increasing primary productivity and shifts in water mixing regime. [ABSTRACT FROM AUTHOR]

A detailed Holocene tephrostratigraphic framework has been developed for two predominately varved lake sediment sequences from NE Germany (Lake Tiefer See) and central N Poland (Lake Czechowskie). A total of thirteen tephras and cryptotephras of Icelandic provenance were detected and chemically fingerprinted in order to define correlatives and to integrate known tephra ages into the sediment chronologies. Out of these, three cryptotephras (Askja-AD1875, Askja-S and Hässeldalen) were identified in both records, thus allowing a detailed synchronization of developing high-resolution palaeoenvironmental proxy data. The early Holocene Saksunarvatn Ash layer and the middle Holocene Lairg-B and Hekla-4 cryptotephras in Lake Tiefer See are further important anchor points for the comparison with other high-resolution palaeoclimate records in Central and Northern Europe. Tentative correlations of cryptotephras have been made with a historical basaltic Grimsvötn eruption (∼AD890 – AD856) and three late Holocene rhyolitic eruptions, including the 2.1 ka Glen Garry and two unknown high-silicic cryptotephras of probably Icelandic provenance (∼1.9 cal ka BP). [ABSTRACT FROM AUTHOR]

The varved sediment of Lake Gościąż (Central Poland) is one of the most detailed and complete climate archives of the Late Glacial and the Holocene in Central Europe. Here, we present microfacies analyses in combination with μXRF core scanning and a detailed varve chronology of a new and continuous GOS18 sediment record. This record presents six lithozones that mark the most prominent depositional and geochemical changes during the Holocene and Late Glacial. Varve boundaries and five main varve microfacies types were distinguished under petrographic microscope. Analysis provides detailed insights into depositional processes and its changes since the Late Glacial. Microfacies components were used to interpret processes leading to varve formation. A new and independent chronology is obtained by triple varve counting on petrographic thin sections that is complemented by 137Cs measurements and 14C AMS dating of terrestrial plant remains. The age-depth model consists of three parts: (1) the upper part (0–520 cm) that is primarily based on varve counting, (2) the middle part (520–758 cm) obtained through age-depth modelling and (3) the lower part (758–1897 cm) developed by varve counting. The bottom of the composite profile coincides with the onset of lacustrine sedimentation in the late Allerød at 12,834 +134/-233 varve yr BP. The largest shift in geochemistry, expressed by log(Ca/Ti) and log(Si/Ti) ratios show a rapid increase of calcite precipitation and primary productivity at 7940 +112/-168 varve yr BP. Possible triggers for this include local changes in hydrology as the formation of "Na Jazach" system due to the Ruda River development and fluctuations of lake water level. • Combining varve counting, radiometric methods and age-depth relation modeling. • Development of the new chronology for Lake Gościąż, central Poland. • Varve microfacies and their environmental implications from Allerød to present time. • Detailed insights into depositional processes and abrupt geochemical shifts. [ABSTRACT FROM AUTHOR]

• Lake sediment-derived environmental reconstruction is presented for the 4.2 ka event. • Summer temperatures and climate humidity remained stable during the event. • We found likely indication of more severe winters between 4.0 and 4.25 ka BP. • A pulse of podzolization, likely favored by winter cooling, was reported ~4.2 ka BP. • The terrestrial vegetation and the lake biota remained unaffected by the event. Many regions around the world experienced abrupt climate change with far-reaching societal and environmental effects at ca. 4.2 cal. ka BP. As one of the most distinct climatic events of the last 11.7 ka, it has been used to establish the formal boundary between the mid- and late-Holocene. Although the 4.2 ka event was not pronounced in East-Central Europe, its exact impact on the area has yet to be evaluated. The aim of this paper is twofold: (1) to reconstruct the functioning of the selected lake and terrestrial ecosystems from northern Poland around the time of the 4.2 ka event, and (2) to disentangle the drivers of the recorded environmental changes (local factors vs. climate impact). We studied the sedimentary record of Lake Spore, focusing on the period between 3.8 and 4.5 cal. ka BP using numerous biotic and abiotic proxies, such as chironomids, cladocerans, pollen and spores, δ13C org , δ15N org , δ18O carb , δ13C carb , TOC/N, Fe, S, LOI 550 , and LOI 950. The chironomid-derived reconstruction of mean July air temperature did not change during the 4.2 ka event. Pollen accumulation rate (PAR) data showed lower pollen production of some tree taxa during the period 4.0–4.25 cal. ka BP that is consistent with low PARs recorded for the corresponding period in the sediments of nearby (~75 km) Lake Suminko. This change might have occurred due to either regional-scale forest disturbance or cooler winters resulting from an exceptionally strong Siberian High during the 4.2 ka event. Distinct peaks of Fe and δ13C carb at 4.2 cal. ka BP likely record a pulse of podzolization. Although soil transformation processes were common in East-Central Europe after ca. 5 cal. ka BP due to general climate cooling, they could have been enhanced at Lake Spore during the 4.2 ka event, if winters were more severe. The δ13C org , δ15N org , TOC/N and δ18O carb records point to a water level rise after 4.2 cal. ka BP that most likely resulted from soil transformation in the catchment, not a change in effective precipitation. The composition of the terrestrial vegetation and the lake fauna and flora remained largely unaffected by the 4.2 ka event. [ABSTRACT FROM AUTHOR]