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Independent Arctic records of temperature and precipitation from the same proxy archives are rare. Nevertheless, they are important for providing detailed information on long-term climate changes and temperature-precipitation relationships in the context of large-scale atmospheric dynamics. Here, we used chironomid and cladoceran fossil assemblages to reconstruct summer airtemperature and water-level changes, during the past 400 years, in a small lake located in Finnish Lapland. Temperatures remained persistently cold over the Little Ice Age (LIA), but increased in the 20th century. After a cooler phase in the 1970s, the climate rapidly warmed to the record-high temperatures of the most recent decades. The lake-level reconstruction suggested persistently wet conditions for the LIA, followed by a dry period between ~1910 and 1970 CE, when the lake apparently became almost dry. Since the 1980s, the lake level has returned to a similar position as during the LIA. The temperature development was consistent with earlier records, but a significant local feature was found in the lake-level reconstruction – the LIA appears to have been continuously wet, without the generally depicted dry phase during the 18th and 19th centuries. Therefore, the results suggest local precipitation patterns and enforce the concept of spatially divergent LIA conditions. This work was supported by the Emil Aaltonen Foundation (T.P.L., grants numbers 160156, 170161, 180151), Kone Foundation (T.P.L., grant number 090140) and Academy of Finland (L.N., grant numbers 287547, 308954). Support for mobility by the EU Climate-KIC’s Pioneers into Practice program is also appreciated. Help in the fieldwork was provided by Annukka Galkin and the Kevo Research Station. We are grateful for Dr. János Korponai and an anonymous reviewer for their constructive comments on the manuscript.

The sediment profile from Lake Goscia(z) over dot in central Poland comprises a continuous, seasonally resolved and exceptionally well-preserved archive of the Younger Dryas (YD) climate variation. This provides a unique opportunity for detailed investigation of lake system responses during periods of rapid climate cooling (YD onset) and warming (YD termination). The new varve record of Lake Goscia(z) over dot presented here spans 1662 years from the late Allerod (AL) to the early Preboreal (PB). Microscopic varve counting provides an independent chronology with a YD duration of 1149+14/-22 years, which confirms previous results of 1140 +/- 40 years. We link stable oxygen isotopes and chironomid-based air temperature reconstructions with the response of various geochemical and varve microfacies proxies especially focusing on the onset and termination of the YD. Cooling at the YD onset lasted similar to 180 years, which is about a century longer than the terminal warming that was completed in similar to 70 years. During the AL/YD transition, environmental proxy data lagged the onset of cooling by similar to 90 years and revealed an increase of lake productivity and internal lake re-suspension as well as slightly higher detrital sediment input. In contrast, rapid warming and environmental changes during the YD/PB transition occurred simultaneously. However, initial changes such as declining diatom deposition and detrital input occurred already a few centuries before the rapid warming at the YD/PB transition. These environmental changes likely reflect a gradual increase in summer air temperatures already during the YD. Our data indicate complex and differing environmental responses to the major climate changes related to the YD, which involve different proxy sensitivities and threshold processes.

Fens have been forming in the river valleys of central Poland since the Bølling and went through a transformation from fully aquatic to semiterrestrial habitats during the Younger Dryas/Holocene transition. This drove plant and invertebrate communities and left a distinct pattern in chemical sediment composition, which is why river valley peatlands are sensitive palaeo-archives of climatic, hydrological and edaphic changes. Here we reconstruct the Late Weichselian history of the Bęczkowice fen in the upper Luciąża River valley using geochemical, pollen, Cladocera and Chironomidae proxies. Pollen-based age estimation indicates that the analysed peat sequence dates from the Bølling to Early Holocene. The layers 190-170 cm and 125-105 cm of the studied core were reworked by fluvial processes. Chironomidae and Cladocera communities indicate mostly limnetic conditions during the Allerød and early Younger Dryas. Peatland pools were supplied mostly by Luciąża River floods, but also by groundwater. Since the onset of the Holocene, the water level has dropped, eliminating aquatic midges and water fleas, and supporting taxa typical of astatic waters and wet soil.

Independent Arctic records of temperature and precipitation from the same proxy archives are rare. Nevertheless, they are important for providing detailed information on long-term climate changes and temperature-precipitation relationships in the context of large-scale atmospheric dynamics. Here, we used chironomid and cladoceran fossil assemblages to reconstruct summer air-temperature and water-level changes, during the past 400 years, in a small lake located in Finnish Lapland. Temperatures remained persistently cold over the Little Ice Age (LIA), but increased in the 20th century. After a cooler phase in the 1970s, the climate rapidly warmed to the record-high temperatures of the most recent decades. The lake-level reconstruction suggested persistently wet conditions for the LIA, followed by a dry period between similar to 1910 and 1970 CE, when the lake apparently became almost dry. Since the 1980s, the lake level has returned to a similar position as during the IAA. The temperature development was consistent with earlier records, but a significant local feature was found in the lake-level reconstruction the LIA appears to have been continuously wet, without the generally depicted dry phase during the 18th and 19th centuries. Therefore, the results suggest local precipitation patterns and enforce the concept of spatially divergent LIA conditions.

The sediment profile from Lake Gościąż in central Poland comprises a continuous, seasonally resolved and exceptionally well‐preserved archive of the Younger Dryas (YD) climate variation. This provides a unique opportunity for detailed investigation of lake system responses during periods of rapid climate cooling (YD onset) and warming (YD termination). The new varve record of Lake Gościąż presented here spans 1662 years from the late Allerød (AL) to the early Preboreal (PB). Microscopic varve counting provides an independent chronology with a YD duration of 1149+14/–22 years, which confirms previous results of 1140±40 years. We link stable oxygen isotopes and chironomid‐based air temperature reconstructions with the response of various geochemical and varve microfacies proxies especially focusing on the onset and termination of the YD. Cooling at the YD onset lasted ~180 years, which is about a century longer than the terminal warming that was completed in ~70 years. During the AL/YD transition, environmental proxy data lagged the onset of cooling by ~90 years and revealed an increase of lake productivity and internal lake re‐suspension as well as slightly higher detrital sediment input. In contrast, rapid warming and environmental changes during the YD/PB transition occurred simultaneously. However, initial changes such as declining diatom deposition and detrital input occurred already a few centuries before the rapid warming at the YD/PB transition. These environmental changes likely reflect a gradual increase in summer air temperatures already during the YD. Our data indicate complex and differing environmental responses to the major climate changes related to the YD, which involve different proxy sensitivities and threshold processes., National Science Centre, Virtual Institute of Integrated Climate and Landscape Evolution Analysis (ICLEA)

The sediment profile from Lake Gościąż in central Poland comprises a continuous, seasonally resolved and exceptionally well‐preserved archive of the Younger Dryas (YD) climate variation. This provides a unique opportunity for detailed investigation of lake system responses during periods of rapid climate cooling (YD onset) and warming (YD termination). The new varve record of Lake Gościąż presented here spans 1662 years from the late Allerød (AL) to the early Preboreal (PB). Microscopic varve counting provides an independent chronology with a YD duration of 1149+14/–22 years, which confirms previous results of 1140±40 years. We link stable oxygen isotopes and chironomid‐based air temperature reconstructions with the response of various geochemical and varve microfacies proxies especially focusing on the onset and termination of the YD. Cooling at the YD onset lasted ~180 years, which is about a century longer than the terminal warming that was completed in ~70 years. During the AL/YD transition, environmental proxy data lagged the onset of cooling by ~90 years and revealed an increase of lake productivity and internal lake re‐suspension as well as slightly higher detrital sediment input. In contrast, rapid warming and environmental changes during the YD/PB transition occurred simultaneously. However, initial changes such as declining diatom deposition and detrital input occurred already a few centuries before the rapid warming at the YD/PB transition. These environmental changes likely reflect a gradual increase in summer air temperatures already during the YD. Our data indicate complex and differing environmental responses to the major climate changes related to the YD, which involve different proxy sensitivities and threshold processes., National Science Centre, Virtual Institute of Integrated Climate and Landscape Evolution Analysis (ICLEA)