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We present here radiocarbon dating results from two boreal lakes In Finland, which are permanently (meromictic) or seasonally stratified and contain continuous sequences of annually laminated sediments that started to form In the early Holocene. The radiocarbon dating results of different organic components were compared with the varve-based sediment chronologies. The deviation between the Lake Valkiajarvi varve chronology (8400 varve years ±2-3% error estimate) and 33 14C dates taken from insoluble and soluble organic phases vary inconsistently throughout the Holocene. In extreme cases mean calibrated radiocarbon dates with 95.4% confidence levels (2σ) are -2350 and +2040 years offset when compared with the varve chronology. On average, the radiocarbon dates are offset by ca. +550 years. The deviation between the Lake Nautajarvl varve chronology (9898 varve years ±1% error estimate) and 26 14C dates analyzed with conventional and AMS methods indicates that radiocarbon dates are systematically older by 500-1300 years (about 900 years on average). This significant offset mean that radiocarbon dates obtained from organic bulk sediment of meromictic and seasonally hypoxic lakes must be cautiously interpreted because of the reservoir effect and carbon cycling at the sediment-water Interface. Direct evidence was obtained from the dating of soluble fraction and insoluble organic matter from near bottom water In the monimolimnion of Lake Valkiajarvi, which yielded 14C ages of 560 ±80 BP and 2070 ±140 BP, respectively. Our study reinforces previous results that age-depth models based on bulk sediment radiocarbon dates obtained on sediments of stratified lakes are of limited value for accurate dating of changes in land use and especially the commence of agriculture. [ABSTRACT FROM AUTHOR] more...

The Early Metal Period (1800 cal BC-AD 300) of the Finnish inland regions is characterized by a scarcity of archaeological remains. Its latest stages, in particular, have proved to be difficult to interpret. This paper discusses the continuity of settlement in the Early Metal Period as indicated by archaeological survey and pollen-analytical data. The study area is situated in Repovesi National Park in southeastern Finland. The pollen analysis was constructed from a sediment sequence taken from Lake Katajajarvi. The archaeological survey data from Repovesi National Park supports earlier hypotheses of the small number of Early Metal Period sites. In the pollen data, the first anthropogenic impact is recorded from about 2600 BC onwards, with weak signs of cultivation around 2370 BC. From around 1900 BC onwards a clear change in tree, shrub and herb pollen percentages indicates anthropogenic impact, possibly grazing, in the area. The pollen-analytical results also revealed a cultivation period of about 900 years at the end of the Early Metal Period, providing proof of continuity in settlement during a period characterized by a scarcity of archaeological material. A new beginning of cultivation from cal AD 1160 to 1250 onwards can be considered as indicating population growth, developing settlements and the colonization of new areas. The results from Repovesi are challenging from an archaeological point of view, because they represent slash-and-burn cultivation that appears to have been practised in total wilderness conditions. Comparison of the Lake Katajajarvi results with other areas raises new questions that call for a discussion of early slash-and-burn cultivation in new perspective. [ABSTRACT FROM AUTHOR] more...

Model-based estimates suggest that lake sediments may be a significant, long-term sink for organic carbon (C) at regional to global scales. These models have used various approaches to predict sediment storage at broad scales from very limited data sets. Here, we report a large-scale direct assessment of the standing stock and sedimentation rate of C for a representative set of lakes in Finland. The 122 lakes were selected from the statistically selected Nordic Lake Survey database, they cover the entire country and the water quality represents the average lake water quality in Finland. Unlike all prior estimates, these data use sediment cores that comprise the entire sediment record. The data show that within Finland, aquatic ecosystems contain the second largest areal C stocks (19 kg C m−2) after peatlands (72 kg C m−2), and exceed by significant amounts stocks in the forest soil (uppermost 75cm; 7.2 kg C m−2) and woody biomass (3.4 kg C m−2). Kauppiet al.(1997). The Finnish estimate extrapolated over the boreal region gives a total C pool in lakes 19–27 Pg C, significantly lower than the previous model-based estimates. [ABSTRACT FROM AUTHOR] more...

High-resolution physical analyses (varve thickness and relative X-ray density) were conducted on a 3000-year varved sediment sequence in Lake Korttajärvi, central Finland. Climate and the local environment strongly influence the properties of the lake sediments, and, through a combination of physical proxies, severe and favourable climate periods and anthropogenic effects on sedimentation with an annual to decadal resolution could be detected. We observed previously identified historical climate periods in the Lake Korttajärvi varve record. The Medieval Climate Anomaly (often termed the Medieval Warm Period) of AD 980-1250, which is characterized by highly organic sediment and a minor minerogenic flux during mild winters, started and terminated abruptly, but also included a short (30-year) colder period lasting between AD 1115 and AD 1145. The Little Ice Age, however, was not clear in our record, although there were two minor cooling periods in AD 1580-1630 and AD 1650-1710. Natural variability in the sediment record was disrupted by increased human impact in the catchment area at AD 1720. There is a distinct positive anomaly in mineral matter accumulation between 907 and 875 BC, which indicates more severe climate conditions. This period exists contemporary with a cold event, recorded worldwide, c . 2800 years ago. [ABSTRACT FROM AUTHOR] more...

Several till-covered organic deposits, principally lake gyttja, in Finnish Lapland have been correlated with the last (i.e. Eemian) interglacial on the basis of their lithostratigraphic position and pollen stratigraphy. Most of the sequences are short, but together with three longer sequences from Finnish Lapland and one from Swedish Lapland (Leveäniemi) they provide a complete picture of Eemian vegetational and climatic development. The Tepsankumpu site was revisited, and the till-covered thick freshwater gyttja deposit was studied in detail for pollen in order to search for signals of rapid climatic fluctuations postulated for the earlier part of the Eemian on the basis of Greenland ice core studies. The Eemian pollen stratigraphy in Finnish Lapland closely resembles the Holocene pollen stratigraphy of the area. The abundance of spruce and alder pollen suggests, however, more northerly limits for forest vegetation zones during the Eemian than during the Holocene. Oak also grew closer to Lapland, indicating a warmer climate than during the Holocene climatic optimum. The Tepsankumpu pollen stratigraphy indicates climatic stability over the entire time-span it covers, i.e. the major part of the interglacial. This finding is in conflict with results from Greenland GRIP ice core studies and interpretations of some Continental European Eemian pollen diagrams. [ABSTRACT FROM AUTHOR] more...

Based on field investigations in northern Russia and interpretation of offshore seismic data, we have made a preliminary reconstruction of the maximum ice-sheet extent in the Barents and Kara Sea region during the Early/Middle Weichselian and the Late Weichselian. Our investigations indicate that the Barents and Kara ice sheets attained their maximum Weichselian positions in northern Russia prior to 50 000 yr BP, whereas the northeastern flank of the Scandinavian Ice Sheet advanced to a maximum position shortly after 17 000 calendar years ago. During the Late Weichselian (25 000-10 000 yr BP), much of the Russian Arctic remained ice-free. According to our reconstruction, the extent of the ice sheets in the Barents and Kara Sea region during the Late Weichselian glacial maximum was less than half that of the maximum model which, up to now, has been widely used as a boundary condition for testing and refining General Circulation Models (GCMs). Preliminary numerical-modelling experiments predict Late Weichselian ice sheets which are larger than the ice extent implied for the Kara Sea region from dated geological evidence, suggesting very low precipitation. [ABSTRACT FROM AUTHOR] more...