Late Holocene Changes in Vegetation of the Mrągowo Lakeland (NE Poland) as Registered in the Pollen Record from Lake Salęt
Abstract Pollen analysis of sediments from the upper part of bottom deposits from Lake Salęt allowed reconstruction of main stages of the Late Holocene vegetation transformation in the Mrągowo Lake District (from ca. 3600 cal. years BC) and to correlate some of these changes with immigration and economic activity of local human groups. Significant spreading of secondary semi-natural birch forest, development of horn beam forest and increasing importance of anthropogenic open communities were the most characteristic features of vegetation evolution. A definite break down of elm took place between 2900 and 2500 cal. years BC, slightly after increased contribution of birch in wood lands. Disappearance of hazel around 1200 cal. years BC, accompanied by expansion of horn beam has been observed and should be linked with activity of the Ząbie-Szestno type culture and the Lusatian culture tribes during the Bronze Age, but not with a climate change. Considerable intensification of settlement processes recorded in the younger part of the Subatlantic chronozone was one of the important reasons that were responsible for quick changes in forest structure. Strong and continued deforestation started as early as the end of the 10th century AD and was substantially intensified in the first half of the 13th century.
Temporal variation of prehistoric human settlement recorded in the oxbow lake deposits of San river (Sandomierz Basin, SE Poland)
Abstract This study presents the sedimentological and pollen analysis, and radiocarbon dating of the palaeochannel fill deposits situated on the wide alluvial ridge on which 131 archaeological sites were discovered. The analyzed territory covers the right bank of the San river valley (in the area of the Leszno profile) with an area of 72.5 km2. Increase of fine-grain sand sediments, and the presence of redeposited fragments of clayey silts (soil aggregates) correlates well with the increase man’s activity in the 2nd and the 1st half of the 1 st millennia BC (the decline of the Mierzanowice culture, the Trzciniec culture, the Tarnobrzeg Lusatian culture) as well as in the 1st millennium AD (the Przeworsk culture and the early Medieval settlement) and with transformation of plant communities recorded in the palynological sequence. The layer of sediments at the depth of 85–69 cm with the highest proportion of the finest clay fraction may indicate the reduction of cultivation or abandonment of arable land (the pre-Roman (La Tène) period).
Ostracod-based environmental reconstruction over the last 8,400 years of Nam Co Lake on the Tibetan plateau
From a 332-cm long lacustrine core taken at 60 m water depth and 25 surface sediment samples taken at different water depth sites in Nam Co lake (4,718 m a.s.l.) in the middle-south part of the Tibetan Plateau, we identified nine species of ostracods (Crustacea: Ostracoda) belonging to six genera. Using lithological data, auto-ecological information of the recovered taxa and an ostracod-based transfer function for water depth reconstruction, we distinguished three main environmental stages over the past 8,400 years: during Stage I (8,400–6,800 yr BP), the climate changed from warm-humid to cold-humid, and eventually to cold-arid. The water depth of the site was much lower than today and changed from an estimated 50 to 20–30 m. During Stage II (6,800–2,900 yr BP), environmental conditions were again warm-humid, turning into a cold-arid episode. The lake water depth initially stayed much shallower than today, but then gradually deepened to around 50 m. At the earlier period of Stage III (2,900 yr BP–present), the climate became again warm-humid from cold-arid status. There was a cold-dry event between 1,700 and 1,500 yr BP, which intensified afterward while the surface run off weakened. Early in this stage, lake depth decreased slightly, but then it continuously deepened to 60 m. Our results revealed that central Tibet experienced wavily warm toward tendency in early Holocene, a shift from warm-humid to cold-dry conditions in the middle Holocene, and from warm-humid to cold-dry conditions in the late Holocene. They also show that ostracod assemblages are not only indicative of cold-warm conditions, but are also usable to imply the dry–wet status of a lake area by the inferring water depth variations. Finally, this study provides baseline data on (natural) climate change in this mountain region against which to compare global change impacts.