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Abstract

The article presents the results of a detailed study of the geological structure of the Łeba Barrier in the Rąbka cross-section (Southern Baltic, Poland). The barrier separates Lake Łebsko from the Baltic. Five sedimentary complexes were distinguished there (M2-M6). The spatial variability of the grain-size distribution was examined and succession stages of the mollusc fauna occurring in the individual sedimentary complexes were distinguished. Radiocarbon dating was used to establish the age of the most important events during the process of formation of the barrier, which took place in the course of several relative sea-level changes. The first sedimentary complex (M2) at Rąbka is connected with the second ingression (i2) of the Baltic Sea (ca. 6,700-6,000 14C years BP), sea-level stabilization (6,000-5,500 14C years BP), and at last sea-level lowering (5,500-5,000 14C years BP) in the region of the Gardno-Łeba Coastal Plain. The sedimentary complex M3 developed in a lagoonal environment when the barrier was situated north of its present position (5,000-3,000 14C BP). The next lowering of the sea-level made the lagoon shallower and caused the emergence of small but already subaerial stretches of barrier land with a freshwater fauna in the north (4,880š40 14C BP). With the next ingression stage (i3), which took place between 4,500 and 3,000 BP, the barrier shifted to its present-day position and the lagoon changed into a freshwater lake. From 3,000 to 1,700 14C BP fossil soil and peats developed on the barrier surface as a result of another sea-level lowering. The last ingression stages (i4 and i5), younger than 1,700 BP, built up the barrier, practically in its today's location (sedimentary complexes M4 and M5). The youngest sedimentary complex (M-6) is represented by present-day beach sands.

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Authors and Affiliations

Karol Rotnicki
Stefan W. Alexandrowicz
Anna Pazdur
Tomasz Goslar
Ryszard K. Borówka
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Abstract

We present the last millennium of history of a peatland located in northern Poland. Our results are based on two replicate monoliths taken from a Baltic raised bog. We applied a high-resolution approach and radio car bon dating to the peat material to obtain a de tailed palaeoenvironmental reconstruction. To reconstruct past peatland moisture, we used three prox ies: testate amoebae, plant macrofossils and pollen. Despite different peat accumulation and extensive hiatus in the formerly studied core, both monoliths show a similar pattern of changes. However, the core from this study provides us with more detailed data on S. fuscum disappear ance which correlates well with the data from the other Baltic bog, S³owiñskie B³oto. Our re search shows that pris tine Bal tic bogs can be dated to AD 1350. Słowiñskie Błoto palaeohydrology confirms AD 1300 as the beginning of the hydrological disturbance. In the case of the Stążki and Słowiñskie Błoto bogs, the Little Ice Age (LIA) is recorded between AD 1500 and AD 1800. However, this climatic change might have been blurred by human impact. In the case of the Baltic bogs, their reference virgin state can be dated to AD 1200. After this date, we observed in creasing human impact and climatic in stability connected with the LIA. However, between AD 1800 and 1900, bogs were wet, most possibly due to climatic forcing. This fact suggests that despite human impact, recent peat deposits can still reflect climate. Our research provided in formation related to the time of existence, location and characteristics of the natural/pristine state. High-resolution peatland palaeoecology is crucial for restoration activities, e.g., rewetting and environmental management. The palaeohydrological context (supported by other proxies) of the last 1000 years provides a reliable answer to the question: ‘To rewet or not to rewet?’

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Authors and Affiliations

Mariusz Lamentowicz
Mariusz Gałka
Jacek Pawlyta
Łukasz Lamentowicz
Tomasz Goslar
Grażyna Miotk-Szpiganowicz

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