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Sedimentary evidence of extreme storm surge or tsunami events in the southern Baltic Sea (Rogowo area, NW Poland)

Piotrowski A., Szczuciński W., Sydor P., Kotrys B., Rzodkiewicz M., Krzymińska J.

Geological Quarterly

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2017

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Vol. 61, No. 4

973--986

EN

The Baltic Sea is not typically considered as an area affected by tsunamis. However, during the Late Pleistocene and Holocene several tsunami events have been interpreted from the sedimentary record, mainly in Sweden and Estonia. Furthermore, on the southern coast of the Baltic Sea, there are historical accounts of catastrophical marine floodings called “der Seebär” (“the Sea Bear”). Their descriptions reveal many features typical for tsunami, but their genesis remained unknown and sedimentary evidence for such events has not been found. Here we provide evidence of sandy event layers from the area of Rogowo, NW Poland – the area of historical catastrophic storms as well as “der Seebär” events. The study area is a low-lying coastal plain with an average elevation of –0.5 to +0.5 m a.s.l., protected from the open sea by beach and coastal dune systems up to 5 m high. Sedimentological, micropalaeontological and geochemical analyses along with AMS 14C dating were applied to sedimentary successions seen in 5 major trenches and 198 sediment cores up to 1.5 m long. Two sandy layers were identified in the peat deposits that developed on the plain during the last ~2000 years. They reveal a number of typical features of tsunami deposits (significant lateral extent and thickness, rip-up clasts, chemical and micropalaeontological evidence of marine origin), however, 14C dating along with the historical accounts revealed that the major layer, extending at least 1.2 km from the modern coasts, was probably deposited by arguably the largest storm surge during the last 2000 years, which took place in 1497 AD. These storm deposits were likely formed during inundation of the low-lying coastal plain after major breaching of coastal dunes resulting in tsunami – like flow pattern and thus similar sedimentological effects. A discontinuous sand layer of younger age (18th century) and sharing similar properties to the previous one may be related to “der Seebär” event or another storm surge. The study revealed that the southern Baltic Sea coast may be affected by much greater coastal flooding than known from more recent accounts and observations. Thus, the presented geological record should be taken as an example of a worst-case scenario in coastal zone risk assessment from natural hazards. These events left sedimentary deposits that resemble tsunami deposits. It is likely that, in similar settings where storm surges cause unidirectional inundation of a coastal plain, it may not be possible to establish whether the resulting deposits were laid down from storms or tsunamis.

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Czynniki zmian klimatycznych w środkowym i górnym plejstocenie : ich zapis geologiczny w osadach Oceanu Południowego oraz rdzeniach lodowych

Kotrys B.

Przegląd Geologiczny

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2016

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Vol. 64, nr 1

35--42

EN

Climate changes during the Pleistocene were driven by large-scale orbital perturbations as well as by internal feedbacks on the Earth. One of the main roles in climate modelling is played by the Southern Ocean that is a great source of sea ice, carbon dioxide, dissolved silica and nutrients. Numerous sediment and ice records derived from the Southern Ocean and Antarctica document high-resolution climatic changes that allow us a better understanding of global climate evolution. Consistently with the global climatic trend, several sea surface temperature (SST) records of the Southern Ocean are marked by a distinct shift from low to high glacial/interglacial variability around Termination V (T V), called the Mid-Brunhes Event (MBE). Prior to T V, the Southern Ocean’s SST displays lower values and low variability. It points to a distinct expansion of the Southern Ocean cold water masses and positional changes of hydrographical fronts during most of the lower Middle Pleistocene, which started in the Pliocene. Beside large climatic changes, several abrupt distinct warming and cooling phases have been recognized. Some of them (MIS 22–19, MIS 11 and MIS 5) show similarities to MIS 1, which could be used for future climate predictions. In this paper we would like to present the middle and late Pleistocene climatic mechanisms in the Southern Ocean, and to show SST changes in relation to the hydrographic frontal movement, sea ice development and CO2 oscillations.

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A multidisciplinary study on the palaeoenvironmental history of the Resko Przymorskie Lake spit during the Late Glacial and Holocene (the southern Baltic coast, NW Poland)

Sydor P., Krzymińska J., Rzodkiewicz M., Kotrys B.

Geological Quarterly

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2015

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Vol. 59, No. 3

531--550

EN

The paper presents the results of sedimentological and biostratigraphical analyses from the Resko Przymorskie Lake spit (NW Poland), supported by radiocarbon datings. The study has aimed to recognize the geological structure of the spit and its base and to recognize the palaeoenivronmental changes. Nine sedimentary series composing the Resko Przymorskie Lake spit have been distinguished (I–IX). The oldest sediments are the Vistulian Glaciation till (series I) and fluvioglacial sand and gravel (series II). In the Early Holocene, in the study area there was a river valley (series III) followed by a shallow water basin (series IV), which was replaced by a peat bog (series V). In the Atlantic (7.4 ka cal BP), the water level rose (Littorina transgression) and accumulation of lagoonal sediments started (series VI). Biostratigraphic analysis of deposits in series VI indicates a marine influence. In the Atlantic and Subboreal, the spit moved southwards and fine sand (series VII) was deposited on lagoonal gyttja and silt (series VI). In the western part of the study area, peat accumulated (series VIII), dated at 6.7 ka cal BP (Late Atlantic). The youngest series IX is composed of aeolian fine sand in white dunes that formed in the last 400 years.

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Rekonstrukcje paleotemperatur w strefie Frontu Polarnego Oceanu Południowego (sektor atlantycki) na podstawie środkowo-górnoplejstoceńskich promienic z odwiertu ODP Leg 177 Site 1091

Kotrys B.

Przegląd Geologiczny

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2014

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Vol. 62, nr 9

448--455

EN

Quantitative analysis of radiolarian assemblages, carried out at the Ocean Drilling Program (ODP) Leg 177 Site 1091 (Atlantic sector of the Southern Ocean), provides a well-established summer sea surface temperature (SSST) record from the Polar Front Zone extending back into the Middle Pleistocene at orbital- -submillennial resolution. In order to estimate the SSST, the Imbrie & Kipp method (IKM) and the artificial neural network (ANN) were applied. The SSST records derived from the IKM and ANN display close similarities in paleotemperature fluctuations, amplitudes and absolute values. The ANN-derived SSST estimations display a pattern of slightly more distinct warm events that is closest to the records obtained from EDC (EPICA Dome C) ice cores and ODP Site 1090. The warm events indicate a distinct shift in the extent of the Southern Ocean cold water sphere that must have affected the ocean–atmosphere–ice field interactions and the configuration of high-latitude wind fields. Consistently with the global trend of paleotemperature fluctuation, the SSST record is marked by a distinct shift from low to high glacial/interglacial variability around Termination V. Prior to Termination V, the SSST displays coldest values and low variability. It points to a distinct expansion of the Southern Ocean cold water masses and positional changes of hydrographical fronts during most of the lower Middle Pleistocene.