Diatom Analysis Research Articles

Environment of bottom sediments formation from the Lake Dedovo in the Voronya River valley (Kola Peninsula), according to diatom analysis (preliminary data)

Abstract. The study presents preliminary results of the species composition and distribution of diatoms in the core of bottom sediments of the Lake Dedovo located in the Voronya River valley (Kola Peninsula). It was determined that sedimentation occurred in the periglacial basin during Late glacial. After there was a large basin that connected with the sea, but this basin was freshwater due to the large influx of melt water. The level of this basin was at the same elevation for a long time at the beginning of the Holocene. According to preliminary radiocarbon dating, the isolation of the lake depression from a large freshwater basin occurred at the end of the Early beginning of Middle Holocene. Lake Dedovo develops as an independent basin with a diverse freshwater diatom flora after the isolation.

Detailed results of diatom analysis of bottom sediments from lake Big Miassovo (Chelyabinsk region, Russia)

Diatoms are good indicators of a variety of lake water conditions including salinity, pH, light availability, temperature and nutrient levels, but diatoms as palaeoindicators are relatively poorly studied in the Chelyabinsk region. The diatom results of analysis a 498 cm long continuous sediments core from the Lake Big Miassovo (Southern Urals, Russia) are presented. The core was collected in July 2018 from central part of the lake from a depth of 24 m. Diatom analysis of 51 samples revealed 124 taxa, belonging to 47 genera. Diatom diagram has been divided into two diatom zones and five subzones on the basis on changing diatom abundances and taxa composition. The predominance of cosmopolitan, alkaliphilic benthic, oligogalobic species with the growth under the moderate temperatures is noted. The prevalence of Handmannia comta diatom in sediments have been established. The first period reflected the stage of an oligotrophic-mesotrophic lake with a low water level. The second period is characterized by an increase in the number of planktonic species and diversity of diatoms communities, the formation of a deep water body in a warm climate.

Paleoecological reconstruction of ecosystem of Lake Imandra (Russia, Murmansk region) based on diatom analysis of sediments

Abstract. This paper provides information about diatom assemblages in sediments of large arctic reservoir (Lake Imandra). The distribution of the taxonomic composition and structure of diatoms for several centuries has been studied. The periods and causes of changes in the state of the lake ecosystem are determined, and a conclusion about future trends is made. The data obtained can be used for monitoring the ecological state of the environment and water bodies.

Comparative Analysis of Chloroplast Genomes of Thalassiosira Species

Thalassiosira is a species-rich genus in Bacillariophyta with important ecological contribution to primary productivity but can also pose negative impact on ecology by developing harmful algal blooms (HABs). However, genomic resources of only a few Thalassiosira species are currently available. Here, we constructed complete chloroplast genomes (cpDNAs) of six Thalassiosira strains (representing six Thalassiosira species T. rotula, T. profunda, T. nordenskioeldii, T. tenera, T. weissflogii, and Thalassiosira sp.), and compared them with published cpDNAs of other diatoms. Comparative analysis revealed that Thalassiosira cpDNAs have generally conventional and conserved quadripartite structure with important exceptions. Gene orders of cpDNAs of Thalassiosira sp. (CNS00561) and T. oceanica were different from that of other Thalassiosira species. Additionally, endosymbiotic gene transfers (EGT) were found to occur in the evolution of Thalassiosira cpDNAs. Furthermore, genomic regions of cpDNAs were found to be highly variable, which could be used to construct molecular markers for distinguishing Thalassiosira species with high resolution and high specificity. This study also demonstrated that Thalassiosira species emerged roughly around 51 MYA and diversified 17–28 MYA. Thalassiosira cpDNAs are not only valuable as super-barcode for phylogenetic analysis, but also important for functional and evolutionary analysis of diatoms.

Geological evidence of an unreported historical Chilean tsunami reveals more frequent inundation

Assessing tsunami hazards commonly relies on historical accounts of past inundations, but such chronicles may be biased by temporal gaps due to historical circumstances. As a possible example, the lack of reports of tsunami inundation from the 1737 south-central Chile earthquake has been attributed to either civil unrest or a small tsunami due to deep fault slip below land. Here we conduct sedimentological and diatom analyses of tidal marsh sediments within the 1737 rupture area and find evidence for a locally-sourced tsunami consistent in age with this event. The evidence is a laterally-extensive sand sheet coincident with abrupt, decimetric subsidence. Coupled dislocation-tsunami models place the causative fault slip mostly offshore rather than below land. Whether associated or not with the 1737 earthquake, our findings reduce the average recurrence interval of tsunami inundation derived from historical records alone, highlighting the importance of combining geological and historical records in tsunami hazard assessment.

Sediment sequence at Muhos, western Finland – a window to the Pleistocene history of the Scandinavian Ice Sheet

In this study, we analysed a ~54‐m sediment core consisting of Quaternary sediments overlying the Neoproterozoic Muhos Formation in central western Finland, adjacent to the Gulf of Bothnia. The sediments recovered were logged, and their sedimentological characteristics defined. Two fine‐grained sediment units were subjected to biostratigraphical studies using pollen and diatom analyses. In addition, two sand‐rich units and a wooden stick were dated by the optically stimulated luminescence (OSL) and 14C‐AMS methods. The core sediments were divided into six units, where several diamicton, sand and gravel, and silt‐and‐clay‐dominated beds were studied. The results indicate that the sediment succession of the core beneath the Holocene Litorina Sea and the Ancylus Lake sediments of the Baltic Basin were deposited in glacial and lacustrine environments that existed in the Oulu River valley during the time period between the Saalian glaciation (MIS 6) and the Holocene. The stratigraphical evidence, supported by the OSL ages, suggests that the Scandinavian Ice Sheet (SIS) entered the Muhos area during the Saalian glaciation, and at least during three separate time intervals in the Weichselian stage. Stratigraphically controlled and age‐bracketed evidence shows that the first Weichselian SIS advance extended further south in the eastern part of Fennoscandia than previously estimated, and that this ice growth phase occurred during the Early Weichselian Herning Stadial (MIS 5d). The subsequent ice growth phases occurred during the Middle (MIS 4) and Late (MIS 2) Weichselian substages. The lacustrine and littoral sediments of the Muhos core were correlated with the late Eemian interglacial (MIS 5e) and two Weichselian interstadials (MIS 5c and MIS 3).

Crawling and adhesion behavior of Halamphora sp. based on different parts of Folium Sennae-like film: Evaluation of analytical methods for anti-diatom experimental results

Anti-diatom testing is a basic method to evaluate the anti-fouling performance of coatings. Many existing results of anti-diatom performances are evaluated based on their attachment number or coverage area, ignoring the influence of the crawling and adhesion behavior of diatoms on the analysis results. Here, a Folium Sennae-like film with multiple structural units was prepared by considering the influence of diatom attachment behaviors on the analysis results. The anti-diatom performances of different parts (divided and called four parts: edge, surface, cross striation, and vertical pattern) on the Folium Sennae-like film were evaluated using the counting and area methods. Obviously, the anti-diatom performance of the Folium Sennae-like film was superior to that of epoxy resin without structure. Under equal areas, the average numbers of diatoms on the cross striation and the vertical pattern were similar to the surface. It was found that the attachment behavior of Halamphora sp. is affected by microstructure units, rather than the combined structure of which the scale is much larger than that of diatoms. Meanwhile, the average attachment area for the unit number of diatoms was calculated. The diatom attachment area without microstructure, surface, cross striation, or vertical pattern was 81.751, 106.950, 73.904, and 84.376 μm2, respectively. Moreover, the static and dynamic motion behaviors of Halamphora sp. were studied, and the theory for Halamphora sp. attachment was modeled in three dimensions. The variable morphology of Halamphora sp. lead to inaccurate results for diatom analyses based on the counting and area methods, which is summarized here. This study discusses the evaluation method of coatings by anti-diatom performance, further promoting the research of diatoms in the field of antifouling.

The Holocene History of the Diatom Community in a Small Water Body on Shemya Island (Aleutian Arc, USA): The Influence of Global and Local Environmental Changes

A diatom analysis of a peat deposit from Shemya Island (Aleutian Arc, USA) is performed, and the dynamics of the diatom community are described. According to the radiocarbon dating, the formation of the deposit began 9300 cal. years BP. Principal component analysis made it possible to relate the dynamics of the diatom community to certain environmental conditions and the factors that influenced the coastal ecosystems during its formation. The following factors (predictors) were considered: the influence of age, zoo- and anthropogenic effects, and changes in climatic conditions. Sea level change was the main driver of the diatom community in the studied water body having a continuous direct and indirect influence on the studied small water body, i.e., by bird colony formation and more humid and coastal conditions. Since 3000–2000 cal. years BP, the anthropogenic factor (hunting depression of the bird colony) also became significant. During the whole water body lifetime and following peat formation, the diatom community was influenced by groups of factors: global factors (e.g., sea level rise) caused gradual change of local factors, which resulted in smooth shifts in community. In contrast, local factor influence (bird colony rise and fall due to human activity) caused abrupt and transient shifts. We can hypothesize that the relatively stable global environmental conditions in the Late Holocene were an auspicious background to see abrupt changes due to influence of the zoogenic and anthropogenic factors. We believe that further works on the material from other islands will make it possible to form a general picture of changes in the diatom communities in the Holocene and interpret it in connection with climatic changes in the region.

Radiocarbon dating of historic mudflat sediments at Airth in the inner Forth estuary and the impact on the estuary of nineteenth century agricultural improvements

ABSTRACT The results of sediment-stratigraphic, diatom and pollen analyses, and AMS 14C dating of salt marsh sediments at Higgin’s Neuk, Airth in the inner Forth estuary in central Scotland are reported. Engineering borehole records of abundant peat within mudflat sediments encouraged work to establish rates of mudflat accretion over the last several centuries. However, six 14C assays on peat closely associated with buried archaeological structures of likely eighteenth century age record later prehistoric and early historic age-estimates. The assays are thought to be correct. The peat is not in situ. It probably originated from the well-documented, extensive late eighteenth and early nineteenth century clearance of raised mosses in the River Forth for agriculture. The sediment-stratigraphic evidence is important because it confirms the scale of the impacts of peat clearance on the inner estuary derived from contemporary documents. The peat may act as a marker horizon in mudflat and salt marsh sediments from which rates of post-eighteenth century mudflat accretion can be derived. At Higgin’s Neuk these were probably very high, given uncertainties in dating controls, around 0.8 cm/yr (1.2 yrs/cm) for the last ca. 150 years, a finding which accords with other studies around the North Sea.

Relationships between Diatom Abundances in Rat Organs and in Environmental Waters.

A diagnosis of drowning remains one of the most challenging issues in forensic science, especially for decomposed bodies. Diatom analysis is considered as an encouraging method for diagnosing drowning. In this study, we developed a drowned rat model using different diatom densities in water. A total of 120 adult Sprague-Dawley rats were used and divided into six groups, wherein experimental groups 1-5 were drowned rats (group A) and postmortem submersion rats (group B) that were submerged in water with five different Cyclotella sp. diatom densities, while the remaining group was used as a blank control. The combination of microwave digestion and vacuum filtration method was used to accomplish efficient tissue digestion and ascertain higher accuracy of diatom determinations within organs. The abundances of diatoms in the lungs, livers, and kidneys were significantly different. The diatom abundances in the lungs, livers, and kidneys were directly proportional to the water diatom densities, and specific quantitative relationships could be approximated by separate regression equations for each organ type. However, the trends associated with the diatom increases among organs slightly differed. In addition, the diatom abundances in the lungs, livers, and kidneys were all positively correlated. Diatoms were not observed in the postmortem submersion groups nor in the blank control groups. The results of this study provide valuable information for establishing a quantitative diatom framework for informing future forensic medicine efforts.

Diversity and Ecology of Diatoms in Pliocene Deposits of the Tunka Valley (Baikal Rift Zone)

Fossil diatoms are an excellent tool for reconstructing the palaeoenvironmental and palaeogeographic changes involving lacustrine systems. In this work, the diatom content of Pliocene sediments recovered from a core extracted in the Tunka Basin (Baikal Rift Zone, Russia) is described. Revealed by light and scanning electron microscopy, 170 species of diatoms were found. Benthic, alkaliphilic, indifferent, cosmopolitan, and oligosaprobe species predominated. Ecological, geographical, and stratigraphic analysis of diatoms showed two ecozones, differing in taxonomic diversity of species. From the data obtained, palaeoenvironmental conditions of these zone formations have been reconstructed. It was shown that during the period corresponding to sedimentation in Ecozone II, the reservoir was cooler, as suggested by the increase of arctic-alpine taxa. The absence of Baikal Pliocene endemics and the presence of local endemics in the Tunka core indicate that there was no geographical connection between the palaeolake of the Tunka Valley and Lake Baikal during the Pliocene.

Marine diatom remains as bioindicators of the uses of pre-Hispanic fishing gear recovered in ritual contexts at Huanchaco, north coast of Peru

The aim of this study is to test whether marine diatom remains recovered from archeological fishing implements (fishing nets and metal fishhooks) found at pre-Hispanic sites of the Huanchaco coastline, north coast of Peru, can be used as indicators to infer whether they were used, and if yes, how they were used by ancient fishermen before their burial ritual. The combined analysis and quantification of fragmented and complete diatom valves from the fishing implements and control samples, which can help to identify potential contaminations from soil deposits, can indicate if the fishermen used them in their daily subsistence activities. This study can help to infer which marine zones were exploited by these ancient fishermen. Marine diatom analysis results were combined with identified fish species consumed and later discarded in the site’s middens. An interesting pattern emerges from the preliminary results of combining both datasets: while all fishing nets were intensively used, metal fishhooks seem to have been very occasionally sunk in the sea. Although these results could simply be the outcome of the type of materials tested and conservation issues, it prompted us to evaluate how fishing technology was used during the first part of the Early Intermediate Period (100–400/450 cal. A.D.) along the north coast of Peru and its impact on the daily subsistence activities of ancient pre-Hispanic fishing settlements.

Acid Digestion Method for Extraction of Diatoms in Drowning Cases: A Review

Diatoms are single celled algae and is the most found phytoplankton in water sources like rivers, lakes, pools, ponds, etc. In cases of drowning, it becomes essential to prove that the person died due to drowning. In this aspect there are basically two conditions that need to be investigated, to prove it. The point of proving that it was an ante mortem drowning helps in determining the crime committed and plays a vital role in the conviction of the accused with the appropriate punishment. In ante mortem drowning the water is swallowed by the individual and since the person is still alive this water gets absorbed and enters the blood stream. Therefore, if a person was actually drowned which resulted in his or her death there is a possibility of finding some content of the water in which the drowning took place inside the individual and the region to look for this is the bone marrow. Further diatoms are the phytoplanktons that reach the bone marrow in cases of ante mortem drowning. Diatoms are present in all water bodies, but the species of diatoms present in each water body varies. Therefore, diatoms have been used in drowning cases to prove the person had drowned and the location where the drowning took place. The analysis of diatoms is still in the process of development. Since they have silica-based cell wall they are strong, and their analysis needs to be done in such a way that procedures employed should be accepted by the court as a valid protocol and subsequently admit the evidence in that particular case. Extraction of diatoms from bone samples is an important step to isolate diatoms from the human tissue. There are many ways to conduct this extraction, but the most efficient technique is not known. This study reviews the studies conducted on the acid digestion procedures for extracting diatoms and it is found that acid digestion method can be used for numerous types of samples. Some protocols were tweaked to get the best results but the basic utilization of acids like nitric acid, hydrochloric acid and sulphuric acid showed good results in the extraction of diatoms from samples of forensic significance.

Comparison of benthic diatom community structures on natural and artificial substrates in marine lake (Adriatic Sea)

In this study, the diatoms of three alternative habitats (epilithon, epiphyton and artificial sub-strate) were compared to understand the differences in composition on artificial and natural sub-strates. For this purpose, the samples were collected weekly between 11th August and 2nd Septem-ber 2016 at a sampling site in a shallow marine lake, Mrtvo More (Dead Sea) on Lokrum Island near Dubrovnik (South Adriatic, Croatia). In addition to detailed light microscopic analysis, ultrastructural analysis of benthic diatoms from Lake Mrtvo More was performed for the first time using scanning electron microscopy (SEM). A total of 97 taxa were identified in 12 samples. Cocconeis scutellum Ehrenberg and Halamphora coffeiformis (C.Agardh) Levkov were the most frequent taxa in the samples. Shannon-Wiener diver-sity index (H’) values varied from 1.78 (in September on Padina sp.) to 4.52 (in August on glass). According to non-metric multidimensional scaling ordination, there were two groups: epilithon and artificial glass substrate as Group1 and macroalgae as Group2. The results of the analysis showed that the diatom communities developing on artificial sub-strates accurately correspond to the diatom community of a rock substrate and thus can be used as a representative alternative tool for studies of epilithic diatoms in further experiments.

Pedocomplex buried under the Cabin of Peter the Great in St. Petersburg (1703): Genesis, properties and paleoenvironmental inferences

A study was conducted on the buried soils identified at the base of the foundation of the Cabin of Peter the Great in Saint Petersburg, Russia, to help trace the Late Holocene landscape evolution in the lower reaches of the Neva River. The Cabin is a small wooden house, which was the first residence of Peter the Great in a newly emerged Saint-Petersburg. The house was built of pine logs on the Neva River's right bank. The time of its construction is now regarded as the city's founding date (1703). The pedocomplex with two buried soils has not been truncated and retains a record of the depositional environment, pedogenesis, vegetation history, and human activity before the construction of the city of Saint Petersburg. This pedocomplex was studied using various field and laboratory methods including soil morphology at macro-, meso-, and microlevels, and a full set of microbiomorphic analyses (diatoms, pollen, spores, phytoliths, plant detritus, and amorphous organic matter) supported by radiocarbon dating. The sediment sequence was formed in a contrasting depositional environment. The microbiomorphic studies indicated that the initial substrate was formed in aquatic environments. The analysis of diatoms suggested that these sediments were accumulated as a result of the River Neva breakthrough from Lake Ladoga to the Gulf of Finland ca 3500 yrs BP, which provided additional evidence for the River Neva formation. Soil analyses revealed two inundation events, with the earlier flood related to the termination of the Lake Ladoga transgression (LT) and the breakthrough of the Neva River, whereas the latter flood was likely to be connected with an increase of the fluvial activity. Those two inundation events were followed by two stages of pedogenesis. Both soils indicated the hiatus in sedimentation and were represented by Subquatic Umbric Gleysols that were the most widespread indigenous soils in the XVII century. The pollen data suggest that human impact started at ca 800 yrs BP and eventually resulted in the deforestation and the initial agricultural exploration of the study area. Saint Petersburg is the only large city in Russia that could be at risk from flooding if the sea level rises due to continuing global warming. Our research shows that the city's historical center was twice subjected to flooding in the Late Holocene, even without rises in the sea level. Therefore, the detailed analysis of the environmental dynamics within the Lower Neva area and the assessment of its possible consequences for the city are of great importance.

The Holocene lake-evaporation history of the afro-alpine Lake Garba Guracha in the Bale Mountains, Ethiopia, based on δ18O records of sugar biomarker and diatoms

AbstractIn eastern Africa, there are few long, high-quality records of environmental change at high altitudes, inhibiting a broader understanding of regional climate change. We investigated a Holocene lacustrine sediment archive from Lake Garba Guracha, Bale Mountains, Ethiopia, (3,950 m asl), and reconstructed high-altitude lake evaporation history using δ18O records derived from the analysis of compound-specific sugar biomarkers and diatoms. The δ18Odiatom and δ18Ofuc records are clearly correlated and reveal similar ranges (7.9‰ and 7.1‰, respectively). The lowest δ18O values occurred between 10–7 cal ka BP and were followed by a continuous shift towards more positive δ18O values. Due to the aquatic origin of the sugar biomarker and similar trends of δ18Odiatom, we suggest that our lacustrine δ18Ofuc record reflects δ18Olake water. Therefore, without completely excluding the influence of the ‘amount-effect’ and the ‘source-effect’, we interpret our record to reflect primarily the precipitation-to-evaporation ratio (P/E). We conclude that precipitation increased at the beginning of the Holocene, leading to an overflowing lake between ca. 10 and ca. 8 cal ka BP, indicated by low δ18Olake water values, which are interpreted as reduced evaporative enrichment. This is followed by a continuous trend towards drier conditions, indicating at least a seasonally closed lake system.

Palaeoecological changes from 580 to 1220 CE from the Indo-Burma region: A biotic assessment from the Barak Valley of Assam, northeast India

The pollen and diatom analyses of soil samples from a 80-cm deep sedimentary core from the Barak valley of Assam provides an explicit understanding of vegetation, climatic and ecological change in the Indo-Burma region from 580 CE (1370 cal. years BP) to 1220 CE (730 cal. years BP). The impact of the Medieval Warm Period (MWP) has been well documented from palynological records. Based on changes in vegetation succession, the Mean Annual Temperature (MAT) and Mean Annual Precipitation (MAP) during four pollen phases CP (1–4) were calculated using the coexistence approach. Between 580 and 760 CE (pre-MWP), the occurrence of major riparian tree pollen taxa like Barringtonia, Duabanga and Sapotaceae along with scanty diatom occurrence indicates a warm and relatively less humid climate attributable to a weak Southwest monsoon with low seasonality. This changed to a strikingly enhanced seasonality from 760 to 940 CE (beginning of MWP), indicating the establishment of the dense forest around the lake under increased warm and humid climatic conditions. During the interval from 940 to 1220 CE (MWP peak), the average values of maximum MAT and MAP were the highest recorded (≈31 °C and ≈2250 mm, respectively). From 1220 CE onwards (post MWP), the decline in arboreal pollen coincides with an exponential rise in cereal pollen clumps and shrubby pollen like Melastoma, Clerodendrum and Justicia adhatoda along with the presence of anthropogenic indicator diatom taxa like Ulnaria ulna and Gomphonema indicating increased landscape changes due to human impact under a relatively less warm and humid climate. In many parts of the world, regional data coverage pertinent to the MCA warming has now reached a point which allows compiling palaeoclimate maps for well-defined time intervals. In this direction, future studies need to address the major climatic data gaps from the Indian sub-continent especially during the last millennia.

The foraminiferal record in the Holocene evolution of the Mecklenburg Bay (south-western Baltic Sea)

Abstract Foraminiferal assemblages were analyzed in a 620-cm long core retrieved from the central part of the Mecklenburg Bay (MB, south-western Baltic Sea) to aid in the reconstruction of environmental changes occurring in the area during the Holocene and to complement a set of previously investigated palaeoenvironmental proxies. A total of five foraminifera-based stratigraphic units were identified, including an initial 80-cm thick layer devoid of foraminifera. The next two units featured an increasing abundance of the foraminiferal assemblage dominated by the calcareous Ammonia group species. Nearly all the calcareous foraminifera found in the core were decalcified. Following the maximum abundance within the 470–410 cm layer, the foraminiferal abundance declined sharply and the assemblage’s dominance structure changed to domination of the agglutinated foraminiferal species, Eggerelloides scaber, which continued up to the top of the core and marked a pronounced shift in environmental conditions (shallower depth, lower salinity, more dynamic sedimentation conditions). The foraminifera-based stratigraphy of the core proved to be complementary to that emerging from previous analyses of diatoms and sediment geochemistry.

Human actions were responsible for both initiation and termination of varve preservation in Lake Vesij\xe4rvi, southern Finland

The influence of lake restoration efforts on lake bottom-water conditions and varve preservation is not well known. We studied varved sediments deposited during the last 80 years along a water-depth transect in the Enonsaari Deep, a deep-water area of the southernmost Enonselkä Basin, Lake Vesijärvi, southern Finland. For the last few decades, the Enonselkä Basin has been subject to ongoing restoration efforts. Varve, elemental, and diatom analyses were undertaken to explore how these actions and other human activities affected varve preservation in the Enonsaari Deep. In contrast to most varved Finnish lakes, whose water columns have a natural tendency to stratify, and possess varve records that span thousands of years, varve formation and preservation in Lake Vesijärvi was triggered by relatively recent anthropogenic stressors. The multi-core varve analysis revealed that sediment in the Enonsaari Deep was initially non-varved, but became fully varved in the late 1930s, a time of increasing anthropogenic influence on the lake. The largest spatial extent of varves occurred in the 1970s, which was followed by a period of less distinguishable varves, which coincided with diversion of sewage from the lake. Varve preservation weakened during subsequent decades and was terminated completely by lake aeration in the 2010s. Despite improvements in water quality, hypolimnetic oxygen depletion and varve preservation persisted beyond the reduction in sewage loading, initial aeration, and biomanipulation. These restoration efforts, however, along with other human actions such as harbor construction and dredging, did influence varve characteristics. Varves were also influenced by diatom responses to anthropogenic forcing, because diatoms form a substantial part of the varve structure. Of all the restoration efforts, a second episode of aeration seems to have had the single most dramatic impact on profundal conditions in the basin, resulting in replacement of a sediment accumulation zone by a transport or erosional zone in the Enonsaari Deep. We conclude that human activities in a lake and its catchment can alter lake hypolimnetic conditions, leading to shifts in lake bottom dynamics and changes in varve preservation.

Reconstruction of the geological history of the Lithuanian Maritime Region from MIS 6 to MIS 3

The Lithuanian onshore section of the south-eastern Baltic Sea region, or the so-called Lithuanian Maritime Region (LMR) – a belt several tens of kilometres wide along the Baltic Sea coast – is characterised by a complicated Quaternary structure and many of unsolved problems related to stratigraphy and palaeogeography. The inter-till lacustrine sediments widespread in the middle part of the Pleistocene thickness play a key role in solving the mentioned problems. The primary inter-till sediments were attributed, as a single lithostratigraphic unit, to the late Saalian Glaciation (MIS 6, Pamarys Sub-Formation; according to the Lithuanian Quaternary Stratigraphic Scheme). Subsequent detailed investigations show that the investigated inter-till succession represents a more complicated sediment complex formed over a wide time interval from the Saalian ice sheet decay at the very end of MIS 6 to the beginning of severe climate cooling during MIS 4. This standpoint is confirmed by the results of a few series of OSL and IR-OSL datings of inter-till sediments, as well as by data of pollen and diatom analysis. The more detailed stratigraphic subdivision of the inter-till sedimentary complex offers a new significant insight into the regional stratigraphic scheme of the Quaternary. As a result of the mentioned investigations, a new original reconstruction of the palaeogeographic situation in the LMR during the MIS 6 – MIS 3 time span was carried out. The lowermost part of the investigated inter-till sediments, attributed to MIS 6, could be correlated with the third MIS 6 warming in Northern Eurasia about 155 ka ago. The reconstruction of the palaeoenvironmental changes starting from MIS 6 and lasting to MIS 3 shows that the Eemian Sea MIS 5e in age was absent in the LMR, while part of the south-eastern Baltic Sea region was covered by a continental ice sheet during MIS 4 and, possibly, the very beginning of MIS 3.