Quartz grains reveal sedimentary palaeoenvironment and past storm events: A case study from eastern Baltic

Sediment record collected from the coastal lake serves as a powerful tool for reconstructing changes in palaeoenvironment and understanding the potential signals of past storminess. In this study, we use several proxies from sediment of the Holocene Thermal Maximum at coastal Lake Lilaste, Latvia. We focus on surface texture of quartz grains from the mineral inorganic fraction as indicators of depositional environments. We then use this as a proxy for potential storm transport and combine with information on granulometry, diatom stratigraphy and chronology to answer the question whether flux of quartz grains in the lake originated from the sea or from the land. Analyses in a binocular and scanning electron microscope reveal that most of the investigated quartz grains originate from dwelling in the seawater and wave action in the nearshore zone. Grains representing very energetic subaqueous environment similar to storm events are also present. Terrestrial record is of minor significance and visible through occurrence of aeolian quartz grains. During drier and colder conditions, an influx of sand with aeolian imprint was delivered to the lake between 8500 and 7800 cal yr BP. Marine and terrestrial conditions alternated between 7800 and 6000 cal yr BP. Storm-induced grains were likely deposited three times: at 7300 cal yr BP, 6600–6400 cal yr BP, and 6200–6000 cal yr BP. Overall stable marine environmental conditions prevailed between 6000 and 4000 cal yr BP except of the last portion of terrestrial-induced sediment at 4100 cal yr BP

On the origin and processes controlling the elemental and isotopic composition of carbonates in hypersaline Andean lakes

H.J. and J.W.B. Rae acknowledge funding from the European Research Council under the European Union’s Horizon 2020 research and innovation program (grant agreement 805246).The Altiplano-Puna Plateau of the Central Andes hosts numerous lakes, playa-lakes, and salars with a great diversity and abundance of carbonates forming under extreme climatic, hydrologic, and environmental conditions. To unravel the underlying processes controlling the formation of carbonates and their geochemical signatures in hypersaline systems, we investigated coupled brine-carbonate samples in a high-altitude Andean lake using a wide suite of petrographic (SEM, XRD) and geochemical tools (δ2H, δ18O, δ13C, δ11B, major and minor ion composition, aqueous modelling). Our findings show that the inflow of hydrothermal springs in combination with strong CO2 degassing and evaporation plays an important role in creating a spatial diversity of hydro-chemical sub-environments allowing different types of microbialites (microbial mounds and mats), travertines, and fine-grained calcite minerals to form. Carbonate precipitation occurs in hot springs triggered by a shift in carbonate equilibrium by hydrothermal CO2 degassing and microbially-driven elevation of local pH at crystallisation. In lakes, carbonate precipitation is induced by evaporative supersaturation, with contributions from CO2 degassing and microbiological processes. Lake carbonates largely record the evaporitic enrichment (hence salinity) of the parent water which can be traced by Na, Li, B, and δ18O, although other factors (such as e.g., high precipitation rates, mixing with thermal waters, groundwater, or precipitation) also affect their signatures. This study is of significance to those dealing with the fractionation of oxygen, carbon, and boron isotopes and partitioning of elements in natural brine-carbonate environments. Furthermore, these findings contribute to the advancement in proxy development for these depositional environments.Peer reviewe

Development of the Būšnieku Lake and Changes of Environmental Conditions During the Holocene

Bakalaura darbā apskatīta nepieciešamība veikt pētījumus Būšnieku ezerā, jo tas ir lagūnas tipa ezers, kuru apdraud antropogēnā ietekme. Lai labāk izprastu, kādi pasākumi nepieciešami tā aizsardzībai, ieskaitot nozīmīgo Natura 2000 teritoriju – Būšnieku ezera krasts, ir svarīgi veikt pētījumus par tā attīstību. Pētījuma lauka darbos iegūto datu analīze (urbumu apraksti), sporu - putekšņu analīžu rezultāti, nogulumu datējumi, kā arī kartogrāfiskā materiāla analīze, tai skaitā Būšnieku ezera apkārtnes karte, ģeoloģiskā karte un ezera ģeoloģiskie šķērsgriezumi ļauj secināt, ka organogēnie nogulumi Būšnieku ezerā uzkrājušies kopš preboreāla laika līdz mūsdienām bez ievērojamiem pārtraukumiem, kā arī iegūts apstiprinājums versijai, ka Ancilus ezera līmenis Latvijas piekrastē ir bijis augstāks nekā Litorīnas jūras līmenis. Darbā ir 78 lapaspuses, tas sastāv no 3 nodaļām, ievada, secinājumiem, kopsavilkuma, literatūras saraksta un 8 pielikumiem. Atslēgas vārdi: Būšnieku ezers, lagūnas tipa ezers, putekšņu analīzes, radioaktīvā oglekļa 14C datēšanas metode.Būšnieku Lake is the lagoonal type lake, which is in endanger by the anthropogenic impact. For that reason it is necessary to research the development of the lake, to understand which is the best method to be used to protect an important territory of „Natura 2000” – Shore of Būšnieku Lake. Results of study including field works (coring, sediment description), pollen analysis, sediment datings, as well as, analysis of cartographic material, geological map and geological crossections of the lake, allow to conclude that Organogenic sediments in the Būsnieki Lake have been accumulated since the Preboreal until nowadays without obvious interruptions. The approval for the version of higher level of the Ancilus Lake than Littorina Sea level has been obtained. The bachelor work contains 78 pages, 3 chapters, introduction, conclusion, summary, list of literature used and 8 appendixes. Key words: Būšnieku Lake, lagoonal type lake, pollen analysis, radiocarbon 14C dating

A palaeocoastline reconstruction for the Käsmu and Pärispea peninsulas (northern Estonia) over the last 4000 years

The marine-freshwater environmental transition, i.e. basin isolation from the Limnea Sea, has been identified in two short sediment cores with respect to their diatom composition, loss-on-ignition and magnetic susceptibility content. The isolation level of the basins was dated by accelerator mass spectrometry radiocarbon measurements. The basins are situated on the southern coast of the Gulf of Finland between altitudes 5.5 and 3.9 m above sea level. The Lohja basin became isolated from the sea around 2300 cal yr BP and Käsmu basin around 1800 cal yr BP as a result of glacio-isostatic uplift. The total land upheaval rate that has been 2.6 mm yr –1 since 2500 cal yr BP has currently decreased to 2.0 mm yr –1. We present a GIS-based 3D palaeogeographic reconstruction of the palaeocoastline changes in northern Estonia for two peninsulas, Pärispea and Käsmu, as well as compose a shoreline displacement curve for the study area, which is a compilation of previous and ongoing investigations

Determining reference conditions of hemiboreal lakes in Latvia, NE Europe: a palaeolimnological approach

The current status of a lake can be evaluated via monitoring, but such data can only provide information about the last few decades to a century at best. In most cases, the natural state of a lake cannot be ascertained. This is even more challenging if the apparent anthropogenic effects on the environment over the last millennia are considered. We used data on fossil algae from five evenly distributed hemiboreal lakes in geographically different regions in Latvia, NE Europe to assess the amount of compositional change or turnover (i.e., the beta-diversity) in the algae datasets for the last 2000 years by using a Detrended Canonical Correspondence Analysis. Our results show that the algae turnover increases towards the present day with distinct shifts during times characterised by extensive and intensive agriculture establishment, and political and economic changes. Because the anthropogenic impact on the landscape and lakes before AD 1200 was relatively minor, we propose that algae composition at that time can be assumed to represent the natural reference conditions for most Latvian lakes.We used data on fossil algae to assess the beta-diversity in hemiboreal lakes in Latvia.Results show that the algae turnover increases towards the present day. Anthropogenic impact on the landscape and lakes were relatively minor before AD 1200.We propose that the natural reference conditions of lakes are prior AD 1200

Late-Holocene relative sea-level changes and palaeoenvironment of the Pre-Viking Age ship burials in Salme, Saaremaa Island, eastern Baltic Sea

Two unique Pre-Viking Age ship burials were found from Salme village, Saaremaa Island, eastern Baltic Sea, containing remains of seven men in the smaller and 34 men in the larger ship. According to the archaeological interpretations, these ships belonged to a viking crew possibly from the Stockholm-Mälaren region, eastern Sweden. Geoarchaeological research was conducted in the area to reconstruct Late-Holocene relative sea-level (RSL) changes and shoreline displacement to provide environmental context to these burials. In this paper we present a Late-Holocene shore displacement curve for the Saaremaa Island and GIS-based palaeogeographic reconstructions for the Salme area. The curve shows an almost linear RSL fall from 5.5 to 0.8 m a.s.l. between 1000 BC and 1300 AD with an average rate of 2 mm/year. A slowdown in regression may be attributed to accelerated sea-level rise after the Little Ice Age and during the industrial period, being consistent with the tide-gauge measurements from the 20th century. Palaeogeographic reconstructions indicate the existence of a strait in the Salme area during the burial of the ships. The eastern part of the strait with water depth up to 2.8 m was about 80–100 m wide. The relatively steep and wind-protected shores in that part of the strait were probably the best places in the area for landing the viking ships. According to sedimentological evidence and diatom data, the narrowing of Salme palaeostrait occurred between 1270 and 1300 AD. Salme I and II ships were buried at 650–770 AD into the sandy-gravelly coastal deposits which had accumulated there in the open coastal zone about 710–450 years earlier. Reconstructions show that the ships were located about 2–2.5 m above coeval sea level and more than 100 m from the coastline. Thus, both ships were probably moved from the shore to the higher ground for burial

Holocene relative shore-level changes and development of the Ģipka lagoon in the western Gulf of Riga

Holocene relative shore-level changes and development of the G ipka palaeolagoon in the western Gulf of Riga are reconstructed using multiproxy analyses by combining litho-, biostratigraphical and chronological data with remote sensing and geophysical data. The results show the development of the G ipka basin from the Ancylus Lake/Initial Litorina Sea coastal zone (before c. 9.1 cal. ka BP) to coastal fen (c. 9.1 to 8.4 cal. ka BP) and gradual development of the Litorina Sea lagoon (c. 8.4 to 4.8 cal. ka BP) and its transition to a freshwater coastal lake (c. 4.8 to 4.6 cal. ka BP), fen (c. 4.6 to 4.2 cal. ka BP), and river floodplain (since c. 4.2 cal. ka BP). The highest shorelines of the Ancylus Lake and Litorina Sea were mapped at an elevation of 12–11 and 9 m a.s.l., respectively. A new relative shore level (RSL) curve for the western Gulf of Riga was constructed based on RSL data from the G ipka area and from nearby Ruhnu Island studied earlier. The reconstruction shows that the beginning of the lastmarine transgressionin the western Gulf of Riga started at c. 8.4 cal. ka BP, and concurred with the 1.9 m RSL rise event recorded from the North Sea basin. Diatom analysis results indicate the existence of the G ipka lagoon between c. 7.7 and 4.8 cal. ka BP, with the highest salinityc. 6.1 cal. ka BP. During the existence of the brackish lagoon, settlement sites of the Neolithic hunter–gatherer groups existed on the shores of the lagoon in the period c. 6.0 to 5.0 cal. ka BP