Uued publikatsioonid geoloogia instituudi teadlastelt
Anneli Poska avaldas koos kaasautoritega artikli ajakirjas Climatic Change (WoS mõjufaktor IF 3.496; kategooria Q1)
Belle, S., Poska, A., Hossann, C., Tõnno, I. 2017. 14,000 years of climate-induced changes in carbon resources sustaining benthic consumers in a small boreal lake (Lake Tollari, Estonia). Climatic Change 145, 205-219. Published online: 16. September 2017.
In order to forecast the influence of future climate change on lake ecosystems, the paleolimnological approaches are needed to understand the impact of past climate variability. We reconstruct temporal changes in carbon resources sustaining chironomid biomass over the last 14,000 years, by means of carbon stable isotope analysis of subfossil chironomids (δ13CHC), with the aim of identifying the response of carbon processing in the benthic food web to climate change. We find a negative linear correlation between reconstructed summer mean air temperature and δ13CHC values, revealing that (i) the contribution of allochthonous organic carbon to the chironomid biomass is high during the coldest and low-productive period, (ii) the aquatic organic matter is the main carbon source during intermediate climate conditions, and (iii) a significant part of the chironomid biomass is sustained by methane-derived carbon during the Holocene Thermal Maximum and the Bølling-Allerød. This study confirms that climate change may significantly affect the recycling process of organic carbon in the benthic food web of small lakes. However, deforestation and agricultural practices within the catchment area induced important organic matter inputs into the lake sediments, which seem to disrupt the observed relationship between climate variability and carbon processing in the benthic food web. In this context, complementary studies are needed to better understand the combined effects of the ongoing global warming and human activities on the lake carbon cycling.
Siim Veskil kaasautoritega ilmus veebiversiooni artikkel ajakirjas Review of Palaeobotany and Palynology (WoS mõjufaktor IF 1.817; kategooria Q1/Q2)
Stivrins, N., Soininen, J., Tõnno, I., Freiberg, R., Veski, S., Kisand, V. 2017. Towards understanding the abundance of non-pollen palynomorphs: A comparison of fossil algae, algal pigments and sedaDNA from temperate lake sediments. Review of Palaeobotany and Palynology xx, xx-xx. Published online: 10. November 2017.
Given the increased interest in non-pollen palynomorphs (microscopic objects other than pollen identified from pollen slides) in palaeoecological studies, it is necessary to seek a deeper understanding of the reliability of these results. We combined quantitative information of algal pigments and sedimentary ancient DNA (sedaDNA) of phylotaxonomical resolution to validate the richness and abundance of fossil algae in the sediment of a small temperate lake. For the first time, fossil and sedaDNA algae data were combined in a composite data-set and used to reconstruct algae turnover rates over the last 14,500 years. This comparison serves as both an example of how fossil algae can be used to answer various research questions and as a method of revealing to what extent we can rely on palaeoecological interpretations based solely on the fossil algae record from pollen slides.
Oliver Lehnertil ilmus veebiversiooni artikkel ajakirjas GFF (WoS mõjufaktor IF 1.142; kategooria Q2/Q3)
Muhamad, H., Juhlin, C., Sopher, D., Lehnert, O., Arslan, A., Meinhold, G. 2017. High-resolution seismic imaging of Paleozoic rocks in the Mora area, Siljan Ring structure, central Sweden. GFF xx, xx-xx. Published online: 23. October 2017.
The Late Devonian Siljan Ring structure in Sweden is the largest known impact structure in Europe. The present-day structure comprises a central dome that is about 20–30 km in diameter, which is surrounded by a ring-shaped depression. In this study, we focus on the southwestern part of the Siljan Ring with the aim to map the structure of the Paleozoic sedimentary rocks. Four 2D high-resolution seismic lines with a total length of about 3 km were acquired in the Mora area. A three component eighty-unit land streamer, combined with wireless recorders, was used for data acquisition along with a weight drop source. Processing of the data shows that clear reflections are present, but results are less distinct where external noise was present during acquisition or the maximum source-receiver offset was too short. Petrophysical measurements on core samples, core log data and a density model along one line were used to guide the interpretation of the seismic sections. These data demonstrate that fault blocks are present in the study area and that the individual blocks have been affected differently by impact-related tectonics.
Tõnu Martma avaldas koos kaasautoritega teadusartikli ajakirjas Atmospheric Chemistry and Physics (WoS mõjufaktor IF 5,318; kategooria Q1)
Ruppel, M.M., Soares, J., Gallet, J.-C, Isaksson, E., Martma, T., Svensson, J., Kohler, J., Pedersen, C.A., Manninen, S., Korhola, A., Ström, J. 2017. Do contemporary (1980–2015) emissions determine the elemental carbon deposition trend at Holtedahlfonna glacier, Svalbard? Atmospheric Chemistry and Physics 17, 12779-12795. Published online: 26. October 2017.
The climate impact of black carbon (BC) is notably amplified in the Arctic by its deposition, which causes albedo decrease and subsequent earlier snow and ice spring melt. To comprehensively assess the climate impact of BC in the Arctic, information on both atmospheric BC concentrations and deposition is essential. Currently, Arctic BC deposition data are very scarce, while atmospheric BC concentrations have been shown to generally decrease since the 1990s. However, a 300-year Svalbard ice core showed a distinct increase in EC (elemental carbon, proxy for BC) deposition from 1970 to 2004 contradicting atmospheric measurements and modelling studies. Here, our objective was to decipher whether this increase has continued in the 21st century and to investigate the drivers of the observed EC deposition trends. For this, a shallow firn core was collected from the same Svalbard glacier, and a regional-to-meso-scale chemical transport model (SILAM) was run from 1980 to 2015. The ice and firn core data indicate peaking EC deposition values at the end of the 1990s and lower values thereafter. The modelled BC deposition results generally support the observed glacier EC variations. However, the ice and firn core results clearly deviate from both measured and modelled atmospheric BC concentration trends, and the modelled BC deposition trend shows variations seemingly independent from BC emission or atmospheric BC concentration trends. Furthermore, according to the model ca. 99 % BC mass is wet-deposited at this Svalbard glacier, indicating that meteorological processes such as precipitation and scavenging efficiency have most likely a stronger influence on the BC deposition trend than BC emission or atmospheric concentration trends. BC emission source sectors contribute differently to the modelled atmospheric BC concentrations and BC deposition, which further supports our conclusion that different processes affect atmospheric BC concentration and deposition trends. Consequently, Arctic BC deposition trends should not directly be inferred based on atmospheric BC measurements, and more observational BC deposition data are required to assess the climate impact of BC in Arctic snow.
Heiki Bauert publitseeris koos kaasautoritega artikli ajakirjas Palaeogeography, Palaeoclimatology, Palaeoecology (WoS mõjufaktor IF 2.578; kategooria Q1/Q2)
Grappone, J.M., Chaffee, T., Isozaki, Y., Bauert, H., Kirschvink, J.L. 2017. Investigating the duration and termination of the Early Paleozoic Moyero Reversed Polarity Superchron: Middle Ordovician paleomagnetism from Estonia. Palaeogeography, Palaeoclimatology, Palaeoecology 485, 673-686. Published online: 26. July 2017.
Flat-lying Early and Middle Ordovician limestones exposed along the northern margin of Estonia provide key insights into the early Paleozoic biosphere and climatic history of the Baltic Platform and potentially offer a site for calibrating the duration of the proposed Moyero Reversed Polarity Superchron (MRPS). Past paleomagnetic analyses on these rocks have been focused primarily on determining paleomagnetic pole positions and have been hampered by relatively weak remanent magnetizations. We therefore applied techniques of the Rock and Paleomagnetic Instrument Development (RAPID) consortium using thin-walled, low-noise quartz glass sample holders on an automatic system to enhance magnetostratigraphic resolution. Our results, based on over 400 oriented core samples spanning the stratigraphic interval from the Volkhov Stage, into the Uhaku Stage (Dapingian and Darriwillian, Middle Ordovician), expand upon the results of previous work. We isolated a stable characteristic magnetization of reversed polarity and the presence of an interval of magnetically Reversed polarity lasting into the Middle Ordovician. The interval begins in the Dapingian and is interrupted by a short normal period in the mid-Darriwillian (concurrent with the Yangtzeplacognathus protoramosus conodont Subzone) before returning to Reversed polarity. In addition, we recognize a magnetic overprint of apparent normal polarity held in antiferromagnetic phases.
Peep Männik publitseeris koos kaasautoritega artikli ajakirjas Palaeogeography, Palaeoclimatology, Palaeoecology (WoS mõjufaktor IF 2.578; kategooria Q1/Q2)
Chen, Z., Männik, P., Fan, J. 2017. Llandovery (Silurian) conodont provincialism: An update based on quantitative analysis. Palaeogeography, Palaeoclimatology, Palaeoecology 485, 661-672. Published online: 27. July 2017.
The Llandovery conodont provincialism is reassessed based on a larger dataset than that which was available in 1990. The study interval is divided into two time units, the ‘Pre-Telychian’ and Telychian. Three quantitative methods are adopted in the biogeographic analysis, including cluster analysis, non-metric multidimensional scaling, and minimum spanning tree. In the ‘Pre-Telychian’ interval, four provinces can be recognized, i.e., the North American-Baltic-Siberian, Timan-Severnaya Zemlya, Australian, and Yangtze provinces. However, only three provinces can be recognized in the subsequent Telychian interval. The Timan-Severnaya Zemlya Province existed also in this time interval, but Austria and Australia are combined with the ‘Pre-Telychian’ North American-Baltic-Siberian Province and form a new province, the Baltic-Austrian-Siberian-Australian-North American Province (BASAN Province), while Tibet and the ‘Pre-Telychian’ Yangtze Province form the Chinese Province.
The conodont richness shows a latitudinal or temperature-dependent gradient. The conodont fauna was most diverse in the lower latitudes (tropical, arid and partly warm temperate climatic zones). However, the provincialism of the Llandovery conodont faunas demonstrates a longitudinal pattern, which cannot be the result of any latitudinal factors, such as temperature, but could be controlled by longitudinal factors, probably by the circulation of ocean currents. The circulation pattern can also explain the formation of the Telychian BASAN Province, which probably resulted from the Rheic and Panthalassa Ocean gyres. According to the conodont provincialism and the distribution of taxa, five types of conodont species can be recognized, including Limitedly distributed species, BASAN species, Equatorial species, Shallow-Sea Realm species, and Cosmopolitan species.
The conodont fauna showed a significant change in provincialism from the Ordovician to the Silurian, i.e., from a latitudinal pattern to a longitudinal pattern. The Hirnantian glaciation may be one of the controlling factors which resulted in the reorganization of the conodont faunas and the change of their living habits and ecological requirement.
Ursula Toom avaldas artikli ajakirjas Estonian Journal of Earth Sciences (WoS mõjufaktor IF 1.053; kategooria Q4)
Vinn, O., Toom, U., Isakar, M. 2017. The earliest cornulitid on the internal surface of the illaenid pygidium from the Middle Ordovician of Estonia. Estonian Journal of Earth Sciences 66, 193−197.
The earliest cornulitid Cornulites sp. appears in the Darriwilian (Lasnamägi Regional Stage) of Estonia. Internal annulation is present in all Middle Ordovician cornulitids and could be a plesiomorphic character for the group. The encrusted trilobites are rare in the Ordovician of Estonia. Illaenid pygidia and cranidia were encrusted by cornulitids and trepostome bryozoans. The encrustation of both Middle Ordovician and Late Ordovician trilobites took place post mortem. The studied hard substrate communities of Middle Ordovician and Late Ordovician trilobite pygidia and cranidia are typical of the Ordovician.
GI teadlased publitseerisid veebiversiooni artikli ajakirjas Lethaia (WoS mõjufaktor IF 2.281; kategooria Q1)
Hints, O., Antonovitš, L., Bauert, G., Nestor, V., Nõlvak, J., Tammekänd, M. 2017. CHITDB: a database for documenting and analysing diversification of Ordovician–Silurian chitinozoans in the Baltic region. Lethaia xx, xx-xx. Published online: 12. October 2017.
Chitinozoans are a key group in Ordovician and Silurian biostratigraphy, and the Baltic region hosts some of the largest collections of these microfossils in the world. Here, we present an online database – ‘CHITDB’ – for documenting and analysing the distribution of chitinozoans in the Baltic region. The system is integrated with the Estonian geocollections database and includes a public query portal (<http://chitinozoa.net>), which allows browsing and searching for chitinozoan taxa, samples, sections, references and SEM images, downloading raw data by sections, and generating range charts, summary reports and CONOP9 input files. The chitinozoan database holds currently over 35000 occurrence records of 300 chitinozoan taxa from 6400 micro-palaeontological samples and 100 sections. Quantitative stratigraphical analysis of this data set enabled compilation of the highest resolution chitinozoan diversity curves through the Ordovician and Silurian to date, and assessment of the rates of evolutionary changes. The new model incorporates K-bentonite and carbon isotope data that help to constrain time relationships between bioevents and environmental changes. The highest chitinozoan diversity in the Baltic region is encountered in late Darriwilian to mid-Katian and in the Telychian, when the standing diversity reached 30–35 species. Overall, the latest Ordovician and Silurian faunas show more dynamic diversity patterns, with higher extinction and origination rates, than was typical for most of the Ordovician Period.
Järeldoktorant Yan Liangil ilmus artikkel ajakirjas Review of Palaeobotany and Palynology (WoS mõjufaktor IF 1.817; kategooria Q1/Q2)
Liang, Y., Servais, T., Tang, P., Liu, J., Wang, W. 2017. Tremadocian (Early Ordovician) chitinozoan biostratigraphy of South China: An update. Review of Palaeobotany and Palynology 247, 149-163. Published online: 4. September 2017.
The lowest Ordovician (Tremadocian) chitinozoan biostratigraphy of the South China Palaeoplate has been reviewed and updated, based on new investigation from the Upper Yangtze area. The systematic paleontology of Lagenochitina pestovoensis Obut 1973 and Lagenochitina destombesi Elaouad-Debbaj 1988, has been revised. Previous identifications of L. destombesi from South China are considered questionable, and the L. destombesi Biozone, recognized from Baltica, northern Gondwana and peri-Gondwana, is therefore no longer used for the middle-upper part of the Tremadocian in South China. Two chitinozoan biozones are recognized, including the Lagenochitina pestovoensis Biozone (lower) and the Euconochitina symmetrica Biozone (upper) for the middle and upper part of the South Chinese Tremadocian. International correlation of the E. symmetrica Biozone indicates that the base of this biozone in South China is lower than the records in North America and northern Gondwana, and that the biozone is confined within the upper Tremadocian in South China.
Ursula Toom avaldas trükis artikli ajakirjas Palaeontology (WoS mõjufaktor IF 3.132; kategooria Q1)
Wright, D. F., Toom, U. 2017. New crinoids from the Baltic region (Estonia): fossil tip-dating phylogenetics constrains the origin and Ordovician–Silurian diversification of the Flexibilia (Echinodermata). Palaeontology 60, 893-910. Published online: 30. August 2017.
This study documents previously unknown taxonomic and morphological diversity among early Palaeozoic crinoids. Based on highly complete, well preserved crown material, we describe two new genera from the Ordovician and Silurian of the Baltic region (Estonia) that provide insight into two major features of the geological history of crinoids: the early evolution of the flexible clade during the Great Ordovician Biodiversification Event (GOBE), and their diversification history surrounding the end-Ordovician mass extinction. The unexpected occurrence of a highly derived sagenocrinid, Tintinnabulicrinus estoniensis gen. et. sp. nov., from Upper Ordovician (lower Katian) rocks of the Baltic palaeocontinent provides high-resolution temporal, taxonomic and palaeobiogeographical constraints on the origin and early evolution of the Flexibilia. The Silurian (lower Rhuddanian, Llandovery) Paerticrinus arvosus gen. et sp. nov. is the oldest known Silurian crinoid from Baltica and thus provides the earliest Baltic record of crinoids following the aftermath of the end-Ordovician mass extinction. A Bayesian ‘fossil tip-dating’ analysis implementing the fossilized birth–death process and a relaxed morphological clock model suggests that flexibles evolved c. 3 million years prior to their oldest fossil record, potentially involving an ancestor–descendant relationship (via ‘budding’ cladogenesis or anagenesis) with the paraphyletic cladid Cupulocrinus. The sagenocrinid subclade rapidly diverged from ‘taxocrinid’ grade crinoids during the final stages of the GOBE, culminating in maximal diversity among Ordovician crinoid faunas on a global scale. Remarkably, diversification patterns indicate little taxonomic turnover among flexibles across the Late Ordovician mass extinction. However, the elimination of closely related clades may have helped pave the way for their subsequent Silurian diversification and increased ecological role in post-Ordovician Palaeozoic marine communities. This study highlights the significance of studies reporting faunas from undersampled palaeogeographical regions for clade-based phylogenetic studies and improving estimates of global biodiversity through geological time.
Aivo Lepland ja Tõnu Martma kaasautoritega publitseerisid teadusartikli ajakirjas Chemical Geology (WoS mõjufaktor IF 3.347; kategooria Q1)
Sauer, S., Crémière, A., Knies, J., Lepland, A., Sahy, D., Martma, T., Noble, S.R. Schönenberger, J., Klug, M., Schubert, C.J. 2017. U-Th chronology and formation controls of methane-derived authigenic carbonates from the Hola trough seep area, northern Norway. Chemical Geology 470, 164-179. Published online: 12. September 2017.
We investigated methane-derived authigenic carbonate (MDAC) crusts and nodules from a cold seep site on the northern Norwegian continental shelf in ca. 220 m water depth to determine the timing and mode of their formation. Gas bubbling observed during remotely operated vehicle (ROV)-assisted sampling of MDAC crusts revealed ongoing seep activity. Authigenic carbonates were present as crusts on the seafloor and as centimetre-size carbonate-cemented nodules at several intervals within an adjacent sediment core. Aragonite-dominated mineralogy of the MDAC crusts suggests formation close to the seafloor at higher rates of sulphate-dependent anaerobic oxidation of methane (AOM). In contrast, dolomite-cemented nodules are consistent with the formation at the sulphate-methane-transition zone deeper within the sediment at lower rates of AOM. The δ13C-carbonate values of bulk rock and of micro-drilled aragonite samples vary between − 22.2‰ and − 34.6‰ (VPDB). We interpret the carbon in aragonite to be mainly derived from the anaerobic oxidation of thermogenic methane, with a minor contribution from seawater dissolved inorganic carbon (DIC). AOM activity is supported by high concentrations of AOM-related biomarkers of archaea (archaeol and 2-sn-hydroxyarchaeol) and sulphate-reducing bacteria (iso and anteiso-C15:0 fatty acids) in the crusts. The dolomite nodules exhibit higher δ13C-carbonate values (− 12‰ VPDB) suggesting a smaller amount of methane-derived carbon, presumably due to the contribution of DIC migrating from depth, and lower AOM rates. The latter is supported by orders of magnitude lower concentrations of archaeol and sn-2-hydroxyarchaeol in the sediment interval containing the largest dolomite nodules. δ18O values of pure aragonite samples and dolomite nodules indicate the precipitation of carbonate close to isotopic equilibrium with seawater and no influence of gas hydrate-derived water. U-Th dating of two MDAC crusts shows that they formed between 1.61 ± 0.02 and 4.39 ± 1.63 ka BP and between 2.65 ± 0.02 and 4.32 ± 0.08 ka BP. We infer both a spatial and temporal change in methane flux and related MDAC formation at this seep site. These changes might be caused by regional seismic events that can affect pore pressure or re-activation of migration pathways thus facilitating fluid flow from deep sources towards the seabed.
Peep Männikul ilmus artikkel ajakirjas GFF (WoS mõjufaktor IF 1.142; kategooria Q2/Q3)
Gubanov, A.P., Ebbestad, J.-O.R., Männik, P. 2017. The problematic mollusc Jinonicella from the Silurian of North America. GFF 139, 216-218. Published online: 09. March 2017.
The small problematic mollusc Jinonicella kolebabai Pokorný, 1978 is described from the lower Silurian Laketown Dolostone at Barn Hills in Utah, USA. The associated conodonts suggest a late Telychian age for the assemblage, which makes this the oldest occurrence of this species. Previous Silurian records of Jinonicella were known from the Sheinwoodian to Ludfordian of Bohemia, the Czech Republic, Gotland, Sweden and the Carnic Alps of Austria.
Anatoli Molodkovil ilmus veebiversiooni publikatsioon ajakirjas Quaternary International (WoS mõjufaktor IF 2.199; kategooria Q2/Q3)
Sokołowski, R.J., Janowski L., Hrynowieck, A., Molodkov, A. 2017. Evolution of fluvial system during the Pleistocene warm stage (Marine Isotope Stage 7) – A case study from the Błądzikowo Formation, N Poland. Quaternary International xx, xx-xx. Published online: 4. October 2017.
This paper discusses successive changes in the evolution of the fluvial system observed throughout the Błądzikowo Formation at the Mrzezino key site in northern Poland. The study focuses on the development of fluvial sedimentation during Marine Isotope Stage 7. The sedimentary record of the Pleistocene at the study site shows a well-developed sequence that is over 30 m thick. The Błądzikowo Formation shows a quick evolution of the fluvial system from a high-energy sandy braided river, to a meandering sandy river and, finally, to a low-energy meandering/anastomosing river with significant suspension settling. This transition is explained as a decrease in flow energy, increase in aggradation ratio and expansion of accommodation space during deposition time. A change in the fluvial system has not been manifested in the variations of the plant cover. Palynological analysis indicates that climate conditions were generally stable, cool and humid (boreal). Sediment transport occurred towards the N-NW, through a valley with a NW-SE axis. Infrared optically stimulated luminescence (IR-OSL) dating shows the sequence formed from 225.6 ± 17.2 to 210.5 ± 16.6 ka. Well preserved fluvial cycles and 35 m of thickness suggest the intensive accumulation of the Błądzikowo Formation with decreasing ratio of lateral erosion. It suggests an increasing influence of base level rise on evolution of fluvial system, mostly during MIS 7.
Ursula Toom ja kaasautorid avaldasid trükise ajakirjas Carnets de Géologie (WoS mõjufaktor IF 0.878; kategooria Q3)
Vinn, O., Ernst, A., Toom, U. 2017. Rare rugosan-bryozoan intergrowth from the Upper Ordovician of Estonia. Carnets de Géologie 17, 145-151. Published online: 16. October 2017.
Two relatively large specimens of the rugosan Lambelasma sp. are fully intergrown with the bryozoan Stigmatella massalis colony. The intergrown specimen occurs in the Oandu Regional Stage (lower Katian) of Estonia and constitutes the earliest record of bryozoan-rugosan intergrowth from Baltica. Most likely this symbiotic association was accidental. Rugosans presumably benefitted from the bryozoan, which served as an anchor to stabilize them in hydrodynamically active waters. The lack of malformations and no decrease in the size of bryozoan zooids near the rugosans indicate a lack of negative effect of the rugosans on the bryozoan. Bryozoan-rugosan symbiosis is only known from the Ordovician of Baltica and Laurentia.
Oliver Lehnertil ilmus artikkel ajakirjas Lethaia (WoS mõjufaktor IF 2.281; kategooria Q1)
Lefebvre, B., Gutiérrez-Marco J.C., Lehnert O., Martin E.L.O., Nowak H., Akodad M., El Hariri K., Servais T. 2017. Age calibration of the Lower Ordovician Fezouata Lagerstätte, Morocco. Lethaia xx, xx-xx. Published online: 19. September 2017.
The Fezouata Lagerstätte, discovered in the Lower Ordovician rocks of Morocco, is a Konservat-Lagerstätte of prime scientific importance. It provides access not only to the ‘shelly’ (skeletonized) part of its fossil assemblages, but also to non-biomineralized to lightly sclerotized organisms and to exceptionally preserved soft tissues of a complex ecosystem, mixing elements of both the ‘Cambrian Explosion’ and the ‘Great Ordovician Biodiversification Event’ (GOBE). The Fezouata Lagerstätte occurs at different intervals in the Fezouata Shale, a formation ranging from the lower Tremadocian to the upper Floian (Lower Ordovician). In spite of recent major advances in the detailed biostratigraphy of the Fezouata Shale, there is currently no consensus on the precise age of the fossiliferous levels yielding exceptionally preserved assemblages. Consequently, all available biostratigraphical evidence based on several fossil groups is here critically reviewed and discussed. It can be concluded that exceptional preservation is restricted to a few thin, discontinuous, lens-shaped horizons occurring in two distinct parts of the Fezouata Shale: a lower interval (260–330 m above the base of the formation) and an upper interval (570–620 m). Integrated biostratigraphical studies, essentially based on investigations of graptolites, acritarchs and conodonts, indicate that the lower interval can be correlated with the upper Tremadocian, whereas the upper interval corresponds to the middle Floian.
Siim Veski kaasautoritega publitseerisid ajakirjas Journal of Quaternary Science (WoS mõjufaktor IF 2.469; kategooria Q2)
Stivrins, N., Buchan, M.S., Disbrey, H.R., Kuosmanen, N., Latałowa, M., Lempinen, J., Muukkonen, P., Słowiński, M., Veski, S., Seppä, H. 2017. Widespread, episodic decline of alder (Alnus) during the medieval period in the boreal forest of Europe. Journal of Quaternary Science 32, 903-907. Published online: 7. September 2017.
We report pollen-stratigraphical evidence for an abrupt, episodic and widespread population decline of alder (Alnus), one of the most common boreal tree genera, during the medieval period in northern Europe. Decline of alder pollen values was observed both in forest hollow pollen records reflecting local vegetation of pristine forests and in pollen percentage and pollen accumulation data from lake sediments. The event began roughly at AD 600 and the recovery took place at AD 1000. Human impact is an unlikely cause because the decline is specific to alder and there is no evidence for a concurrent episode of human impact. It is possible that the decline was caused or influenced by a severe drought. Another potential cause is a sudden, widespread pathogen outbreak, especially as alder is known to be sensitive to the impacts of fungal pathogens such as the oomycete Phytophthora.
Doktorant Merlin Liiv koos kaasautoritega avaldas oma esimese esiautorlusega teadusartikli ajakirjas Vegetation History and Archaeobotany (WoS mõjufaktor IF 1.908; kategooria Q1/Q2)
Liiv, M., Alliksaar, T., Freiberg, R., Heinsalu, A., Ott, I., Tõnno, I., Vassiljev, J., Veski, S. 2017. Drastic changes in lake ecosystem development as a consequence of flax retting: a multiproxy palaeolimnological study of Lake Kooraste Linajärv, Estonia. Vegetation History and Archaeobotany xx, xx-xx. Published online: 29. November 2017.
This study demonstrates the power of multiproxy palaeolimnological analyses in investigating environmental changes in the Lake Kooraste Linajärv ecosystem through historical time in response to flax retting. Flax retting history was proven by applying pollen and macrofossil evidence and by using several biotic and geochemical proxies on a sediment core. Continuous findings of flax pollen and macrofossil remains in lake sediments were considered as strong evidence for the occurrence of retting. Analyses of the well-dated sediment core show the consequences of flax retting in the lake. As a result, the once clear soft water oligotrophic endorheic lake with limited sedimentation has turned into a hypertrophic high-sedimentation lake with anoxic bottom water, strong stratification and intense water blooms. Despite the fact that flax retting was forbidden in Estonia around ad 1950s and retting has not occurred over the last six decades, anthropogenic alterations were so pervasive in the past, that they have prevented any lake water improvements until the present-day.
Meie endised välisdoktorandid avaldasid veebiversiooni artikli ajakirjas Estuarine, Coastal and Shelf Science (WoS mõjufaktor IF 2.176; kategooria Q2)
Kalińska-Nartiša, E., Stivrins, N., Grudzinska, I. 2017. Quartz grains reveal sedimentary palaeoenvironment and past storm events: A case study from eastern Baltic. Estuarine, Coastal and Shelf Science xx, xx-xx. Published online: 28. November 2017.
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.