Danube loess stratigraphy - Towards a pan-European loess stratigraphic model

The Danube River drainage basin is the second largest river catchment in Europe and contains a significant and extensive region of thick loess deposits that preserve a record of a wide variety of recent and past environments. Indeed, the Danube River and tributaries may themselves be responsible for the transportation of large volumes of silt that ultimately drive loess formation in the middle and lower reaches of this large catchment. However, this vast loess province lacks a unified stratigraphic scheme. European loess research started in the late 17th century in the Danube Basin with the work of Count Luigi Ferdinand Marsigli. Since that time numerous investigations provided the basis for the pioneering stratigraphic framework proposed initially by Kukla (1970, 1977) in his correlations of loess with deep-sea sediments. Loess-palaeosol sequences in the middle and lower reaches of the Danube River basin were a key part of this framework and contain some of the longest and most complete continental climate records in Europe, covering more than the last million years. However, the very size of the Danube loess belt and the large number of countries it covers presents a major limiting factor in developing a unified approach that enables continental scale analysis of the deposits. Local loess-palaeosol stratigraphic schemes have been defined separately in different countries and the difficulties in correlating such schemes, which often change significantly with advances in age-dating, have limited the number of basin-wide studies. A unified basin-wide stratigraphic model would greatly alleviate these difficulties and facilitate research into the wider significance of these loess records. Therefore we review the existing stratigraphic schemes and define a new Danube Basin wide loess stratigraphy based around a synthetic type section of the Mošorin and Stari Slankamen sites in Serbia. We present a detailed comparison with the sedimentological and palaeoclimatic records preserved in sediments of the Chinese Loess Plateau, with the oxygen isotope records from deep-sea sediments, and with classic European Pleistocene stratigraphic subdivisions. The hierarchy of Danubian stratigraphic units is determined by climatically controlled environmental shifts, in a similar way to the Chinese loess stratigraphic scheme. A new unified Danube loess stratigraphic model has a number of advantages, including preventing confusion resulting from the use of multiple national schemes, a more transparent basis, and the potential to set Pleistocene palaeoenvironmental changes recorded in the Danube catchment area into a global context. The use of a very simple labelling system based on the well-established Chinese loess scheme facilitates interpretation of palaeoenvironmental information reported from the Danube Basin loess sites in a wider more accessible context that can be readily correlated world-wide. This stratigraphic approach also provides, for the first time, an appropriate framework for the development of an integrated, pan-European and potentially pan-Eurasian loess stratigraphic scheme. © 2015 Elsevier B.V

Lessons from the AMS 14C and OSL/IRSL-dating of the Dunaszekcső loess record, Hungary

Reliable chronologies are prerequisites of appropriate proxy interpretations from terrestrial archives of Quaternary climate and environmental change. Loess records may provide a wealth of paleoenvironmental information, yet they are usually poorly dated. This mostly means low resolution dating of loess profiles and also imprecise chronologies, i.e. age-depth models that have uncertainties of millennial magnitude. This prevents us from addressing issues like synchroneity of abrupt climatic/environmental events on millennial time scales. Two different means of dating are commonly applied for loess sequences: luminescence and radiocarbon dating. Major problems are low precision of luminescence ages and the general lack of organic macrofossils (e.g. charcoal) in loess that can reliably be dated using 14C. Other datable phases in loess are mollusc shells, rhizoliths and organic matter. Evidences are growing that rhizoliths are unreliable phases for 14C-dating and organic matter 14C ages are often seriously compromised by rejuvenation in loess sequences. Also mollusc shells are often regarded as unreliable material for 14C-dating, as they may incorporate 14C-deficient (or dead) carbon from the local carbonate-rich substrate during shell formation, thereby producing anomalously old ages by up to 3000 years. In this study an attempt has been made to address some of the dating issues and problems mentioned above by triple-dating (AMS 14C and OSL/IRSL) of the Dunaszekcső loess-paleosol sequence (South-Hungary). While the OSL/IRSL techniques directly date the sediment (quartz and K-feldspar grains) and provide burial ages, radiocarbon yield ages from phases like organic matter, mollusc shells and rhizoliths and determines the time elapsed since the living system was last in equilibrium with atmospheric 14C and became closed after burial. As revealed in this study all loess rhizoliths sampled at three different depths (4.00 m: 9744-10156 2σ age range in cal yr BP, 5.00 m: 8013-8167 cal yr BP and 6.00 m: 9534-9686 cal yr BP) yield Holocene ages, so absolute ages cannot be gained this way for loess deposition. As charcoals are widely accepted as phases yielding very reliable 14C ages, mollusc shell 14C ages were tested against charcoal ages. Here we focused on molluscs with smaller (< 10 mm) shells as some evidence exists that some species do not incorporate dead carbon into their shells or at least in low amounts. Our results demonstrate that Succinella oblonga and Vitrea crystallina yield statistically indistinguishable ages (2σ age ranges: 29990-30830 and 29600-30530 cal yr BP) when compared with the charcoal 14C age (29960-30780 cal yr BP, depth 8.20 m), and others like Clausilia sp. and Chondrula tridens give slightly older ages than the charcoals and show larger age anomalies (500-900 14C yr). Compared to the charcoal ages at 8.20-8.25 m depth, the post-IR IRSL225 age of 28520±1120 yr (2σ age range: 26280-30760 yr) from a depth of 7.75 m match quite well the charcoal ages (Dsz-Ch1, 2σ: 29960-30780 cal yr BP and Dsz-Ch2, 2σ: 29350-30150 cal yr BP). At the same time, the post-IR OSL approach seems to slightly underestimate (2σ: 20640-26960 yr), while the post-IR IRSL290 overestimate (2σ: 30260-37100 yr) the expected/true age of deposition at the respective depth (7.75 m). At a depth of 4.00 m, slight underestimation of mollusc AMS 14C ages (Trochulus hispidus, 2σ: 22370-22740 cal yr BP, Arianta arbustorum, 2σ: 24470-25120 cal yr BP) by post-IR OSL (2σ: 17140-21980 yr) and a moderate to significant overestimation by OSL (2σ: 26760-33800 yr) and post-IR IRSL290 (2σ: 27660-35740 yr) has been recognized. Again, the post-IR IRSL225 age (2σ: 23180-26900 yr) lies the closest to the AMS 14C ages. To decide which technique, AMS 14C or OSL/IRSL yields more accurate ages is not possible without independent absolute chronological data based on another method. Yet, we think that the consistent 14C ages of charcoals and small molluscs (two phases having very different origin and genesis) suggest that these ages are reliable and may reflect the real age of sedimentation. Clearly, the precision of 14C ages are an order of magnitude better (calibrated 2σ age ranges 500-800 yr) than the luminescence ages (2σ age ranges: 3700-7900 yr) and this may be another reason for creating age-depth models based purely on 14C ages, if high precision is needed. The use of a mixture of ages (i.e. 14C and OSL/IRSL) seems to counterproductive in this respect and we suggest to separate the results of the two techniques in modeling. OSL/IRSL-based age models are useful in checking the accuracy of 14C-based chronologies for the last 50 ka and vice versa and proxy interpretations should be tested against both 14C and OSL/IRSL age models independently

Late Pleistocene millennial scale cycles of aeolian sedimentation in the Dunaszekcső loess record, south Hungary: preliminary data and interpretations

Millennial scale warm-cold oscillations in air temperature over Greenland and rapid sea surface temperature changes were recorded in ice cores and North Atlantic sediments for the last glaciation. These events must have been associated with profound environmental changes in Europe, and indeed, millennial scale oscillations in grain size records have been found in loess deposits of Europe and Asia. Unfortunately, the timing of these events are still unresolved due to chronological uncertainties on the order of thousands of years. Major problems are the low precision of luminescence ages and the general lack of materials that can reliably be dated using 14C. As demonstrated by 24 OSL/IRSL ages, the Dunaszekcső loess-palaeosol sequence is an archive of climate and environmental changes of the last glacial-interglacial cycles. For the upper part of the section (<33 cal yr BP), the chronology is further refined based on charcoal and mollusc shell radiocarbon ages. Here we show that AMS 14C ages of some mollusc species having small shells (<10 mm) seem to yield reliable ages in a comparison with charcoal 14C ages. These radiocarbon ages are consistent, have low variability and define age-depth models with sufficient precision to examine the timing of paleoenvironmental changes in the context of North Atlantic climatic variations. Bayesian age-depth modeling was performed using Bacon for a depth of 865-500 cm and a time span of 33-25 kyr based on 16 radiocarbon ages. Mean confidence ranges are 674 yr with a minimum of 416 yr at 630 cm and a maximum of 917 yr at 865 cm. Such a sub-millennial scale age model precision has formerly been unprecedented for loess profiles. Sedimentation rates calculated from the Bayesian age-depth model vary between 0.3 and 1.1 mm year‒1 (=m kyr‒1) with the maximum at 27.390±230 cal yr BP. Estimated bulk dust flux for the studied site and the given time span range from 493 to 1666 g m‒2 yr‒1, calculating with a dry density of loess of 1500 kg m‒3. Both the sedimentation rate and dust flux show millennial scale variations, together with the median grain size (Md) of bulk loess that is considered an integrated proxy of wind strength, dust source distance and source aridity. The Md proxy reveal sub-millennial scale variations, too, but the interpretation of such oscillations are far from straightforward. Nevertheless, the millennial scale variations in the Aeolian sedimentation imply strong and rapid changes in the frequency (and magnitude?) of dust storm events for the period of 33-25 kyr. Further preliminary observations are that grain size (Md) maxima lag behind the NGRIP dust peaks (Ca2+) by ca. 300-500 years and grain size minima closely follows Ca2+ and δ18O minima (GI-4 and 3). It must be noted, however, that the 300-500 years lags are within age model uncertainties

Two possible source regions for Central Greenland last glacial dust

Dust in Greenland ice cores is used to reconstruct the activity of dust-emitting regions and atmospheric circulation. However, the source of dust material to Greenland over the last glacial period is the subject of considerable uncertainty. Here we use new clay mineral and <10 µm Sr–Nd isotopic data from a range of Northern Hemisphere loess deposits in possible source regions alongside existing isotopic data to show that these methods cannot discriminate between two competing hypothetical origins for Greenland dust: an East Asian and/or central European source. In contrast, Hf isotopes (<10 µm fraction) of loess samples show considerable differences between the potential source regions. We attribute this to a first-order clay mineralogy dependence of Hf isotopic signatures in the finest silt/clay fractions, due to absence of zircons. As zircons would also be absent in Greenland dust, this provides a new way to discriminate between hypotheses for Greenland dust sources

High Risks of Losing Genetic Diversity in an Endemic Mauritian Gecko: Implications for Conservation

Genetic structure can be a consequence of recent population fragmentation and isolation, or a remnant of historical localised adaptation. This poses a challenge for conservationists since misinterpreting patterns of genetic structure may lead to inappropriate management. Of 17 species of reptile originally found in Mauritius, only five survive on the main island. One of these, Phelsuma guimbeaui (lowland forest day gecko), is now restricted to 30 small isolated subpopulations following severe forest fragmentation and isolation due to human colonisation. We used 20 microsatellites in ten subpopulations and two mitochondrial DNA (mtDNA) markers in 13 subpopulations to: (i) assess genetic diversity, population structure and genetic differentiation of subpopulations; (ii) estimate effective population sizes and migration rates of subpopulations; and (iii) examine the phylogenetic relationships of haplotypes found in different subpopulations. Microsatellite data revealed significant population structure with high levels of genetic diversity and isolation by distance, substantial genetic differentiation and no migration between most subpopulations. MtDNA, however, showed no evidence of population structure, indicating that there was once a genetically panmictic population. Effective population sizes of ten subpopulations, based on microsatellite markers, were small, ranging from 44 to 167. Simulations suggested that the chance of survival and allelic diversity of some subpopulations will decrease dramatically over the next 50 years if no migration occurs. Our DNA-based evidence reveals an urgent need for a management plan for the conservation of P. guimbeaui. We identified 18 threatened and 12 viable subpopulations and discuss a range of management options that include translocation of threatened subpopulations to retain maximum allelic diversity, and habitat restoration and assisted migration to decrease genetic erosion and inbreeding for the viable subpopulations

Results on mating disruption by sex pheromones against moth pests of apple in integrated and organic orchards

The study was aimed to study that how mating disruption by hand applied dispensers can reduce the number of damage caused by Cydia pomonella, Adoxophyes orana and Pandemis heparana in four integrated and organic apple orchards. In the first orchard (Gacsály), protection against moth caterpillars ensured by IPM and conventional production systems were equally good, but worse than that of the orchard part where mating disruption was applied by 1000 dispensers/ha. In second orchard (Nyírbogdány), the highest incidence of codling moth damage was measured in the hilly part (17%), while in the plot where 440 dispensers/ha pheromone dosage was applied, the damage incidence was 11%. The smallest damage incidence was at the flat part, where 666 dispensers /ha was applied. In the third and fourth orchards (Eperjeske), codling moth damage on fruits was below 7% in the larger and smaller orchards where 1000 dispensers/ha was applied. At Eperjeske, the codling moth damage increased by 32.3% in the field treated with Bacillus thuringiensis product but without using mating disruption. The results verified that the use of 1000 dispensers/ha as suggested by the manufactures is essential, especially in the first year of application. The results also suggested that better results can be achieved in flat areas and the larger plot size also enables a more efficient reduction of the damage

Results on mating disruption by sex pheromones against moth pests of apple in integrated and organic orchards

The study was aimed to study that how mating disruption by hand applied dispensers can reduce the number of damage caused by Cydia pomonella, Adoxophyes orana and Pandemis heparana in four integrated and organic apple orchards. In the first orchard (Gacsály), protection against moth caterpillars ensured by IPM and conventional production systems were equally good, but worse than that of the orchard part where mating disruption was applied by 1000 dispensers/ha. In second orchard (Nyírbogdány), the highest incidence of codling moth damage was measured in the hilly part (17%), while in the plot where 440 dispensers/ha pheromone dosage was applied, the damage incidence was 11%. The smallest damage incidence was at the flat part, where 666 dispensers /ha was applied. In the third and fourth orchards (Eperjeske), codling moth damage on fruits was below 7% in the larger and smaller orchards where 1000 dispensers/ha was applied. At Eperjeske, the codling moth damage increased by 32.3% in the field treated with Bacillus thuringiensis product but without using mating disruption. The results verified that the use of 1000 dispensers/ha as suggested by the manufactures is essential, especially in the first year of application. The results also suggested that better results can be achieved in flat areas and the larger plot size also enables a more efficient reduction of the damage

Characterization of a novel RNA polymerase II arrest site which lacks a weak 3′ RNA–DNA hybrid

Transcript elongation by RNA polymerase II is blocked at DNA sequences called arrest sites. An exceptionally weak RNA–DNA hybrid is often thought to be necessary at the point of arrest. We have identified an arrest site from the tyrosine hydroxylase (TH) gene which does not fit this pattern. Transcription of many sequence variants of this site shows that the RNA–DNA hybrid over the three bases immediately preceding the major arrest point may be strong (i.e. C:G) without interfering with arrest. However, arrest at the TH site requires the presence of a pyrimidine at the 3′ end and arrest increases when the 3′-most segment is pyrimidine rich. We also demonstrated that arrest at the TH site is completely dependent on the presence of a purine-rich element immediately upstream of the RNA–DNA hybrid. Thus, the RNA polymerase II arrest element from the TH gene has several unanticipated characteristics: arrest is independent of a weak RNA–DNA hybrid at the 3′ end of the transcript, but it requires both a pyrimidine at the 3′ end and a polypurine element upstream of the RNA–DNA hybrid