Environmental significance of magnetic properties of Gley soils near Rosslau (Germany)

Geophysical methods are widely applied to soils for resolving different tasks in precision agriculture, pollution evaluation, erosion estimation, etc. Environmental magnetic methods were applied in our study on a collection of soil samples from area near Rosslau (Germany), which was gathered on the basis of a field electromagnetic induction study. Magnetic laboratory analyses include magnetic susceptibility, isothermal remanent magnetization (IRM), anhysteretic remanent magnetization (ARM), thermomagnetic analyses for determination of the kind of magnetic minerals present in soils. The results reveal the presence of statistically significant inverse correlations between magnetic susceptibility, as well as remanent magnetizations ARM and IRM, and conductivity values. This maybe ascribed to influence of topography and water regime on the iron oxide forms in soil and the influence of soil moisture on soil conductivity. Magnetic measurements on soil cores showed close correspondence between soil horizons outlined in 1 m-long cores, and depth changes in mass-specific magnetic susceptibility. Existing relationships between magnetic characteristics, soil reaction pH, and nutrients’ content (total nitrogen, carbon and sulphur) have been explored by cluster analysis and general regression model statistics. The results reveal the presence of significant correlations between nutrients’ content, magnetic susceptibility and the grain size sensitive ratio ARM/χ. These are expressed by numerical equations, representing pedotransfer functions, which predict the content of Nitrogen, Carbon and Sulphur through combination of magnetic parameters and soil pH. The obtained pedotransfer functions for the particular case of Gley soils and Fluvisols studied could be used for application of magnetic methods in agricultural practice as a fast and inexpensive proxy evaluation of the content of these nutrition elements.     

A MIS 3 charcoal and pollen record and quantitative precipitation inferences from the Jingerwa section of the Nihewan Basin,north-central China

Pollen and charcoal data from the Jingerwa section of the Nihewan Basin, north-central China, were used to reconstruct vegetation and climate changes during Marine Isotope Stage (MIS) 3. Mean annual precipitation changes were quantified by applying pollen-climate transfer functions. Sparse vegetation cover dominated by herbs indicates relatively dry climate between 51 and 43 cal ka BP. Between 43 and 35 cal ka BP, a Pinus-dominated forest reached its maximum extent, implying that climate was wetter than today. Severe fire episodes during that period suggest warm temperatures. Between 35 and 32 cal ka BP, forest retreat and the expansion of dryland vegetation are indicative of drier climates. Slightly wetter conditions prevailed between 32 and 29 cal ka BP, as indicated by the expansion of ferns. Our results suggest that the climate conditions in the Nihewan Basin during middle and late MIS 3 were probably wetter than today. This may have been caused by intensification of Asian monsoon circulation in response to greater insolation in June at 30°N. However, increases in summer temperatures and evaporation, triggered by peak summer insolation levels, may have led to a reduction in humidity around 35 cal ka BP.     

Subfossil Cladocera from surface sediment in thermokarst lakes in northeastern Siberia,Russia, in relation to limnological and climatic variables

Subfossil Cladocera were sampled and examined from the surface sediments of 35 thermokarst lakes along a temperature gradient crossing the tree line in the Anabar-river basin in northwestern Yakutia, northeastern Siberia. The lakes were distributed through three environmental zones: typical tundra, southern tundra and forest tundra. All lakes were situated within the continuous permafrost zone. Our investigation showed that the cladoceran communities in the lakes of the Anabar region are diverse and abundant, as reflected by taxonomic richness, and high diversity and evenness indices (H = 1.89 ± 0.51; I = 0.8 ± 0.18). CONISS cluster analysis indicated that the cladoceran communities in the three ecological zones (typical tundra, southern tundra and forest-tundra) differed in their taxonomic composition and structure. Differences in the cladoceran assemblages were related to limnological features and geographical position, vegetation type, climate and water chemistry. The constrained redundancy analysis indicated that T_July, water depth and both sulphate (SO₄ ^2?) and silica (Si⁴⁺) concentrations significantly (p ≤ 0.05) explained variance in the cladoceran assemblage. T_July featured the highest percentage (17.4 %) of explained variance in the distribution of subfossil Cladocera. One of the most significant changes in the structure of the cladoceran communities in the investigated transect was the replacement of closely related species along the latitudinal and vegetation gradient. The results demonstrate the potential for a regional cladoceran-based temperature model for the Arctic regions of Russia, and for and Yakutia in particular.     

Biomarker and compound-specific δ<Superscript>13</Superscript>C evidence for changing environmental conditions and carbon limitation at Lake Koucha,eastern Tibetan Plateau

A sediment core from Lake Koucha (eastern Tibetan Plateau) was investigated using organic biomarkers and their stable carbon isotope signatures. The correlation between TOC content, total amount of aquatic macrophyte-derived n-alkanes (e.g. nC₂₃) and δ¹³C values of TOC and nC₂₃ indicates that Lake Koucha was macrophyte-dominated before 8 cal ka BP. Shortly after the lake turned from a saline to a freshwater system at 7.2 cal ka BP, a variety of algal and bacterial markers such as hopanoids and isoprenoids emerged, of which phytane, pentamethylicosene (PMI), moretene and diploptene are particularly abundant. Phytane and PMI show different isotopic signals (≈−18 and ≈−28‰, respectively), which indicates that they originated from different sources. Phytane may have been derived from cyanobacteria, while methanogenic archaea may be the source of PMI. The isotopic depletion of diploptene and moretene (≈−60‰) indicates the presence of methanotrophs. After 6.1 cal ka BP, the saturated C₂₀ highly branched isoprenoid (HBI) became the dominant constituent of the aliphatic hydrocarbon fraction. Such dominance has rarely been reported in lacustrine environments, and indicates a strong presence of algae (most likely diatoms) or cyanobacteria. At 4.7 cal ka BP, the appearance of an unsaturated C₂₅ HBI, which is a specific biomarker for diatoms, was noted. Furthermore, the level of nC₁₇-alkane was observed to increase in abundance in the uppermost two samples. These results suggest that the lake was phytoplankton-dominated during the last 6.1 ka. Relatively low biomarker concentrations and δ¹³C values at 6.0, 3.1 and 1.8 cal ka BP indicate the occurrence of cool periods, which is in agreement with inferences from other locations on the Tibetan Plateau. The δ¹³C values of nC₂₃ range from −23.5 to −12.6‰, with high values at the peak of macrophyte abundance at ca. 11 cal ka BP and at the phytoplankton maximum between ca 6.1 and 2.8 cal ka BP. Thus, aquatic macrophyte-derived mid-chain n-alkanes have been found to be excellent indicators of carbon-limiting conditions, which lead to the assimilation of isotopically-enriched carbon species. The limitation of carbon sources could be a localized phenomenon occurring in dense plant stands (as in the older section of the core), or it may be induced by high primary productivity (as in the younger section). Since the δ¹³C value of the inorganic carbon source may vary, the offset between the δ¹³C values of nC₂₃ and TIC could serve as a more precise proxy for carbon-limiting conditions in lacustrine environments, which could in turn be interpreted with respect to lacustrine paleo-productivity.     

Biolaminoid facies in a peritidal sabkha: Permian Platy Dolomite of northern Poland

The Platy Dolomite, a carbonate unit in the Zechstein Formation (Upper Permian) of the Leba Elevation, Poland, was deposited in a semi-closed or completely separated back-barrier sabkha environment. This arid, hypersaline zone is comparable to the recent Gavish Sabkha, Sinai. The processes which formed the modern Gavish Sabkha are similar to those responsible for the biolaminoid formation in the Platy Dolomite series. The deposition of this Platy Dolomite was mainly the result of microbial activity building extensive microbial mats. The Platy Dolomite is characterized by loosely packed microbial biolaminoids (a less significantly laminated build-up of biogenetic sediments) with horizontally or obliquely to vertically orientated filaments. Intermediary coated grains occur. Densely packed, flat laminated stromatolitic rocks, pure oolites, and bioclastic sedimentary strata are rarely intercalated with the biolaminoid beds. Laboratory and field investigations indicate that carbonate formation was induced by the chemoorganotrophic bacterial decay of cyanobacterial mats. Magnesium was bound and absorbed by organic matter and later liberated by anaerobic decay. Early diagenetic processes formed Mg²⁺- and Ca²⁺-enriched solutions in which carbonates precipitated biologically and chemically. A system of biogenic carbonate formation of the Platy Dolomite microbiolite series is proposed and supported by the results of microbiological laboratory studies.     

Genetic implications of new lead isotope measurements on Schwarzwald vein and Upper Triassic sediment galenas

We report the results of a lead isotopic investigation of galena from vein deposits from the Southern Schwarzwald (33 samples) and from various localities (6) from the galena horizon of the South German Keuper. The total range of isotopic ratios for the veins and the Keuper leads is:18,29 <²⁰⁶Pb/²⁰⁴Pb < 18,97; 15,59 <²⁰⁷Pb/²⁰⁴Pb < 15,70; 38,42 <²⁰⁸Pb/²⁰⁴Pb < 38,90. The lead isotopic systems give anomalous ages when compared with lead evolution models ofHolmes (1946, 47)Houtermans (1946),Stacey &Kramers (1975) andCumming &Richards (1975). This indicates a more complex lead evolution than allowed for in these models.Small but significant variations in the isotopic ratios of lead were observed in galenas from within a number of veins and between veins. Also leads in galena from Hercynian veins within granitic host rocks in the Southern Schwarzwald were found to be more radiogenic than galena leads in veins found in gneisses in the Central Schwarzwald. These results strongly suggest a local influence on the lead isotopic compositions of the vein galenas and also place constraints on the age of the veins and models of vein formation.Galenas from Tertiary veins were found to have lower²⁰⁷Pb/²⁰⁴Pb ratios in comparison with ratios observed in Hercynian vein leads, suggesting that the Tertiary veins contain a compound of older retarded lead from a source not identified in the present study.The Keuper sedimentary galenas were found to have relatively homogenous lead isotopic ratios which fall within the range of isotopic compositions of the Hercynian vein leads. The galenas from the Upper Triassic (Keuper) are slightly more radiogenic than the more isotopically variable galena leads from the uppermost Permian (Kupferschiefer;Wedepohl et al. 1978).

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Zusammenfassung An Bleiglanzen von Gängen des mittleren und südlichen Schwarzwaldes (33 Proben) und von verschiedenen Lokalitäten (6) der Bleiglanzbank des süddeutschen Keupers wurden massenspektrometrische Blei-Isotopen-Untersuchungen durchgeführt.Die Werte fallen in die Bereiche: 18,29 <²⁰⁶Pb/²⁰⁴Pb < 18,97; 15,59 <²⁰⁷Pb/²⁰⁴Pb < 15,70; 38,42 <²⁰⁸Pb/²⁰⁴Pb < 38,90. Aus den Blei-Isotopenverhältnissen erhält man anomale Blei-Entwicklungsalter, wenn man die Modellevon Holmes (1946, 47),Houtermans (1946),Stacey &Kramers (1975) undCumming &Richards (1975) zugrunde legt. Das zeigt, daß die Entwicklung dieses Bleis komplexer ablief, als die genannten Modelle annehmen.Kleine aber signifikante Unterschiede in der Blei-Isotopenzusammensetzung wurden für Proben eines Gangsystems und zwischen den verschiedenen Gängen beobachtet. Das Blei aus Bleiglanzen von variscischen Gängen des St. Blasien-Granits (Südostschwarzwald) ist radiogener als das der Gänge in den Gneisen des Zentral-Schwarzwaldes. Diese Beobachtung zeigt, daß die Blei-Isotopenwerte mit der lokalen geologischen Situation verknüpft sind und ist von Bedeutung für die Diskussion der Alter und Entstehungs-modelle der Bleiglanze.Bleiglanz aus den als Tertiär angesehenen Gängen zeigt niedere²⁰⁷Pb/²⁰⁴-Verhältnisse als die variscischen Gang-Bleiglanze. Daraus kann man auf eine ältere zurückgebliebene Bleikomponente schließen, deren Quelle jedoch noch nicht gefunden wurde. Die Bleiglanze aus der Keuper-Bleiglanzbank ergaben relativ einheitliche Isotopenverhältnisse, welche in die Verteilung der Schwarzwälder Bleie fallen. Sie sind etwas radiogener als die isotopisch sehr variablen Bleiglanz-Isotopenwerte des Zechsteins (Kupferschiefer;Wedepohl et al. 1978).

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Résumé Une étude isotopique du plomb a été effectué sur des galènes provenant de filons de la Forêt Noire Centrale et du Sud (33 échantillons) et de différentes localités (6) de l'horizon à galène du Keuper du Sud de l'Allemagne.Les valeurs de plomb se situent dans les intervalles suivants: 18,29 <²⁰⁶Pb/²⁰⁴Pb < 18,97; 15,59 <²⁰⁷Pb/²⁰⁴Pb < 15,70; 38,42 <²⁰⁸Pb/²⁰⁴Pb < 38,90.Les rapports isotopiques du plomb indiquent des âges d'évolution de plomb anormaux, si l'on prend pour base les modèles d'évolution deHolmes (1946, 47),Houtermans (1946),Stacey &Kramers (1975) etCumming &Richards (1975). Cela montre que l'évolution du plomb s'est déroulée d'une façon plus complexe que ne le supposent les modèles mentionnés. Des différences minimes mais significatives ont été observées dans la composition isotopique du plomb, pour des échantillons d'un système filonien et entre différents filons. Le plomb des galènes des filons hercyniens du granite de St. Blasien (Forêt Noire du Sud Est) est plus radiogénique que celui des filons trouvés dans les gneiss de la Forêt Noire Centrale. Cette observation montre que la composition isotopique du plomb est liée à la situation géographique locale et est d'une grande importance pour la discussion des âges et des modèles de formation des galènes.Les rapports²⁰⁷Pb/²⁰⁴Pb des galènes des filons considérés comme d'âge tertiaire sont moins élevés que ceux des galènes d'âge hercynien, ce qui permet de supposer une composante de plomb plus âgée, «retardée» dont on n'a pu jusqu'ici déceler la source. Le plomb des galènes du Keuper a une composition isotopique relativement homogène, qui se trouve dans la gamme de celle observée pour le plomb des galènes de la Forêt Noire. Leur plomb est légèrement plus radiogénique que celui des galènes du Zechstein qui a une composition isotopique très variable (Kupferschiefer;Wedepohl et al., 1978).

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— (33 ) (6 ) - . : 18,29 <²⁰⁶Pb/²⁰⁴Pb < 18,97; 15,59 <²⁰⁷Pb/²⁰⁴Pb < 15,70; 38,42 <²⁰⁸Pb/²⁰⁴Pb < 38,90. , Holmes'a, 1946; Houterman'a, 1946, Stacey & Kramer'a, 1975 Cumming & Richard'a, 1975, . , , , ., , . St. Blasien (- ) , . , , . ²⁰⁷Pb/²⁰⁴Pb, . , . , . , , .

     

An ostracod-conductivity transfer function for Tibetan lakes

About 145 freshwater to hypersaline lakes of the eastern Tibetan Plateau were investigated to develop a transfer function for quantitative palaeoenvironmental reconstructions using ostracods. A total of 100 lakes provided sufficient numbers of ostracod shells. Multivariate statistical techniques were used to analyse the influence of a number of environmental variables on the distributions of surface sediment ostracod assemblages. Of 23 variables determined for each site, 19 were included in the statistical analysis. Lake water electrical conductivity (8.2%), Ca% (7.6%) and Fe% (4.8%, ion concentrations as % of the cations) explained the greatest amounts of variation in the distribution of ostracod taxa among the 100 lakes. Electrical conductivity optima and tolerances were calculated for abundant taxa. A transfer function, based on weighted averaging partial least squares regression (WA-PLS), was developed for electrical conductivity (r ² = 0.71, root-mean-square-error of prediction [RMSEP] = 0.35 [12.4% of gradient length], maximum bias = 0.64 [22.4% of gradient length], as assessed by leave-one-out cross-validation) based on 96 lakes. Our results show that ostracods provide reliable estimates of electrical conductivity and can be used for quantitative palaeoenvironmental reconstructions similarly to more commonly used diatom, chironomid or pollen data.     

Late Pleistocene to Holocene vegetation and climate changes in northwestern Chukotka (Far East Russia) deduced from lakes Ilirney and Rauchuagytgyn pollen records

This paper presents two new pollen records and quantitative climate reconstructions from northern Chukotka documenting environmental changes over the last 27.9 ka. Open tundra- and steppe-like habitats dominated between 27.9 and 18.7 cal. ka BP. Betula and Alnus shrubs might have grown in sheltered microhabitats but disappeared after 18.7 cal. ka BP. Although the climate was rather harsh, local herb-dominated communities supported herbivores as is evident by the presence of coprophilous spores in the sediments. The increase in Salix and Cyperaceae ~16.1 cal. ka BP suggests climate amelioration. Shrub Betula appeared ~15.9 cal. ka BP, and became dominant after ~15.52 cal. ka BP, whilst typical steppe communities drastically reduced. Very high presence of Botryococcus in the Lateglacial sediments reflects widespread shallow habitats, probably due to lake level increase. Shrub Alnus became common after ~13 cal. ka BP reflecting further climate amelioration. Simultaneously, herb communities gradually decreased in the vegetation reaching a minimum ~11.8 cal. ka BP. A gradual decrease of algae remains suggests a reduction of shallow-water habitats. Shrubby and graminoid tundra was dominant ~11.8–11.1 cal. ka BP, later Salix stands significantly decreased. The forest-tundra ecotone established in the Early Holocene, shortly after 11.1 cal. ka BP. Low contents of green algae in the Early Holocene sediments likely reflect deeper aquatic conditions. The most favourable climate conditions were between ~10.6 and 7 cal. ka BP. Vegetation became similar to the modern after ~7 cal. ka BP but Pinus pumila came to the Ilirney area at about 1.2 cal. ka BP. It is important to emphasize that the study area provided refugia for Betula and Alnus during MIS 2. It is also notable that our records do not reflect evidence of Younger Dryas cooling, which is inconsistent with some regional environmental records but in good accordance with some others.     

Antarctic shallow water benthos in an area of recent rapid glacier retreat

The West Antarctic Peninsula is one of the fastest warming regions on Earth. Faster glacier retreat and related calving events lead to more frequent iceberg scouring, fresh water input and higher sediment loads, which in turn affect shallow water benthic marine assemblages in coastal regions. In addition, ice retreat creates new benthic substrates for colonization. We investigated three size classes of benthic biota (microbenthos, meiofauna and macrofauna) at three sites in Potter Cove (King George Island, West Antarctic Peninsula) situated at similar water depths but experiencing different disturbance regimes related to glacier retreat. Our results revealed the presence of a patchy distribution of highly divergent benthic assemblages within a relatively small area (about 1 km²). In areas with frequent ice scouring and higher sediment accumulation rates, an assemblage mainly dominated by macrobenthic scavengers (such as the polychaete Barrukia cristata), vagile organisms and younger individuals of sessile species (such as the bivalve Yoldia eightsi) was found. Macrofauna were low in abundance and very patchily distributed in recently ice‐free areas close to the glacier, whereas the pioneer nematode genus Microlaimus reached a higher relative abundance in these newly exposed sites. The most diverse and abundant macrofaunal assemblage was found in areas most remote from recent glacier influence. By contrast, the meiofauna showed relatively low densities in these areas. The three benthic size classes appeared to respond in different ways to disturbances likely related to ice retreat, suggesting that the capacity to adapt and colonize habitats is dependent on both body size and specific life traits. We predict that, under continued deglaciation, more diverse, but less patchy, benthic assemblages will become established in areas out of reach of glacier‐related disturbance.