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Climatic variation affects the physicochemical properties of geomaterials and its impact on the mechanical performance of infrastructure depends on the nature and origin of the material. The long-term behavior of sand, like any other construction material, can only be fully understood by evaluating its engineering properties under extreme climatic conditions such as repeated cycles of freezing-thawing (FT), wetting-drying (WD), and heating-cooling (HC). In this study, sand samples of different origin, including beach sand and dune sand (relatively aged sands), and quarry dust (relatively young grains) were subjected to 20 independent cycles of FT, WD, and HC. Scanning electron microscopy, x-ray diffraction, and x-ray fluorescence tests were performed for microstructural, surface texture, and chemical composition of the sand samples. Moreover, direct shear test results present the engineering properties such as peak shear strength, strain at failure, and friction angle of each sand sample at the end of various cycles. It is concluded that the findings of this study may provide an improved understanding of how natural sands of different origins respond to various environmental exposure conditions.

Aim: Hyper‐arid sandy and rocky fields rank among the least biologically diverse habitats of the desert biome, yet knowledge of local biodiversity patterns is also extremely poor. In the Sahara Desert, palaeoclimate oscillations affected the extent of hyper‐arid habitats, but it is unclear how these dynamics determined the evolution and distribution of local specialists. Herein, we assessed cryptic diversity, diversification patterns and spatial connectivity within a Sahara‐widespread group of dryland‐adapted lizards. Location: Sahara‐Sahel ecoregions. Taxon: Acanthodactylus scutellatus species group. Methods: Inter‐ and intraspecific phylogenetic structure, divergence times, spatial genetic patterns and cryptic diversity were assessed using nuclear and mitochondrial loci. The effects of topography and land cover on phylogeographic structure and diversity were tested with generalized linear models. Interspecific hybridization was evaluated using 11 microsatellites across the group's major sympatry zone, predicted based on ecological niche models. Results: Species of Acanthodactylus scutellatus group exhibit Late Miocene origins, followed by extensive intraspecific divergence throughout the Pliocene. The northern Sahara worked as a major diversification hotspot, harbouring a patchwork of small‐ranged, divergent lineages. These lineages are parapatric or sympatric and present concordant nuclear and mitochondrial differentiation, suggesting species status. Genetic connectivity increases in southern latitudes, with wide‐ranging lineages spanning from the Red Sea to the Atlantic coast. Within these potential corridors, mountain outskirts and sand fields in the Sahara interior seemingly acted as origins for recent population expansions. Genetic diversity and connectivity are favoured by terrain roughness and soft‐sand cover respectively. Three species inhabit the Atlantic Sahara sympatry zone without evidence of gene flow. Main conclusions: Overlooked species‐level diversity within a major specialist group of Sahara drylands exposes the recurrent knowledge shortfalls present in hyper‐arid desert environments. Humidity and sandy habitat shifts triggered potential successions of population isolation and re‐connectivity, which favoured cladogenesis in northern desert regions and population expansions across southern east–west corridors. [ABSTRACT FROM AUTHOR]

The formation and development of a small Mediterranean deltaic system are investigated through a primary seismic stratigraphic interpretation of a high-resolution seismic profile network, combined with multiple bathymetric data (including multibeam bathymetric imagery) and collated with shallow sediment cores collected with a vibro-corer device. The submarine delta of the Adra River is divided into a basal patchy seismic unit and five wedge-shaped younger seismic units that are related to the Holocene highstand stabilization. Limited age control indicates that the two uppermost seismic units are very recent, most likely related to a dearth of fluvial fluxes led by channel deviations and by sediment retention. The formation of the three older seismic units is correlated to three humid periods during the Middle Holocene, Late Holocene and Little Ice Age, under a general context of progressive aridification of southeastern Iberia. The stacking patterns and spatial distribution of individual seismic units document a history of episodic progradation of successive prodeltaic lobes, with a long-term evolution mediated by climatically-induced changes in the river basin and more recent anthropogenic interventions. Overall, the subaqueous deltaic system registers the complete modification of a deltaic system that evolves from a fluvial-dominated delta to recent wave-dominated wedges. In between, the deltaic system exhibits a progressive asymmetric character, due to the instauration of Atlantic waters on the shelf and their subsequent eastward redistribution. The Adra deltaic system is proposed as an outstanding example of a small deltaic system that reacts almost immediately to the complex interaction between natural changes in the system and anthropogenic interventions in the drainage basin. • The progressive growth and change of governing agents in a small deltaic system is reconstructed. • Late Holocene evolution from a fluvial-dominated delta to wave-dominated sediment wedges. • Distinct influences of climatic cycles and anthropogenic interventions. • Major phases of deltaic growth roughly correlate with other similar phases in the Mediterranean. [ABSTRACT FROM AUTHOR]

Abstract Aim To infer relationships between populations of the semi‐arid, mallee eucalypt, Eucalyptus behriana, to build hypotheses regarding evolution of major disjunctions in the species' distribution and to expand understanding of the biogeographical history of southeastern Australia. Location Southeastern Australia. Taxon Eucalyptus behriana (Myrtaceae, Angiospermae). Methods We developed a large dataset of anonymous genomic loci for 97 samples from 11 populations of E. behriana using double digest restriction site‐associated DNA sequencing (ddRAD‐seq), to determine genetic relationships between the populations. These relationships, along with species distribution models, were used to construct hypotheses regarding environmental processes that have driven fragmentation of the species’ distribution. Results Greatest genetic divergence was between populations on either side of the Lower Murray Basin. Populations west of the Basin showed greater genetic divergence between one another than the eastern populations. The most genetically distinct population in the east (Long Forest) was separated from others by the Great Dividing Range. A close relationship was found between the outlying northernmost population (near West Wyalong) and those in the Victorian Goldfields despite a large disjunction between them. Conclusions Patterns of genetic variation are consistent with a history of vicariant differentiation of disjunct populations. We infer that an early disjunction to develop in the species distribution was that across the Lower Murray Basin, an important biogeographical barrier separating many dry sclerophyll plant taxa in southeastern Australia. Additionally, our results suggest that the western populations fragmented earlier than the eastern ones. Fragmentation, both west and east of the Murray Basin, is likely tied to climatic changes associated with glacial‐interglacial cycles although it remains possible that major geological events including uplift of the Mount Lofty Ranges and basalt flows in the Newer Volcanics Province also played a role.

Aim: The biogeographic history of the Sahara‐Sahel desert is tightly linked to its extreme and fluctuating palaeoclimate and diverse topography. For the mesic species inhabiting the region, coastal areas and the Nile Valley are perceived as the main pathways to disperse through desert habitats, but past connections may have also occurred throughout currently isolated mountain regions. Herein, we test the trans‐Sahara mountain corridor hypothesis (i.e., mesic connectivity across Central Sahara highlands) and its role in the diversification of a small terrestrial vertebrate. Location: North Africa and Arabia. Taxon: Acanthodactylus boskianus (Squamata: Lacertidae). Methods: We integrated multi‐locus mitochondrial and nuclear phylogenies with species' climate‐niche modelling, including palaeo‐projections. Genetic analyses aimed to assess the species' genetic structure, identify its main mitochondrial lineages and nuclear diversity, and reconstruct its ancestral biogeography. Species' climate‐niche stability was modelled independently for the Late Pleistocene‐Holocene and the Plio‐Pleistocene, to infer historical climatic refugia and dispersal corridors. Results: Four spatially structured mitochondrial lineages, integrating several parapatric sub‐lineages, originated during the Plio‐Pleistocene. Nuclear data revealed nine potential candidate species. Climatic refugia were located in mountains and desert fringes, remaining consistent for the Late Pleistocene‐Holocene and the Plio‐Pleistocene. Recurrent North‐South climatic corridors were located along the desert periphery, while others less frequent were found across Central Sahara. Ancestral biogeography analyses recovered a recent Pleistocene colonization of the Sahel throughout eastern Sahara and either Sahara or Sahel origin for Central Sahara populations. Main conclusions: Species' diversification was triggered by a combination of Plio‐Pleistocene climatic cycles across a complex topographic region, where mountains acted as the main diversification hotspots. The historical role of Central Sahara highlands as main non‐peripheral mesic refugia was corroborated. In addition, intermittent climatic connections linked Mediterranean and Sahel ecoregions with Central Sahara refugia, suggesting the existence of alternative trans‐Sahara dispersal routes to the putative coastal and Nile corridors. [ABSTRACT FROM AUTHOR]

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The study of aquatic vegetation in the littoral of the dimictic water bodies of taiga is of particular interest in case of long-term observations carried out under conditions of climate fluctuations. During the low-water period, drying of the littoral with a decrease in the water level leads to the changes in phytomass of macrophytes, as well as in the composition of species and their distribution by depth. The area of littoral covered with ice in winter is also large in the low-water period; it affects the growth of perennial plants. When the water level decreases, the sand beach replaces the sand and pebble beach; it leads to the disappearance of epilithon and the predominance of rooting plants. The features of vegetation were determined for each period of water content. The low-water period is characterised mostly by grass-type vegetation; the high-water period is characterised by vegetation of mixed type.

Aim: To infer relationships between populations of the semi‐arid, mallee eucalypt, Eucalyptus behriana, to build hypotheses regarding evolution of major disjunctions in the species' distribution and to expand understanding of the biogeographical history of southeastern Australia. Location: Southeastern Australia. Taxon: Eucalyptus behriana (Myrtaceae, Angiospermae). Methods: We developed a large dataset of anonymous genomic loci for 97 samples from 11 populations of E. behriana using double digest restriction site‐associated DNA sequencing (ddRAD‐seq), to determine genetic relationships between the populations. These relationships, along with species distribution models, were used to construct hypotheses regarding environmental processes that have driven fragmentation of the species' distribution. Results: Greatest genetic divergence was between populations on either side of the Lower Murray Basin. Populations west of the Basin showed greater genetic divergence between one another than the eastern populations. The most genetically distinct population in the east (Long Forest) was separated from others by the Great Dividing Range. A close relationship was found between the outlying northernmost population (near West Wyalong) and those in the Victorian Goldfields despite a large disjunction between them. Conclusions: Patterns of genetic variation are consistent with a history of vicariant differentiation of disjunct populations. We infer that an early disjunction to develop in the species distribution was that across the Lower Murray Basin, an important biogeographical barrier separating many dry sclerophyll plant taxa in southeastern Australia. Additionally, our results suggest that the western populations fragmented earlier than the eastern ones. Fragmentation, both west and east of the Murray Basin, is likely tied to climatic changes associated with glacial‐interglacial cycles although it remains possible that major geological events including uplift of the Mount Lofty Ranges and basalt flows in the Newer Volcanics Province also played a role. [ABSTRACT FROM AUTHOR]

Buried or elevated coastal ridges may serve as archives of past variations in sea level and climate conditions. Sometimes such ridges or coastal scarps appear in patterns, particularly on uplifting coasts with adequate sediment supply. Along the seacoasts of Estonia, where relative-to-geoid postglacial uplift can vary between 1.7 and 3.4 mm/yr, at least 27 areas with rhythmic geomorphic patterns have been identified from LiDAR images and elevation data. Such patterns were mainly found on faster emerging and well-exposed, tideless coasts. These are mostly located at heights between 1 and 21 m above sea level, the formation of which corresponds to a period of up to 7500 years. Up to approximately 150 individual ridges were counted on some cross-shore sections. Ten of these ridge patterns that formed less than 4500 years ago were chosen for detailed characterization and analysis in search of possible forcing mechanisms. Among these more closely studied cases, the mean ridge spacing varied between 19 and 28 m. Using land uplift rates from the late Holocene period, the timespans of the corresponding cross sections were calculated. The average temporal periodicity of the ridges was between 23 and 39 years with a gross mean value of 31 years. Considering the regular nature of the ridges, they mostly do not reflect single extreme events, but rather a decadal-scale periodicity in storminess in the region of the Baltic Sea. Although a contribution from some kind of self-organization process is possible, the rhythmicity in ancient coastal ridge patterns is likely linked to quasi-periodic 25−40-year variability, which can be traced to Estonian long-term sea level records and wave hindcasts, as well as in regional storminess data and the North Atlantic Oscillation index.

Several tundra wader species occasionally nesting in the former Orenburg Province in the second half of the 19th century were reported by the prominent researchers of the avifauna of that region E.A. Eversmann, N.A. Zarudnyi, and P.P. Sushkin among others. In most cases, the scientists based their assumptions on circumstantial evidence alone, for instance, summer records of adult birds and migrating broods. Taking into account the specific biology of the species in question, such data could not be regarded as sufficient proof for the species' nesting. In the middle of the 20th century, these data were revised and quite justly criticized: this led to varying conclusions regarding the nesting of tundra wader species in the region as having been wrong. The matter seemed to be settled. Yet it should be noted that, along with circumstantial data on the nesting of northern waders, the early researchers had also reported very solid facts like finding nests with clutches of eggs and nonflying chicks (including the Red-necked Phalarope and the Little Stint). For certain reasons, those facts were not considered during the revision that followed. Firstly, it was difficult to find an explanation for such outstanding evidence in the middle of the 20th century. Secondly, no new nests of those species were found that could confirm the 19th century researchers as having been right. Furthermore, the idea that long-term cycles of climate changes influence the dynamics of bird nesting areas became widely accepted only by the end of the 20th century. Nowadays when this idea has been thoroughly developed, the possibility of the former nesting of some tundra wader species in arid regions does not seem so incredible. It seems likely that Zarudnyi and Sushkin were the last scientists to witness the nesting of tundra wader populations in the Orenburg region as over time due to climate warming the waders might have left the region for good. [ABSTRACT FROM AUTHOR]

The relationship between soil formation and sedimentation on the floodplain of the Utyaganka River (the Ural River basin) in the Arkaim Reserve (Chelyabinsk oblast, Southern Ural, Russia) was studied. Pedological, palynological, and mineralogical research methods were applied, and 15 radiocarbon dates of soil humus and sediments were obtained. The thickness of the Holocene sediments on the low floodplain is 4–5 m. Their top 1.5-m-thick layer formed in the recent 2000 yr contains three buried (partially superposed) soils formed at the mean rate of 13.3 cm/100 yr. Alluvial soddy soils with solonetzic and salinity features reflect intensive anthropogenic erosion in the river basin and characterize the Little Ice Age and the dry and warm Viking Age. At the depth of 1.5–5 m, there are up to five buried soils separated from one another by alluvium layers; they were formed in the period of 12 000–2000 BP at the rate of 1.9–3.1 cm/100 yr. Among them, the soils that developed 4200–2000 BP are characterized by varying humus content and solonetzicity; they are enriched with carbonates and reflect sharp fluctuations in atmospheric moistening against the background of dominating arid and continental climate. The soils formed 5500–4200 BP are gleyed, moderately humified, and calcareous; they testify to a more humid and warm climate than now. This period was characterized by the maximal area of forests (the pollen of tree species reaches 67%). The period of 8000–5500 BP was specified by warm and dry climate, which is indicated by soil properties and palynological data (15% of tree pollen). Soils formed 9500–8000 BP on stony proluvium-alluvium are eroded mucky gley soils; they reflect sharp fluctuations of the climate at the end of the glacial epoch. Floods were probably accompanied not only by alluvium accumulation but also by regular erosion of the surface and a decrease in the thickness of the humus horizon. This resulted in the renewal of soils and slowed down the increase in the thickness of humus horizon and in the intensity of alluvium accumulation. The average portion of humified soil layers reaches 26% of the total thickness of alluvial sediments. [ABSTRACT FROM AUTHOR]

Rainfall-induced landslides constitute a major cause of damage and fatalities throughout the intramontane basins of the Andes. The geological and climatic setting plays a key role in the generation of a high number of landslides in this area. For this reason, a greater understanding of the relationship between landslide frequency and climate conditions is necessary to mitigate human and economic losses. Accordingly, this paper presents an analysis of rainfall variables associated with a series of dated landslides (153 in total) in the southern Ecuador basin of Loja. This analysis was performed by applying an affordable empirical method that enables the calculation of critical rainfall threshold (CRT) curves. This calculation is based on an in-depth examination of rainfall parameters, such as cumulative precipitation and mean intensity, linked to a wide range of rainfall duration (from 1 to 90 days). The inspection of these parameters was addressed considering their frequency, which was calculated by using partial duration series (PDS), taking into account the entire rainfall record. This work has revealed that only 24% of landslides were triggered by rainfall conditions with maximum return periods greater than 1 year, whereas the rest did not exceed that return period. After finding the best correlation between the maximum return periods and the maximum mean intensity, a minimum power law function was adjusted to the CRT curve that correlates duration and cumulative rainfall. The values for this CRT function resulted in 5.14 and 0.83 for its scaling constant (α) and shape parameter (β), respectively. In addition, a spectral analysis was conducted to detect climatic cycles on the entire rainfall record. In general, a clear correlation could not be established between climatic frequencies and significant rainfall events inducing landslides, although similarly return periods were found for a critical rainfall event of March 2015 (10.4 years) and the SUNSPOT cycles (10.5-12 years). The results derived from this research are significantly valuable for the prevention of future mass-movements, although additional data will be crucial to update and calibrate CRT curves to study the influence of climate on landslide event frequency and magnitude in Loja. [ABSTRACT FROM AUTHOR]

This study proposes to combine seismic stratigraphic interpretation of very high-resolution sub-bottom chirp profiles acquired along the Santos Basin slope on the Southern Brazilian Margin during the SANBA project to recently published results from five continuous long cores acquired in the Santos Basin (sampling sediments as old as 772 ka with detailed biostratigraphic and chronostratigraphic data). The seismic-core correlation is consistent over the area and shows that 100,000 years cycles' terminations (G/IG transitions, identified on long sediment cores) do correlate to strong seismic reflectors identified regionally on chirp profiles. In particular, the last eight 100,000 years cycles (down to MIS19) are well-identified throughout the area. Additional higher-resolution sea-level drops or cooling events (e.g., MIS4, MIS7b, MIS9b) can sometimes be distinguished on the chirp profiles but only in areas with sufficiently high sedimentation rates (around 10 cm/ka). At MIS12, we observe a change in seismic architecture with more numerous, more closely spaced seismic reflectors but with smaller amplitudes. According to the available data, this change also corresponds to a change in sedimentation rates (smaller rates before MIS12), which may be related to the mid-Brunhes Transition (at 430 ka) and/or the imprint of 400 ka Milankovitch cycles. Two cores show a specific Nanno Foram Ooze at this transition towards the following Super-interglacial MIS11. This study demonstrates the ability and the reliability of very high-resolution chirp profiles to record continuously the stacking of G/IG climatic cycles on the slope of the Santos Basin despite relatively low subsidence rates on this old passive margin and small direct input from rivers. Therefore, the study points to the continuous feeding of the margin by sediment brought up laterally by currents, most probably mainly Brazilian Current (BC) that follows the shelfbreak down to the South. • Sub-bottom profiles from the slope of Santos Basin record Glacial/Interglacial transitions as prominent reflectors. • Reflectors correspond to change from silty clay and sand layers (during glacials) to Marl deposition during interglacial. • The last eight 100,000 years cycles (down to MIS19) are well identified on profiles and cores. • At MIS12, we observe a change in seismic architecture and sedimentation rates corresponding to the mid-Brunhes Event. [ABSTRACT FROM AUTHOR]

A simple statistical model is developed for the dynamics of the mean global annual temperature. The model combines the logarithmic effect of carbon dioxide concentration increase and the input by climatic cycles. Model parameters are determined from data of instrumental observations for 1850-2010. The model confirms the presence of climatic cycles with the period of 10.5 and 68.8 years in the global temperature dynamics. The trajectories of the global temperature changes for the XXI century are obtained under the scenarios of carbon dioxide concentration changes from the 5th IPCC Assessment Report. The comparison revealed that the global temperature trajectories from the Report are 0.9-1.8 °C above those obtained in the model.

Lithostratigraphic and magnetic-susceptibility logs for four sections in the Blue Lias Formation are combined with a re-assessment of the ammonite biostratigraphy. A Shaw plot correlating the West Somerset coast with the Devon/Dorset coast at Lyme Regis, based on 63 common biohorizon picks, together with field evidence, demonstrate that intra-formational hiatuses are common. Compared to laminated shale deposition, the climate associated with light marl is interpreted as both drier and stormier. Storm-related non-deposition favoured initiation of limestone formation near the sediment–water interface. Areas and time intervals with reduced water depths had lower net accumulation rates and developed a greater proportion of limestone. Many homogeneous limestone beds have no ammonites preserved, whereas others contain abundant fossils. Non-deposition encouraged shallow sub-sea-floor cementation which, if occurring after aragonite dissolution, generated limestones lacking ammonites. Abundant ammonite preservation in limestones required both rapid burial by light marl during storms as well as later storm-related non-deposition and near-surface carbonate cementation that occurred prior to aragonite dissolution. The limestones are dominated by a mixture of early framework-supporting cement that minimized compaction of fossils, plus a later micrograde cement infill. At Lyme Regis, the relatively low net accumulation rate ensured that final cementation of the limestones took place at relatively shallow burial depths. On the West Somerset coast, however, much higher accumulation rates led to deeper burial before final limestone cementation. Consequently, the oxygen-isotope ratios of the limestones on the West Somerset coast, recording precipitation of the later diagenetic calcite at higher temperatures, are lower than those at Lyme Regis. [ABSTRACT FROM AUTHOR]

Highlands, hydrographic systems and coastal areas have been hypothesised to form corridors across the hyperarid Sahara desert in North Africa, allowing dispersal and gene flow for non-xeric species. Here we aim to provide a genetic test for the trans-Saharan corridor model, and predict the location and stability of ecological-corridors, by combining phylogeography and palaeoclimatic modelling. The model was the Psammophis schokari (Schokari sand racer) group, fast-moving and widely distributed generalist colubrids occurring mostly in arid and semiarid scrublands. We combined dated phylogenies of mitochondrial and nuclear markers with palaeoclimatic modelling. For the phylogeographic analysis, we used 75 samples of P. schokari and P. aegyptius , and Bayesian and Maximum-Likelihood methods. For the ecological models, we used Maxent over the distribution of P. schokari and West African lineages. Models were projected to past conditions (mid Holocene, Last Glacial Maximum and Last Inter-Glacial) to infer climatic stable areas. Climatic stability was predicted to be mostly restricted to coastal areas and not spatially continuous. A putative temporary trans-Saharan corridor was identified in Eastern Sahara, with a more stable one along the Atlantic coast. Six parapatric lineages were identified within P. schokari , four occurring in North Africa. These likely diverged during the Pliocene. The Tamanraset River might have been a vicariant agent. African lineages may have experienced further subsequent diversification during the late Pleistocene. The main P. schokari refugia were probably located along the northern margins of the Sahara, allowing its North-to-South colonization. Trans-Saharan corridors seem to have played a role in P. schokari biogeography, allowing colonization of central Saharan mountains and Sahel. Some might have worked as refugia , and even the most stable corridors may have sections working as filters, depending on each climatic phase. We expect the use of trans-Saharan corridors to decrease for more mesic species or with less dispersal capabilities. [ABSTRACT FROM AUTHOR]

Composite lightweight wood panels are being increasingly used in construction in Spain. Their growing use should be accompanied by necessary guarantees based on studies of their properties. As it is prescriptive and in addition to others tests, in the present work is examinated the durability of these panels when exposed to the climatic conditions, a characteristic of great importance for wood products, according to Guide ETAG 016, the current standard defining the ageing tests to be used. However, due to the use class of this material, there are indications that the testing outlined in this Guide is inappropriate for assessing the ageing of wood-based sandwich panels. Alternative tests are here proposed that recreate rather better the real conditions under which these products are used. Covering the samples in a waterproof sheeting permeable to the outward movement of water vapour, which is in fact used in the installation, provided the best procedure for testing these panels.

The Argentinean Chaco region has been considered the center of origin of Drosophila buzzatii in South America because it contains most of the chromosomal polymorphism detected in natural populations. Two hypotheses have been put forward to explain the distribution of D. buzzatii in Brazil, one proposing that it has only recently passively colonized Brazil via human dispersal and the other suggesting that D. buzzatii has actively migrated to Brazil some time ago. Data from chromosomal inversions support recent colonization, whereas data from allozymes and mtDNA variation indicate that D. buzzatii has been in Brazil longer, favoring an active dispersal hypothesis. In our present work we analyzed data on 56 South American flies, mostly from Brazil, sequenced for the 5’ end of the mtDNA COI gene. The combined use of many neutrality tests and phylogeographic methods (e.g. nested clade analysis) indicated high gene flow throughout most of the range of D. buzzatii, although significant population structure was still detected. The high nucleotide diversity in the Northeast region of Brazil and the results from the nested clade analysis suggest that D. buzzatii has been in Brazil longer than proposed by the passive dispersal hypothesis. Our data indicate that D. buzzatii has been distributed throughout Brazil and Argentina since the Quaternary, though more data from different localities and markers need to be gathered to determine how the occupation of South America by D. buzzatii has occurred.

Aim Our aims were to investigate the spatial genetic structure of Micrablepharus atticolus and to assess the relative importance of differentiation in plateaus versus depressions, in areas of historical stability versus instability, and in central versus peripheral regions. Location The Brazilian Cerrado. Methods We compared the elevational range of M. atticolus with that of its sister species, Micrablepharus maximiliani, to investigate their putative elevational segregation. We identified past (6, 21 and 130 ka) and current variables associated with the distribution of M. atticolus. Based on cytochrome b sequences, we compared genetic diversity indexes and neutrality statistics between plateau/depression, stable/unstable and core/periphery populations. We identified geographically homogeneous and maximally differentiated groups of populations and tested the association between genetic and geographical distances. Finally, we traced elevational range on the phylogeny and tested for a significant phylogenetic signal associated with elevation. Results We found no elevational segregation between M. atticolus and M. maximiliani. There is high genetic diversity and structuring among populations, with the primary differentiation occurring between north-eastern and south-western Cerrado localities. We recognized three main groups of populations that roughly correspond to the southern, central-northern and north-western portions of the Cerrado, which diverged between 3.5 and 1.5 Ma. Genetic diversity indices indicated no differences between plateaus and depressions or stable and unstable areas, but samples from peripheral isolates in south-western Amazonia exhibited low haplotype and nucleotide diversity and signs of population expansion. Main conclusions The diversification of M. atticolus in the Cerrado was primarily affected by events in the late Neogene. We found no support for the plateau/depression and stability/instability hypotheses, but we did find support for the core/periphery hypothesis. The spatial patterns seemingly resulted from a combination of shifting environmental conditions during climatic cycles, with repeated colonizations of plateaus and depressions, isolation by distance, and divergence in and recolonization of peripheral isolates within Amazonia. [ABSTRACT FROM AUTHOR]

Abstract: An assumption of the existence of natural climatic oscillations driven by solar activity enables an explanation of phase differences between variations in solar activity and rainfall level in Fortaleza, Brazil. Decadal and interdecadal variations in rainfall level can be reproduced using a forced oscillation equation with a driving force term that describes the variation in the sunspot number and with the assumption of the existence of 31.7-year interdecadal and 12.96-year decadal natural climatic oscillations. This equation satisfactorily reproduces the periodicity with a length of approximately 22yr in the interdecadal rainfall variation before and up to the middle of the past century as well as the subsequent phase inversion, period and amplitude increase in the variation that followed the corresponding increases in the interdecadal sunspot number variation. The equation accurately reproduces the irregular phase shifts between decadal variations in rainfall level and in sunspot number over the entire 160yr of recorded observations. [Copyright &y& Elsevier]

We present here the first profiles of acetate and formate concentrations in Antarctic ice for time periods that include the great climatic changes of the past. Data are from two Antarctic deep ice cores recovered on the central East Antarctic Plateau (EDC) and in the Dronning Maud Land (EDML) facing the Atlantic Ocean (European EPICA Project). Except the sporadic arrival of diluted continental plumes during glacial extrema, the main source of acetate deposited over the EDC does not seem to have changed significantly over the past 300 kyr and is related to marine biogenic activity. A more detailed study of the past 55 kyr leads to the conclusion that acetate reaching the EDML during a large part of the last glacial maximum was emitted by the Patagonian continental biomass and was uptaken along with nitric acid at the surface of mineral dust. Changes in formate concentrations are characterised by less scattered and lower values at both sites during glacial periods. We propose that the present marine source of formic acid (Legrand et al., 2004) drastically decreased but did not completely vanish under cold climate conditions, whereas the share of methane oxidation in formic acid production became prominent. [ABSTRACT FROM AUTHOR]

Hypoxia has been observed in Hood Canal, Puget Sound, WA, USA since the 1970s. Four long sediment cores were collected in 2005 and age-dated to resolve natural and post-urbanization signatures of hypoxia and organic matter (OM) sources in two contrasting basins of Puget Sound: Main Basin and Hood Canal. Paleoecological indicators used for sediment reconstructions included pollen, stable carbon and nitrogen isotopes (δC and δN), biomarkers of terrestrial OM (TOM), biogenic silica (BSi), and redox-sensitive metals (RSM). The sedimentary reconstructions illustrated a gradient in RSM enrichment factors as Hood Canal > Main Basin, southern > northern cores, and pre-1900s > 1900-2005. The urbanization of Puget Sound watersheds during the 1900s was reflected as shifts in all the paleoecological signatures. Pollen distributions shifted from predominantly old growth conifer to successional alder, dominant OM signatures recorded a decrease in the proportion of marine OM (MOM) concomitant with an increase in the proportion of TOM, and the weight % of BSi decreased. However, these shifts were not coincidental with an overall increase in the enrichment of RSM or δN signatures indicative of cultural eutrophication. The increased percentage of TOM was independently verified by both the elemental ratios and lignin yields. In addition, isotopic signatures, BSi, and RSMs all suggest that OM shifts may be due to a reduction in primary productivity rather than an increase in OM regeneration in the water column or at the sediment/water interface. Therefore, the reconstructions suggested the Hood Canal has been under a more oxygenated 'stance' during the twentieth century compared to prior periods. However, these 2005 cores and their resolutions do not encompass the period of high resolution water column measurements that showed short-lived hypoxia events and fish kills in Hood Canal during the early twenty-first century. The decoupling between the increased watershed-scale anthropogenic alterations recorded in the OM signatures and the relatively depleted RSM during the twentieth century suggests that physical processes, such as deep-water ventilation, may be responsible for the historical variation in oxygen levels. Specifically, climate oscillations may influence the ventilation and/or productivity of deep water in Puget Sound and particularly their least mixed regions. [ABSTRACT FROM AUTHOR]

The paper analyzes data of the long-term monitoring of Hepaticola hepatica (Bancroft, 1893) Hall, 1916 prevalence in rodents in subtaiga small-leaf forests of the Northern Baraba lowland (the Severnyi raion of Novosibirsk oblast). The study found that the prevalence was (10.4 ± 1.02)% in Arvicola terrestris L., 1758; 4.5% in Microtus agrestis L., 1761; 3.4% in M. oeconomus Pall.,1776; 1.4% in Clethrionomys glareolus Schreb., 1780; 1.0% in C. rutilus Pall., 1779; and 0.2% in Apodemus agrarius Pall., 1771. A. terrestris was shown to become dominant in rodent communities during its outbreaks and play the main role in completing the life cycle of the parasite. During low density of A. terrestris, the H. hepatica reservoir in the biocenosis is maintained by other rodent species. [ABSTRACT FROM AUTHOR]

Abstract: Few previous studies have given significant consideration to the palaeosols in aeolian sand sheet sedimentary successions and, mainly, to their palaeoenvironmental and stratigraphic meaning in interaction with the deposits. These themes are considered in this study that deals with the depositional architecture and the factors controlling the construction, accumulation and preservation of an ancient aeolian sand sheet, that forms part of the Adamantina and Marília formations, in the Bauru Basin (Late Cretaceous, Brazil). In the NW portion of the Bauru Basin, these two units, ca 220m thick, consist of sandstone, and secondarily of sandy conglomerate and mudstone, and are characterised by vertically alternated palaeosols and deposits. Facies analyses of the deposits and macroscopic characterisation of the palaeosols in 45 outcrops were integrated with laboratory analyses that consisted in descriptions of slabs of rock samples, petrographic analyses, clay mineralogy determination, geochemical analyses of the major oxides, and micromorphological characterisation of the palaeosols. Three architectural elements were recognised: palaeosols, wind-ripple-dominated aeolian sand sheet deposits, and ephemeral river deposits. The palaeosols constitute 66% of the entire sedimentary succession, and consist principally of Aridisols and, subordinately, of Alfisols, Vertisols, and Entisols. The wind-ripple-dominated aeolian sand sheet deposits (25%) are composed of sandstone, organised in translatent climbing wind-ripple strata, and secondarily of sandstone and mudstone deposited by infrequent floods. The ephemeral river deposits (9%) consist of sandy conglomerates 4m thick and ca 2km wide. Wind-ripple-dominated aeolian sand sheet deposits formed during relatively dry climate period on an unstable topographic surface of an aeolian sand sheet, where aeolian deposition or erosion prevailed. Palaeosols and ephemeral river deposits formed in a more humid climate period on a stable topographic surface of the aeolian sand sheet. Six bounding surfaces permitted the subdivision of the study formations into genetic geological bodies, revealing different spatial and temporal orders. Two first order surfaces separate mature palaeosol profiles (Aridisols, Alfisols, and Vertisols) from overlying aeolian deposits or other mature palaeosol profiles. A second order surface separates immature palaeosols (Entisols) from overlying aeolian deposits. A third order surface constitutes the channel bottom. A fourth order surface is located at the bottom of flood deposits. A fifth order surface divides translatent wind-ripple. The constructional phase of the aeolian sand sheet occurred during the relatively dry climate period, when the available sediment was supplied from the material originally deposited by rivers and stored during a more humid period (primary supply), and by soil erosion during a drier climate (secondary supply). The accumulation surface was controlled during the drier climate by cemented Bk horizons over Aridisols and by the force of the wind blowing over the other soils or deposits. Otherwise, during the more humid climate, the accumulation surface was a stabilised surface represented by the soil. Preservation was dominated by tectonically induced subsidence and burial. [Copyright &y& Elsevier]

Holocene relative sea level changes and palaeogeography of the uplifting Tihu ridge-swale beach system in the functionally tideless Baltic Sea were reconstructed using airborne LiDAR elevation data, ground-penetrating radar surveys, sedimentological proxies, recent models of Fennoscandian uplift due to glacial isostatic adjustment, and GIS-based terrain modelling. Considering that aeolian contribution to the ridge growth was relatively small and uniform along the studied profiles, it was possible to utilize an age estimation method based on terrain elevation and pre-determined RSL curves. The tested relative sea level curves converged around a linear trend during the past 7 ka, the rate of which (3.1–3.2 mm/a) is strongly correlated with relative-to-geoid uplift model output. We found that the Tihu system started to emerge from the sea ~5.4 ka ago. In its older part, it includes a complex of elevated barrier spits where both the isostatic uplift and gradual sediment aggradation due to longshore transport contributed to its nucleation and initial progradation. In its lower (younger) section, a forced progradation "staircase" of palaeocoastlines was formed in a regime of sediment deficit and low-energy hydrodynamic conditions. Analysis of near-cyclic occurrences of beach/foredune ridges and larger ridge sets within the Tihu ridgeplain revealed time intervals of enhanced storminess during 5.4–4.9, 4.8–4.5, 4.6–4.3, 4.1–3.8, 3.7–3.4, 3.2–2.9, 2.7–2.4, and 2.2–1.9 ka BP. Serving as a new independent proxy for past storminess and high sea level events in Estonia, these phases match well with some previous European Atlantic storminess reconstructions for Mid- to- Late Holocene. • Evolution of the Tihu ridgeplain studied based on relative sea level modelling • The palaeospit emerged ~5400 years ago, it has grown due to 3.1 mm/a postglacial uplift and beach ridge/foredune build-up • The ridgeplain consists of ~100 low ridges, and scattered between, higher ridge groups reflecting palaeostorminess episodes • Eight major stormy periods identified at the eastern coast of the Baltic Sea [ABSTRACT FROM AUTHOR]

Abstract: Pollen analysis of the Early Pleistocene Montalbano Jonico section in southern Italy reveals cyclic changes driven by climate and eustasy, as illustrated by mesothermic vs. steppe elements for climate, and Pinus vs. Caryophyllaceae, Amaranthaceae–Chenopodiaceae and Ephedra for eustasy. These results are directly compared with oxygen isotope data on Globigerina bulloides constrained within a biostratigraphic framework based on nannofossils and foraminifers, facilitating a new age calibration for the section. Marine isotopic stages 37 to 23 (1.250–0.900 Ma) are recorded, and compared with global and Mediterranean oxygen isotope curves. High-frequency changes in pollen are related to the Mediterranean curve (Globigerinoides ruber) from ODP Site 967, and superimposed the LR04 stack curve. During the Early Pleistocene, pollen recorded global and regional climate changes related to obliquity and precession, respectively, and regional tectonic evolution. Precession forcing was caused by Mediterranean wetness related to precession. The intensified precession effect over climatic cycles, that is expected during the Middle Pleistocene Transition, is not recorded in the Montalbano Jonico interval A vegetation changes. [Copyright &y& Elsevier]

Abstract: We have confirmed the solar origin of insolation cycles of 11,500, 4400, 3950, 2770, 2500, 2090, 1960, 1670, 1460, 1280, 1195, 1145, 1034, 935, 835, 750 and 610yrs found in speleothem luminescence by their presence in other indices of the solar wind. The 11,500-yr solar cycle can produce climatic variations similar to those caused by the orbital variations. We discovered a sub-annual cycle of 27 days in one very high-resolution speleothem proxy paleoclimatic record, attributed to solar rotation, which causes the periodic appearance of active zones on the visible solar surface, which are the major emitters of solar wind. Solar wind modulates cosmic ray flux at the Earth, while cosmic rays influence the atmospheric transparency, thus producing a multiplication of solar variations in insolation. Small variations of the solar activity can produce a measurable influence on insolation. [Copyright &y& Elsevier]

Abstract: Declines in avian populations are a global concern, particularly for species that migrate between Arctic-temperate and tropical locations. Long-term population studies offer opportunities to detect and document ecological effects attributable to long-term climatic cycles such as the El Niño/Southern Oscillation (ENSO). In this study, we report possible population-level effects of such climatic cycles on shorebird species that use two non-breeding season sites in Ecuador (Santa Elena peninsula area, near La Libertad). During our 9-year study period (1991/1992–1999/2000), there was a particularly strong ENSO warm phase event during 1997/1998. Population trend data for three species of shorebird, Western Sandpipers (Calidris mauri), Semipalmated Sandpipers (C. pusilla), and Least Sandpipers (C. minutilla), indicated abundances generally declined during the 1990s, but there was an increase in the proportion of first-year birds and their abundance in the years following the 1997/1998 ENSO warm phase. There was some support for variation in apparent survivorship associated with the onset of the ENSO warm phase event in our population models, based on capture–mark–recapture data. Following the 1997/1998 ENSO event onset, individuals for all three species were significantly lighter during the non-breeding season (F 1,3789 =6.6, p =0.01). Least-squares mean mass (controlling for size, sex and day of capture) for first-year birds dropped significantly more than for adults following ENSO (first-year mass loss=0.69±0.12g; adult mass loss=0.34±0.11g, F 1,3789 =5.31, p =0.021), and least-squares mean mass dropped most during the period when sandpipers prepare for northward migration by gaining mass and moulting into breeding plumage. Least Sandpipers may have declined the most in mean mass following ENSO (0.76±0.19g), whereas Semipalmated Sandpipers were 0.52±0.12g lighter, and Western Sandpipers 0.40±0.13g lighter, but overall variation among species before (1992/1993–1996/1997) and after (1997/1998–1999/2000) ENSO was not significant (F 2,3787 =1.52, p =0.22). Anomalously warm and wet conditions associated with strong ENSO warm phases during the non-breeding season may either act directly on shorebirds (increasing metabolic demands) and/or indirectly through reductions in prey availability. Reduced mass and mass gain may explain lower survivorship, particularly in adults, which are more likely to migrate northward in the spring than are first-year birds, at least in Western Sandpipers. Our results suggest a potential mechanism selecting for life history strategies suitable for withstanding long-term fluctuating climatic cycles such as ENSO. [Copyright &y& Elsevier]

Abstract: In this work we have performed a detailed analysis, using signal processing tools, to study time series of data (temperature proxy) extracted from the GRIP ice-core records and we relate it with the evolution of atmospheric CO2 within the last glacial period. Our method is based in considering the warm periods known as Dansgaard–Oeschger (D/O) events and posterior returns to the cold stage as a climatic cycle. After the warming phase, D/O events relax to the initial cold state in three different ways, what gives rise to three classes of cycles. Also, the Younger/Dryas–Bolling/Allerod (Y/D–B/A) cycle corresponds to one of the classes obtained. We have found that all cycles start with identical warming phases which seem completely unrelated to variations in CO2 concentration. We discuss on the consequences for global climatology of such steady pattern of cycles. [Copyright &y& Elsevier]

Based on temperature reconstruction and proxy data from 14 sites in the Northern Hemisphere, this paper focused on comparing the cycles of temperature variations between the Arctic and other areas, including Atlantic, Europe, China, Asia, Pacific, Indian Ocean, and America during the transition from the last Interstade to the Last Glacial Maximum, from the Last Glacial Maximum to megathermal period in Holocene and the transition of the Little Ice Age (LIA) by the methods of Singular Spectrum Analysis (SSA) and Maximum Entropy Spectrum (MES). The results showed that environmental changes in the Arctic are most similar to that in the North American and better similar to Asia, Atlantic and Pacific, the least similar to Indian Ocean and Europe. The 1500-year oscillation of temperature existed both in Arctic and Europe. [ABSTRACT FROM AUTHOR]

Abstract: The drastic climatic changes which characterise the cooling trend of the last few million years of Earth history led to variations in eustatic sea level that had tremendous impact on the geology and ecology of continental margins. Reconstructing a sea-level curve back in time is not an easy task. Observations of shoreline positions are always a local measurement of Relative Sea Level that needs to be corrected from the effect of tectonic and thermal subsidence, sediment loading, compaction and glacio-hydro isostasy. Extensive studies have been done for the last deglaciation and for the last 100,000 yr cycle. But very few studies deal with position of sea level during earlier cycles, simply because conditions are very rarely favourable for the preservation of such witnesses. The shelf of the Golfe du Lion (Western Mediterranean) reveals a unique record of shoreline paleopositions during glacial maxima of at least the last five circa 100 kyr glacial/interglacial cycles. In fact it is the entire glacial deltaic lobe of up to 50 m thick (from delta front or shoreface to prodelta) that has been preserved in place and which provides direct and independent constraints for relative sea-level minima. We measure a relative sea level of: −112m, −128, −134, −246 and −262 m for MIS 2, 6, 8, 10 and 12 respectively. After corrections taking into account postdepositional movement of strata (subsidence), we find, that sea level dropped to a depth of −102±6 m during the last three glaciations (MIS2, MIS6, MIS8) but reached exceptionally low values of more than −150±10 m during the preceding glaciations MIS10 and MIS 12 at about 340 and 434 kyr BP. This general time framework and sedimentological interpretation has been confirmed by preliminary results from two deep drillings during the PROMESS cruise (july 2004), which validate our methodology. However, no detailed and absolute datings of such witnesses are available so far, so that we cannot prove that these levels are the lowest ever reached during each glacials, but they correspond undoubtedly to the last preserved shoreface before rapid sea-level rise. We also suggest that the abrupt change in sea-level maxima might be the overprint of 400 kyr orbital periodicity cycles. Last but not least, these results prove that the Golfe du Lion is indeed a unique laboratory to study paleoclimates and sea-level variations on a larger time scale. Further work is needed for a complete glacio-hydro-sedimento isostatic modelling of each sequence and each glacial to further constraint local sea level versus global sea level and quantify, in particular the relative effect of glacio-hydro isostatic effect (which differ according to ice sheet extend) but also of erosion–sedimentation isostatic effect (erosion on land and deposition on the outer shelf and slope). [Copyright &y& Elsevier]

Abstract: Concentrations of Li, Mg, Cr, Mn, Co, Cu, As, Rb, Cd, Ba and Bi have been determined by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) in various sections of the new Dome C EPICA Antarctic ice core, down to the depth of 2193m, covering a time period of two climatic cycles. The time resolution of these records is at least twice as good as previously published ultra trace elements profiles obtained from the Vostok ice core. During the ∼217kyr period spanned by this record, a high variability in concentrations is observed for most elements, with low values during warm periods and high values during cold periods. The highest concentrations are recorded at the times of the last two glacial maxima (∼20 and ∼140kyr BP). The timing and the amplitude of the main concentration peaks match remarkably well the insoluble dust concentration profile. It confirms that dust was the main carrier of atmospheric trace elements to East Antarctica during the cold periods. For Ba, Co, Cu and Rb the crustal contribution was also dominant during warm periods. For other elements the situation is more complex during interglacial periods, when other sources such as volcanic quiescent emissions, became possibly significant for several trace elements such as Cd and Bi. Peculiarly high concentration values are observed for Cd and Bi for a short depth interval dated at ∼18kyr BP. It is the same depth interval in which elevated F− values were previously observed. These very high concentrations are attributed to fallout from major local volcanic emissions at that time. [Copyright &y& Elsevier]

The Velay sequence (France) provides a unique, continuous, palynological record spanning the last four climatic cycles. A pollen-based reconstruction of temperature and precipitation displays marked climatic cycles. An analysis of the climate and vegetation changes during the interglacial periods reveals comparable features and identical major vegetation successions. Although Marine Isotope Stage (MIS) 11.3 and the Holocene had similar earth precessional variations, their correspondence in terms of vegetation dynamics is low. MIS 9.5, 7.5, and especially 5.5 display closer correlation to the Holocene than MIS 11.3. Ecological factors, such as the distribution and composition of glacial refugia or postglacial migration patterns, may explain these discrepancies. Comparison of ecosystem dynamics during the past five interglacials suggests that vegetation development in the current interglacial has no analogue from the past 500,000 years. [ABSTRACT FROM AUTHOR]

Abstract: The wide continental shelf of the Gulf of Lion (up to 70km) has been the object of numerous investigations since the early days of oceanography. Yet, the question of sequences duration, the mechanisms of deposition and factors implied remained unanswered. A study of a very dense grid of Very High Resolution (VHR) seismic reflection (Sparker) data associated with surficial cores both, collected by IFREMER between 1992 and 2001 on the outer shelf and upper slope offshore of Sète in the Languedoc region gives a new insight into these issues. Analysis of the 3D geometry of the sedimentary record reveals a basic depositional pattern consisting of a pair of horizontally juxtaposed and downlapping prisms. Prism PI with low angle clinoforms (<1°) lies on the upper part of the shelf and is interpreted to be prodeltaic-offshore deposits. Prism PII with steeply dipping clinoforms (∼4°) lies on the outer shelf between 40 and 70km from the present day coastline and is interpreted to be littoral deposits. Results obtained from integrating lithology, palynology, micropaleontology, seismic stratigraphy, stratigraphic simulation, support the hypothesis that the basic depositional pattern records a 100 000-years glacioeustatic (interglacial/glacial) cycle. As previously suggested by Aloïsi [Aloïsi, J.C., 1986. Sur un modèle de sédimentation deltaïque: contribution à la connaissance des marges passive, Thèse de Doctorat d''Etat. Université de Perpignan, 162 pp], prisms PI corresponds to deposition at high sea level and prisms PII to deposition during low sea level at glacial maxima. Five sequences of paired prisms capped by five major erosion surfaces have been identified and modelled showing that the corresponding glacioeustatic cycles (the last five cycles at least) are recorded on the shelf of the western part of the Gulf of Lion. [Copyright &y& Elsevier]

The proposal that cometary dust particles play a significant role in the emergence and evolution of both life and disease on suitable planets was first made some 25 years ago by Hoyle and Wickramasinghe. Fundamental to this proposal was a process of punctuated seeding by particular (bio)chemical species believed to originate naturally and predominantly in larger comets, say those with diameters greater than about 100 kilometres. Rather less well known is a parallel proposal likewise favoured by Hoyle that a particular giant comet, the most recent to settle in cis-Jovian space, accounting for the latest significant phase of evolution on Earth, also had a significant part to play in the cultivation by homo sapiens of its civilization and culture. Such proposals may be seen by many as examples of excessively lateral thinking but they by no means lack independent support and have important implications for the otherwise uncertain origin of the latest ice-age (basic to climatology) and for the otherwise uncertain generation of early calendars (basic to the management of society). Aspects of these proposals are considered here in relation to a much respected supposedly Chaldean calendar probably passed down by the dynastic Isins (also the Essenes?) which evidently bears witness to known early mathematical and astronomical skills but which largely ceased to be available to subsequent scholarship beyond the Early Christians (ca. 100 CE) pending its (recent) recovery through the medium of Dead Sea Scrolls. [ABSTRACT FROM AUTHOR]

Stalagmite laminae provide a high-resolution geological record of climate change. In this paper, moving spectral analysis is used to analyse a stalagmite lamina thickness record to study climatic variability. It was found that the dominant cycles of the lamina thickness sequence are 2, 3.3, 5–6, 10–12, 14–18, 133 and 194 years. Some of the cycles are the same as the cycles of modern climatic indices, such as the QBO (Quasi Biennial Oscillation) of 2 years, the QTO (Quasi Triple-year Oscillation) cycle of about 3.5 years, the QFO (Quasi Five-year Oscillation) cycle of 5–6 years and the QEO (Quasi Eleven-year Oscillation) cycle of 11 years. It was also found that there are different dominant cycles in different time periods. Usually, the dominant cycles are stronger in wet periods when the microlaminae are thicker. In dry periods, the microlaminae are thinner and the power of the dominant cycles is also weaker. Another feature is that the power of the dominant cycles and their long-term periods and frequencies appear to change. These phenomena are important for understanding the climatic changes in Beijing area over the last 1 ka. [ABSTRACT FROM AUTHOR]

There are too few active comets to account for the observed zodiacal dust. Rather we look to the collisional fragmentation and erosion of sub-kilometre meteoroids in orbit close to the ecliptic. Since 1975 we have also been aware of an apparently massive meteoroidal swarm in probable 7:2 mean motion resonance with Jupiter, seemingly at the heart of the Taurid Complex and connecting therefore with the near-ecliptic system through the so-called Štohl Stream. The notable absence of pre-1786 apparitions of 2P/Encke took on a new significance with the 1983 detection by IRAS of its asymmetric trail inside this resonance. Thus it was possible all these meteoroidal components were ultimately derived from a continuously eroded, substantially dormant, librating progenitor within the trail whose more volatile inclusions are exposed from time to time and expelled either singly or severally as independent comets. A Taurid progenitor of this kind (proto-Encke) dominating the inner Solar System environment probably then accounts for most of the recorded enhancements of the larger meteoroid flux to Earth, including ‘Tunguska’ bodies as well. Terrestrial dust insertions which control mean temperature and hence climate are also inferred based upon the libration and nodal precession half-periods of proto-Encke (∼0.2 kyr, ∼2.5 kyr respectively) albeit the longer of these cycles was not at first evident in the terrestrial record (Asher & Clube 1993). Recently however this cycle appears to have been confirmed as a significant (long term) global warming/meridional atmospheric circulation / iceberg calving cycle with the correct phase producing the so-called mini-Heinrich and Heinrich events of the Holocene and late Upper Pleistocene respectively, i.e., during the past ∼60 kyr BP. The comparative stability of this terrestrial cycle, in contrast with the weakness of the observed resonance, suggests a fairly recent diversion therefore from a much stronger sungrazing 7:2 Jovian resonance in which proto-Encke's and Jupiter's longitudes of perihelion are related by ϖ pE ≈ ϖ J or ϖ J + π. Thus both the Hephaistos Stream and the Taurid Complex could have formed together during a recent close planetary encounter, say with Mercury ∼5 kyr BP. It follows that we envisage a single large progenitor in 7:2 Jovian sungrazing resonance for 50 kyr or so which undergoes repeated tidal stress: a continuous dust-induced major glaciation is thus sustained on Earth for most of this dynamical timescale before a disruptive planetgrazing event finally brings its sungrazing status to an end and produces the present meteoroidal complex. This evolutionary sequence almost certainly requires that the original sungrazing stream still exists (without its source): a potentially significant fact because it may have a direct bearing on both the observed zodiacal bands and the original progenitor orbit as well as the known periodic variation of solar radiance and convected magnetic field, of possible relevance to the solar cycle. While these aspects have to be further explored, the purpose of the present investigation is to describe some preliminary modelling with a view to inferring the likely dynamical history of proto-Encke. [ABSTRACT FROM AUTHOR]