A high resolution proxy-climate record from an arctic lake with annually-laminated sediments on Devon Island, Nunavut, Canada

Sediments from a 3 ha lake (75 °34.34N, 89 °18.55W) from the coastal region of northern Devon Island, Nunavut, Canada, contain discrete laminations in the deepest part of the basin. The laminations are varves as indicated by the correspondence between counts and thickness measurements of the couplets and ²¹⁰Pb dating. A 14 cm core representing 150 years of sedimentation contained laminated couplets consisting of a lighter inorganic layer with a higher percentage of calcium and magnesium, alternating with fine darker bands, typically more cohesive, and comprising higher proportions of silica and carbon. A reddish oxidation zone with higher iron and aluminum frequently separates the laminations. The dark layer represents a biogenic component deposited in summer and is made cohesive by bacterial filaments among the other particles. The light inorganic layer represents clastic deposition from allochthonous sources. Deposition rates were relatively consistent through the core with an increase in varve thickness in the 1950s. Diatom concentrations in the sediments increased by two orders of magnitude in this century, with major increases in the 1920s and 1950s. The increase in varve thickness and diatom abundance coincides with an increase in summer melt percentage in an ice core from the Devon Island Ice Cap (Koerner, 1977). The relatively high sedimentation rate (0.15 cm yr^-1) coupled with the consistency of deposition makes this lake a significant indicator for recent climate changes of the Canadian Arctic Archipelago.     

Epiphytic diatoms as flood indicators

The hydroecology of floodplain lakes is strongly regulated by flood events. The threat of climate warming and increasing human activities requires development of scientific methods to quantify changes in the frequency of short-lived flood events, because they remain difficult to identify using conventional paleolimnological and monitoring approaches. We developed an approach to detect floods in sediment records by comparing the abundance and composition of epiphytic diatom communities in flooded and non-flooded ponds of the Peace-Athabasca Delta (PAD), Canada, that grew on submerged macrophytes (Potamogeton zosteriformis, P. perfoliatus) and an artificial substrate (polypropylene sheets) during the open-water season of 2005. Analysis of similarity tests showed that epiphytic diatom community composition differs significantly between flooded and non-flooded ponds. After accounting for the “pond effect,” paired comparisons of the three substrates determined that variation in community composition between the artificial substrate and macrophytes was similar to that between the macrophyte taxa. Similarity percentage analysis identified diatom taxa that discriminate between flooded and non-flooded ponds. The relative abundance of ‘strong flood indicator taxa’ was used to construct an event-scale flood record spanning the past 180 years using analyses of sedimentary diatom assemblages from a closed-drainage pond (PAD 5). Results were verified by close agreement with an independent paleoflood record from a nearby flood-prone oxbow pond (PAD 54) and historical records. Comparison of epiphytic diatoms in flooded and non-flooded lakes in this study provides a promising approach to detect changes in flood frequency, and may have applications for reconstructing other pulse-type disturbances such as hurricanes and pollutant spills.     

Will the Russians return from the near abroad?

The author "examines a range of issues surrounding the involuntary migration of Russian populations from the non-Russian republics of the former USSR. Among the questions addressed are possible magnitudes of in-migration into Russia (with special attention paid to conditions in one of the major source regions, Central Asia), attitudes in Russia regarding appropriate policy with respect to treatment of co-nationals in the near abroad and whether their return to Russia would have a positive or negative impact, and conditions in areas of Russia that presently are absorbing the greatest numbers of migrants. The assertion that Russian policy should seek aggressively to prevent the out-migration of Russian populations [from] the near abroad is assessed critically."     

The ethnocultural component of tourism development in the Altai Republic

A characterization is provided for the recreation resources of the Altai Republic. The diversity of the national-ethnical composition of the population of the Altai Republic is determined as well as analyzing the spatial distribution of the ethnoses on its territory. The coefficients of ethnical diversity are calculated for all administrative districts. The territories with a different level of ethnical diversity and a different combination of ethnical groups are determined. The study revealed a connection of ethnical diversity and natural conditions of the territory and the concentration of separate ethnoses in definite landscapes. A characterization is provided for the ethnocultural tourism and recreation resources of the Altai Republic within the context of administrative districts. Information is provided concerning the territorial distribution of separate ethnical groups, traditional kinds of their nature management, religion, main national dishes, elements of national costume, national festivities and rites, etc. An analysis of the spatial distribution of the ethnocultural recreation resources identified promising clusters (nodes) or destinations for the arrangement of special ethnocultural tourist routes. Schematic maps are provided, which display the ethnical diversity in the districts of the region, and promising districts for the organization of ethnocultural tourist routes.     

Modes to replace transitional asymptotic ray fields in a vertically inhomogeneous earth model

Summary. Asymptotic ray theory (ART) fails in transition regions near critically reflected, bottom glancing or caustic-forming rays in a vertically inhomogeneous layered earth. These deficiencies are repaired here by replacing the transitional ray fields with guided modes plus truncation remainders. Exact ray-mode equivalences and their high-frequency asymptotic approximations are formulated, and their validity and efficiency are verified by numerical comparisons for SH motion in a two-layer earth model comprised of an inhomogeneous sediment above an homogeneous semi-infinite bedrock.     

Anomalies of some tidal waves of UT1

Summary. The M _f and M _m waves of UT1 have been analysed from the BIH data during the period 1967.0 to 1984.0 in order to derive the Love number k .
These analyses performed during successive intervals of this period show some anomalies in the values of the Love number k derived from the M _f wave. Large variations with time of the amplitude and the phase appear for this wave while the values derived from the M _m wave present a good stability during the whole period.
The spectrum of the UT1-residuals (as obtained by removing the theoretical zonal tidal UT1 terms) shows the existence of a perturbation wave near the M _f period. This wave lies in the range 13.5–13.9 day according to the analysed interval; it could be related with the perturbation wave noticed by some authors near the M _f gravimetric wave.     

Integrated provenance record of a forearc basin modified by slab‐window magmatism: detrital‐ zircon geochronology and sandstone compositions of the Paleogene Arkose Ridge Formation,south‐central Alaska

This study presents an integrated provenance record for ancient forearc strata in southern Alaska. Paleocene–Eocene sedimentary and volcanic strata >2000 m thick in the southern Talkeetna Mountains record nonmarine sediment accumulation in a remnant forearc basin. In these strata, igneous detritus dominates conglomerate and sandstone detrital modes, including plutonic and volcanic clasts, plagioclase feldspar, and monocrystalline quartz. Volcanic detritus is more abundant and increases upsection in eastern sandstone and conglomerate. U‐Pb ages of >1600 detrital zircons from 19 sandstone samples document three main populations: 60–48 Ma (late Paleocene–Eocene; 14% of all grains), 85–60 Ma (late Cretaceous–early Paleocene; 64%) and 200–100 Ma (Jurassic–Early Cretaceous; 11%). Eastern sections exhibit the broadest distribution of detrital ages, including a principal population of late Paleocene–Eocene ages. In contrast, central and western sections yield mainly late Cretaceous–early Paleocene detrital ages. Collectively, our results permit reconstruction of individual fluvial drainages oriented transverse to a dissected arc. Specifically, new data suggest: (1) Detritus was eroded from volcanic‐plutonic sources exposed along the arcward margin of the sampled forearc basin fill, primarily Jurassic–Paleocene magmatic‐arc plutons and spatially limited late Paleocene–Eocene volcanic centers; (2) Eastern deposystems received higher proportions of juvenile volcanic detritus through time from late Paleocene–Eocene volcanic centers, consistent with emplacement of a slab window beneath the northeastern part of the basin during spreading‐ridge subduction; (3) Western deposystems transported volcanic‐plutonic detritus from Jurassic–Paleocene remnant arc plutons and local eruptive centers that flanked the northwestern part of the basin; (4) Diagnostic evidence of sediment derivation from accretionary‐prism strata exposed trenchward of the basin fill is lacking. Our results provide geologic evidence for latest Cretaceous–early Paleocene exhumation of arc plutons and marine forearc strata followed by nonmarine sediment accumulation and slab‐window magmatism. This inferred history supports models that invoke spreading‐ridge subduction beneath southern Alaska during Paleogene time, providing a framework for understanding a mature continental‐arc/forearc‐basin system modified by ridge subduction. Conventional provenance models predict reduced input of volcanic detritus to forearc basins during progressive exhumation of the volcanic edifice and increasing exposure of subvolcanic plutons. In contrast, our results show that forearc basins influenced by ridge subduction may record localized increases in juvenile volcanic detritus during late‐stage evolution in response to accumulation of volcanic sequences formed from slab‐window eruptive centers.