A study on the O–C diagram and pulsation behaviour of KZ Hydra

New differential time-series observations of KZ Hya were secured using the V filters, and 28 new times of light maximum were identified. We collected 157 times of light maximum from the literature, unpublished data and open database, and proceeded to investigate the variations of the O–C values for light maxima with the total of 185 times of light maximum. A quasi-sinusoidal character of the O–C diagram was confirmed, and this was interpreted as a light travelling time effect due to a companion moving in an eccentric (e=0.23) orbit with a period of about 24.77 years. The periods of KZ Hya were investigated and nine frequencies were determined using the Fourier decomposition method. All nine were harmonic frequencies and no other frequency was identified.     

Cryoplanation terraces: Indicators of a permafrost environment

Cryoplanation terraces are bedrock steps or terraces on ridge crests and hilltops. The tread or “flat” area is 10 to several hundred meters wide and long and slopes from 1 to 5° parallel to the ridge crests. Terrace scarps may be from 1 to 75 m high. Terraces are cut into all bedrock types and are best developed on closely jointed, fine-grained bedrock. The scarps and treads are covered with frost-rived rubble 1 to 2 m thick. The rubble on treads is perennially frozen at a depth of 1 to 2 m or less on sharp but inactive terraces in Alaska.Cryoplanation terraces exist in many parts of the world in present or past periglacial environments. They occur chiefly in nonglaciated regions and near the general altitude of snowline. Cryoplanation terraces form by scarp retreat as the result of nivation. Surficial debris is removed across the terrace tread by mass-wasting. Terrace morphology depends mainly upon climate, bedrock type, and terrace orientation.No climatic data are available from active terraces. Indirect evidence indicates that climatic requirements include low snowfall and cold summer temperatures. Shallow permafrost is necessary to provide moisture and a base for mass movement as well as a base for nivation.Hundreds of sharp but inactive terraces occur in some areas in Alaska where the summer temperature is colder than 10°C. When these terraces were active, temperatures were colder. Recent work in Alaska indicates that terraces were active in some areas when the mean July temperature was about 4°C. The mean annual air temperature probably was in the neighborhood of ′12°C or colder.     

Ice wedge casts and past permafrost distribution in North AmericaFossile eiskeile und dauerfrost in der vergangenheit in NordamerikaPseudomorphoses des coins de glace et distribution du permafrost au passé en Amérique du Nord

Ice wedge casts are the most accurate and widespread indicators of past permafrost. Many ice wedge casts exist in Alaska, some in areas of existing ice wedges. In addition to indicating paleotemperature conditions and a wider distribution of permafrost in Wisconsinan time than now, casts in Alaska also indicate permafrost in Iliinoian and pre-lllinoian time. Hundreds of ice wedge casts are now known in temperate North America and are described from about 22 widespread localities coast to coast in Canada and United States. Permafrost existed in late Wisconsinan time, 20,000 to 10,000 years ago, along the glacial border in temperate United States. Later permafrost formed north of the glacial border as the continental ice sheet withdrew exposing drift to the rigorous periglacial climate. Ice wedge casts indicate that the ? 7 °C mean annual air isotherm was about 2000 km farther south in late Wisconsinan time than now.     

A bimillennial-length tree-ring reconstruction of precipitation for the Tavaputs Plateau, Northeastern Utah

Despite the extensive network of moisture-sensitive tree-ring chronologies in western North America, relatively few are long enough to document climatic variability before and during the Medieval Climate Anomaly (MCA) ca. AD 800-1300. We developed a 2300-yr tree-ring chronology extending to 323 BC utilizing live and remnant Douglas-fir (Pseudotsuga menziesii) from the Tavaputs Plateau in northeastern Utah. A resulting regression model accounts for 70% of the variance of precipitation for the AD 1918-2005 calibration period. Extreme wet and dry periods without modern analogues were identified in the reconstruction. The MCA is marked by several prolonged droughts, especially prominent in the mid AD 1100s and late 1200s, and a lack of wet or dry single-year extremes. The frequency of extended droughts is not markedly different, however, than before or after the MCA. A drought in the early AD 500s surpasses in magnitude any other drought during the last 1800 yr. A set of four long high-resolution records suggests this drought decreased in severity toward the south in the western United States. The spatial pattern is consistent with the western dipole of moisture anomaly driven by El Niño and is also similar to the spatial footprint of the AD 1930s “Dust Bowl” drought.     

A continuous multi-millennial record of surficial bivalve mollusk shells from the São Paulo Bight,Brazilian shelf

To evaluate the potential of using surficial shell accumulations for paleoenvironmental studies, an extensive time series of individually dated specimens of the marine infaunal bivalve mollusk Semele casali was assembled using amino acid racemization (AAR) ratios (n = 270) calibrated against radiocarbon ages (n = 32). The shells were collected from surface sediments at multiple sites across a sediment-starved shelf in the shallow sub-tropical São Paulo Bight (São Paulo State, Brazil). The resulting ¹⁴C-calibrated AAR time series, one of the largest AAR datasets compiled to date, ranges from modern to 10,307 cal yr BP, is right skewed, and represents a remarkably complete time series: the completeness of the Holocene record is 66% at 250-yr binning resolution and 81% at 500-yr binning resolution. Extensive time-averaging is observed for all sites across the sampled bathymetric range indicating long water depth-invariant survival of carbonate shells at the sediment surface with low net sedimentation rates. Benthic organisms collected from active depositional surfaces can provide multi-millennial time series of biomineral records and serve as a source of geochemical proxy data for reconstructing environmental and climatic trends throughout the Holocene at centennial resolution. Surface sediments can contain time-rich shell accumulations that record the entire Holocene, not just the present.     

Partitioning of organic matter in continental margin sediments among density fractions

Hydrodynamic processes sort and redistribute organic matter (OM) and minerals on continental margins. Density fractionations were conducted on sediments from diverse margins (Mexico margin, Gulf of Mexico, Mississippi River delta, Eel River margin) to investigate the nature, provenance and age of OM among density fractions. Mass, elemental (C and N), lignin, and surface area distributions, as well as stable carbon and radiocarbon isotopic compositions were measured. The lowest density fractions (< 1.6 g cm^− 3) contained the highest organic carbon (OC) (up to 45%) and lignin concentrations (up to 8 mg g^− 1) due to abundant woody debris, whereas high density fractions (> 2.5 g cm^− 3) were OC-poor (%OC < 0.5) mineral material. Most sediment mass was found in the mesodensity fractions (1.6 to 2.5 g cm^− 3) that contained the highest proportion of OC (up to ~ 75%) for each sediment. Stable carbon isotope compositions (δ¹³C − 25.5‰ to − 22.9‰) show terrigenous OC as a significant component of density isolates from the river-dominated sediments (Gulf of Mexico, Mississippi River, and Eel margin), whereas the Mexico margin, least influenced by riverine input, was dominated by autochthonous marine OC (δ¹³C ~ − 21.5‰). Radiocarbon compositions of density fractions indicate significant pre-aged OC (Δ¹⁴C as low as − 900‰) in river-influenced sediments but not on the Mexico margin (Δ¹⁴C > − 200‰). Ratios of vanillic acid to vanillin (Ad/Al)v among lignin oxidation products increase with increasing particle density suggesting variable lignin sources or selective degradation of lignin among the different density fractions.     

Petrographic and trace element analysis of uranium-rich tufa calcite, middle Miocene Barstow Formation, California, USA

An integrated petrographic and spectroscopic (X‐ray diffraction, phosphor imaging and synchrotron X‐ray absorption spectroscopy) study of tufas from the Miocene Barstow Formation, California, relates sample morphology, mineralogy and geochemical composition. The tufas, composed mainly of calcite that formed at the interface between an ancient alkaline lake and ground or spring waters, have textures similar to those of microbially mediated terrestrial stromatolites and travertines. The tufas have elevated concentrations of a number of trace elements including Mn, Fe, Sr and U. Synchrotron X‐ray fluorescence analyses show that U concentrations can exceed 500 p.p.m. X‐ray absorption spectroscopy indicates that the U in these samples is incorporated as U(IV). It is suggested here that alkaline lake waters had a high U/Ca ratio and tufa calcite formed where groundwater or (possibly epithermal) springs brought in Ca and trace elements such as Sr. The rapid, and possibly microbially mediated, precipitation of calcite allowed for incorporation of high concentrations of trace metals as either structural substitutes or extremely fine‐scale inclusions.