Late Pleistocene paleoecology of arctic ground squirrel (Urocitellus parryii) caches and nests from Interior Alaska's mammoth steppe ecosystem, USA

Botanical analyses of fossil and modern arctic ground squirrel (Urocitellus parryii) caches and nests have been used to reconstruct the past vegetation from some parts of Beringia, but such archives are understudied in Alaska. Five modern and four fossil samples from arctic ground squirrel caches and nests provide information on late Pleistocene vegetation in Eastern Beringia. Modern arctic ground squirrel caches from Alaska's arctic tundra were dominated by willow and grass leaves and grass seeds and bearberries, which were widespread in the local vegetation as confirmed by vegetation surveys. Late Pleistocene caches from Interior Alaska were primarily composed of steppe and dry tundra graminoid and herb seeds. Graminoid cuticle analysis of fossil leaves identified Calamagrostis canadensis, Koeleria sp. and Carex albonigra as being common in the fossil samples. Stable carbon isotopes analysis of these graminoid specimens indicated that plants using the C₃ photosynthetic pathways were present and functioning with medium to high water-use efficiency. Fossil plant taxa and environments from ground squirrel caches in Alaska are similar to other macrofossil assemblages from the Yukon Territory, which supports the existence of a widespread mammoth steppe ecosystem type in Eastern Beringia that persisted throughout much of the late Pleistocene.     

Chronology of latest Pleistocene mountain glaciation in the western Wasatch Mountains, Utah, U.S.A.

Understanding the timing of mountain glacier and paleolake expansion and retraction in the Great Basin region of the western United States has important implications for regional-scale climate change during the last Pleistocene glaciation. The relative timing of mountain glacier maxima and the well-studied Lake Bonneville highstand has been unclear, however, owing to poor chronological limits on glacial deposits. Here, this problem is addressed by applying terrestrial cosmogenic ¹⁰Be exposure dating to a classic set of terminal moraines in Little Cottonwood and American Fork Canyons in the western Wasatch Mountains. The exposure ages indicate that the main phase of deglaciation began at 15.7 ± 1.3 ka in both canyons. This update to the glacial chronology of the western Wasatch Mountains can be reconciled with previous stratigraphic observations of glacial and paleolake deposits in this area, and indicates that the start of deglaciation occurred during or at the end of the Lake Bonneville hydrologic maximum. The glacial chronology reported here is consistent with the growing body of data suggesting that mountain glaciers in the western U.S. began retreating as many as 4 ka after the start of northern hemisphere deglaciation (at ca. 19 ka).     

The application of foraminifera to reconstruct the rate of 20th century sea level rise, Morbihan Golfe, Brittany, France

Foraminiferal assemblages preserved within salt-marsh sediment can provide an accurate and precise means to reconstruct relative sea level due to a strong relationship with elevation, which can be quantified using a transfer function. We collected a set of surface samples from two salt marshes in the Morbihan Golfe, France to determine foraminiferal distribution patterns. Dominant taxa included Jadammina macrescens, Trochammina inflata, Haplophragmoides spp. and Miliammina fusca. We developed a foraminifera-based transfer function using a modern training set of 36 samples and 23 species. The strong relationship between observed and predicted values (r²_jack = 0.7) indicated that foraminiferal distribution is primarily controlled by elevation with respect to the tidal frame and precise reconstructions of former sea level are possible (RMSEP_jack = 0.07 m). The application of the transfer function to a short salt-marsh core (0.32 m) allowed the reconstruction of former sea levels, which were placed in a chronological framework using short-lived radionuclides (²¹⁰Pb and ¹³⁷Cs). The agreement between the foraminifera-based sea level curve and the Brest tide-gauge record confirms the reliability of transfer function estimates and the validity of this methodology to extend sea level reconstructions back into the pre-instrumental period. Both instrumental and microfossil records suggest an acceleration of sea level rise during the 20th century.     

Phosphate oxygen isotopes: Insights into sedimentary phosphorus cycling from the Benguela upwelling system

Marine sediments are the main sink in the oceanic phosphorus (P) cycle. The activity of benthic microorganisms is decisive for regeneration, reflux, or burial of inorganic phosphate (P_i), which has a strong impact on marine productivity. Recent formation of phosphorites on the continental shelf and a succession of different sedimentary environments make the Benguela upwelling system a prime region for studying the role of microbes in P biogeochemistry. The oxygen isotope signature of pore water phosphate (δ¹⁸O_P) carries characteristic information of microbial P cycling: Intracellular turnover of phosphorylated biomolecules results in isotopic equilibrium with ambient water, while enzymatic regeneration of P_i from organic matter produces distinct offsets from equilibrium. The balance of these two processes is the major control for δ¹⁸O_P.Our study assesses the importance of microbial P cycling relative to regeneration of P_i from organic matter from a transect across the Namibian continental shelf and slope by combining pore water chemistry (sulfate, sulfide, ferrous iron, P_i), steady-state turnover rate modeling, and oxygen isotope geochemistry of P_i.We found δ¹⁸O_P values in a range from 12.8‰ to 26.6‰, both in equilibrium as well as pronounced disequilibrium with water. Our data show a trend towards regeneration signatures (disequilibrium) under low mineralization activity and low P_i concentrations, and microbial turnover signatures (equilibrium) under high mineralization activity and high P_i concentrations. These findings are opposite to observations from water column studies where regeneration signatures were found to coincide with high mineralization activity and high P_i concentrations. It appears that preferential P_i regeneration in marine sediments does not necessarily coincide with a disequilibrium δ¹⁸O_P signature. We propose that microbial P_i uptake strategies, which are controlled by P_i availability, are decisive for the alteration of the isotope signature. This hypothesis is supported by the observation of efficient microbial P_i turnover (equilibrium signatures) in the phosphogenic sediments of the Benguela upwelling system.     

Application of sulphur isotope ratios to examine weaning patterns and freshwater fish consumption in Roman Oxfordshire, UK

This study investigates the application of sulphur isotope ratios (δ³⁴S) in combination with carbon (δ¹³C) and nitrogen (δ¹⁵N) ratios to understand the influence of environmental sulphur on the isotopic composition of archaeological human and faunal remains from Roman era sites in Oxfordshire, UK. Humans (n = 83), terrestrial animals (n = 11), and freshwater fish (n = 5) were analysed for their isotope values from four locations in the Thames River Valley, and a broad range of δ³⁴S values were found. The δ³⁴S values from the terrestrial animals were highly variable (−13.6‰ to +0.5‰), but the δ³⁴S values of the fish were clustered and ³⁴S-depleted (−20.9‰ to −17.3‰). The results of the faunal remains suggest that riverine sulphur influenced the terrestrial sulphur isotopic signatures. Terrestrial animals were possibly raised on the floodplains of the River Thames, where highly ³⁴S-depleted sulphur influenced the soil. The humans show the largest range of δ³⁴S values (−18.8‰ to +9.6‰) from any archaeological context to date. No differences in δ³⁴S values were found between the males (−7.8 ± 6.0‰) and females (−5.3 ± 6.8‰), but the females had a linear correlation (R² = 0.71; p < 0.0001) between their δ¹⁵N and δ³⁴S compositions. These δ³⁴S results suggest a greater dietary variability for the inhabitants of Roman Oxfordshire than previously thought, with some individuals eating solely terrestrial protein resources and others showing a diet almost exclusively based on freshwater protein such as fish. Such large dietary variability was not visible by analysing only the carbon and nitrogen isotope ratios, and this research represents the largest and most detailed application of δ³⁴S analysis to examine dietary practices (including breastfeeding and weaning patterns) during the Romano-British Period.     

Effect of Mars analogue dust deposition on the automated detection of calcite in visible/near-infrared spectra

We have developed an artificial neural net detector for use on board Mars rovers that correctly identifies calcite under Mars analogue dust (JSC Mars-1 regolith simulant) layers up to ∼100 μm thickness and 80% aerial coverage. Both the detector output and the band depth of the ∼2300 nm CO⁼₃ absorption are linearly related to the surface area of exposed calcite. This detector provides a means for rapid and robust automated recognition of calcite on Mars in areas of active aeolian erosion.     

The largest scale perturbations: A window on the physics of the beginning

I present results of new statistical techniques for the interpretation of the temperature and polarization maps and power spectra of the cosmic microwave background. We show that the power deficit at low ℓ in the WMAP1 data is consistent with a statistical fluctuation at the 10% level; that future high S/N maps of the temperature and polarization anisotropies can be combined into a reconstruction of the metric perturbations imprinted during inflation; and that machine learning techniques can accelerate cosmological parameter estimation by orders of magnitude while being highly accurate and robust.