Peak Last Glacial weathering intensity on the North American continent recorded by the authigenic Hf isotope composition of North Atlantic deep-sea sediments

We have retrieved radiogenic hafnium (Hf) isotope compositions (ɛHf) from authigenic Fe–Mn oxyhydroxides of deep northwest Atlantic sediments deposited over the past 26 ka to investigate the oceanic evidence of changes in dissolved weathering inputs from NE America during the last deglaciation. The extraction of seawater-derived Hf isotopic compositions from Fe–Mn oxyhydroxides is not a standard procedure. Comparisons between the Al/Hf ratios and Hf isotopic compositions of the chemically extracted authigenic phase on the one hand, and those of the corresponding detrital fractions on the other, provide evidence that the composition of past seawater has been reliably obtained for most sampled depths with our leaching procedures. This is endorsed most strongly by data for a sediment core from 4250 m water depth at the deeper Blake Ridge, for which consistent replicates were produced throughout. The Hf isotopic composition of the most recent sample in this core also closely matches that of nearby present day central North Atlantic seawater. Comparison with previously published seawater Nd and Pb isotope compositions obtained on the same cores shows that both Hf and Pb were released incongruently during incipient chemical weathering, but responded differently to the deglacial retreat of the Laurentide Ice Sheet. Hafnium was released more congruently during peak glacial conditions of the Last Glacial Maximum (LGM) and changed to typical incongruent interglacial ɛHf signatures either during or shortly after the LGM. This indicates that some zircon-derived Hf was released to seawater during the LGM. Conversely, there is no clear evidence for an increase in the influence of weathering of Lu-rich mineral phases during deglaciation, possibly since relatively unradiogenic Hf contributions from feldspar weathering were superimposed. While the authigenic Pb isotope signal in the same marine sediment samples traced peak chemical weathering rates on continental North America during the transition to the Holocene a similar incongruent excursion is notably absent in the Hf isotope record. The early change towards more radiogenic ɛHf in relation to the LGM may provide direct evidence for the transition from a cold-based to a warm-based Laurentide Ice Sheet on the Atlantic sector of North America.

Effects of meaning and symmetry on judgments of size

Research has shown that people judge words as having bigger font size than non-words. This finding has been interpreted in terms of processing fluency, with higher fluency leading to judgments of bigger size. If so, symmetric numbers (e.g., 44) which can be processed more fluently are predicted to be judged as larger than asymmetric numbers (e.g., 43). However, recent research found that symmetric numbers were judged to be smaller than asymmetric numbers. This finding suggests that the mechanisms underlying size judgments may differ in meaningful and meaningless materials. Supporting this notion, we showed in Experiment 1 that meaning increased judged size, whereas symmetry decreased judged size. In the next two experiments, we excluded several alternative explanations for the differences in size judgments between meaningful and meaningless materials in earlier studies. This finding contradicts the notion that the mechanism underlying judgments of size is processing fluency.

Plant diversity and ecosystem multifunctionality peak at intermediate levels of woody cover in global drylands

Aim The global spread of woody plants into grasslands is predicted to increase over the coming century. While there is general agreement regarding the anthropogenic causes of this phenomenon, its ecological consequences are less certain. We analysed how woody vegetation of differing cover affects plant diversity (richness and evenness) and the surrogates of multiple ecosystem processes (multifunctionality) in global drylands, and how these change with aridity. Location Two hundred and twenty-four dryland sites from all continents except Antarctica, widely differing in their environmental conditions (from arid to dry-subhumid sites) and relative woody cover (from 0 to 100). Methods Using a standardized field survey, we measured the cover, richness and evenness of perennial vegetation. At each site, we measured 14 soil variables related to fertility and the build-up of nutrient pools. These variables are critical for maintaining ecosystem functioning in drylands. Results Species richness and ecosystem multifunctionality were strongly related to woody vegetation, with both variables peaking at a relative woody cover (RWC) of 41–60. This relationship shifted with aridity. We observed linear positive effects of RWC in dry-subhumid sites. These positive trends shifted to hump-shaped RWC–diversity and multifunctionality relationships under semi-arid environments. Finally, hump-shaped (richness, evenness) or linear negative (multifunctionality) effects of RWC were found under the most arid conditions. Main conclusions Plant diversity and multifunctionality peaked at intermediate levels of woody cover, although this relationship became increasingly positive in wetter environments. This comprehensive study accounts for multiple ecosystem attributes across a range of levels of woody cover and environmental conditions. Our results help us to reconcile contrasting views of woody encroachment found in the current literature and can be used to improve predictions of the likely effects of encroachment on biodiversity and ecosystem services.

Holes localized on a Skyrmion in a doped antiferromagnet on the honeycomb lattice: Symmetry analysis

Using the low-energy effective field theory for hole-doped antiferromagnets on the honeycomb lattice, we study the localization of holes on Skyrmions, as a potential mechanism for the preformation of Cooper pairs. In contrast to the square lattice case, for the standard radial profile of the Skyrmion on the honeycomb lattice, only holes residing in one of the two hole pockets can get localized. This differs qualitatively from hole pairs bound by magnon exchange, which is most attractive between holes residing in different momentum space pockets. On the honeycomb lattice, magnon exchange unambiguously leads to f-wave pairing, which is also observed experimentally. Using the collective-mode quantization of the Skyrmion, we determine the quantum numbers of the localized hole pairs. Again, f-wave symmetry is possible, but other competing pairing symmetries cannot be ruled out.

Gauged R-symmetry and its anomalies in 4D N=1 supergravity and phenomenological implications

We consider a class of models with gauged U(1) R symmetry in 4D N=1 super-gravity that have, at the classical level, a metastable ground state, an infinitesimally small (tunable) positive cosmological constant and a TeV gravitino mass. We analyse if these properties are maintained under the addition of visible sector (MSSM-like) and hidden sector state(s), where the latter may be needed for quantum consistency. We then discuss the anomaly cancellation conditions in supergravity as derived by Freedman, Elvang and Körs and apply their results to the special case of a U(1) R symmetry, in the presence of the Fayet-Iliopoulos term (ξ) and Green-Schwarz mechanism(s). We investigate the relation of these anomaly cancellation conditions to the “naive” field theory approach in global SUSY, in which case U(1) R cannot even be gauged. We show the two approaches give similar conditions. Their induced constraints at the phenomenological level, on the above models, remain strong even if one lifted the GUT-like conditions for the MSSM gauge couplings. In an anomaly-free model, a tunable, TeV-scale gravitino mass may remain possible provided that the U(1) R charges of additional hidden sector fermions (constrained by the cubic anomaly alone) do not conflict with the related values of U(1) R charges of their scalar superpartners, constrained by existence of a stable ground state. This issue may be bypassed by tuning instead the coefficients of the Kahler connection anomalies (b K , b CK ).