Impact of predation on the polychaete Hediste diversicolor in estuarine intertidal flats

In estuarine sediment flats benthic macroinvertebrates are intensively consumed by a variety of predators, such as aquatic birds and nekton (mostly fish and crustaceans). However, there is still a lack of conclusive studies that evaluate if this predation has a relevant impact on the populations of those invertebrates, which are a key element of the estuarine food chain. In the Tagus estuary we experimentally tested and quantified the impact of predation on the polychaete Hediste diversicolor, one of the most important prey for a variety of predators in many estuaries. Using an exclusion experiment, we compared the seasonal variation in the densities of H. diversicolor from February to November in sediment plots (1) available to both bird and nekton predators, (2) just to nekton, and (3) without predators. We also followed changes in the abundance of potential predators throughout the study. The lowest densities were systematically observed in the plots accessible to all predators, followed by those which excluded just birds, and finally by those that excluded all predators. The exclosures were in place for 9 months, at the end of which the average density of H. diversicolor in the plots protected from all predators was eight times greater than in those without any protection. These results demonstrate that predation had a major impact on the densities of H. diversicolor. The relative importance of bird and nekton predation varied along the study, and this seems to be determined by different peaks of abundance of the two types of predators. However, when present in high densities, birds and nekton seem to have a similar impact on H. diversicolor. Our results suggest that predation is a key factor on the population dynamics of H. diversicolor. In addition, the levels of predation that we observed suggest that this polychaete can be a limited resource, and this could have major ecological consequences for predators for which it is a key prey.     

Large-scale silicate liquid immiscibility: a possible example from northeastern Brazil

Ultrapotassic, peralkalic silica-saturated plutons (580 Ma) are widespread in the Cachoeirinha-Salgueiro foldbelt, northeastern Brazil. They consist of alkali-feldspar syenites with pyroxenite as co-magmatic inclusions and syn-plutonic or late-stage dikes. Pyroxenite and syenite have the same mineral phases (aegirine-augite, microcline, sphene, apatite, blue amphibole, magnetite), but only in different proportions. Rare inclusions of a “mixed” rock (about 60% syenite+40% pyroxenite in an emulsion-like texture) are also present. Pyroxenes in the three units are all only slightly zoned, silica-saturated and extremely low in Al₂O₃ (0.2–1.4%). Amphiboles are mostly K-rich richterite, characterized by high SiO₂, low Al₂O₃ and TiO₂ contents and low Mg#.

The three rock types have similar REE chondrite-normalized patterns, with negative slopes and lack of Eu anomaly, with the total REE in the pyroxenite greater than that of the syenite. Trace element patterns for the mixed rock are intermediate between those for the pyroxenite and syenite. Major element partitioning between pyroxenite and syenite has the same sense as that one observed between immiscible liquids in volcanic lavas and trace element partitioning is similar to the experimentally determined partition of immiscible liquid pairs.

The rocks have similar high δ¹⁸O values (avg. w.r.+ 8‰_SMOW, corrected from pyroxene), high initial ⁸⁷Sr/⁸⁶Sr ratios (about 0.710), and low ¹⁴³Nd/¹⁴⁴Nd (avg. 0.51104).

Field and geochemical characteristics indicate chemical equilibrium among the three rock types and suggest liquid immiscibility between syenite and pyroxenite, the mixed rock representing the original magma composition.     

Assessing multidecadal runoff (1970–2010) using regional hydrological modelling under data and water scarcity conditions in Peruvian Pacific catchments

In a context of water scarcity in Peruvian Pacific catchments as a crucial issue for Peru, added to the paucity of data availability, we propose a methodology that provides new perspectives for freshwater availability estimation as a base reference for unimpaired conditions. Under those considerations, a regional discharge of 709 m³/s to the Pacific Ocean is estimated with a significant increasing trend of about 43 m³/s per decade over the 1970 – 2010 period. To represent the multidecadal behaviour of freshwater runoff along the region, a regional runoff analysis is proposed based on hydrological modelling at annual and monthly time step for unimpaired conditions over the whole 1970 – 2010 period. Differential Split‐Sample Tests are used to assess the hydrological modelling robustness of the GR1A and GR2M conceptual lumped models, showing a satisfactory transposability from dry to wet years inside the thresholds defined for Nash–Sutcliffe and bias criteria. This allowed relating physical catchment characteristics with calibrated and validated model parameters, thus offering a regional perspective for dryland conditions in the study area (e.g., the anticlockwise hysteresis relationship found for seasonal precipitation–runoff relationship) as well as the impacts of climate variability and catchment characteristics.     

The XMM Cluster Survey: forecasting cosmological and cluster scaling-relation parameter constraints

We forecast the constraints on the values of  σ₈, Ω_m  and cluster scaling-relation parameters which we expect to obtain from the XMM Cluster Survey (XCS). We assume a flat Λ cold dark matter Universe and perform a Monte Carlo Markov Chain analysis of the evolution of the number density of galaxy clusters that takes into account a detailed simulated selection function. Comparing our current observed number of clusters shows good agreement with predictions. We determine the expected degradation of the constraints as a result of self-calibrating the luminosity–temperature relation (with scatter), including temperature measurement errors, and relying on photometric methods for the estimation of galaxy cluster redshifts. We examine the effects of systematic errors in scaling relation and measurement error assumptions. Using only  ( T , z )  self-calibration, we expect to measure Ω_m to ±0.03 (and  Ω_Λ  to the same accuracy assuming flatness), and σ₈ to ±0.05, also constraining the normalization and slope of the luminosity–temperature relation to ±6 and ±13 per cent (at 1σ), respectively, in the process. Self-calibration fails to jointly constrain the scatter and redshift evolution of the luminosity–temperature relation significantly. Additional archival and/or follow-up data will improve on this. We do not expect measurement errors or imperfect knowledge of their distribution to degrade constraints significantly. Scaling-relation systematics can easily lead to cosmological constraints 2σ or more away from the fiducial model. Our treatment is the first exact treatment to this level of detail, and introduces a new 'smoothed ML' (Maximum Likelihood) estimate of expected constraints.     

Quaternary reactivation of a basement structure in the Barreirinhas Basin, Brazilian Equatorial Margin

The Pirapemas Lineament is a remarkable 200-km-long, NE-SW trending structure in the Barreirinhas Basin, one of the several Brazilian coastal basins. This lineament splits the study area in two sectors of distinctive morphology, drainage patterns, and sedimentary covers. Terrain northward of the lineament presents a smooth topography with sub-parallel to sub-dendritic drainage patterns, whereas a dissected plateau characterized by incised valleys and rectangular drainage pattern occurs southward, suggesting a structural control by joints and faults. Geological field data, crossed with thermal luminescence (TL) and optically stimulated luminescence (OSL) dating, revealed that the surface southward of the lineament consists mostly of Miocene and late Pleistocene sedimentary deposits, represented by the Barreiras Formation and the Post-Barreiras sediments, respectively. In contrast, relatively younger sands mantle most of the northward terrain, as indicated by well-preserved paleodune deposits that grade into active aeolian dunes of the Lençóis Maranhenses National Park. Geomorphological and geological data analysis suggests that the northern sector is under the effect of subsidence, proving that the Pirapemas Lineament is an active agent modeling the landscape in the region. Geophysical data (gravity and seismic) confirm that such a structural feature is the surface expression of an active deep-seated basement fault.     

Non-gravitational force modeling of Comet 81P/Wild 2: I. A nucleus bulk density estimate

The nucleus of Comet 81P/Wild 2 is modeled by assuming various smooth triaxial ellipsoidal or irregular body shapes, having different rotational periods, spin axis orientations, and thermophysical properties. For these model nuclei, a large number of surface activity patterns (e.g., maps of active and inactive areas) are studied, and in each case the resulting water production rate and non-gravitational force vector versus time are calculated. By requiring that the model nuclei simultaneously reproduce certain properties of the empirical water production curve and non-gravitational changes of the orbit (focusing on changes of the orbital period and in the longitude of perihelion), constraints are placed on several properties of the nucleus. The simulations suggest that the mass of Comet 81P/Wild 2 is , resulting in a rather low bulk density, (depending on the assumed nucleus volume), and that the nucleus rotation is prograde rather than retrograde. The active area fraction is difficult to constrain, but at most 60% of the nucleus is likely to have near-surface ice.     

Assessing the impact of climate change on representative field crops in Israeli agriculture: a case study of wheat and cotton

Climate changes, associated with accumulation of greenhouse gases, are expected to have a profound influence on agricultural sustainability in Israel, a semi-arid area characterized by a cold wet winter and a dry warm summer. Accordingly this study explored economic aspects of agricultural production under projected climate-change scenarios by the “production function” approach, as applied to two representative crops: wheat, as the major crop grown in Israel’s dry southern region, and cotton, representing the more humid climate in the north. Adjusting outputs of the global climate model HadCM3 to the specific research locations, we generated projections for 2070–2100 temperatures and precipitations for two climate change scenarios. Results for wheat vary among climate scenarios; net revenues become negative under the severe scenario (change from −145 to −273%), but may increase under the moderate one (−43 to +35%), depending on nitrogen applied to the crop. Distribution of rain events was found to play a major role in determining yields. By contrast, under both scenarios cotton experiences a considerable decrease in yield with significant economic losses (−240 and −173% in A2 and B2 scenarios, respectively). Additional irrigation and nitrogen may reduce farming losses, unlike changes in seeding dates.     

Changes in snowmelt runoff timing in the contiguous United States

Changes in timing of snowmelt-fed streamflow have great importance for water supply, flood management, and ecological processes, as well as being a common indicator of climate change. In this study, snowmelt runoff timing change in the contiguous United States between 1957 and 2016 was investigated by analysing data from 97 streamflow gages. The annual snowmelt runoff timing shift was identified using ‘Center Time (CT)’ and ‘Spring Pulse Onset (SPO)’ methods, jointly with the monthly fractional streamflow (MFS) analysis, conducted between January and June. Since snowmelt-derived streamflow timing change is mainly induced by regional meteorological factors, such as air temperature and precipitation, their trends and relationship with CT were also examined. Shifts toward earlier snowmelt runoff timing were found by both methods, CT (8.3 days on average) and SPO (8.5 days on average). Although the results of the CT change are stronger than the SPO change, both outcomes are mostly correlated, particularly in the central and northwestern parts of the country. MFS trends support the outcomes of CT and SPO. In January, February, and especially March, a higher number of the stations indicated increasing trends in MFS. In April, May, and June, their number decreased and the number of gages with diminishing trends rose sharply. The timing difference is highly related to temperature change. Annual average temperature and temperature in the melting period increase considerably. The annual average temperature is significantly negatively correlated with CT in the vast majority of the regions. Although precipitation is not as effective as the temperature, its trends have impacts on snowmelt runoff timing change depending on the region and elevation. These results demonstrate the importance of the impacts of snowmelt runoff timing changes due to global warming on the regional and large-scale hydrology in the contiguous United States.     

Multistage rifting evolution of the Colorado basin (offshore Argentina): Evidence for extensional settings prior to the South Atlantic opening

The identification of three independent rifting events in the Colorado basin area highlights the complexity of its Mesozoic rifting history, which ended in the Early Cretaceous with the opening of the South Atlantic Ocean. A first rifting event, associated with the extensional reactivation of previously compressive thrusts of the Ventania‐Cape fold belt, is transected by faults forming the main depocenters of the Colorado and possibly the adjacent Salado basin. The second and main rifting stage is correlated with the Early Jurassic Karoo rifting. In the Early Cretaceous, WNW–ESE extension produced NNE‐trending landward‐dipping faults, concentrated in the outer 100–200 km of the continental crust domain, possibly coeval with SDR emplacement. This is the first identification of three superimposed rifting settings in the southern South Atlantic realm and is key to understanding the complex Mesozoic breakup history of SW Gondwana.