A detailed paleomagnetic and rock-magnetic investigation around Cretaceous-Paleogene boundary: the Autlan (Western Mexico) volcanic sequence revisited

We present a detailed rock-magnetic and paleomagnetic survey from Autlan volcanic succession in western Mexico. The principal aim of this study is to extend paleomagnetic data from Autlan lavas in order to confirm vertical-axis rotation observed in reconnaissance study and to evaluate long-term variation of the geomagnetic field strength based on existing and global data. The mean inclination (44.7°) is in agreement with the expected inclination for 60 and 70 Ma, as derived from available reference poles for the North American craton. The declination (333.6°), however, is significantly different from those expected, which suggests a statistically significant counterclockwise tectonic rotation ranging between 10° ± 6° and 14° ± 7°. As a measure of paleosecular variation (PSV), we obtained a geomagnetic field dispersion of 9.6° (upper and lower limits: 7.2°–11.9°) in perfect agreement with the previously published PSV compilation of selected Cretaceous data from lavas. The mean virtual dipole moments available for Autlan lavas are about 65% of the present geomagnetic axial dipole but are in reasonably good agreement with other comparable quality determinations between 5 and 90 Ma. This reinforces the hypothesis that low geomagnetic field strengths persisted for the entire Jurassic extending into the Upper Cretaceous.     

Hierarchical spatial modeling of the presence of Chagas disease insect vectors in Argentina. A comparative approach

We modeled the spatial distribution of the most important Chagas disease vectors in Argentina, in order to obtain a predictive mapping method for the probability of presence of the vector species. We analyzed both the binary variable of presence-absence of Chagas disease and the vector species richness in Argentina, in combination with climatic and topographical covariates associated to the region of interest. We used several statistical techniques to produce distribution maps of presence–absence for the different insect species as well as species richness, using a hierarchical Bayesian framework within the context of multivariate geostatistical modeling. Our results show that the inclusion of covariates improves the quality of the fitted models, and that there is spatial interaction between neighboring cells/pixels, so mapping methods used in the past, which assumed spatial independence, are not adequate as they provide unreliable results.     

Spatial clustering of Ultra Steep Spectrum sources and galaxies

We present measurements of the clustering properties of galaxies in the field of redshift range 0.5 ≲ z ≲ 1.5 Ultra Steep Spectrum radio sources selected from the Sydney University Molonglo Sky Survey and the National Radio Astronomy Observatories Very Large Array Sky Survey. Galaxies in these USS fields were identified in deep near-infrared observations, complete down to   K _s= 20  , using the IRIS2 instrument at the Anglo-Australian Telescope. We used the redshift distribution of   K _s < 20  galaxies taken from Cimatti et al. (2002) to constrain the correlation length r ₀. We find a strong correlation signal of galaxies with   K _s < 20  around our USS sample. A comoving correlation length   r ₀= 14.0 ± 2.8  h ⁻¹ Mpc  and γ= 1.98 ± 0.15 are derived in a flat cosmological model universe.
We compare our findings with those obtained in a cosmological N -body simulation populated with galform semi-analytic galaxies. We find that clusters of galaxies with masses in the range   M = 10^13.4–14.2  h ⁻¹ M_⊙  have a cluster–galaxy cross-correlation amplitude comparable to those found between the USS hosts and galaxies. These results suggest that distant radio galaxies are excellent tracers of galaxy overdensities and pinpoint the progenitors of present day rich clusters of galaxies.     

Benthic input rates predict seagrass (Posidonia oceanica) fish farm-induced decline

Fish farms represent a growing source of anthropogenic disturbance to benthic communities, and efficient predictors of such impacts are urgently needed. We explored the effects of fish farm benthic organic and nutrient inputs on the population dynamics of a key seagrass species (Posidonia oceanica) in four Mediterranean deep meadows adjacent to sea bream and sea bass farms. We performed two annual plant censuses on permanent plots at increasing distance from farms and measured benthic sedimentation rates around plots. High shoot mortality rates were recorded near the cages, up to 20 times greater than at control sites. Recruitment rates increased in variability but could not compensate mortality, leading to rapid seagrass decline within the first 100 m from cages. Seagrass mortality increased with total sedimentation rates (K=0.55, p<0.0002), and with organic matter (K=0.50, p=0.001), total nitrogen (K=0.46, p=0.002) and total phosphorus (K=0.56, p<3.10(-5)) inputs. P. oceanica decline accelerated above a phosphorus loading threshold of 50mg m(-2)day(-1). Phosphorus benthic sedimentation rate seems a powerful predictor of seagrass mortality from fish farming. Coupling direct measurements of benthic sedimentation rates with dynamics of key benthic species is proposed as an efficient strategy to predict fish farm impacts to benthic communities.     

Blocking Episodes in the Southern Hemisphere: Impact on the Climate of Adjacent Continental Areas

This work presents an updated climatology of blocking episodes for the Southern Hemisphere between 1960 and 2000, based on data from NCEP/NCAR reanalysis. Five contiguous areas of blocking activity are considered; Southeastern Pacific, Southwestern Pacific, Atlantic, Indian and Oceania. The impact of the three most important areas of onset blocking episodes (Southeastern Pacific, Atlantic and Oceania) upon the climate of the adjacent continental areas (South America and Australia) was evaluated. Composites of the meteorological variables (temperature and precipitation) were obtained for periods of diagnosed blockings. The impact of the blocking episodes over the climate of South America and Australia is highlighted whenever anomaly fields of temperature and precipitation are significant at the 5% and 10% levels, respectively. Impacts of Southeastern Pacific and Atlantic blockings are observed on the temperature field over several regions of South America. Significantly higher (lower) temperatures than climatology occur in southern Brazil, northern Argentina, Uruguay and Paraguay, and lower (higher) than climatology in the extreme south of South America for the Southeastern Pacific (Atlantic) blocking episodes. Precipitation over South America is also affected by the Southeastern Pacific and Atlantic blockings in different ways. The Southeastern Pacific blocking has higher impact on precipitation in summer (dry conditions in northeast Brazil) and spring (wet conditions in central and southern Brazil), while the Atlantic blocking affects precipitation in autumn and winter (wet conditions in parts of central and southern Brazil). The blocking cases over Oceania affect southeastern Australia with normal to higher than climatological precipitation and with negative temperature anomalies in that region. Finally we provide a detailed analysis of a South Atlantic blocking episode, which occurred between the 4^th and the 8^th of June 1997. This event shows clearly the split of the jet stream into two branches (subtropical and polar) surrounding the anticyclonic sector, and satellite imagery revealed the presence of transient systems in the periphery of the blocking anticyclone responsible for high values of precipitation in the southeastern sector of South America.     

DNA barcode,taxonomic and ecological notes for the identification of the invasive amphipod Monocorophium acherusicum (Costa, 1851)

We report the occurrence of the invasive amphipod Monocorophium acherusicum in Mar del Plata port, Argentina, using morphological and molecular analysis and estimated mean abundance to detect monthly variations of this population. We compared M. acherusicum morphology with that of M. insidiosum and Crassicorophium bonelli, the two most similar locally occurring species, to establish the diagnostic characteristics for the correct identification of them; moreover, we provide some taxonomic notes about others corophiids regionally distributed. M. acherusicum were collected in a subtidal biofouling community and its mean abundance was maximum in summer. In the molecular analysis, the maximum-likelihood tree showed that specimens from Mar del Plata were clustered with M. acherusicum specimens from GenBank and Boldsystems. We support and confirm the species identity in Mar del Plata port using DNA barcoding and with taxonomic methods.     

High downward flux of mucilaginous aggregates in the Ligurian Sea during summer 2002: similarities with the mucilage phenomenon in the Adriatic Sea

The DYFAMED sediment trap station in the Ligurian Sea (NW Mediterranean) has been active since 1986 and today comprises the longest time‐series of downward particle flux in the Mediterranean Sea. As such, it provides valuable information on the interannual variability of the particle flux, and also documents possible recent changes in the NW Mediterranean pelagic ecosystems. We report an unprecedented episode of downward flux of mucilaginous material at the DYFAMED station during summer 2002 in association with singular hydrometeorological conditions. The rain of mucilaginous aggregates clogged a PPS5 sediment trap at 260 m depth and was also clearly detected at 1080 m depth. The possible factors governing the development and sinking of the mucilaginous material are discussed. A very sharp increase of sea surface temperature during June and the presence of freshened waters in the surface the following month resulted in a stronger than usual stratification of the upper water column throughout the summer season. We suggest that the steepness of the vertical density gradient was responsible for the unusual accumulation of mucous aggregates. Additionally, a diatom bloom took place during the nutrient‐depleted conditions typical of summer, a factor which may have contributed to feed the pycnocline with transparent exopolymer substances. A storm occurring in the beginning of August relaxed the stratification and promoted the deposition of the mucilaginous aggregates accumulated in the upper water column during the preceding months. Important similarities of ambient conditions preceding the apparition of mucilaginous material in our open‐sea site and those reported in the Adriatic Sea during major mucilage events, suggest that general climatic conditions, rather than local factors, drive the occurrence of major accumulations of mucilaginous material in the water column at both sub‐basins of the Mediterranean Sea. In this regard, the strength of the air temperature increase during the onset of the stratified season is proposed as a major controlling factor.     

Volcanic emissions and atmospheric pollution:A study of nanoparticles

The influence of emissions of an active volcano on the composition of nanoparticles and ultrafine road dust was identified in an urban area of the Andes.Although many cities are close to active volcanoes,few studies have evaluated their influence in road dust composition.Air quality in urban areas is significantly affected by nonexhaust emissions(e.g.road dust,brake wear,tire wear),however,natural sources such as volcanoes also impact the chemical composition of the particles.In this study,elements from volcanic emissions such as Si>Al>Fe>Ca>K>Mg,and Si-Al with K were identified as complex hydrates.Similarly,As,Hg,Cd,Pb,As,H,Cd,Pb,V,and salammoniac were observed in nanoparticles and ultrafine material.Mineral composition was detected in the order of quartz>mullite>calcite>kaolinite>illite>goethite>magnetite>zircon>monazite,in addition to salammoniac,a tracer of volcanic sources.The foregoing analysis reflects the importance of carrying out more studies relating the influence of volcanic emissions in road dust in order to protect human health.The road dust load(RD₁₀)ranged between 0.8 and 26.8 mg m^?2in the city.