Statistical Study and Prediction of Variability of Erythemal Ultraviolet Irradiance Solar Values in Valencia,Spain

The goal of this study was to statistically analyse the variability of global irradiance and ultraviolet erythemal (UVER) irradiance and their interrelationships with global and UVER irradiance, global clearness indices and ozone. A prediction of short-term UVER solar irradiance values was also obtained. Extreme values of UVER irradiance were included in the data set, as well as a time series of ultraviolet irradiance variability (UIV). The study period was from 2005 to 2014 and approximately 250,000 readings were taken at 5-min intervals. The effect of the clearness indices on global irradiance variability (GIV) and UIV was also recorded and bi-dimensional distributions were used to gather information on the two measured variables. With regard to daily GIV and UIV, it is also shown that for global clearness index (k_t) values lower than 0.6 both global and UVER irradiance had greater variability and that UIV on cloud-free days (k_t higher than 0.65) exceeds GIV. To study the dependence between UIV and GIV the χ² statistical method was used. It can be concluded that there is a 95% probability of a clear dependency between the variabilities. A connection between high k_t (corresponding to cloudless days) and low variabilities was found in the analysis of bi-dimensional distributions. Extreme values of UVER irradiance were also analyzed and it was possible to calculate the probable future values of UVER irradiance by extrapolating the values of the adjustment curve obtained from the Gumbel distribution.     

Climate controls on rainfall isotopes and their effects on cave drip water and speleothem growth: the case of Molinos cave (Teruel,NE Spain)

The interpretation of stable isotopes in speleothems in terms of past temperature variability or precipitation rates requires a comprehensive understanding of the climatic factors and processes that influence the δ¹⁸O signal in the way through the atmosphere to the cave, where carbonate precipitates acquiring its final isotopic composition. This study presents for the first time in the Iberia Peninsula an integrated analysis of the isotopic composition of rainfall (δ¹⁸O_p) during 2010–2012 years and, through a detailed monitoring survey, the transference of the primary isotopic signal throughout the soil and epikarst into the Molinos cave (Teruel, NE Spain). Both air temperature and amount of precipitation have an important effect on δ¹⁸O_p values, clearly imprinting a seasonal variability modulated by an amount effect when rainfall events are more frequent or intense. Air mass history and atmospheric circulation influences are considered through the study of weather types, synoptic-scale climate patterns and large-scale atmospheric circulation indexes (North Atlantic Oscillation and Western Mediterranean Oscillation) revealing a dominant source effect on δ¹⁸O_p values in this region where tropical North Atlantic and Western Mediterranean are the two moisture source regions. A delay of 2–3 months occurs between the dripwater oxygen isotopic composition (δ¹⁸O_d) respect to δ¹⁸O_p values as a consequence of large residence time in the epikarst. Limited calcite precipitates are found from winter to spring when δ¹⁸O_d values are less negative and dripwater rates are constant. This study suggests that NE Iberian δ¹⁸O_calcite proxy records are best interpreted as reflecting a combination of parameters, not just paleotemperature or paleorainfall and, if extending present-day situation towards the recent past, a biased signal towards winter values should be expected in Molinos speleothem records.     

Middle Miocene peralkaline ignimbrites in the Hermosillo region (Sonora, Mexico): Geodynamic implications

Scattered ignimbritic mesas crop out in the Hermosillo region (Sonora, Mexico). These rocks that have been dated at 12.5 Ma (Middle Miocene) have the petrography and chemical characteristics of comendites. Such a flare-up of peralkaline acidic volcanism, after a long period of subduction-related arc volcanism, emphasises an important change in the source of volcanism. It corresponds to the latest stage of continental extension prior to the marine invasion and the development of spreading centres in the Gulf of California. To cite this article: J. Vidal Solano et al., C. R. Geoscience 337 (2005).     

Deep incision in an Aptian carbonate succession indicates major sea‐level fall in the Cretaceous

Long‐term relative sea‐level cycles (0·5 to 6 Myr) have yet to be fully understood for the Cretaceous. During the Aptian, in the northern Maestrat Basin (Eastern Iberian Peninsula), fault‐controlled subsidence created depositional space, but eustasy governed changes in depositional trends. Relative sea‐level history was reconstructed by sequence stratigraphic analysis. Two forced regressive stages of relative sea‐level were recognized within three depositional sequences. The first stage is late Early Aptian age (intra Dufrenoyia furcata Zone) and is characterized by foreshore to upper shoreface sedimentary wedges, which occur detached from a highstand carbonate platform, and were deposited above basin marls. The amplitude of relative sea‐level drop was in the order of tens of metres, with a duration of <1 Myr. The second stage of relative sea‐level fall occurred within the Late Aptian and is recorded by an incised valley that, when restored to its pre‐contractional attitude, was >2 km wide and cut ≥115 m down into the underlying Aptian succession. With the subsequent transgression, the incision was backfilled with peritidal to shallow subtidal deposits. The changes in depositional trends, lithofacies evolution and geometric relation of the stratigraphic units characterized are similar to those observed in coeval rocks within the Maestrat Basin, as well as in other correlative basins elsewhere. The pace and magnitude of the two relative sea‐level drops identified fall within the glacio‐eustatic domain. In the Maestrat Basin, terrestrial palynological studies provide evidence that the late Early and Late Aptian climate was cooler than the earliest part of the Early Aptian and the Albian Stage, which were characterized by warmer environmental conditions. The outcrops documented here are significant because they preserve the results of Aptian long‐term sea‐level trends that are often only recognizable on larger scales (i.e. seismic), such as for the Arabian Plate.     

Temperate rainforest response to climate change and disturbance agents in northwestern Patagonia (41°S) over the last 2600 years

We present detailed pollen and charcoal records from Lago Pichilafquén (~ 41°S) to decipher the effects of climate change and varying disturbance regimes on the composition and structure of the vegetation on the Andean foothills of northwestern Patagonia during the last 2600 yr. Here, temperate rainforests have dominated the landscape since 2600 cal yr BP with variations ranging from cool-temperate and wet north Patagonian rainforests to relatively warm and summer-drought-resistant Valdivian rainforests. We interpret relatively warm/dry conditions between 1900–2600, 690–750 and 320–430 cal yr BP, alternating with cold/wet conditions between 1500–1900, 750–1100 and 430–690 cal yr BP. Rapid deforestation and spread of plants introduced by Europeans occurred at 320 and 140 cal yr BP. The record includes five tephras with ages of 2130, 1460, 1310, 1210, and 340 cal yr BP, all of which precede local fire events and increases in trees favored by disturbance by less than 100 yr. We conclude that centennial-scale changes in the southern westerlies were the primary driver of vegetation shifts in northwestern Patagonia over the last 2600 yr. Within this interval, local disturbance regimes altered the structure, composition, and dynamics of the lowland rainforest vegetation during several discrete, short-lived episodes.     

Radial basis functions with compact support for multivariate geostatistics

Matrix-valued radially symmetric covariance functions (also called radial basis functions in the numerical analysis literature) are crucial for the analysis, inference and prediction of Gaussian vector-valued random fields. This paper provides different methodologies for the construction of matrix-valued mappings that are positive definite and compactly supported over the sphere of a d-dimensional space, of a given radius. In particular, we offer a representation based on scaled mixtures of Askey functions; we also suggest a method of construction based on B-splines. Finally, we show that the very appealing convolution arguments are indeed effective when working in one dimension, prohibitive in two and feasible, but substantially useless, when working in three dimensions. We exhibit the statistical performance of the proposed models through simulation study and then discuss the computational gains that come from our constructions when the parameters are estimated via maximum likelihood. We finally apply our constructions to a North American Pacific Northwest temperatures dataset.     

Magnetic and thermal energies in the solar wind

Magnetic and thermal energy densities measured in the solar wind by the spacecraft Vela-3/IMP-3, Explorer-34 and HEOS-1 are compared. A linear relation seems to exist, on the average, between these parameters, suggesting a possible equipartition of energy between plasma and magnetic field.     

Precise radiocarbon dating of Late-Glacial cooling in mid-latitude South America

Variability of atmospheric ¹⁴C content often complicates radiocarbon-based chronologies; however, specific features such as periods of constant ¹⁴C age or steep changes in radiocarbon ages can be useful stratigraphic markers. The Younger Dryas event in the Northern Hemisphere is one of those periods, showing conspicuous ¹⁴C wiggles. Although the origin of those variations is not fully understood, we can make practical use of them and determine: (i) whether the Younger Dryas was global in extent; if so, (ii) were the initial cooling and the final warming synchronous worldwide; and (iii) what are the implications of these similarities/differences? Here we report high-resolution AMS ¹⁴C chronologies from the mid-latitudes of South America that pinpoint a cool episode between 11,400 and 10,200¹⁴C yr B.P. The onset of the final cool episode of the Late Glacial in the southern mid-latitudes, i.e., the Huelmo/Mascardi Cold Reversal, preceded the onset of the Younger Dryas cold event by ∼550 calendar years. Both events ended during a radiocarbon-age plateau at ∼10,200¹⁴C yr B.P. Thus, the Huelmo/Mascardi Cold Reversal encompasses the Younger Dryas, as well as a couple of short-term cool/warm oscillations that immediately preceded its onset in the North Atlantic region.     

Across shore variability and trophodynamic features of meiofauna in a microtidal beach of the NW Mediterranean

The across shore variability and trophodynamics of meiofauna were studied in a microtidal beach of the Thyrrenian Sea (NW Mediterranean). Two sites were sampled at Collelungo beach (Maremma Park, Italy) subjected to different regimes of sediment erosion and deposition. At each site, four levels were sampled in November 2002 and May 2003 along a transect from the supralittoral zone to the surf zone. Sediment cores were taken down to a depth of 10 cm and meiofaunal abundance and community structure were analyzed and related to the principal trophic resources (quantity and quality of organic matter, chlorophyll a, bacteria density and biomass).Meiofaunal abundance ranged between 14 ind. 10 cm⁻² and 716 ind. 10 cm⁻² in the top 0–10 cm of sediment. Abundance was lower in the surface (0–2 cm) than in the deeper (5–10 cm) sediment layers but no significant differences were found between the two sites.Multivariate BIOENV analysis showed that dryness, grain size (related to physical processes) and bacterial biomass, were the main variables explaining meiofauna distribution in these beaches. Meiofaunal densities and number of taxa were always higher at the swash level, while lower abundances were observed at the dry sampling level (+5 m). This across shore trend was also observed for the quality of the organic matter (PRT/CHO) and bacterial densities. Nematode assemblage structure at the swash sampling level showed a dominance of non-selective deposit feeders (1B), with Xyalidae as the dominant family (56%), followed by Thoracostomopsidae (14%) and Selachnematidae (12%).According to the findings, physical and biological variables at the swash level create optimal living conditions for the meiobenthos, making the swash a key area within the beach ecosystem, with potential implications within basic and applied ecological studies.