Interannual Variability of Atmospheric CO<Subscript>2</Subscript> Concentrations over Central Siberia from ZOTTO Data for 2009–2015

The interannual variations in the characteristics of the seasonal cycle (annual and seasonal amplitudes, winter emission, dates of annual minimum and maximum, and phase) and in the growth rate of atmospheric carbon dioxide concentration over Central Siberia are analyzed for the period from May 2009 to January 2016. The results are based on the continuous monitoring of CO₂ concentration at the Zotino Tall Tower Observatory (ZOTTO, www.zottoproject.org). It is found that the seasonal amplitude of CO₂ concentration in the atmo spheric surface layer over Western Siberia is 26.4 ± 0.8 μmol/mol (no long-term trend toward its increase was revealed), the annual mean growth rate of CO₂ is 2.34 μmol/mol per year, its variations range from 1 to 4 μmol/mol per year.     

First Images of Impulsive Millimeter Emission and Spectral Analysis of the 1994 August 18 Solar Flare

We present here the first images of impulsive millimeter emission of a flare. The flare on 1994 August 18 was simultaneously observed at millimeter (86 GHz), microwave (1-18 GHz), and soft and hard X-ray wavelengths. Images of millimeter, soft and hard X-ray emission show the same compact ( 8) source. Both the impulsive and the gradual phases are studied in order to determine the emission mechanisms. During the impulsive phase, the radio spectrum was obtained by combining the millimeter with simultaneous microwave emission. Fitting the nonthermal radio spectra as gyrosynchrotron radiation from a homogeneous source model with constant magnetic field yields the physical properties of the flaring source, that is, total number of electrons, power-law index of the electron energy distribution, and the nonthermal source size. These results are compared to those obtained from the hard X-ray spectra. The energy distribution of the energetic electrons inferred from the hard X-ray and radio spectra is found to follow a double power-law with slope 6–8 below 50 keV and 3–4 above those energies. The temporal evolution of the electron energy spectrum and its implication for the acceleration mechanism are discussed. Comparison of millimeter and soft X-ray emissions during the gradual phase implies that the millimeter emission is free-free radiation from the same hot soft X-ray emitting plasma, and further suggests that the flare source contains multiple temperatures.     

Suspended sediment transport analysis in two Italian instrumented catchments

Suspended sediment transport in streams is an effective indicator of soil erosion at the watershed scale. This process was studied using the data obtained from two continuous monitoring stations installed in Italian watersheds, the Rio Cordon and Torrente Carapelle. The catchments have substantially different climatic, morphological and land use characteristics. The Rio Cordon, a small Alpine watershed, has been monitored since 1986, while in the Torrente Carapelle, a medium-size Mediterranean watershed, the monitoring station has provided data since 2007. Several flood events with suspended sediment transport were isolated in the two catchments, excluding those determined by snowmelt in the Rio Cordon as this process does not affect the Carapelle watershed. Analysis of the events showed different behavior in terms of hysteresis loop trends between water discharge (m³ s^-1) and suspended sediment concentration (g l^-1) values, as the Rio Cordon confirms clockwise relationships most frequently, while counter-clockwise trends represent the majority of cases for the Carapelle Torrent. The different behavior of the two watersheds was further analyzed by evaluating relationships between the main hydrological parameters related to suspended sediment transport. Runoff controls the total sediment budget in both catchments. In contrast, it was noted that the runoff process does not interfere in the magnitude of the suspended sediment transport in the Rio Cordon catchment, while variations due to the larger size of the catchment area characterize the events in the Carapelle watershed. Lastly, a flow peak threshold that determines the advance or delay of the hydrograph peak with respect to the sedigraph peak was established for the Carapelle Torrent, while it was not reported in the Rio Cordon.     

The coastal ocean off Oregon from 1961 to 2000: is there evidence of climate change or only of Los Niños?

A zonal hydrographic section along 44.65°N, from the coast of Oregon to 300 km offshore, was occupied regularly (at least seasonally) from 1961 to 1971 and then sporadically until recently. Regular monitoring of this section to 160 km offshore resumed in July 1997 as part of the GLOBEC Long Term Observational Program; the recent data provide observations in Oregon coastal waters of El Niño 1997–98 and La Niña conditions that followed. The complete seasonal data from the decade 1961–1971 provide a basis for comparison with the recent temperature and salinity sections, steric height profiles, geostrophic velocity, and water mass characteristics. These data, and sporadic observations in intervening years, allow us to compare conditions during several ENSO events with the recent event and to search for evidence of climate change. The PFEL Coastal Upwelling Index, sea level from the University of Hawaii Sea Level Center, the Multivariate ENSO Index (MEI), the Pacific Decadal Oscillation (PDO), and outflow from the Columbia River are used to distinguish local and remote causes of variability in physical oceanographic conditions off Oregon. The sequence of El Niño/La Niña/El Niño in 1963–66, during a cool phase of PDO, provides a comparison to El Niño/La Niña of 1997–2000. El Niño in 1982–83 and 1997–98, during a warm phase of PDO, caused the largest oceanographic anomalies in the 40 years. The comparison indicates warming of the coastal ocean off Oregon and suggests a modulation of ENSO effects by PDO. Such modulation would mask evidence for secular climate change in our 40-year oceanographic data series.     

Life Cycle,Growth and Secondary Production in a Brackish-Water Population of the Polychaete Notomastus latericeus (Capitellidae) in the Mediterranean Sea

Abstract. Three years of observations on a population of Notomastus latericeus Sars from Acquatina lagoon (Lecce, Italy) are reported. The population dynamics, life cycle, and reproduction were investigated in order to explain periodic density variations of this species. Some physical parameters of the water column were measured and sediment analyses were performed to characterize the environment. Secondary production was also estimated as part of a functional study of the benthic system in the Acquatina lagoon. The species is opportunistic; its density is apparently correlated to variation in salinity, but its presence in the lagoon is dependent on recruitment success and competition with other polychaete species.     

Charophyta: their use in paleolimnology

Charophyta are common algae in limnic waters from many regions and are an interesting group from an evolutionary point-of-view, as they are believed to be related to the Chlorophyceae and land plants. Paleontological-botanical systematics are discussed, taking into consideration some new advances. Charophytes live in all types of inland waters and are sensitive to ecological change, and so they are very useful paleolimnological markers. Gaps concerning gyrogonite morphology in extant taxa and their responses to different environmental conditions must be described. This paper discusses data concerning ecological factors affecting the distribution of Argentinian Charophyta (principally distributed between 30°S and 40°S), gyrogonite morphology related to different ecological conditions, and the way that Charophyta can modify the environment.This is the fifth in a series of papers published in this issue on Paleolimnology in Southern South America. Dr C. A. Fernández served as guest editor for these papers.     

Using beryllium-7 to evaluate soil erosion processes in agricultural lands in semiarid regions of Central Argentina

This work presents the results of a soil erosion study using the ⁷Be technique. This technique estimates the water erosion/deposition from the comparison between ⁷Be soil content of a reference site and an eroded or sedimented site. The soil samples were collected from an agricultural area of the semiarid region of Argentina near San Luis City, which has a marked rainfall season. The area has been used for crop cultivation, being subjected to plowing practices. The ⁷Be in the Reference Site was in the first centimeter of soil, showing the typical exponential decreasing of ⁷Be soil content with depth, with the ⁷Be inventories value being 340?±?50 Bq m^?2 for the dry season and 571?±?48 Bq m^?2 for the rainy season. The ⁷Be technique was applied to a potential eroded site subjected to traditional tillage practices (plowing). A net soil erosion value of 13.5 t ha^?1 (1.35 kg m^?2) was obtained. From the assumptions of the applied technique, we can draw the inference that this erosion was caused by rains produced in the month prior to the date of soil sampling.     

Effects of topography and crustal heterogeneities on the source estimation of LP event at Kilauea volcano

The main goal of this study is to improve the modelling of the source mechanism associated with the generation of long period (LP) signals in volcanic areas. Our intent is to evaluate the effects that detailed structural features of the volcanic models play in the generation of LP signal and the consequent retrieval of LP source characteristics. In particular, effects associated with the presence of topography and crustal heterogeneities are here studied in detail. We focus our study on a LP event observed at Kilauea volcano, Hawaii, in 2001 May. A detailed analysis of this event and its source modelling is accompanied by a set of synthetic tests, which aim to evaluate the effects of topography and the presence of low velocity shallow layers in the source region. The forward problem of Green's function generation is solved numerically following a pseudo-spectral approach, assuming different 3-D models. The inversion is done in the frequency domain and the resulting source mechanism is represented by the sum of two time-dependent terms: a full moment tensor and a single force. Synthetic tests show how characteristic velocity structures, associated with shallow sources, may be partially responsible for the generation of the observed long-lasting ringing waveforms. When applying the inversion technique to Kilauea LP data set, inversions carried out for different crustal models led to very similar source geometries, indicating a subhorizontal cracks. On the other hand, the source time function and its duration are significantly different for different models. These results support the indication of a strong influence of crustal layering on the generation of the LP signal, while the assumption of homogeneous velocity model may bring to misleading results.     

Taxonomic distinctness in Mediterranean marine nematodes and its relevance for environmental impact assessment

Taxonomic distinctness has been applied successfully for the exploration of biodiversity patterns, yet its relevance in environmental impact assessment is far from being unquestioned. In this study, we assessed the potential of taxonomic distinctness to discern perturbed and unperturbed sites by analysing Mediterranean nematode assemblages. Geographic and habitat-related effects on the performance of the index were also explored. Above all, our findings do not corroborate the conjecture that taxonomic distinctness could be largely unaffected by natural variability, habitat features, and biogeographic context, casting doubts on potential generalization concerning its application as an indicator of environmental stress. Taxonomic distinctness represents an excellent metric to identifying taxonomic properties of ecological systems but, as for other ecological indices, it should be viewed as a complementary tool in environmental impact assessment, due to its sensitiveness to specific environmental features of systems being investigated.