Bacterial response to seasonal changes in labile organic matter composition on the continental shelf and bathyal sediments of the Cretan Sea

Bacterial abundance, biomass and cell size were studied in the oligotrophic sediments of the Cretan Sea (Eastern Mediterranean), in order to investigate their response to the seasonal varying organic matter (OM) inputs. Sediment samples were collected on a seasonal basis along a transect of seven stations (ranging from 40 to 1570 m depth) using a multiple-corer. Bacterial parameters were related to changes in chloroplastic pigment equivalents (CPE), the biochemical composition (proteins, lipids, carbohydrates) of the sedimentary organic matter and the OM flux measured at a fixed station over the deep basin (1570 m depth). The sediments of the Cretan Sea represent a nutrient depleted ecosystem characterised by a poor quality organic matter. All sedimentary organic compounds were found to vary seasonally, and changes were more evident on the continental shelf than in deeper sediments. Bacterial abundance and biomass in the sediments of the Cretan Sea (ranging from 1.02 to 4.59 × 10⁸ cells g⁻¹ equivalent to 8.7 and 38.7 μgC g⁻¹) were quite high and their distribution appeared to be closely related to the input of fresh organic material. Bacterial abundance and biomass were sensitive to changes in nutrient availability, which also controls the average cell size and the frequency of dividing cells. Bacterial abundance increased up to 3-fold between August '94 and February '95 in response to the increased amount of sedimentary proteins and CPE, indicating that benthic bacteria were constrained more by changes in quality rather than the quantity of the sedimentary organic material. Bacterial responses to the food inputs were clearly detectable down to 10 cm depth. The distribution of labile organic compounds in the sediments appeared to influence the vertical patterns of bacterial abundance and biomass. Cell size decreased significantly with water depth. Bacterial abundance and biomass were characterised by clear seasonal changes in response to seasonal OM pulses. The strong coupling between protein flux and bacterial biomass together with the strong bacterial dominance over the total biomass suggest that the major part of the carbon flow was channelled through the bacteria and the benthic microbial loop.     

A control-volume finite-element method for three-dimensional multiphase basin modeling

In this paper we describe a 3D control-volume finite-element method to solve numerically the coupled partial differential equations (PDEs) governing geological processes involved in the evolution of sedimentary basins. These processes include sediment deposition and deformation, hydrocarbon generation, multiphase fluid flow, and heat transfer in deforming porous media.     

Plane state of stress and transverse oscillations of a simply supported rectangular plate

This paper deals with a general discussion of the subject matter. Recent literature is analyzed including some incorrect treatments of particular cases. Finally, a variational solution is obtained for the case where a linear distribution of stresses is applied to the plate boundaries. The lower natural frequencies are then tabulated as a function of the governing geometric and mechanical parameters.     

Changes in cetacean presence,relative abundance and distribution over 20 years along a trans‐regional fixed line transect in the Central Tyrrhenian Sea

From 1989 to 1992, systematic cetacean surveys were carried out twice weekly along a trans‐regional fixed transect in the Central Tyrrhenian Sea, utilising passenger ferries as research platforms. Using the same protocol and supervised by the same investigators, the research restarted in 2007, providing the opportunity to compare consistent data over a long 20‐year period. The monitored transect (Civitavecchia‐Golfo Aranci) runs along a strategic area just outside the southeastern border of the Pelagos Sanctuary. Over the last two decades, an increasing trend of temperature and salinity, in the deep and intermediate layers, has been documented in the region, as well as general changes over the Mediterranean basin. These changes, together with the increasing impact of some pressures (e.g. maritime traffic) may have led to changes in oceanographic and anthropogenic features and, subsequently, in cetacean presence and distribution. The research aimed to verify whether any changes occurred in the pattern of cetacean occurrence over the 20‐year period along the representative transect in the Central Tyrrhenian Sea. Data from 90 summer weekly runs undertaken in the 1990s were compared with data obtained from 95 runs undertaken in the 2000s. Each ferry run was considered an independent statistical unit: the encounter rate (ER = number of sightings per hour spent on effort) was calculated to compare relative abundance between periods, years and months. Spatial analysis was performed on geographical data using Kernel analysis to map the distribution of sightings. Logistic regression (GLM) was performed to compare habitat preference. Total encounter rate in the 1990s (ER = 0.59 ± CI 0.08) was significantly lower (P < 0.01) compared with the 2000s (ER = 0.94 ± CI 0.15). The same seven out of eight species known for their regular presence in the Mediterranean Sea were sighted in both the investigated periods. The most common species were striped dolphin (Stenella coeruleoalba), fin whale (Balaenoptera physalus) and common bottlenose dolphin (Tursiops truncatus). Neither the pilot whale nor any other rare or occasional species were sighted during the 6 years of the study. Despite the time span, no dramatic changes were observed for any species, bar fin whale, in terms of distribution, relative abundance, group size or habitat preference. Sightings of fin whale have surprisingly increased (+300%, P< 0.001), and their spatial and temporal distribution and habitat preference showed a radical difference between the two periods. The 2000s surveys confirmed the existence of high density areas of cetaceans, especially of fin whale, and the consequent necessity of specific legislative acts for cetacean conservation.     

Investigating on the 1920 Garfagnana earthquake (Mw=6.5): Evidences of site effects in Villa Collemandina (Tuscany,Italy)

This paper presents a comprehensive ground response study for the municipality of Villa Collemandina in Northern Tuscany (Italy). This site was selected following a macroseismic analysis of the 1920 Garfagnana earthquake (M_w=6.5), which, at Villa Collemandina, produced damage and losses that were larger than at any other site near the earthquake epicentre, thus indicating the presence of possible site effects. Hence, both experimental and numerical methods are applied in order to investigate the ground response at different locations within the Villa Collemandina municipality. Results obtained from the spectral analysis of earthquake recordings using the reference site method and those from a 2-dimensional dynamic simulation reveal the presence of site effects due to the buried geomorphology (basin-like effects), allowing us to explain the severe damage and losses produced by the 1920 Garfagnana earthquake. As a further result, horizontal to vertical spectral ratio techniques and 1D soil modelling are proved to be inadequate for an effective characterization of the ground response at sites that, like Villa Collemandina, present a complex local geology.     

Multiwavelength study of X-ray selected star-forming galaxies within the Chandra Deep Field-South

We have combined multiwavelength observations of a selected sample of star-forming galaxies with galaxy evolution models in order to compare the results obtained for different star formation rate (SFR) tracers and to study the effect that the evolution of the star-forming regions has on them. We also aimed at obtaining a better understanding of the corrections due to extinction and nuclear activity on the derivation of the SFR. We selected the sample from Chandra data for the well studied region Chandra Deep Field -South (CDFS) and chose the objects that also have ultraviolet (UV) and infrared (IR) data from Galaxy Evolution Explorer ( GALEX ) and Great Observatories Origins Deep Survey (GOODS) Spitzer , respectively.
Our main finding is that there is good agreement between the extinction corrected SFR(UV) and the SFR(X), and we confirm the use of X-ray luminosities as a trustful tracer of recent star formation activity. Nevertheless, at SFR(UV) larger than about  5 M_⊙ yr⁻¹  there are several galaxies with an excess of SFR(X) suggesting the presence of an obscured active galactic nucleus (AGN) not detected in the optical spectra. We conclude that the IR luminosity is driven by recent star formation even in those galaxies where the SFR(X) is an order of magnitude higher than the SFR(UV) and therefore may harbour an AGN. One object shows SFR(X) much lower than expected based on the SFR(UV); this SFR(X) 'deficit' may be due to an early transient phase before most of the massive X-ray binaries were formed. An X-ray deficit could be used to select extremely young bursts in an early phase just after the explosion of the first supernovae associated with massive stars and before the onset of massive X-ray binaries.