Organic carbon fluxes through the mesozooplankton and their variability at different time-scales in the Gullmarsfjord,Sweden

Study of rate process responses and carbon transfer rates in the plankton is a well developed field, but attention has focused on seasonal or longer scales and knowledge on variability patterns and modulating mechanisms at shorter scales is very limited. Here we investigated variability in pelagic carbon transfer rates on daily and seasonal scales in the Gullmar Fjord, Sweden. Hierarchical sampling was carried out in five campaigns in different seasons each of which consisted of 8–12 d with sampling every other day. Algal ingestion, copepod egg and pellet production and vertical flux measured as pigments and pellets varied significantly between days as well as between seasons. Algal ingestion was highest in autumn (weight-specific rate: 0.3–1 d⁻¹) and at the start of the spring bloom (0.3–1.5 d⁻¹), while egg production was highest in summer–autumn (0.1–0.5 d⁻¹). Vertical flux peaked in summer with 4–6 mg pigment m⁻² d⁻¹ and up to 150 mg pellet Cm⁻² d⁻¹. Consonant responses between species were observed indicating a common food source for the mesozooplankton. Changes in trophic functions occurred on scales of days and the coupling between pelagic processes and vertical flux was strong. There were, however, both positive and negative responses which could not be explained by simple predator–prey interactions. The food quality in terms of prey type and biochemical composition are suggested as crucial factors for the variability both within the pelagic environment as well as for the vertical flux out of the upper layers in the ocean.     

Earth's spin and volcanic eruptions: evidence for mutual cause‐and‐effect interactions?

The angular velocity of Earth's rotation shows decadal oscillations due to the lunisolar gravitational torque, as well as inter‐ or intra‐annual changes arising from the angular momentum exchange between the atmosphere and the solid Earth. The energies involved in the Length of Day (LOD) variations may affect the crustal deformation rate and seismic energy release on a global scale. We found significant correlation between the occurrences of major volcanic eruptions and the LOD pattern since AD 1750. On a multiyear scale, eruption frequency worldwide increases with LOD changes. Moreover, the injection of sulphur gases into the atmosphere during major eruptions is accompanied by significant inter‐annual LOD variations. This provides evidence of complex mutual cause‐and‐effect interactions: stress changes induced by multiyear variations in Earth's spin may affect climactic volcanic activity; also, the atmosphere's dynamic response to volcanic plumes may result in global changes of wind circulation and climate, with consequent LOD variations.     

Central Mediterranean tephrochronology between 313 and 366 ka: New insights from the Fucino palaeolake sediment succession

Thirty-two tephra layers were identified in the time-interval 313–366 ka (Marine Isotope Stages 9–10) of the Quaternary lacustrine succession of the Fucino Basin, central Italy. Twenty-seven of these tephra layers yielded suitable geochemical material to explore their volcanic origins. Investigations also included the acquisition of geochemical data of some relevant, chronologically compatible proximal units from Italian volcanoes. The record contains tephra from some well-known eruptions and eruptive sequences of Roman and Roccamonfina volcanoes, such as the Magliano Romano Plinian Fall, the Orvieto–Bagnoregio Ignimbrite, the Lower White Trachytic Tuff and the Brown Leucitic Tuff. In addition, the record documents eruptions currently undescribed in proximal (i.e. near-vent) sections, suggesting a more complex history of the major eruptions of the Colli Albani, Sabatini, Vulsini and Roccamonfina volcanoes between 313 and 366 ka. Six of the investigated tephra layers were directly dated by single-crystal-fusion ⁴⁰Ar/³⁹Ar dating, providing the basis for a Bayesian age–depth model and a reassessment of the chronologies for both already known and dated eruptive units and for so far undated eruptions. The results provide a significant contribution for improving knowledge on the peri-Tyrrhenian explosive activity as well as for extending the Mediterranean tephrostratigraphical framework, which was previously based on limited proximal and distal archives for that time interval.     

Millennial-scale shifts in microtidal ecosystems during the Holocene: dynamics and drivers of change from the Po Plain coastal record (NE Italy)

Framed into a robust stratigraphic context, multivariate analyses on the Holocene palaeobiological record (pollen, benthic foraminifers, ostracods) of the Po coastal plain (NE Italy) allowed the investigation of microtidal ecosystems variability and driving parameters along a 35-km-long land–sea transect. Millennial-scale ecosystem shifts are documented by coeval changes in the meiofauna, reflecting variations in organic matter–water depth (shallow-marine environments) and degree of confinement-salinity (back-barrier settings). In-phase shifts of vegetation communities track unsteady water-table levels and river dynamics in freshwater palustrine areas. Five environmental–ecological stages followed one another crossing four tipping points that mark changes in relative sea level (RSL), climate and/or fluvial regime. At the culmination of Mediterranean RSL rise, after the 8200 event, remarkable growth of peatlands took place in the Po estuary, while low accumulation rates typified the shelf. At the transgressive–regressive turnaround (~7000 cal a bp ), the estuary turned into a delta plain with tidally influenced interdistributary embayments. River flow regime oscillations after the Climate Optimum (post-5000 cal a bp ) favoured isolation of the bays and the development of brackish wetlands surrounded by wooded peatlands. The youngest threshold (~800 cal a bp ), which led to the establishment of the modern delta, reflects a major avulsion of the Po River.     

Effects of offshore platforms on soft-bottom macro-benthic assemblages: a case study in a Mediterranean gas field

The exploitation of fossil fuels in the Mediterranean Sea will likely lead to an increase in the number of offshore platforms, a recognized threat for marine biodiversity. To date, in this basin, few attempts have been made to assess the impact of offshore gas and oil platforms on the biodiversity of benthic assemblages. Here, we adopted a structured experimental design coupled with high taxonomic resolution to outline putative effects of gas platforms on soft-bottom macrofauna assemblages in the North Ionian Sea. The analysis was based on a total of 20,295 specimens of 405 taxa, almost entirely identified at species level. Multivariate and univariate analyses showed idiosyncratic patterns of assemblage change with increasing distance from the platforms. Potential reasons underlying such inconsistency are analyzed and the view that structured experimental monitoring is a crucial tool to quantify the extent and magnitude of potential threats and to provide sound baseline information on biodiversity patterns is supported.     

Reed (Phragmites australis) decline in a brackish wetland in Italy

A comparative field study was carried out at two sites (a healthy site and a declining site) in a brackish wetland in northern Italy, with the objective to investigate the symptoms and the possible causes leading to reed (Phragmites australis) decline in this area. The declining reed plants presented many of the symptoms (clumping habit, smaller size, weaker culms, abnormal rhizome and root anatomy, low starch levels in rhizomes) comprised within the so-called reed die-back syndrome, frequently observed in central European wetlands but never recorded previously in (Sub)Mediterranean regions. Soil nutrient levels did not differ much between the two sites, with nitrate concentrations in the soil being even higher at the healthy site (1.54 microg g(-1); die-back site 0.76 microg g(-1)). Hence, eutrophication did not seem to represent a major cause in determining reed decline in this area. High sulphate concentrations in saltwater associated with low soil redox potentials (-215 mV) due to waterlogging resulted in high soil sulphide concentrations. Concentrations of organic acids, especially acetic acid, did not differ remarkably between sites. High sulphide levels presumably accounted for abnormal anatomical formations (callus blocking aerenchyma channels), lower rates of net CO2 exchange and reduced reserve storage, observed at the die-back site. This was associated with a lower mechanical resistance of reed culms which accelerated reed mortality in the die-back areas. We concluded that high sulpihde levels in permanently waterlogged soils may result in die-back of reed stands in Mediterranean wetlands.     

Modal model identification of structures under unmeasured seismic excitations

Techniques developed for structural identification of a structural model are typically based on information regarding the response and the forcing actions. However, in some situations it can be necessary, or simply useful, to refer only to the measured responses. In this paper we describe a technique suitable for identifying the modal model of a spatial frame in the frequency domain when the seismic input is unknown both in time contents and direction. In some previous theoretical works we established that this identification problem has a unique solution when at least three time‐history responses are known. Here numerical techniques are developed which allow the evaluation of the modal quantities in practice. Numerical applications are carried out on plane and spatial framed structures by using a modal model which may be complete, including all the structure's modes, or incomplete, including only the lowest modes. In most cases the obtained results are satisfactory. Copyright © 2005 John Wiley & Sons, Ltd.     

Evidence of positive tectonic inversion in the north-central sector of the Sicily Channel (Central Mediterranean)

In order to unravel the tectonic evolution of the north-central sector of the Sicily Channel (Central Mediterranean), a seismo-stratigraphic analysis of single- and multi-channel seismic reflection profiles has been carried out. This allowed to identify, between 20 and 50 km offshore the central-southern coast of Sicily, a ~80-km-long deformation belt, characterized by a set of WNW–ESE to NW–SE fault segments showing a poly-phasic activity. Within this belt, we observed: i) Miocene normal faults reactivated during Zanclean–Piacenzian time by dextral strike-slip motion, as a consequence of the Africa–Europe convergence; ii) releasing and restraining bend geometries forming well-developed pull-apart basins and compressive structures. In the central and western sectors of the belt, we identified local transpressional reactivations of Piacenzian time, attested by well-defined compressive features like push-up structures and fault-bend anticlines. The reconstruction of timing and style of tectonic deformation suggest a strike-slip reactivation of inherited normal faults and the local subsequent positive tectonic inversion, often documented along oblique thrust ramps. This pattern represents a key for an improved knowledge of the structural style of foreland fold-and-thrust belts propagating in a preexisting extensional domain. With regard to active tectonics and seismic hazards, recent GPS data and local seismicity events suggest that this deformation process could be still active and accomplished through deep-buried structures; moreover, several normal faults showing moderate displacements have been identified on top of the Madrepore Bank and Malta High, offsetting the Late Quaternary deposits. Finally, inside the northern part of the Gela Basin, multiple slope failures, originated during Pleistocene by the further advancing of the Gela Nappe, reveal tectonically induced potential instability processes.