New results of 40Ar/39Ar dating constrain the timing of transition from fissure-type to central volcanism at Mount Etna (Italy)

Recent geological studies performed at Etna allow reassessing the stratigraphic frame of the volcano where distinct evolutionary phases are defined. This stratigraphic reconstruction was chronologically constrained on the basis of a limited number of U–Th and K–Ar age determinations whose uncertainty margins are sometimes too wide. For this reason, we successfully adopted at Etna the ⁴⁰Ar/³⁹Ar technique that allowed obtaining more precise age determinations. The incremental heating technique also gives information on sample homogeneity, and potential problems of trapped argon. Five samples were collected from stratigraphically well-controlled volcanic units in order to chronologically define the transition between the fissure-type volcanism of the Timpe phase to the central volcanism of the Valle del Bove Centers. Isotopic ages with an uncertainty margin of 2–4% have been obtained emphasizing that this transition occurred (130–126 ka) without significant temporal hiatus.     

Early diagenesis in rapidly accumulating sediments on the Alboran slope, ODP site 976

The oxidation and reduction that occur during early diagenesis of sediments has been studied in the interstitial waters of a rapidly accumulating sedimentary sequence from the Mediterranean margin of Spain. A series of reactions that are mediated by progressively lower free energy derived from oxidation of organic matter is evident in the sedimentary sequence. Iron and manganese are rapidly reduced. Phosphate and alkalinity maxima at a subbottom depth of 15?m indicate maximal organic matter degradation. Methane first appears at ～20?m subbottom after sulfate is depleted, and its concentrations quickly climb.     

Are fossil groups a challenge of the cold dark matter paradigm?

We study six groups and clusters of galaxies suggested in the literature to be 'fossil' systems (i.e. to have luminous diffuse X-ray emission and a magnitude gap of at least 2 mag R between the first and the second ranked member within half of the virial radius), each having good quality X-ray data and Sloan Digital Sky Survey (SDSS) spectroscopic or photometric coverage out to the virial radius. The poor cluster AWM 4 is clearly established as a fossil system, and we confirm the fossil nature of four other systems (RX J1331.5+1108, RX J1340.6+4018, RX J1256.0+2556 and RX J1416.4+2315), while the cluster RX J1552.2+2013 is disqualified as fossil system. For all systems, we present the luminosity functions within 0.5 and 1 virial radius that are consistent, within the uncertainties, with the universal luminosity function of clusters. For the five bona fide fossil systems, having a mass range  2 × 10¹³–3 × 10¹⁴ M_⊙  , we compute accurate cumulative substructure distribution functions (CSDFs) and compare them with the CSDFs of observed and simulated groups/clusters available in the literature. We demonstrate that the CSDFs of fossil systems are consistent with those of normal observed clusters and do not lack any substructure with respect to simulated galaxy systems in the cosmological Λ cold dark matter (ΛCDM) framework. In particular, this holds for the archetype fossil group RX J1340.6+4018 as well, contrary to earlier claims.     

Lagrangian coherent structures in the planar elliptic restricted three-body problem

This study investigates Lagrangian coherent structures (LCS) in the planar elliptic restricted three-body problem (ER3BP), a generalization of the circular restricted three-body problem (CR3BP) that asks for the motion of a test particle in the presence of two elliptically orbiting point masses. Previous studies demonstrate that an understanding of transport phenomena in the CR3BP, an autonomous dynamical system (when viewed in a rotating frame), can be obtained through analysis of the stable and unstable manifolds of certain periodic solutions to the CR3BP equations of motion. These invariant manifolds form cylindrical tubes within surfaces of constant energy that act as separatrices between orbits with qualitatively different behaviors. The computation of LCS, a technique typically applied to fluid flows to identify transport barriers in the domains of time-dependent velocity fields, provides a convenient means of determining the time-dependent analogues of these invariant manifolds for the ER3BP, whose equations of motion contain an explicit dependency on the independent variable. As a direct application, this study uncovers the contribution of the planet Mercury to the Interplanetary Transport Network, a network of tubes through the solar system that can be exploited for the construction of low-fuel spacecraft mission trajectories. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Thermohaline variability and Antarctic bottom water formation at the Ross Sea shelf break

We use hydrological and current meter data collected in the Ross Sea, Antarctica between 1995 and 2006 to describe the spatial and temporal variability of water masses involved in the production of Antarctic Bottom Water (AABW). Data were collected in two regions of known outflows of dense shelf water in this region; the Drygalski Trough (DT) and the Glomar-Challenger Trough (GCT). Dense shelf water just inshore of the shelf break is dominated by High Salinity Shelf Water (HSSW) in the DT and Ice Shelf Water (ISW) in the GCT. The HSSW in the northern DT freshened by ∼0.06 in 11 y, while the ISW in the northern GCT freshened by ∼0.04 in 8 y and warmed by ∼0.04 °C in 11 y, dominated by a rapid warming during austral summer 2001/02. The Antarctic Slope Front separating the warm Circumpolar Deep Water (CDW) from the shelf waters is more stable near GCT than near DT, with CDW and mixing products being found on the outer DT shelf but not on the outer GCT shelf. The different source waters and mixing processes at the two sites lead to production of AABW with different thermohaline characteristics in the central and western Ross Sea. Multi-year time series of hydrography and currents at long-term moorings within 100 km of the shelf break in both troughs confirm the interannual signals in the dense shelf water and reveal the seasonal cycle of water mass properties. Near the DT the HSSW salinities experienced maxima in March/April and minima in September/October. The ISW in the GCT is warmest in March/April and coolest between August and October. Mooring data also demonstrate significant high-frequency variability associated with tides and other processes. Wavelet analysis of near-bottom moored sensors sampling the dense water cascade over the continental slope west of the GCT shows intermittent energetic pulses of cold, dense water with periods from ∼32 h to ∼5 days.     

Spatio-temporal variability and vertical distribution of a low rocky subtidal assemblage in the north-west Mediterranean

Natural assemblages show large variability at multiple scales in space and time as a consequence of several abiotic and biological factors. This study was conducted in conditions of high turbidity of the water and examined the spatio-temporal variability and the vertical distribution at two different depths of a low rocky subtidal assemblage. Algal and invertebrate organisms were sampled at a range of spatial scales extending from meters to a few kilometers, over a period of 21 months. Results indicated that patterns of distribution and abundance of organisms differed between the two depths and at the smallest spatial scales examined. These differences were due to differences in relative abundance rather than differences in composition of taxa. Results showed that assemblages varied largely among dates of sampling, suggesting that temporal variability of these organisms may be more important than previously stated. The patchy distribution and the peculiar life traits of most taxa of these assemblages allowed the concept of metapopulation and metacommunity to be applied to this system. This might have implications for predictions of the responses of subtidal assemblages to environmental changes due to anthropogenic activities.     

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.