Temperature and precipitation projections for the Antarctic Peninsula over the next two decades: contrasting global and regional climate model simulations

This study presents near future (2020–2044) temperature and precipitation changes over the Antarctic Peninsula under the high-emission scenario (RCP8.5). We make use of historical and projected simulations from 19 global climate models (GCMs) participating in Coupled Model Intercomparison Project phase 5 (CMIP5). We compare and contrast GCMs projections with two groups of regional climate model simulations (RCMs): (1) high resolution (15-km) simulations performed with Polar-WRF model forced with bias-corrected NCAR-CESM1 (NC-CORR) over the Antarctic Peninsula, (2) medium resolution (50-km) simulations of KNMI-RACMO21P forced with EC-EARTH (EC) obtained from the CORDEX-Antarctica. A further comparison of historical simulations (1981–2005) with respect to ERA5 reanalysis is also included for circulation patterns and near-surface temperature climatology. In general, both RCM boundary conditions represent well the main circulation patterns of the historical period. Nonetheless, there are important differences in projections such as a notable deepening and weakening of the Amundsen Sea Low in EC and NC-CORR, respectively. Mean annual near-surface temperatures are projected to increase by about 0.5–1.5 \(^{\circ }\)C across the entire peninsula. Temperature increase is more substantial in autumn and winter (\(\sim \) 2 \(^{\circ }\)C). Following opposite circulation pattern changes, both EC and NC-CORR exhibit different warming rates, indicating a possible continuation of natural decadal variability. Although generally showing similar temperature changes, RCM projections show less warming and a smaller increase in melt days in the Larsen Ice Shelf compared to their respective driving fields. Regarding precipitation, there is a broad agreement among the simulations, indicating an increase in mean annual precipitation (\(\sim \) 5 to 10%). However, RCMs show some notable differences over the Larsen Ice Shelf where total precipitation decreases (for RACMO) and shows a small increase in rain frequency. We conclude that it seems still difficult to get consistent projections from GCMs for the Antarctic Peninsula as depicted in both RCM boundary conditions. In addition, dominant and common changes from the boundary conditions are largely evident in the RCM simulations. We argue that added value of RCM projections is driven by processes shaped by finer local details and different physics schemes that are introduced by RCMs, particularly over the Larsen Ice Shelf.

     

Halophyte recruitment in a salt marsh restoration site

In restored salt marshes, seedling recruitment can be limited where large areas of soil are exposed and physical conditions are harsh. On a 0.7-ha excavated marsh plain, we studied recruitment as a function of abiotic (elevation) and biotic factors in 2 × 2 m plots planted with 0, 1, 3, or 6 species from the pool of 8 native halophytes. The random draws of 3-species and 6-species assemblages produced approximately equal numbers of plants per species for the experiment as a whole, yet only three species recruited> 10 seedlings per plot.Salicornia virginica andSalicornia bigelovii each produced> 15,000 seedlings in 1998, andSuaeda esteroa produced> 2,500 seedlings in 1999. For these 3 species, seedling recruitment increased with elevation in 1998, but this trend weakened in 1999, when species richness affected recruitment (fewer seedlings in more species-rich plots). Abiotic effects preceded biotic interactions in determining seedling recruitment patterns early in the development of the salt marsh. Effects of species richness appeared to be scale-dependent in that having all species present in the site likely enhanced overall recruitment (all species had 2 or more seedlings), while plantings of 6 species in a 2 × 2 m plot reduced seedling density.S. virginica was the only species that increased its presence and relative cover in the experimental site over the 4-yr study. Protocols for planting southern California salt marsh restoration sites could omit this species, but all others probably need to be introduced to restore diverse vegetation.     

The 1906 eruption of Vesuvius: from magmatic to phreatomagmatic activity through the flashing of a shallow depth hydrothermal system

The April 1906 eruption of Vesuvius is the type-example of the final eruptions that close the short cycles of semi-persistent activity that characterized the volcano in the 1631–1944 period. The eruption had a marked explosive character that accompanied the emission of lava from several vents on the southern slopes of the volcano. The observed sequence of events was characterized by repeated fluctuations of the magma level within the conduit, by large lava fountains, by conduit partial collapses, and by the final explosive decapitation of the summit cone. Contemporary chronicles, although frequently contradictory, allow reconstruction of the eruption, which can be divided into four main phases: (1) lateral lava effusions; (2) lava fountains; (3) gas-pyroclasts column; (4) low dense clouds. Pyroclastic deposits of the Monte Somma ridge and northeastern slope can be related to observed and described events and mainly refer to the 2nd and 3rd phases. The increase in the degree of fragmentation of the juvenile component together with the marked increase of the lithic component and morphologic evidence emphasize the repeated occurrence of magmawater interaction. This was most spectacular in the 3rd phase of the eruption in which, after the decapitation of the cone, a high gas-pyroclasts eruption column was formed. Because of the nature of the lithic fragments (mainly hydrothermally altered and metasomatic rocks), the huge amount of steam, and the high lithic/juvenile ratio, it is unlikely that the largest part of the energy in play was related to the contact between magma and cold phreatic water. We suggest that most of the steam involved in this phase of the eruption came from flashing of the hydrothermal system connected to the very shallow feeding system of the volcano and formed as a consequence of repeated subsurface intrusions between 1872 and 1906. Juvenile products were ejected through the eruption, and represent (at least) two different magma bodies: the first (older) was erupted during the initial phase of the eruption and was exhausted at the beginning of the lava fountains phase, when fresh magma was involved in the eruption.     

Detritus Rolling Down a Vertical Cliff of the Ligurian Sea (Italy): The Écological Role in Hard Bottom Communities

Abstract. The detritus rolling down a vertical cliff was studied at Portofino Promontory (Ligurian Sea, Italy) at 16 m depth (January 1988- January 1989). The large amount of collected sediment is mainly due to the position of the traps; they collected not only the sedimenting material, but also the detritus rolling down along the cliff. The amount of sediment matter is 7 times greater in winter than in summer, showing a good correlation with rough seas and rain that cause a "mechanical cleaning" of animal and plant debris (Sérpulid tubes, shells, exuvias. leaves) along the cliff.
The Total Suspended Matter (TSM) in the water column shows maximum values in March and September. The organic fraction has an average concentration of 0.81 mg 1^-l. The phytoplanktonic biomass, measured as Chi a , shows an annual cycle with a peak in spring (1–2.7μg·l^-1). while in other periods of the year the value is about 0.3-0.5 μg·1^-1. A significant relationship was found between organic detritus in the collected sédiments and the Chi a in the water column. The great influence of the rocky wall detritus on the normal trend of the TSM in the coastal water column is pointed out.     

Comparison Between the Energy Flow Networks of Two Habitats in the Venice Lagoon

Abstract. The energy flows of two habitats are quantified and compared by using a trophic network model. The habitats are representative of two typical subsystems of the Venice Lagoon: the seagrass meadows, which represent a mature stage in the ecological succession of lagoon environments, and the Tapes philippinarum fishing grounds, which are subjected to mechanical clam harvesting.
The results obtained for the 'seagrass habitat'are consistent with other field studies, confirming the'key-stone'role played by phanerogams in a lagoon environment. The results for the 'Tapes habitat'show that the energy flow from the sediment to the water column is extremely important. Indeed, the high T. philippinarum biomass cannot be supported solely by the primary production of the local phytoplankton. Instead, this biomass could be supported by a supply provided by the sediment resuspension caused by intensive clam fishing. These findings suggest the presence of a positive feedback between fishing effort and T. philippinarum standing crop.     

A methodological approach to water quality assessment in an ungauged basin,Buenos Aires,Argentina

The Reconquista River is one of the most polluted rivers in Latin America. This paper aims at identifying the dynamics of water quality in an area with low or “background” concentrations of pollutants within the Reconquista River system in order to better define levels of pollution in the main system. In order to describe the dynamics of water quality in the background area, we propose a methodology based on flow estimation with the instantaneous unit hydrograph model and on measurements of physical and chemical water variables under different hydrological conditions. Because of high dissolved oxygen and low ammonium and o-phosphate concentrations, the Arroyo Durazno, a tributary stream of the Reconquista River, is defined as a background area. When a storm event begins, the concentration of nitrates and the electrical conductivity diminish. An increase in dissolved organic carbon suggests an important input of carbon from hillslope runoff. The proportion of fulvic and humic acids also increases. On the receding limb of the hydrograph, nitrate concentration was lower than during maximum flow and organic carbon concentration remained high. This behavior, known as the “flushing effect”, suggests that the soluble material accumulated in the drainage area during dry periods is transported to the stream by leaching or “lixiviation” and surface runoff, thus raising solute concentrations during the first few hours of the storm. Water quality changes rapidly, even in background areas, due to its dependence on the flow. The methodology followed in this paper can also be applied to other basins with similar characteristics. Due to the difficulty in defining baseline areas for surface waters, a knowledge of background water quality and its dynamics is essential for understanding pollution trends and anthropogenic impacts on rivers.     

Origin and emplacement of ultramafic–mafic intrusions in the Erro-Tobbio mantle peridotite (Ligurian Alps, Italy)

The Erro-Tobbio peridotites (Voltri Massif, Ligurian Alps) represent subcontinental lithospheric mantle tectonically exhumed during Permo–Mesozoic extension of the Europe–Adria lithosphere. Previous studies have shown that exhumation started during Permian times, and occurred along kilometer-scale lithospheric shear zones which enhanced progressive deformation and recrystallization from spinel- to plagioclase-facies conditions. Ongoing field and petrologic investigations have revealed that the peridotites experienced, during uplift, a composite history of diffuse melt migration and multiple episodes of ultramafic–mafic intrusions. In this paper we present the results of field, structural and petrologic–geochemical investigations into a sector of the Erro-Tobbio peridotite unit that preserves well this multiple intrusion history. Melt impregnation in the peridotites is evidenced by significant plagioclase enrichment and crystallization of unstrained orthopyroxene replacing kinked mantle olivine and clinopyroxene; impregnating melts were thus opx-saturated. Melt–rock interaction caused chemical changes in mantle minerals (e.g. Al decrease and REE increase in cpx; Ti and Cr# enrichment in spinel). Nevertheless, clinopyroxenes still exhibit LREE depletion (Ce_N/Sm_N = 0.006–0.011), indicating a depleted signature for the percolating melts. Melt impregnation was thus related to diffuse porous flow migration of depleted MORB-type melt fractions that modified their compositions towards opx saturation by mantle–melt interaction during ascent. The impregnated peridotites are intruded by a hectometer-scale stratified cumulate body, mostly consisting of troctolites and plagioclase wehrlites, showing gradational, interfingered contacts with the host mantle rocks. Subsequent intrusion events are revealed by the occurrence of olivine gabbros as decameter-wide lenses, variably thick (centimeter- to meter-scale) dykes and thin dykelets, which crosscut both the peridotite foliation and the magmatic layering in the cumulates. Overall, major and trace element compositions of minerals in the intrusives indicate that they represent variably differentiated cumulus products crystallized from rather primitive N-MORB-type aggregated melts. Slightly more evolved compositions are shown by olivine gabbros, relative to the troctolites and plagioclase wehrlites of the cumulate body. Mineral chemistry features (e.g. the Fo–An correlation and high Na, Ti, Mg# in cpx) indicate that the studied intrusive rocks crystallized at moderate pressure conditions (3–5 kbar, i.e. 9–15 km depth). Our study thus points to a progressive transition from porous flow melt migration to emplacement of magmas in fractures, presumably related to progressive change of lithospheric mantle rheology during extension-related uplift and cooling.     

Effects of column axial force – bending moment interaction on inelastic seismic response of steel frames

It is well known that axial force – bending moment interaction (N–M interaction) affects to a large extent the cyclic inelastic behaviour of structural elements, especially columns in framed structures, with reduction in bending capacity and loss of available ductility. A few studies have also shown that significant inelastic axial shortening affects the response of column elements subjected to medium–high levels of axial loads and cyclic bending. This paper is primarily aimed at evaluating the effects of column N–M interaction on the inelastic seismic response of steel frames. By considering the contemporaneous action of vertical loads, due to gravity, and of horizontal seismic excitation, it is shown that the progressive axial shortening of adjacent columns may differ substantially, thus inducing significant relative settlements at the ends of the connecting beams and, then, remarkable amplifications in beam plastic rotations. An evaluation of additional beam plastic rotations induced by column N–M interaction is carried out for real structures by investigating the inelastic response of steel frames designed according to European standards under horizontal and vertical earthquake excitations. Copyright © 2003 John Wiley & Sons, Ltd.