Trophic importance of diatoms in an intertidal Zostera noltii seagrass bed: Evidence from stable isotope and fatty acid analyses

A current predominant paradigm emphasizes the role of epiphytic algae for invertebrates in most seagrass food webs. However, in some intertidal Zostera noltii beds, epiphyte biomass is very low compared to microphytobenthos and seagrass biomasses. We assessed the role of microphytobenthos in a temperate intertidal Z. noltii bed by combining stable isotope and fatty acid (FA) analyses on primary producers, composite sources — suspended particulate organic matter (SPOM) and sediment surface organic matter (SSOM) — and the main macrofaunal consumers. Z. noltii showed high δ¹³C (−9.9‰) and high 18:2(n-6) and 18:3(n-3) contents. Microphytobenthos was slightly more ¹³C-depleted (−15.4‰) and had high levels of diatom markers: 14:0, 16:1(n-7)c, 20:5(n-3). Low mean δ¹³C (−22.0‰) and large amounts of diatom and bacteria (18:1(n-7)c) markers indicated that SPOM was mainly composed of a mixture of fresh and decayed pelagic diatoms. Higher mean δ¹³C (−17.9‰) and high amounts of diatom FAs were found in SSOM, showing that microphytobenthic diatoms dominate. Very low percentages of 18:2(n-6) and 18:3(n-3) in consumers indicated a low contribution of Z. noltii material to their diets. Grazers, deposit and suspension-deposit feeders had δ¹³C close to microphytobenthos and high levels of diatom FAs, confirming that microphytobenthos represented the main part of their diet. Lower δ¹³C and higher amounts of flagellate FAs – 22:6(n-3) and 16:4(n-3) – in suspension feeders indicated that their diet resulted from a mixture of SPOM and microphytobenthos. These results demonstrate that invertebrates do not consume high amounts of seagrass and highlight the main role of benthic diatoms in this intertidal seagrass bed.     

A reappraisal of the metamorphic history of EH3 and EL3 enstatite chondrites

The thermal history of a series of EH3 and EL3 chondrites has been investigated by studying the degree of structural order of the organic matter (OM) located and characterized in matrix areas by Raman micro-spectroscopy. By comparison with unequilibrated ordinary chondrites (UOCs) and CO and CV carbonaceous chondrites, the following petrologic types have been assigned to various E chondrites: Sahara 97096 and Allan Hills 84206: 3.1-3.4; Allan Hills 85170 and Parsa: 3.5; Allan Hills 85119: 3.7; Qingzhen, MacAlpine Hills 88136 and MacAlpine Hills 88184: 3.6-3.7. The petrologic type of Qingzhen is consistent with the abundance of the P3 noble gas component, a sensitive tracer of the grade of thermal metamorphism. The petrologic types are qualitatively consistent with the abundance of fine-grained matrix for the whole series. No significant effects of shock processes on the structure of OM were observed. However such processes certainly compete with thermal metamorphism and the possibility of an effect cannot be fully discarded, in particular in the less metamorphosed objects. The OM precursors accreted by the EH3 and EL3 parent bodies appear to be fairly similar to those of UOCs and CO and CV carbonaceous chondrites. Raman data however show some slight structural differences that could be partly accounted for by shock processes. The metamorphic history of EH3 and EL3 chondrites has often been described as complex, in particular regarding the combined action of shock and thermal metamorphism. Because OM maturity is mostly controlled by the temperature of peak metamorphism, it is possible to distinguish between the contributions of long duration thermal processes and that of shock processes. Comparison of the petrologic types with the closure temperatures previously derived from opaque mineral assemblages has revealed that the thermal history of EH3 and EL3 chondrites is consistent with a simple asteroidal onion shell model. Thermal metamorphism in enstatite chondrites appears to be fairly similar to that which takes place in other chondrite classes. The complex features recorded by mineralogy and petrology and widely reported in the literature appear to be mostly controlled by shock processes.     

Late Pleistocene (MIS 3–4) climate inferred from micromammal communities and δO of rodents from Les Pradelles,France

The middle Paleolithic stratigraphic sequence of Les Pradelles (Charente, France) spans from the end of Marine Isotope Stage (MIS) 4 until the middle of MIS 3. Micromammal remains are present in all the stratigraphic levels, offering a rare opportunity to address the questions of both environmental and climatic fluctuations throughout this period. Climate modes were studied through the taphonomy, biodiversity and oxygen isotope compositions of phosphate (δ¹⁸O_p) from 66 samples of rodent tooth enamel. The δ¹⁸O_p values from the lower sedimentary levels provide summer mean air temperatures of 19 ± 2°C (level 2/1) and of 16 ± 2°C (levels 2A, 2B and 4A). Within the middle of sequence (level 4B), a paleobiodiversity change can be identified with an increase of Dicrostonyx torquatus, which is associated with the largest amplitude in δ¹⁸O_p values and the highest maximal δ¹⁸O_p values. At the top of the sequence (level 5-2), a biodiversity change is observed with the increase of Microtus arvalis, but without any change in δ¹⁸O_p values. The association of cold rodent species with unexpected high and large amplitudes in the δ¹⁸O_p values of their teeth, possibly indicative of aridity, suggests their deposition during a Heinrich event.     

Orbital imprint on Holocene palaeohydrological variations in west‐central Europe as reflected by lake‐level changes at Cerin (Jura Mountains,eastern France)

This paper presents a lake‐level record for the Holocene at Lake Cerin (Jura Mountains, eastern France). It is based on a range of sedimentological techniques validated in previous studies, with a combination of systematic lithostratigraphic investigations of the infillings accumulated in the lacustrine basin, and sediment analyses of two selected cores. The chronology is based on 10 radiocarbon dates and pollen stratigraphy. On a millennial scale, the Cerin lake‐level record shows three distinct successive phases characterised by higher lake‐level conditions until ca. 9000 cal. a BP, followed by a maximal lowering at ca. 9000–8500 cal. a BP, and a progressive rise until the present. This rise was punctuated by centennial‐scale fluctuations, with major events around 4000, 2800 and after 1500 cal. a BP. Considered on a multimillennial scale, the general pattern of palaeohydrological changes reconstructed at Cerin reflects the impact of orbitally driven summer insolation. This is in agreement with other regional and extra‐regional palaeoclimatic records, although every record shows peculiarities in timing and shape depending on the proxy used for reconstruction. In this general context, centennial to multicentennial oscillations appear to have been second‐order events in comparison with the major influence of the orbital factor. Copyright © 2011 John Wiley & Sons, Ltd.     

Monitoring water flow in a clay-shale hillslope from geophysical data fusion based on a fuzzy logic approach

Seismic and electrical resistivity tomography allow subsurface characterization from acoustic P-waves (Vp), shear S-waves (Vs) velocities, and electrical resistivity (ρ). Both geophysical methods were used to monitor water flow during a controlled rainfall experiment on a clay-shale hillslope located in the Laval catchment at Draix (Alpes-de-Haute-Provence, France). The objectives of the rainfall experiment were to analyse the water infiltration processes and identify possible water pathways by combining multi-method observations. The seismic data provide information on fissure density and the electrical resistivity data provide information on soil water content within the hillslope. Changes of the Vp and electrical resistivity fields with time show some similar pattern. To go further in the analysis of the water flow a geophysical data fusion strategy based on fuzzy set theory is applied. The computed fuzzy cross-sections based on expert hypotheses show the possibility for the material to be saturated during the rainfall experiment. The data fusion process is repeated in time for each acquisition set. The relative difference between the obtained fuzzy cross-sections is calculated and reveals possible locations where water may be transferred within the hillslope.     

The multivariate (co)variogram as a spatial weighting function in classification methods

The multivariate variogram and the multivariate covariogram are used as spatial weighting functions for forming spatially homogeneous groups automatically. The groups are created after either deflating similarities between distant samples with the multivariate covariogram or by inflating dissimilarities between distant samples with the multivariate variogram. These approaches can be seen as generalization of the Oliver and Webster proposal. Two data sets show the efficiency of the two weighting functions when compared to the classical approach which does not take spatial information into account. In one case study, the weighting of similarities by the multivariate covariogram showed more interpretable results than the weighting of dissimilarities by the multivariate variogram.     

Long-term fish and macro-crustacean community variation in a Mediterranean lagoon

The fish and macro-crustacean community of the Vaccarès lagoon (Rhône River delta, South France) was sampled monthly from 1993 to 2002. The lagoon salinity shifted from 15 in 1993 to 5 in 1994–1997 and went back to 15 in 1999–2002. Connections with the sea also varied during the study period with larger openings in 1996–1997. During the study period, the community changed to revert in 2002 to a state similar to 1993. These changes consisted of a sequence of increased and decreased patterns of freshwater species and some marine species. Typical lagoon species tended to resist to salinity changes. Freshwater species colonised the lagoon when the salinity was low. Marine species may have varied both in relation to connections with the sea and to indirect effects of freshwater outflow. This study shows that community changes following environmental variations can be delayed in time, and emphasises the need for long-term studies.     

Example of Neogene tectonic indentation in the Eastern Betic Cordilleras: the Arc of Aguilas (Southeastern Spain)

Abstract

Neogene deformations have deeply disturbed the initial architecture of the pile of nappes within the Eastern Betic zone. The Arc of Aguilas, displaying a southeast-facing concavity, is a spectacular example of such a post-nappe structuration. Miocene deposits involved in the torsion of the Arc provide a chronology of the deformation. The Arc of Aguilas is one element within a system of rigid-plastic indentation including the following units, from the inner (SE) to the outer (NW) zones : — A rigid block, little deformed, located in the present day abyssal plain, play the part of the indenter.

— A structural pad corresponding to the Aguilas Arc itself. It was severely folded during Miocene times.

— A large peripheral zone mainly subjected to faulting during the Neogene (essentially strike-slip faults). These faults control the evolution of different types of sedimentary basins during the Late Neogene (Tortonian to Pliocene).

Two large shear zones: N020 sinistral (Palomares and Terreros faults), N100 dextral (Las Moreras faults) guided the deformation of the Aguilas Arc within a compressive stressfield of which major tensor axis oscillated between NW-SE and N-S.     

The Upper Rhône Delta Sedimentary Record in the Arles-Piton Core: Analysis of Delta-Plain Subenvironments, Avulsion Frequency, Aggradation Rate and Origin of Sediment Yield

Results from analyses of the Arles‐Piton sediment core, retrieved from the apex of the Rhône Delta, highlight processes of Holocene deltaic construction controlled mainly by hydrosedimentary variability and channel avulsions. The alluvial suite was investigated for grain size, sedimentary structures, CaCO₃, organic matter, heavy minerals and chrono‐stratigraphy (¹⁴C and archaeological/historical dates). The study shows the succession of six facies associations: a distributary channel (before 6157‐5843 BC), a swamp (5719‐5530/4796‐4463 BC), a distal flood plain (5719‐5530/4796‐4463 BC), a distributary channel (4796‐4463/2900‐2503 BC), a proximal flood plain (2900‐2503 BC/AD 270‐290), and a crevasse splay (after AD 270‐290). Substantial changes in hydrodynamics are strongly linked to three channel avulsions (before 6157‐5843 BC, after 4796‐4463 BC and after 2900‐2503 BC). A correlation with the whole channel avulsion history of the Rhône Delta allowed us to propose an average rhythm of channel avulsion of c. 1450 years. From 5719‐5530 BC to AD 270‐290, the flood plain aggraded at the average rate of 2.5 mm/a. The aggradation rates were higher both in the proximal and distal flood plains, where sedimentation process is continuous. They were lower both in the active distributary channels, because of frequent truncation of the alluvial suite, and the abandoned channels where detritic inputs are minimum. The sediment supply arriving to the upper Rhône Delta was derived mainly from proximal source areas (Massif Central, Southern Alps) during the last 8000 years, except during the hydrological changes of Roman antiquity during which detritic inputs were derived firstly from the Northern Alps and Southern Alps, and secondly from the Massif Central.     

Adakitic magmas in the Ecuadorian Volcanic Front: Petrogenesis of the Iliniza Volcanic Complex (Ecuador)

The Iliniza Volcanic Complex (IVC) is a poorly known volcanic complex located 60 km SSW of Quito in the Western Cordillera of Ecuador. It comprises twin peaks, North Iliniza and South Iliniza, and two satellite domes, Pilongo and Tishigcuchi. The study of the IVC was undertaken in order to better constrain the role of adakitic magmas in the Ecuadorian arc evolution. The presence of volcanic rocks with an adakitic imprint or even pristine adakites in the Ecuadorian volcanic arc is known since the late 1990s. Adakitic magmas are produced by the partial melting of a basaltic source leaving a garnet rich residue. This process can be related to the melting of an overthickened crust or a subducting oceanic crust. For the last case a special geodynamic context is required, like the subduction of a young lithosphere or when the subduction angle is not very steep; both cases are possible in Ecuador. The products of the IVC, made up of medium-K basaltic andesites, andesites and dacites, have been divided in different geochemical series whose origin requires various interactions between the different magma sources involved in this subduction zone. North Iliniza is a classic calc-alkaline series that we interpret as resulting from the partial melting of the mantle wedge. For South Iliniza, a simple evolution with fractional crystallization of amphibole, plagioclase, clinopyroxene, magnetite, apatite and zircon from a parental magma, being itself the product of the mixing of 36% adakitic and 64% calc-alkaline magma, has been quantified. For the Santa Rosa rhyolites, a slab melting origin with little mantle interactions during the ascent of magmas has been established. The Pilongo series magma is the product of a moderate to high degree (26%) of partial melting of the subducting oceanic crust, which reached the surface without interaction with the mantle wedge. The Tishigcuchi series shows two stages of evolution: (1) metasomatism of the mantle wedge peridotite by slab melts, and (2) partial melting (10%) of this metasomatized source. Therefore, the relative ages of the edifices show a geochemical evolution from calc-alkaline to adakitic magmas, as is observed for several volcanoes of the Ecuadorian arc.