Impacts of Kelvin wave forcing in the Peru Humboldt Current system: Scenarios of spatial reorganizations from physics to fishers

Because climate change challenges the sustainability of important fish populations and the fisheries they support, we need to understand how large scale climatic forcing affects the functioning of marine ecosystems. In the Humboldt Current system (HCS), a main driver of climatic variability is coastally-trapped Kelvin waves (KWs), themselves originating as oceanic equatorial KWs. Here we (i) describe the spatial reorganizations of living organisms in the Humboldt coastal system as affected by oceanic KWs forcing, (ii) quantify the strength of the interactions between the physical and biological component dynamics of the system, (iii) formulate hypotheses on the processes which drive the redistributions of the organisms, and (iv) build scenarios of space occupation in the HCS under varying KW forcing. To address these questions we explore, through bivariate lagged correlations and multivariate statistics, the relationships between time series of oceanic KW amplitude (TAO mooring data and model-resolved baroclinic modes) and coastal Peruvian oceanographic data (SST, coastal upwelled waters extent), anchoveta spatial distribution (mean distance to the coast, spatial concentration of the biomass, mean depth of the schools), and fishing fleet statistics (trip duration, searching duration, number of fishing sets and catch per trip, features of the foraging trajectory as observed by satellite vessel monitoring system). Data sets span all or part of January 1983 to September 2006. The results show that the effects of oceanic KW forcing are significant in all the components of the coastal ecosystem, from oceanography to the behaviour of the top predators – fishers. This result provides evidence for a bottom-up transfer of the behaviours and spatial stucturing through the ecosystem. We propose that contrasting scenarios develop during the passage of upwelling versus downwelling KWs. From a predictive point of view, we show that KW amplitudes observed in the mid-Pacific can be used to forecast which system state will dominate the HCS over the next 2–6 months. Such predictions should be integrated in the Peruvian adaptive fishery management.     

The grain-size characterisation of coastal sand from the Somme estuary to Belgium: Sediment sorting processes and mixing in a tide- and storm-dominated setting

Sand-rich Holocene to modern clastic deposits in the eastern English Channel and the southern North Sea coasts of France and Belgium occur extensively as nearshore-sand bank, estuarine-tidal flat, aeolian dune and beach sub-environments. Sand samples (n = 665) collected from these deposits suggest the presence of three different populations: a largely dominant (83%) medium to fine quartz sand population (“b”), and finer- (14%) and coarser-grained (4%) populations (respectively “c” and “a”). The distribution of these populations among the four sub-environments reflects tide- and storm-dominated sorting and transport processes and a variable degree of mixing. These populations are derived from a mixture of very fine- to very coarse-grained fluvial, outwash and paraglacial sediments deposited on the beds of the eastern English Channel and southern North Sea during the late Pleistocene lowstand. The nearshore-sand bank environment, which also corresponds to the main offshore source area of the coastal deposits, exhibits population heterogeneity reflecting the variability of hydrodynamic conditions and sediment sorting in this zone. The nearshore topography of tidal ridges, banks and troughs in these tidal seas leads to variable bed and tide- and storm-induced shear stress conditions. These conditions only allow for the mobilisation and onshore transport of some of the finer fractions (populations “b” and “c”), leaving an offshore mixture of these finer populations with coarser, less mobilisable sediments (population “a”). Once in the coastal zone, these two finer populations undergo further hydrodynamic sorting and segregation. Variably sorted very fine sands to silts (population “c”) are trapped in the low-energy estuarine-tidal flat sub-environment, while the highly homogeneous population “b” is further sorted in aeolian dune and beach sub-environments. This sorting occurs via a coastal sand transport pathway linking the Somme estuary mouth to the southern North Sea bight where tidal range and wave energy decrease relative to the English Channel. Since this sand transport pathway enables longshore transport of hydrodynamically sorted medium to fine sand derived directly from the immediate nearshore zone, it has further contributed to a net flux of this sand population from the eastern English Channel sea bed to the southern North Sea.     

A Mössbauer and FTIR study of synthetic amphiboles along the magnesioriebeckite – ferri-clinoholmquistite join

A series of amphiboles along the magnesioriebeckite—Na₂Mg₃Fe³⁺ ₂Si₈O₂₂(OH)₂– ferri-clinoholmquistite—Li₂Mg₃Fe³⁺ ₂Si₈O₂₂(OH)2 - join, defined by the ^BLi^B Na_–1 exchange vector, were hydrothermally synthesized at 700°C, 0.4 GPa, NNO + 1 redox conditions. Powder XRD and SEM-EDAX showed a very high (> 90%) amphibole yield for all samples. X-ray patterns were indexed in the C2/m space group; refined cell-parameters show a linear decrease of a and as a function of chemistry. IR spectra in the OH-stretching region show four main and rather sharp bands; these are assigned to Mg and Fe²⁺ at M(1,3), and indicate that the obtained amphiboles depart from the nominal octahedral composition (^M1,3Mg₃). The IR spectra also show that there is an increasing filling-up of the A-site for increasing Na in the system (increasing solid-solution toward, arfvedsonite). Mössbauer spectra show four well-defined quadrupole doublets which are assigned to Fe³⁺ at M2 and to Fe²⁺ at M1, M3 and M4, respectively. The Fe³⁺/Fe²⁺ content derived from fitted peak areas show variable Fe³⁺ concentration along the series. Mössbauer spectra also show a distinct alteration of ⁵⁷Fe hyperfine parameters with changing Na–Li at M4. The most evident variation is observed for the quadrupole splitting of Fe³⁺ at M2, which increases by 50% from ferri-clinoholmquistite to magnesio-riebeckite; this suggest that the M2 octahedron in ferri-clinoholmquistite is much closer to the ideal geometry than the M2 octahedron in magnesio-riebeckite. Mössbauer spectra show also a well-defined increase in the Fe²⁺ quadrupole splitting of the M1 and M3 octahedra, which is attributed to the Na–Li distribution at the B-sites.     

Pollution au plomb dans la Savoie antique (II–IIIe s. apr. J.-C.) en relation avec une installation métallurgique de la cité de Vienne

In Lake Anterne (NW French Alps), the Roman period is characterised by a lead contamination more important than that of the 1970s, due to the use of leaded gasoline. The maximum of this contamination period has been varve-dated 220 AD, i.e., during the optimum of Roman civilization in the Alps. Crossing palaeoenvironmental and archaeological evidences points out the economic importance of the town of Passy for the City of Vienne and yields a new example of lead contamination due to local metallurgical activity rather than distant impact of the exploitation of the Spanish Rio Tinto mine. To cite this article: F. Arnaud et al., C. R. Geoscience 338 (2005).     

Reassessment of the ‘Abbevillien’ in the perspective of new discoveries from the Lower Palaeolithic and Quaternary sites of Abbeville (Somme,northern France)

North-West Europe yields few traces of early human occupation, in particular for the Acheulean. In this context, the Somme Valley in northern France offers a route to Britain during various Pleistocene low sea levels, and has provided numerous evidence of Lower Palaeolithic human occupation through fieldwork initiated during the 19th century. These localities are associated with the original definition in the 1930s by the French prehistorian Abbé Henri Breuil of the ‘Abbevillien’ (Abbevillian facies), based on lithic pieces including crudely made bifaces recovered in particular in some famous key localities of Abbeville, Carpentier, Léon and Moulin Quignon quarries. The history of the term and its definition subsequently gave rise to debates concerning the chronocultural framework of Palaeolithic assemblages among the scientific community of prehistorians over time, from Jacques Boucher de Perthes, Gabriel de Mortillet, Geoffroy d'Ault du Mesnil, Victor Commont, Henri Breuil and François Bordes. New investigations at these three localities, all associated with the High Terrace of the Somme system, pushed back the age of the expansion of the Acheulean both in northern France and in Western Europe to c. 670–650 000 years. They imply that early hominins were able to settle in North-West Europe during both climatic temperate and cold phases. Our work, including new excavations and associated field observations of the three Abbeville localities involved at the onset of the controversy, allows a re-examination of the Abbevillian and contributes to the discussion of the history of Prehistoric Science and the Earliest ‘Acheuleans’ in North-West Europe.     

Study of the spatial and historical distribution of sediment inorganic contamination in the Toulon bay (France)

This study presents trace elements levels in surface and deep sediments of the Toulon bay (SE France) subjected to anthropogenic inputs (navy base, harbors, etc.). The studied elements (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) are defined as priority contaminants in aquatic systems. Fifty-five points scattered on the entire bay were sampled, allowing the determination of contaminants distribution with a high resolution. Several approaches were used to assess the degree of contamination and the potential toxicity of the Toulon bay sediments: comparison to the French legislation, surface-weighted average metal concentrations, enrichment factors (EF), geoaccumulation indices (Igeo), trace element stock calculation and comparison to sediment quality guidelines. A principal component analysis was performed to reveal common behavior of the studied contaminants. Results demonstrated the very high contamination of the small bay, especially in Hg (EF up to 1500), Cu, Pb and Zn, with export to the large bay further governed by hydrodynamics.     

Analysis with C- and X-band satellite SAR data of the Portalet landslide area

This paper describes the use of the Stable Point Network technique, a Persistent Scatterer Interferometry SAR technique, for the analysis of the Portalet landslide area (Central Pyrenees, Spain). For this purpose, different SAR datasets acquired by ERS-1, ERS-2, ENVISAT and TerraSAR-X satellites have been analysed. The use of different SAR images acquired by satellite radar sensors operating at different microwave lengths has allowed for a comparative assessment and illustration of the advantages and disadvantages of these satellites for landslide detection and monitoring. In the introduction, differential interferometry and the study area are briefly described. Then the specifics of the SPN processing and the results of the different datasets are described and compared. In Analysis of the results: the Portalet landslide area, the Portalet landslide area is introduced and the radar displacement measurements are analysed with available geo-information data. Additionally, X-band measurements are compared with those gathered by a ground-based SAR for a previous project. Finally, the most relevant conclusions of this work are discussed.     

Using Climber's Guidebooks to Assess Rock Fall Patterns Over Large Spatial and Decadal Temporal Scales: An Example from the Swiss Alps

High‐mountain geomorphic processes enjoy increasing scientific and societal interest. This is because these processes are perceived to be changing more than elsewhere and because their effects on infrastructure and tourism are significant. Rock fall is among the processes that receive most attention due to its presumed intimate relation with permafrost, which is widely degrading. However, over decadal temporal scales and for entire mountain ranges, there is very limited information on the changes in frequency and location of rock fall. This hampers our understanding. Here, I assess the value of information contained in a 146‐year record of climber's guidebooks of the Bernese Alps in Switzerland to derive changes in rock fall danger. The results show that guidebooks’ authors, themselves experienced climbers, perceived increases in rates and changes in positions of rock fall. The increases were mainly reported since the year 2000. It appears that datasets derived from guidebooks can provide valuable context for more detailed, higher resolution data sources.     

Is a regional flood signal reproducible from lake sediments?

The evolution of flood activity with global warming remains uncertain. To better assess flood–climate relationships, lake sediments are increasingly being investigated because they could provide regional flood histories long enough to cover past climate changes. However, site‐specific sedimentary processes may bias flood reconstructions. The aim of this article is to investigate these effects through the reconstruction of two distinct flood records from independent, neighbouring sedimentary basins of the same lake (Lake Allos in the Mediterranean French Alps), i.e. under the same climate conditions. Understanding of sedimentary processes is crucial in order to adapt the sampling strategy and the flood‐intensity proxy to each sedimentary system and, thereby, reconstruct a complete and reliable flood history. Thanks to this detailed approach, the main trends of the regional flood variability can be reproduced; i.e. periods of high flood‐frequency, ranges of flood‐frequency values and timing of the most intense events. In detail, some differences appeared associated to the various stream capacities to erode and transport flood sediments to the lake system, implying variable sensitivity of sedimentary systems in recording floods. Comparing regional flood records based on independent sedimentary systems from similar environments could thus be a complementary approach to assessing past flood intensity. Such an approach could open particularly interesting perspectives because reconstructing the long‐term evolution of flood intensity is a key challenge in the geosciences.