Chemical and Mineralogical Signatures of Archaeological Features at the Mailhot‐Curran Iroquoian Site,Eastern Canada

The St. Lawrence Iroquoians built villages in southwestern Quebec (Canada) along the St. Lawrence River. They left behind longhouses, hearths, middens, and storage pits like those discovered at the Mailhot‐Curran archaeological site in Saint‐Anicet. Here, we contrast the properties of Iroquoian features with undisturbed soil to define the chemical and mineralogical signature of hearths, middens, and pits. The native soil has a neutral pH and consists of an Ah horizon overlaying a Bm horizon dominated by quartz and feldspars. In the hearths, ashes are characterized by neoformed calcite and apatite with carbonates, higher total P, and enrichment in amorphous inorganic Al, Fe, and Si. The rubified layer of hearths contain poorly crystallized Fe oxides. The mineralogy of the rubified layer is dominated by authigenetic ankerite, an Fe‐carbonate mineral identified here for the first time in Iroquoian hearths. Middens have the highest organic matter content and contain more organically complexed Al and Fe than the soil. The storage pits have low pH values and carbonate content and contain high levels of amorphous Si and total P. Our work establishes the pedologic signature of three Iroquoian features despite significant alteration of their properties by post‐occupational biogeochemical processes.     

Sources of particulate and dissolved organic carbon in the St Lawrence River: isotopic approach

We investigate sources of both dissolved and particulate organic carbon in the St Lawrence River from its source (the Great Lakes outlet) to its estuary, as well as in two of its tributaries. Special attention is given to seasonal interannual patterns by using data collected on a bi‐monthly basis from mid‐1998 to mid‐2003. δ¹³C measurements in dissolved inorganic carbon, dissolved organic carbon (DOC) and particulate organic carbon (POC), as well as molar C : N in particulate organic matter (POM), are used to bring insight into the dynamic between aquatic versus terrigenous sources. In addition, ¹⁴C activities of DOC were measured at the outlet of the St Lawrence River to its estuary to assess a mean age of the DOC exported to the estuary. In the St Lawrence River itself, aquatically produced POC dominates terrestrially derived POC and is depleted in ¹³C by approximately 12‰ versus dissolved CO₂. In the Ottawa River, the St Lawrence River's most important tributary, the present dataset did not allow for convincing deciphering of POC sources. In a small tributary of the St Lawrence River, aquatically produced POC dominates in summer and terrestrially derived POC dominates in winter. DOC seems to be dominated by terrestrially derived organic matter at all sampling sites, with some influence of DOC derived from aquatically produced POC in summer in the St Lawrence River at the outlet of the Great Lakes and in one of its small tributaries. The overall bulk DOC is relatively recent (¹⁴C generally exceeding 100% modern carbon) in the St Lawrence River at its outlet to the estuary, suggesting that it derives mainly from recent organic matter from topsoils in the watershed. Copyright © 2005 John Wiley & Sons, Ltd.     

Variation and temporal patterns in the composition of the surface ichthyoplankton in the southern Bay of Biscay (W. Atlantic)

From September 2000 to December 2006, surface plankton samples were collected on a monthly basis, from a station located in the southern Bay of Biscay (43°37N; 1°43W France), near the deep Capbreton canyon. In this paper, the results for the ichthyoplankton assemblage are presented. Among the 62 taxa recorded, only 35 were present in the larval stage whilst only 10 were represented by their eggs. Taxa represented by both stages (eggs+larvae; N=17) had the highest abundance. The presence in the surface plankton assemblage of species, at either or both stage, is interpreted within the context of the bathymetric distribution of species. The maxima in abundance and diversity occurred in February–March, for eggs, and May–June, for larvae. This 3-month time-lag between the stages is proposed to be related to the timing of egg spawning and larval recruitment to the pelagic environment. Mean egg abundances (82.4±29.8 eggs/10 m²) were 10-fold higher than the larval abundances (7.1±1.8 larvae/10 m²). Despite pronounced monthly variability, no statistically significant decrease in either egg or larvae abundance was observed during this 6-year study period. Compared with previous published studies, this study shows that the peak in ichthyoplankton diversity occurred two months earlier. In addition, the spawning period occurred over the whole year, even during autumn and winter. Using ordination techniques, the annual sequence appearance of taxa are described at the study site: Gadiforms, Ammodytidae and Pleuronectiforms were present during the winter whilst Sparidae, Blennidae, Labridae and Gobiidae, formed the summer group. Only three species, European anchovy Engraulis encrasicolus, European pilchard Sardina pilchardus and Atlantic horse mackerel Trachurus trachurus were recorded throughout the year.     

Estimate of the Transition Value of Librational Invariant Curves

We investigate the break-down threshold of librational invariant curves. As a model problem, we consider a variant of a mapping introduced by M. Hénon, which well describes the dynamics of librational motions surrounding a stable invariant point. We verify in concrete examples the applicability of Greene's method, by computing the instability transition values of a sequence of periodic orbits approaching an invariant curve with fixed noble frequency. However, this method requires the knowledge of the location of the periodic orbits within a very good approximation. This task appears to be difficult to realize for a libration regime, due to the different topology of the phase space. To compute the break-down threshold, we tried an alternative method very easy to implement, based on the computation of the fast Lyapunov indicators and frequency analysis. Such technique does not require the knowledge of the periodic orbits, but again, it appears very difficult to have a precision better than Greene's method for the computation of the critical parameter.     

Dynamical contribution to sea surface salinity variations in the eastern Gulf of Guinea based on numerical modelling

In this study, we analyse the seasonal variability of the sea surface salinity (SSS) for two coastal regions of the Gulf of Guinea from 1995 to 2006 using a high resolution model (1/12°) embedded in a Tropical Atlantic (1/4°) model. Compared with observations and climatologies, our model demonstrates a good capability to reproduce the seasonal and spatial variations of the SSS and mixed layer depth. Sensitivity experiments are carried out to assess the respective impacts of precipitations and river discharge on the spatial structure and seasonal variations of the SSS in the eastern part of the Gulf of Guinea. In the Bight of Biafra, both precipitations and river runoffs are necessary to observe permanent low SSS values but the river discharge has the strongest impact on the seasonal variations of the SSS. South of the equator, the Congo river discharge alone is sufficient to explain most of the SSS structure and its seasonal variability. However, mixed layer budgets for salinity reveal the necessity to take into account the horizontal and vertical dynamics to explain the seasonal evolution of the salinity in the mixed layer. Indeed evaporation, precipitations and runoffs represent a relatively small contribution to the budgets locally at intraseasonal to seasonal time scales. Horizontal advection always contribute to spread the low salinity coastal waters offshore and thus decrease the salinity in the eastern Gulf of Guinea. For the Bight of Biafra and the Congo plume region, the strong seasonal increase of the SSS observed from May/June to August/September, when the trade winds intensify, results from a decreasing offshore spread of freshwater associated with an intensification of the salt input from the subsurface. In the Congo plume region, the subsurface salt comes mainly from advection due to a strong upwelling but for the Bight of Biafra, entrainment and vertical mixing also play a role. The seasonal evolution of horizontal advection in the Bight of Biafra is mainly driven by eddy correlations between salinity and velocities, but it is not the case in the Congo plume.     

MÉTHODE D'ÉTUDE DES NAPPES LIBRES DANS LES AQUIFÈRES ANISOTROPES

Abstract

The necessary and sufficient conditions for non-zero phase shift and non-zero attenuation in linear flood routing can be derived from the continuity equation alone and are found to depend on the existence of an imaginary part in the expression for frequency or in the expression for wave number. It is shown that in linear flood routing the phase lag between flow rate and area of flow is directly related to the attenuation per unit wave length. The effects of using various forms of the momentum equation, in addition to the continuity equation, are exemplified by deriving analytical expressions in terms of the frequency, both for attenuation per unit channel length and for phase shift, for the kinematic wave, the general diffusion analogy, and the complete St. Venant equation.     

Spatio-temporal analysis of territorial changes from a multi-scale perspective

The full integration of time dimensions in GIS still represents a research challenge. A number of systems provide ways to visualise harmonised timestamped geographical data onto maps, with interpolated curves representing how these data have changed over time. However, these systems frequently mask the concerns linked to changes in territorial organisations and the harmonisation of data. In fact, the development of a territory should be considered in connection with its neighbourhood, governance and genealogy relationships. This article focuses on the difficulties linked with the ‘change of support problem’, which can arise when conducting spatio-temporal analysis of data. First, we present a data model handling the changing relationships between territories. Then, we illustrate how this model can be instantiated using examples that have taken place in Europe. We show how the model can address questions such as that of change blindness. Finally, we explain how hierarchical and genealogical relationships can be used inside an interactive cartographic tool for spatio-temporal analysis. It provides various views of the same phenomena at multiple scales, through an approach that takes into account the changes in territorial organisation.     

An opportunity to connect the morphodynamics of alternate bars with their sedimentary products

Field investigations that help clarify local sedimentary processes involved in the migration of alternate bars as a consequence of flood events are lacking. A simple approach combining scour chains, stratigraphy and frequent bathymetric surveys is proposed to connect the dynamics of free migrating alternate bars present in disconnected channels of large sandy‐gravelly rivers with their sedimentary products and vice versa. The results show that the spatial distribution of bars before a flood partly governs the scour and fill processes and that the sediment transport rates vary significantly on a single cross‐section. This can be due to preferential axes of the migration of the bars determined by their location on the cross‐section, the bank direction and the discharge. The approach allows the reconstruction of local sedimentary processes involved in alternate bar migration by combining maximum scour depths reached during a flood with frequent channel bed topography surveys and post‐flood stratigraphy. It is also possible to distinguish deposited and preserved sediments compared with sediments by‐passed during the flood. Copyright © 2011 John Wiley & Sons, Ltd.     

New constraints on the delivery of cometary water and nitrogen to Earth from the N/N isotopic ratio

New independent constraints on the amount of water delivered to Earth by comets are derived using the ¹⁵N/¹⁴N isotopic ratio, measured to be roughly twice as high in cometary CN and HCN as in the present Earth. Under reasonable assumptions, we find that no more than a few percent of Earth’s water can be attributed to comets, in agreement with the constraints derived from D/H. Our results also suggest that a significant part of Earth’s atmospheric nitrogen might come from comets. Since the ¹⁵N/¹⁴N isotopic ratio is not different in Oort-cloud and Kuiper-belt comets, our estimates apply to the contribution of both types of objects.