Settlement potential and constraints on the Lower Médoc coastline: results of the LITAQ project and considerations on coastal palaeo-risks in protohistoric times
The adaptation of territorial systems to the ongoing climate change is an issue which implies to test past populations abilities to cope, to “bounce back” or to adapt during similar past environmental changes. The chronostratigraphical and archaeological results, obtained in the frame of the LITAQ project, make it possible to better understand changes encountered by a coastal system (now on the shore front) whose intense occupation since the Neolithic period was linked to the exploitation of specific resources (salt, grazing), then inherent to a fluvial mouth and estuarine system, at present fossilized under the modern dune. One of the issues raised by these results is linked to the decline of salt-related activities during the whole Bronze period, whereas it is bracketed by a period of growing during the Neolithic (for which we were far from measuring the real amplitude) and by the first Iron Age during which salt production appears to be the main motivation for the settlement and the use of coastal marshes. However, the chronological gap, of about thirteen centuries, recorded between the Early Bronze Age (~2200 BC) and the Late Bronze Age (~900 BC), prevents us from using climate changes as a deterministic and unique factor of land-use changes of the Médoc Peninsula around the first millennium. The complex rhythms, that accompany those changes during this period and the subsequent Iron Age, invite us to consider the territorial vulnerability in a context of hydrogeomorphological modifications of the coast synchronously to those of natural components involved in the salt production process. Modalities of the spatial development of this activity (as deduced from the analysis of inventoried remains) in a context of restricted tidal exchanges (i.e. barred estuary), testify to the adaptability of protohistoric Médocan communities, which faced a slow and progressive disturbance of the coastal system; they attest also to the past resilience, in its systemic sense, of a territory nowadays far from major influences.
(Quaternaire. vol. 30, n° 1142-2904, pp. 97-111, 25/04/2019)
PRODIG, UP1, IRD, EPHE, PSL, UP4, UPD7, CNRS, UBM, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PRODIG (UMR_8586 / UMR_D_215 / UM_115), UP1, IRD, UPD7, SU, CNRS, LETG - Brest, LETG, UNICAEN, NU, UA, EPHE, PSL, UBO EPE, UR2, CNRS, IGARUN, UN, LETG - Caen, LETG, UNICAEN, NU, UA, EPHE, PSL, UBO EPE, UR2, CNRS, IGARUN, UN
Stature of dependent forbs is more related to the direct and indirect above‐ and below‐ground effects of a subalpine shrub than are foliage traits
Question: Graminoid/shrubland communities include groups of forbs (herbaceous dicots) that differ in their traits, and in their direct and indirect responses to dominant neighbours. Although we have a growing knowledge of which traits might influence species’ direct responses to dominant neighbours, and in particular the crucial importance of plant stature over foliage traits, less is known about the relationship between species’ traits and direct responses to dominant neighbours. Location: An alpine graminoid/shrubland co‐dominated by the shrub Dasiphora fruticosa and graminoids such as the sedge Kobresia capillifolia on the Tibetan plateau (China). Methods: The above‐ and below‐ground effects of the shrub in the absence or presence of graminoids were manipulated to quantify direct and indirect responses of forb species, which were grouped with a PCA. For the forbs, six traits characterizing both plant stature and foliage properties were measured and a redundancy analysis was used to assess their patterns of direct and indirect responses to the dominant neighbours. Results: We found contrasting direct and indirect responses of forb species to the graminoids, and the above‐ and below‐ground effects of the shrubs, separating the forbs into four species‐groups. A significant positive indirect net effect of the shrubs was observed at the community‐level. Traits of forb species were more tightly related to direct than indirect responses to dominant neighbours, while plant stature had a primary influence over foliage traits, which was only very weakly related to indirect responses. Conclusions: Although plant traits, in particular plant stature, have strong influences on species’ direct responses to dominant neighbours, relationships to indirect interactions are more subtle and variable. This inhibits our prediction of the influence of species’ traits on species composition of the community through indirect interactions.
(Journal of Vegetation Science. vol. 30, n° 1100-9233, pp. 403-412, 25/04/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Holocene palaeoenvironmental evolution of the Médoc peninsula (SW France): insights from the sedimentological study of the “Lède du Gurp” archaeological site
(Quaternaire, n° 1142-2904, pp. 31-46, 25/04/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PACEA, UB, CNRS, LGO, UBS, IFREMER, UBO EPE, CNRS, UBM, CNRS
Divalent Mercury in Dissolved Organic Matter Is Bioavailable to Fish and Accumulates as Dithiolate and Tetrathiolate Complexes
(Environmental Science and Technology. vol. 53, n° 0013-936X, pp. 4880-4891, 19/04/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ESRF, ESRF, ISTerre, IFSTTAR, INSU - CNRS, USMB [Université de Savoie] [Université de Chambéry], CNRS, UGA [2016-2019]
Importance of the vegetation-groundwater-stream continuum to understand transformation of biogenic carbon in aquatic systems – A case study based on a pine-maize comparison in a lowland sandy watershed (Landes de Gascogne, SW France)
During land-aquatic transfer, carbon (C) and inorganic nutrients (IN) are transformed in soils, groundwater, and at the groundwater-surface water interface as well as in stream channels and stream sediments. However, processes and factors controlling these transfers and transformations are not well constrained, particularly with respect to land use effect. We compared C and IN concentrations in shallow groundwater and first-order streams of a sandy lowland catchment dominated by two types of land use: pine forest and maize cropland. Contrary to forest groundwater, crop groundwater exhibited oxic conditions all-year round as a result of higher evapotranspiration and better lateral drainage that decreased the water table below the organic-rich soil horizon, prevented the leaching of soil-generated dissolved organic carbon (DOC) in groundwater, and thus limited consumption of dissolved oxygen (O2). In crop groundwater, oxic conditions inhibited denitrification and methanogenesis resulting in high nitrate (NO3−; on average 1140 ± 485 μmol L−1) and low methane (CH4; 40 ± 25 nmol L−1) concentrations. Conversely, anoxic conditions in forest groundwater led to lower NO3− (25 ± 40 μmol L−1) and higher CH4 (1770 ± 1830 nmol L−1) concentrations. The partial pressure of carbon dioxide (pCO2; 30,650 ± 11,590 ppmv) in crop groundwater was significantly lower than in forest groundwater (50,630 ± 26,070 ppmv), and was apparently caused by the deeper water table delaying downward diffusion of soil CO2 to the water table. In contrast, pCO2 was not significantly different in crop (4480 ± 2680 ppmv) and forest (4900 ± 4500 ppmv) streams, suggesting faster degassing in forest streams resulting from greater water turbulence. Although NO3−concentrations indicated that denitrification occurred in riparian-forest groundwater, crop streams nevertheless exhibited important signs of spring and summer eutrophication such as the development of macrophytes. Stream eutrophication favored development of anaerobic conditions in crop stream sediments, as evidenced by increased ammonia (NH4+) and CH4 in stream waters and concomitant decreased in NO3− concentrations as a result of sediment denitrification. In crop streams, dredging and erosion of streambed sediments during winter sustained high concentration of particulate organic C, NH4+ and CH4. In forest streams, dissolved iron (Fe2+), NH4+ and CH4 were negatively correlated with O2 reflecting the gradual oxygenation of stream water and associated oxidations of Fe2+, NH4+ and CH4. The results overall showed that forest groundwater behaved as source of CO2 and CH4 to streams, the intensity depending on the hydrological connectivity among soils, groundwater, and streams. CH4 production was prevented in cropland in soils and groundwater, however crop groundwater acted as a source of CO2 to streams (but less so than forest groundwater). Conversely, in streams, pCO2 was not significantly affected by land use while CH4 production was enhanced by cropland. At the catchment scale, this study found substantial biogeochemical heterogeneity in C and IN concentrations between forest and crop waters, demonstrating the importance of including the full vegetation-groundwater-stream continuum when estimating land-water fluxes of C (and nitrogen) and attempting to understand their spatial and temporal dynamics.
(Science of the Total Environment. vol. 661, n° 0048-9697, pp. 613-629, 15/04/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UMR ISPA, INRA, Bordeaux Sciences Agro, EPHYSE, INRA, UFF, MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], ULCO, BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA
Imprints of wave climate and mean sea level variations in the dynamics of a coastal spit over the last 250 years: Cap Ferret, SW France
(Earth Surface Processes and Landforms, n° 0197-9337, 12/04/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BRGM
Holocene Environment Changes in the Hachichina Wetland (Gulf of Gabes, Tunisia) Evidenced by Foraminifera and Ostracoda, Geochemical Proxies and Sedimentological Analyses
Four sediment cores, drilled at Younga and Ouadrane Sebkhas (Hachichina wetland), were selected for micropalaeontological, sedimentological, geochronological and geochemical investigation coupled to hierarchical cluster and correspondence analysis. Our research aimed at reconstructing the past biodiversity, the Holocene palaeoenvironmental evolution and the responsible forcing. Subsurface sediments record four major phases: i) the first one is characterized by poorly to very poorly sorted silts, the dominance of the lagoonal/estuarine ostracod and the lagoonal/marine foraminifera and high values of terrestrial geochemical element ratios, such as K/Al and Fe/Al, which indicate an estuarine lagoon; ii) two major marine transgressions, TR1 and TR2, allowing the settlement of widely opened lagoons towards 7160-8680 and 5070-5520 cal yr BP, are marked by the enhancement of the marine/brackish ostracods and marine foraminifera, the improvement of species number, individuals number and H and E index values and of the marine element ratios such as Cl/Al and Sr/Al; iii) the opening of the lagoon is hampered by the action of drift currents allowing the genesis of sand spit and the settlement of a closed lagoon, towards 2610-3610 cal yr BP, characterized by the enhancement of lagoonal/estuarine ostracods and lagoonal/marine foraminifera and the increase of the individuals number; iv) the dominance of the lagoonal/estuarine ostracods and the lagoonal/marine foraminifera and the decline of the species number and density mark a brackish lagoon, also characterized by very poorly sorted silts transported by uniform suspension, which evolves to the actual sebkha. This evolution, within a global climate alteration context, from an estuarine environment to the present sebkha passing by an opened lagoon, is linked to the complex hydrographic setting of the sebkhas and of the Ouadrane Wadi outlet discharging in the Hachichina wetland.
(Rivista Italiana di Paleontologia e Stratigrafia. vol. 125, n° 0035-6883, pp. 517-549, 05/04/2019)
FSS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ENIS
Late Holocene Changes in Erosion Patterns in a Lacustrine Environment: Landscape Stabilization by Volcanic Activity Versus Human Activity
(Geochemistry, Geophysics, Geosystems, 02/04/2019)
ULiège, UEC, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ULiège, ULiège, AORI, UTokyo
The dismantling of the Apulian carbonate platform during the late Campanian – early Maastrichtian in Albania
The Apulian carbonate margin is widely preserved across the Adriatic domain and has been extensively studied in the south of Italy. In Albania, Oligocene–Pliocene fold-and-thrust tectonics led to widespread exposure of the Apulian Platform and associated Ionian Basin carbonates. However, the portion linking the platform to the basin is missing, preventing a direct reconstruction of the platform margin. Syn-sedimentary folding and faulting are recognized in the uppermost part of both the platform and basinal/slope series. Mass transport deposits (MTDs) occur within the platform succession incorporated into well-bedded intertidal (stromatolites) to shallow-subtidal (rudist packstones) sedimentary sequences. They display significant lateral variability which is accompanied by both rigid and soft deformation structures. Spectacular slumps made up of sediment density flow deposits are recognized in the adjacent Ionian Basin. The lateral extent of basal shear surfaces, syn-sedimentary faults and folds evidenced in the Ionian Basin points toward multiple regional tectonic triggering events affecting the Apulian Platform margin at that time. Bio- and chrono-stratigraphic analyses suggest that the triggers occurred during the late Campanian – early Maastrichtian. Beyond the obvious interest from a stratigraphic point of view, the study of these events recording the dismantling of the Apulian carbonate platform allows for a better understanding of the triggering mechanisms and the sedimentary characteristics of MTDs and slumps at a basinal scale.
(Cretaceous Research. vol. 96, n° 0195-6671, pp. 83-106, 01/04/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Humans and their environment on the Médoc coastline from the Mesolithic to the Roman period
The northern coast of the Médoc between Soulac-sur-Mer and Montalivet-les-Bains has a rich archaeological heritage that is being directly impacted by coastal erosion. A series of clay-peat palaeosols that formed in ancient estuarine marshes holds evidence of intensive occupation from the Mesolithic until the end of the Roman period. Within this framework, our research focused on the two key sites of La Lède du Gurp (Grayan-et-l'Hôpital) and L'Amélie (Soulac-sur-Mer), where an interdisciplinary approach based on comparison of archaeological, sedimentary and palaeo-environmental data has made it possible to situate the main phases of occupation in their environmental context. This work has benefited from field documentation that is exceptionally well-preserved in wet sediments sealed beneath the present-day dune system. The most fleeting traces (animal tracks) like the sturdiest anthropic structures are preserved, as are many organic remains. These items provide access to first-rate documentation for reconstructing the range of activities practised in a specific ecosystem: salt production, livestock grazing, shellfish collecting, passage and carriage, and funerary and symbolic practices. Study of occupation over the long term reveals an alternating pattern of dynamic phases and decline phases that seem to be correlated with changes in the local environment.
(Quaternaire. vol. 30, n° 1142-2904, pp. 77-95, 01/04/2019)
UBM, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LETG, UNICAEN, NU, UA, EPHE, PSL, UBO EPE, UR2, CNRS, IGARUN, UN, PRODIG, UP1, IRD, UP4, UPD7, CNRS, PACEA, UB, CNRS, PRODIG (UMR_8586 / UMR_D_215 / UM_115), UP1, IRD, SU, CNRS, UPCité, CReAAH, UM, UR, UR2, CNRS, UFR HHAA, UN, MC, LETG - Brest, LETG, UNICAEN, NU, UA, EPHE, PSL, UBO EPE, UR2, CNRS, IGARUN, UN, HIPS, GEOLAB, UBP, IR SHS UNILIM, UNILIM, UCA [2017-2020], CNRS, UCA, PréTech, UPN, CNRS, TRACES, EHESS, UT2J, Comue de Toulouse, MCC, Inrap, CNRS