Analyses of lake La Thuile sediment core

Lake La Thuile, in the Northern French Prealps (874 m a.s.l.), provides an 18 m long sedimentary sequence spanning the entire Lateglacial/Holocene period. The high resolution multi-proxy (sedimentological, palynological, geochemical) analysis of the uppermost 6.2 meters reveals the Holocene dynamics of erosion in the catchment in response to landscape modifications. The mountain belt is at relevant altitude to study past human activities and the watershed is sufficiently disconnected from large valleys to capture a local sedimentary signal. From 12,000 to 10,000 cal. BP (10 to 8 ka cal. BC), the onset of hardwood species triggered a drop in erosion following the Lateglacial/Holocene transition. From 10,000 to 4500 cal. BP (8 to 2.5 ka cal. BC), the forest became denser and favored slope stabilization while erosion processes were very weak. A first erosive phase was initiated at ca . 4500 cal. BP without evidence of human presence in the catchment. Then, the forest declined at approximately 3000 cal. BP, suggesting the first human influence on the landscape. Two other erosive phases are related to anthropic activities: approximately 2500 cal. BP (550 cal. BC) during the Roman period and after 1600 cal. BP (350 cal. AD) with a substantial accentuation in the Middle Ages. In contrast, the lower erosion produced during the Little Ice Age, when climate deteriorations are generally considered to result in an increased erosion signal in this region, suggests that anthropic activities dominated the erosive processes and completely masked the natural effects of climate on erosion in the late Holocene.

Evaluación de metales pesados en suelos de los oasis irrigados de la Provincia de Mendoza : concentraciones totales de Zn, Pb, Cd y Cu

En Mendoza, Argentina, no existen antecedentes respecto de la presencia de elementos trazas, totales y disponibles, relacionados con el uso de los suelos en los oasis irrigados. El objetivo del trabajo, en esta etapa, fue determinar los contenidos totales de plomo (Pb), cadmio (Cd), cinc (Zn) y cobre (Cu) en la capa superficial de suelos (0-25 cm), diferenciados en siete tipos según una clasificación utilitaria: suelos vírgenes (SV); suelos de banquina (SB); suelos vecinos a banquina (SVB); suelos de agricultura intensiva (SAI); suelos de agricultura protegidos por lucha antigranizo (SLAG); suelos afectados por actividad industrial (SI) y suelos urbanos (SU). Sobre un total de 200 muestras se efectuó una digestión ácida en caliente y en los extractos se determinaron los metales en su fracción total, mediante espectrofotometría de absorción atómica (AAS). El análisis estadístico de los datos muestra que los niveles más elevados de Cu y Cd se detectan en SAI, con medias de 39,3 y 2,5 mg kg-1 respectivamente. En SI se observan los mayores valores de Pb, con una media de 80,6 mg kg-1 y en SU los mayores tenores de Zn, con un valor medio de 740 mg kg-1. La Ciudad de Mendoza, con mayor densidad poblacional, presentó los mayores contenidos de Zn, Pb y Cd. Las concentraciones encontradas se ubican por debajo de las exigencias de la legislación argentina y la mayoría de los suelos pueden clasificarse como no contaminados (SNC) o ligeramente contaminados (SLC). Se prevé completar este estudio con la determinación de las fracciones disponibles de los elementos estudiados, correlacionándolos con variables edáficas físico-químicas como textura, pH y materia orgánica.

Elisa Moyano (coord.). La literatura de Salta. Espacios de reconocimiento y formas de olvido. Salta, Universidad Nacional de Salta, 2005, 210 p.

Fil: Zapata Viani, María Alejandra.

Radiocarbon dating, sedimentation rate, granulometry and organic carbon content of ODP Leg 182 sites

This data report presents sedimentological (grain size) and geochemical (X-ray diffraction, total organic carbon, accelerator mass spectrometry radiocarbon, and percent carbonate) information obtained from the western transect (Sites 1132, 1130, and 1134) and the eastern transect (Sites 1129, 1131, and 1127) in the Great Australian Bight during Leg 182. The purpose is to quantify changing rates of sediment accumulation and changes in sediment type from the late Pleistocene and Holocene, in order to relate these changes to the well-known sea level curve that exists for this time frame. Ultimately, these data can be used to more effectively interpret lithologic variations deeper in the Pleistocene succession, which most likely represent orbitally forced sea level events.

Feldspar Pb-isotope ratios for earliest Pleistocene sediments of the sub-polar North Atlantic Ocean

Relatively little is known in detail about the locations of the early Pleistocene ice-sheets responsible for ice-rafted debris (IRD) inputs to the sub-polar North Atlantic Ocean during intensification of northern hemisphere glaciation (iNHG). To shed new light on this problem, we present the first combined in-depth analysis of IRD flux and geochemical provenance of individual sand-sized IRD deposited in the sub-polar North Atlantic Ocean during the earliest large amplitude Pleistocene glacial, marine isotope stage (MIS) 100 (~2.52 Ma), arguably the key glacial during iNHG. IRD provenance is assessed using laser ablation lead (Pb) isotope analyses of single feldspar grains. We find that the Pb-isotope composition (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb) of individual ice-rafted (>150 µm) feldspars deposited at DSDP Site 611A, ODP Site 981 and IODP Site U1308 during MIS 100 records a shift from predominantly Archaean-aged circum-North Atlantic Ocean continental sources during early glacial ice-rafting events to dominantly Palaeozoic and Proterozoic-aged sources during full glacial conditions. The distribution of feldspars in Pb-Pb space for full glacial MIS 100 more closely resembles that documented for feldspars deposited at the centre of the last glacial IRD belt (at IODP/DSDP Site U1308/609) during ambient (non-Heinrich-event) ice-rafting episodes of MIS 2 (~23.8 ka) than that documented for MIS 5d (~106 ka). Comparison of our early Pleistocene and last glacial cycle datasets suggests that MIS 100 was characterised by abundant iceberg calving from large ice-sheets on multiple continents in the high northern latitudes (not just on Greenland).

Nd and Pb isotopes in ferromanganese crusts

The intensity of North Atlantic Deep Water (NADW) production has been one of the most important parameters controlling the global thermohaline ocean circulation system and climate. Here we present a new approach to reconstruct the overall strength of NADW export from the North Atlantic to the Southern Ocean over the past 14 Myr applying the deep water Nd and Pb isotope composition as recorded by ferromanganese crusts and nodules. We present the first long-term Nd and Pb isotope time series for deep Southern Ocean water masses, which are compared with previously published time series for NADW from the NW Atlantic Ocean. These data suggest a continuous and strong export of NADW, or a precursor of it, into the Southern Ocean between 14 and 3 Ma. An increasing difference in Nd and Pb isotope compositions between the NW Atlantic and the Southern Ocean over the past 3 Myr gives evidence for a progressive overall reduction of NADW export since the onset of Northern Hemisphere glaciation (NHG). The Nd isotope data allow us to assess at least semiquantitatively that the amount of this reduction has been in the range between 14 and 37% depending on location.

Isotope composition of dolomite, calcite and pore-waters of ODP Leg 210 samples

Early diagenetic dolomite beds were sampled during the Ocean Drilling Programme (ODP) Leg 201 at four reoccupied ODP Leg 112 sites on the Peru continental margin (Sites 1227/684, 1228/680, 1229/681 and 1230/685) and analysed for petrography, mineralogy, d13C, d18O and 87Sr/86Sr values. The results are compared with the chemistry, and d13C and 87Sr/86Sr values of the associated porewater. Petrographic relationships indicate that dolomite forms as a primary precipitate in porous diatom ooze and siliciclastic sediment and is not replacing the small amounts of precursor carbonate. Dolomite precipitation often pre-dates the formation of framboidal pyrite. Most dolomite layers show 87Sr/86Sr-ratios similar to the composition of Quaternary seawater and do not indicate a contribution from the hypersaline brine, which is present at a greater burial depth. Also, the d13C values of the dolomite are not in equilibrium with the d13C values of the dissolved inorganic carbon in the associated modern porewater. Both petrography and 87Sr/86Sr ratios suggest a shallow depth of dolomite formation in the uppermost sediment (<30 m below the seafloor). A significant depletion in the dissolved Mg and Ca in the porewater constrains the present site of dolomite precipitation, which co-occurs with a sharp increase in alkalinity and microbial cell concentration at the sulphate-methane interface. It has been hypothesized that microbial 'hot-spots', such as the sulphate-methane interface, may act as focused sites of dolomite precipitation. Varying d13C values from -15 per mil to +15 per mil for the dolomite are consistent with precipitation at a dynamic sulphate-methane interface, where d13C of the dissolved inorganic carbon would likewise be variable. A dynamic deep biosphere with upward and downward migration of the sulphate-methane interface can be simulated using a simple numerical diffusion model for sulphate concentration in a sedimentary sequence with variable input of organic matter. Thus, the study of dolomite layers in ancient organic carbon-rich sedimentary sequences can provide a useful window into the palaeo-dynamics of the deep biosphere.