Isotope characterisation of Villars Cave stalagmites

We present a new mid-latitude speleothem record of millennial-scale climatic variability during OIS3 from the Villars Cave that, combined with former published contemporaneous samples from the same cave, gives a coherent image of the climate variability in SW-France between ~55 ka and ~30 ka. The 0.82 m long stalagmite Vil-stm27 was dated with 26 TIMS U-Th analyses and its growth curve displays variations that are linked with the stable isotopes, both controlled by the climatic conditions. It consists in a higher resolved replicate of the previously published Vil-stm9 and Vil-stm14 stalagmites where Dansgaard-Oeschger (DO) events have been observed. The good consistency between these three stalagmites and the comparison with other palaoeclimatic reconstructions, especially high resolution pollen records (ODP 976 from the Alboran Sea, Monticchio Lake record from southern Italy) and the nearby MD04-2845 Atlantic Ocean record, permits to draw a specific climatic pattern in SW-France during the OIS3 and to see regional differences between these sites. Main features of this period are: 1) warm events corresponding to Greenland Interstadials (GIS) that are characterized by low speleothem d13C, high temperate pollen percentages, warm temperatures and high humidity; among these events, GIS#12 is the most pronounced one at Villars characterized by an abrupt onset at ~46.6 ka and a duration of about 2.5 ka. The other well individualized warm event coincides with GIS#8 which is however much less pronounced and occurred during a cooler period as shown by a lower growth rate and a higher d13C; 2) cold events corresponding to Greenland Stadials (GS) that are clearly characterized by high speleothem d13C, low temperate pollen abundance, low temperature and enhanced dryness, particularly well expressed during GS coinciding with Heinrich events H5 and H4. The main feature of the Villars record is a general cooling trend between the DO#12 event ~45.5 ka and the synchronous stop of the three stalagmites at ~30 ka ±1, with a first well marked climatic threshold at ~41 ka after which the growth rate and the diameter of all stalagmites slows down significantly. This climatic evolution differs from that shown at southern Mediterranean sites where this trend is not observed. The ~30 ka age marks the second climatic threshold after which low temperatures and low rainfalls prevent speleothem growth in the Villars area until the Lateglacial warming that occurred at ~16.5 ± 0.5 ka. This 15 ka long hiatus, as the older Villars growth hiatus that occurred between 67.4 and 61 ka, are linked to low sea levels, reduced ocean circulation and a southward shift of the Polar Front that likely provoked local permafrost formation. These cold periods coincide with both low summer 65°N insolation, low atmospheric CO2 concentration and large ice sheets development (especially the Fennoscandian).

Mössbauer characterisation of sediments from ODP Sites 128-798 and 128-799

57Fe Mössbauer spectra for 26 sediment and 6 carbonate concretion samples from Sites 798 and 799 were recorded at 293 K. Most spectra were deconvolved to two quadrupole doublets without magnetic hyperfine structure. Typical Mössbauer parameters were: isomer shift (I.S.) = 0.34 mm/s and quadrupole splitting (Q.S.) = 0.64 mm/s for the paramagnetic Fe3+ component (partly, pyrite); I.S. = 1.13 mm/s and Q.S. = 2.64 mm/s for the high-spin Fe2+ component derived from iron-bearing aluminosilicates. A few spectra included other high-spin Fe2+ components ascribed to iron-bearing carbonate minerals (e.g., ferroan magnesite), according to the Mössbauer parameters for Fe2+ in the carbonate concretions. We present the distribution of iron among different chemical forms as a function of depth. These data might indicate changes of depositional and diagenetic conditions.

Results of biological and geological bottom investigations carried out during Cruise 43 of R/V Akademik Kurchatov in the South Atlantic

The book is devoted to investigations of benthic fauna and geology of the Southern Atlantic Ocean. These works have been carried out in terms of exploring biological structure of the ocean and are of great importance for development of this fundamental problem. They are based on material collected during Cruise 43 of R/V Akademik Kurchatov in 1985-1986 and Cruise 43 of R/V Dmitry Mendeleev in 1989. Problems of quantitative distribution, group composition and trophic structure of benthos in the Southern Scotia Sea, along the east-west Transatlantic section along 31°30'S, and offshore Namibia in the area of the Benguela upwelling are under consideration in the book. Authors present new data on fauna of several groups of deep-sea bottom animals and their zoogeography. Much attention is paid to analysis of morphological structure of the Scotia Sea floor considered in terms of plate tectonics. Bottom sediments along the Transatlantic section and facial variation of sediments in the area of South Shetland Islands and of the continental margin of Namibia are under consideration.

Distribution of biological, anthropogenic, and volcanic constituents in the San Francisco Bay Coastal System

Although conventional sediment parameters (mean grain size, sorting, and skewness) and provenance have typically been used to infer sediment transport pathways, most freshwater, brackish, and marine environments are also characterized by abundant sediment constituents of biological, and possibly anthropogenic and volcanic, origin that can provide additional insight into local sedimentary processes. The biota will be spatially distributed according to its response to environmental parameters such as water temperature, salinity, dissolved oxygen, organic carbon content, grain size, and intensity of currents and tidal flow, whereas the presence of anthropogenic and volcanic constituents will reflect proximity to source areas and whether they are fluvially- or aerially-transported. Because each of these constituents have a unique environmental signature, they are a more precise proxy for that source area than the conventional sedimentary process indicators. This San Francisco Bay Coastal System study demonstrates that by applying a multi-proxy approach, the primary sites of sediment transport can be identified. Many of these sites are far from where the constituents originated, showing that sediment transport is widespread in the region. Although not often used, identifying and interpreting the distribution of naturally-occurring and allochthonous biologic, anthropogenic, and volcanic sediment constituents is a powerful tool to aid in the investigation of sediment transport pathways in other coastal systems.

(Table 1) Rates of biological activity in deep-sea sediments

Global maps of sulfate and methane in marine sediments reveal two provinces of subsurface metabolic activity: a sulfate-rich open-ocean province, and an ocean-margin province where sulfate is limited to shallow sediments. Methane is produced in both regions but is abundant only in sulfate-depleted sediments. Metabolic activity is greatest in narrow zones of sulfate-reducing methane oxidation along ocean margins. The metabolic rates of subseafloor life are orders of magnitude lower than those of life on Earth's surface. Most microorganisms in subseafloor sediments are either inactive or adapted for extraordinarily low metabolic activity.