ALBERT

Beschreibung: Abstract A balance between primary production, rates of sediment accumulation or dilution, and biological or diagenetic destruction has long been considered a key control on organic carbon preservation in modern offshore marine environments. Additionally, current understanding of sediment transport processes in offshore environments has advanced in the last decade to include variable energy and dynamic mechanisms, requiring a re‐evaluation of ancient deposits in these systems. The Juana Lopez Member of the Mancos Shale preserves organic carbon‐rich mudstone interbedded and interlaminated with sandstone that records high energy traction flow conditions. Core, outcrop and geochemical data from the Juana Lopez Member were used to elucidate sediment provenance and processes controlling organic carbon preservation and distribution in this mudstone‐dominated system. Five dominant lithofacies with varying grain size, sedimentary fabrics, composition and grain origins were differentiated and were deposited in three main environments: the prodelta, fringe zone and low angle offshore ramp. Basal deposits of the Juana Lopez Member consist of siliceous sandstone‐dominated, heterolithic deposits with characteristic sedimentary structures (for example, current ripples and normal grading) that indicate offshore‐directed underflows, or hyperpycnites, delivered from the updip Ferron/Frontier deltaic system. In the upper portion of the Juana Lopez Member, a compositional change to biogenic carbonate‐rich sandstone and mudstone is interpreted to be as a result of increased accommodation in central Utah (USA), associated base‐level rise and shoreline‐parallel sediment transport. Non‐parallel laminated, organic carbon‐rich mudstone is preserved throughout the Juana Lopez Member. Depositional fabrics and trace element signatures suggest that these deposits are the result of dynamic conditions at the sea floor and in the oxic to suboxic water column, further challenging the notion that organic‐bearing mudstone is deposited solely through suspension settling in anoxic waters. Punctuated delivery of organic carbon laden sediment from mixed terrestrial and marine sources resulted in an event‐bed style of organic carbon deposition and preservation.

Beschreibung: Surface and subsurface conditions in the Labrador Sea during Marine Isotope Stage (MIS) 31 at the Integrated Ocean Drilling Program (IODP) Site U1305 off southwest Greenland are reconstructed based on dinocyst and foraminifer assemblages. Isotopic compositions of planktonic ( Neogloboquadrina pachyderma -Np-) and benthic ( Cibicides wuellerstorfi -Cw- and Oridorsalis umbonatus -Ou-) foraminifera provide further information about water properties in the mesopelagic layer as well as at seafloor. Dinocyst proxy-reconstructions indicate low salinities (32-34.5), cool winters (3-6 °C) and mild summers (10-15 °C) in the surface water layer during the MIS 31 "optimum". However, planktonic foraminifer assemblages largely dominated by Np suggest relatively cold subsurface conditions in winter (-2-0 °C) and summer (2-4 °C). Lower δ 13 C-values in Np vs. Cw further suggest either a lesser-ventilated mesopelagic layer than the bottom one, or high organic matter oxidation rates at Np habitat depth. The dinocyst and planktonic foraminifer records together suggest a strong stratification between the surface and subsurface water layers. Isotopic and micropaleontological data thus converge towards paleoceanographical conditions unsuitable for convection and intermediate or deep-water formation in the Labrador Sea during the "warm" MIS 31 interglacial, a situation similar to the one, which prevailed during the "warm" MIS 5e.

Beschreibung: Volcanic eruptions have a significant impact on climate when they inject sulfur gases into the stratosphere. The dynamics of eruption plumes is also affected by climate itself, as atmospheric stratification impacts plumes height. We use an integral plume model to assess changes in volcanic plume maximum rise heights as a consequence of global warming, with atmospheric conditions from an ensemble of global climate models (GCM), using three representative concentration pathways (RCP) scenarios. Predicted changes in atmospheric temperature profiles decrease the heights of tropospheric and lowermost stratospheric volcanic plumes and increase the tropopause height, for the RCP4.5 and RCP8.5 scenarios in the coming three centuries. Consequently, the critical mass eruption rate required to cross the tropopause increases by up to a factor 3 for tropical regions, and up to 2 for high-latitude regions. A number of recent lower stratospheric plumes, mostly in the tropics (e.g., Merapi, 2010), would be expected to not cross the tropopause starting from the late 21 st century, under RCP4.5 and RCP8.5 scenario. This effect could result in a ≃5 − 25% decrease in the average SO 2 flux into the stratosphere carried by small plumes, which frequency is larger than the rate of decay of volcanic stratospheric aerosol, and a ≃2 − 12% decrease of the total flux. Our results suggest the existence of a positive feedback between climate and volcanic aerosol forcing. Such feedback may have minor implications for global warming rate but can prove to be important to understand the long-term evolution of volcanic atmospheric inputs.