A 12.5-kyr history of vegetation dynamics and mire development with evidence of Younger Dryas larch presence in the Verkhoyansk Mountains, East Siberia, Russia

Werner, K., Tarasov, P. E., Andreev, A. A., Müller, S., Kienast, F., Zech, M., Zech, W. & Diekmann, B. 2009: A 12.5‐kyr history of vegetation dynamics and mire development with evidence of Younger Dryas larch presence in the Verkhoyansk Mountains, East Siberia, Russia. Boreas, 10.1111/j.1502‐3885.2009.00116.x. ISSN 0300‐9483. A 415 cm thick permafrost peat section from the Verkhoyansk Mountains was radiocarbon‐dated and studied using palaeobotanical and sedimentological approaches. Accumulation of organic‐rich sediment commenced in a former oxbow lake, detached from a Dyanushka River meander during the Younger Dryas stadial, at ～12.5 kyr BP. Pollen data indicate that larch trees, shrub alder and dwarf birch were abundant in the vegetation at that time. Local presence of larch during the Younger Dryas is documented by well‐preserved and radiocarbon‐dated needles and cones. The early Holocene pollen assemblages reveal high percentages of Artemisia pollen, suggesting the presence of steppe‐like communities around the site, possibly in response to a relatively warm and dry climate ～11.4–11.2 kyr BP. Both pollen and plant macrofossil data demonstrate that larch woods were common in the river valley. Remains of charcoal and pollen of Epilobium indicate fire events and mark a hiatus ～11.0–8.7 kyr BP. Changes in peat properties, C31/C27 alkane ratios and radiocarbon dates suggest that two other hiatuses occurred ～8.2–6.9 and ～6.7–0.6 kyr BP. Prior to 0.6 kyr BP, a major fire destroyed the mire surface. The upper 60 cm of the studied section is composed of aeolian sands modified in the uppermost part by the modern soil formation. For the first time, local growth of larch during the Younger Dryas has been verified in the western foreland of the Verkhoyansk Mountains (～170 km south of the Arctic Circle), thus increasing our understanding of the quick reforestation of northern Eurasia by the early Holocene.     

Holocene climatic variations and postglacial sea-level rise geochemically recorded in the sediments of the brackish karst lake An Loch Mor, western Ireland

Palaeohydrology of the brackish karst lake An Loch Mór (Inis Oirr) was reconstructed based on its 11 600 year sedimentation record. Low calcareous early Holocene sediments, characterized by high TOC contents and deposited at generally low accumulation rates, show a gradual decrease upwards in the concentration of the siliciclastic sediment until c . 7000 cal. yr BP. From c . 9000 cal. yr BP, sediment accumulation became increasingly dominated by the deposition of autochthonous calcite and organic matter. The deposition of autochthonous calcite and its chemical composition (Ca/Sr, Ca/Mg) are determined by the subsurface inflow of freshwater from the catchment of the lake and by the balance between freshwater and seawater influx. During the early Holocene, the lake mainly received input of sea salt by sea-spray. The sediments document the further development from seasonal towards the onset of diurnal infiltration of seawater at c . 5100 cal. yr BP. At that time, the relative sea level must have risen nearly to its present level in Galway Bay. Diurnal seawater infiltration during high tides was controlled by freshwater input. Freshwater inflow from the catchment gradually increased with human impact on local vegetation (EVPT decrease). Permanent diurnal seawater infiltration in concert with this general freshwater increase made the geochemical sedimentation record highly sensitive to changes in annual precipitation. We use information from the palynological record to interpret geochemically inferred freshwater inflow variations in terms of dry and wet climatic periods and document distinct century-scale successions between wet and dry climatic episodes for western Ireland.     

Variability of the Denmark Strait Overflow during the Last Glacial Maximum

The Denmark Strait Overflow (DSO) today compensates for the northward flowing Norwegian and Irminger branches of the North Atlantic Current that drive the Nordic heat pump. During the Last Glacial Maximum (LGM), ice sheets constricted the Denmark Strait aperture in addition to ice eustatic/isostatic effects which reduced its depth (today ∼630 m) by ∼130 m. These factors, combined with a reduced north-south density gradient of the water-masses, are expected to have restricted or even reversed the LGM DSO intensity. To better constrain these boundary conditions, we present a first reconstruction of the glacial DSO, using four new and four published epibenthic and planktic stable-isotope records from sites to the north and south of the Denmark Strait. The spatial and temporal distribution of epibenthic δ¹⁸O and δ¹³C maxima reveals a north-south density gradient at intermediate water depths from σ₀ ∼28.7 to 28.4/28.1 and suggests that dense and highly ventilated water was convected in the Nordic Seas during the LGM. However, extremely high epibenthic δ¹³C values on top of the Mid-Atlantic Ridge document a further convection cell of Glacial North Atlantic Intermediate Water to the south of Iceland, which, however, was marked by much lower density (σ₀ ∼28.1). The north-south gradient of water density possibly implied that the glacial DSO was directed to the south like today and fed Glacial North Atlantic Deep Water that has underthrusted the Glacial North Atlantic Intermediate Water in the Irminger Basin.     

Spatial distribution and optical properties of Saharan dust observed by airborne high spectral resolution lidar during SAMUM 2006

Airborne measurements of pure Saharan dust extinction and backscatter coefficients, the corresponding lidar ratio and the aerosol optical thickness (AOT) have been performed during the Saharan Mineral Dust Experiment 2006, with a high spectral resolution lidar. Dust layers were found to range from ground up to 4–6 km above sea level (asl). Maximum AOT values at 532 nm, encountered within these layers during the DLR Falcon research flights were 0.50–0.55. A significant horizontal variability of the AOT south of the High Atlas mountain range was observed even in cases of a well-mixed dust layer. High vertical variations of the dust lidar ratio of 38–50 sr were observed in cases of stratified dust layers. The variability of the lidar ratio was attributed to dust advection from different source regions. The aerosol depolarization ratio was about 30% at 532 nm during all measurements and showed only marginal vertical variations.     

Bioventing for in situ remediation

Abstract

The availability of oxygen generally controls the rate at which aerobic in situ bioremediation proceeds. Bioventing, which couples soil venting with bioremediation, is often the most effective means of supplying oxygen to unsaturated zone soil. Laboratory treatability studies were conducted which showed that bioventing could be successfully applied to compounds ranging from light hydrocarbons, such as gasoline or diesel, to heavier hydrocarbons, such as fuel oils, as well as other volatile and semivolatile compounds. In many cases, the promotion of biological activity through the addition of nutrients and moisture, and optimization of the bioventing flow rates, may achieve greater contaminant reductions than venting alone.