On local and convective accelerations in steep wave events

The local and convective accelerations of steep irregular wave events have been investigated. These properties are measured by a two-camera PIV technique. Furthermore, the experiments are compared with two different theories including a fully nonlinear and a simplified analytical model. An important result is that the convective term is of the same order of magnitude and of opposite sign as the local acceleration. The convective acceleration term can therefore not be neglected in acceleration and force estimates.     

Lateglacial vegetation development in Denmark – New evidence based on macrofossils and pollen from Slotseng,a small-scale site in southern Jutland

This paper presents the first unambiguous terrestrial palaeoecological record for the late glacial “Bølling warming” in Denmark. Pollen and macrofossil stratigraphies from pre-Bølling to 10,800 cal yr BP are presented from a small kettle hole in Southwest Denmark, during which the lake basin developed from an immature stage after the deglaciation to complete infilling in the early Holocene. Results show that the recently deglaciated landscape bore a discontinuous vegetation of pioneer plants. After the Bølling warming, an open Dryas octopetala-Betula nana community developed with Helianthemum oelandicum. Subarctic species were dominant and local successions were probably delayed by relatively unstable and infertile soils. There is no indication of a climate cooling during the period corresponding to the Older Dryas, but the occurrence of several drought tolerant and steppe species indicates that the period was relatively dry. In the Allerød period the Dryas-B. nana vegetation was initially replaced by an open Salix and grass dominated vegetation and some 400 years later, the first tree birches were documented presumably occupying moist and sheltered soils while drier land remained open. In the Younger Dryas period trees disappeared and the vegetation became open again and dominated by subarctic species. Following climate warming at the Younger Dryas–Holocene transition a shrub community of Empetrum and Juniperus developed. After approximately 200 years it was replaced by birch forest. Overall, the late-glacial vegetation cover had a more open and patchy character than inferred from previous pollen studies as assessment of the vegetation succession based on macrofossil evidence is essential. The inferred general vegetation development corresponds well with results of other studies in the region. Canonical ordinations (RDA) indicate that vegetation changes at the landscape scale during the Lateglacial period were driven by changes in climate, soils and competition for light.     

History of Geology in Norden

The Nordic countries of Denmark, Finland, Iceland, Norway, and Sweden have been closely connected for many centuries, not least from a geological point of view. Scientific cooperation as well as contentions have been common. The earliest known records of ＂geological＂ treatises are from the 16th century, but especially in the 18th century, when the natural sciences flourished all over Europe, Nordic scholars were in the forefront in geochemistry, mineralogy, and paleontology. This was also the century when ＂geology＂ started to be taught at the universities, and science academies were founded in Norden, adding greatly to ＂geological＂ studies. In the 19th century, like in so many other countries, national geological survey organizations and geological societies were founded. In Norden, geological research has long traditions within mineralogy and ore geology, paleontology and stratigraphy, tectonics and structural geology. During the last century, focus has turned also to Quaternary and glacial geology, igneous and metamorphic petrology, geochemistry, micropaleontology, petroleum geology, sedimentology, marine geology, geophysics, geochronology, and research related to geothermal energy and deposition of radioactive waste products. In many of these research areas, Nordic geoscientists have contributed greatly over the years to the development of the science of geology.     

Seasonal variations in groundwater upwelling zones in a Danish lowland stream analyzed using Distributed Temperature Sensing (DTS)

The distribution of groundwater inflows in a stream reach plays a major role in controlling the stream temperature, a vital component shaping the riverine ecosystem. In this study, the Distributed Temperature Sensing (DTS) system was installed in a small Danish lowland stream, Elverdamsåen, to assess the seasonal dynamics of groundwater inflow zones using high spatial (1 m) and temporal (3 minutes) resolution of water temperature measurements. Four simple criteria consisting of 30 min average temperature at 16:00, mean and standard deviation of diurnal temperatures, and the day–night temperature difference were applied to three DTS datasets representing stream temperature responses to the variable meteorological and hydrological conditions prevailing in summer, winter and spring. The standard deviation criterion was useful to identify groundwater discharge zones in summer and spring conditions, while the mean temperature criterion was better for the winter conditions. In total, 20 interactions were identified from the DTS datasets representing summer, 16 in winter and 19 in spring, albeit with only two interactions contributing in all three seasons. Higher baseflow to streamflow ratio, antecedent precipitation and presence of fractured clayey till in the stream reach were deemed as the vital factors causing apparent seasonal variation in the locations of upwelling zones, prompting use of DTS not only in preconceived scenarios of large diurnal temperature change but rather a long‐term deployment covering variable meteorological and hydrological scenarios. Copyright © 2012 John Wiley & Sons, Ltd.     

Iceland's best kept secret

The ‘forgotten fjords’ and ‘deserted inlets’ of NE‐Iceland, in the region between Borgarfjörður Eystri and Loðmundarfjörður, are not only prominent because of their pristine landscape, their alleged elfin settlements, and the puffins that breed in the harbour, but also for their magnificent geology. From a geological point of view, the area may hold Iceland's best kept geological secret. The greater Borgarfjörður Eystri area hosts mountain chains that consist of voluminous and colourful silicic rocks that are concentrated within a surprisingly small area (Fig. 1 ), and that represent the second‐most voluminous occurrence of silicic rocks in the whole of Iceland. In particular, the presence of unusually large volumes of ignimbrite sheets documents extremely violent eruptions during the Neogene, which is atypical for this geotectonic setting. As a group of geoscientists from Uppsala University (Sweden) and the Nordic Volcanological Center (NordVulk, Iceland) we set out to explore this remote place, with the aim of collecting material that may allow us to unravel the petrogenesis of these large volumes of silicic rocks. This effort could provide an answer to a long‐standing petrological dilemma; the question of how silicic continental crust is initially created. Here we document on our geological journey, our field strategy, and describe our field work in the remote valleys of NE‐Iceland.     

PCB contamination from sampling equipment and packaging

Work reported in this paper suggests that there are cases of contamination of soil and water samples by polychlorinated biphenyls (PCB) from paper and plastic packaging. Soil samples, which have been stored in paper bags for more than 20 years, share a similar congener distribution as the bags. Analyses showed a predominance of light congeners. PCB-analyses of water also indicate that water samples could be contaminated by plastic packaging. All analytical results of solid material packaging, as well as soil stored in the packaging, show a high relative amount of light weight PCB congeners. The paper bags that were analysed are made of strong paper and very popular among geochemists because of their watertight quality. These paper bags were manufactured more than 20 years ago. The plastic packaging that was analysed was produced in 1997 and 2008. The analyses of plastic and paper show that the raw material that has been used in the production at different times contains a wide concentration range of PCB. Re-sealable plastic bags, which contained the highest levels of PCB of the plastic material, are used by researchers world-wide as sampling bags for soils and sediments. This paper raises an important issue that packaging may potentially contaminate the samples that they hold.