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Main Species Characteristics of Phytoplankton Spring Blooms in NE Atlantic and Arctic Waters (68–80° N)

A compilation of phytoplankton species abundance data from the spring bloom along the northern Norwegian coast and in the Barents Sea shows that the quantitatively most important species are the prymnesiophyte Phaeocystis pouchetii and the common cold water to temperate diatoms Chaetoceros socialis, Skeletonema costatum sensu lato, Fragilariopsis oceanica, Thalassiosira spp., Chaetoceros furcellatus, Chaetoceros compressus, Chaetoceros debilis and Bacterosira bathyomphala. The relative abundance of diatoms and Phaeocystis varied highly and apparently stochastically between years. P. pouchetii occurred during all stages of the spring bloom and sometimes completely dominated the phytoplankton community. Along the Norwegian coast, the importance of P. pouchetii increased northwards. The species composition in coastal fjords at 70° N is surprisingly similar to that of shelf waters in the Barents Sea (up to 80° N). An exception is S. costatum sensu lato which was seldom observed in Arctic waters. Small flagellates (<10 μm) other than dinoflagellates and P. pouchetii are also important among the Barents Sea spring phytoplankton. Associations of species seem rigid over time and are dominated by C. socialis and P. pouchetii in northern waters. Biogeographical categories of spring bloom species in relation to environmental conditions are discussed.     

The “Boscobel Landslip” of October 1st, 1901—the largest historic landslide in Barbados,West Indies

Barbados is a small Caribbean island located on the crest of an accretionary prism about 125 km east of the Lesser Antilles volcanic island arc. The oldest strata, Eocene sandstones and shales, are overlain by Oligocene–Miocene chalks and marls, in turn overlain by Pleistocene reef and lagoonal limestones that cover about 85 % of the island. The Eocene sediments, which crop out in the Scotland District of Barbados, are prone to soil creep and landslides covering tens to hundreds of hectares. The largest historic landslide, the “Boscobel Landslip,” occurred on 01 October 1901. We used nineteenth-century and more modern topographic and geologic maps, air photographs, and various archival and petrophysical data, to supplement reconnaissance of the landslide in the field. We identified about ten million cubic meters of the displaced material of the landslide, as well as the meteorological and geological conditions that contributed to the Boscobel Landslip. Similar landslides would pose a presently unquantified hazard to inhabitation and future development in the Scotland District.     

Efficient block preconditioners for the coupled equations of pressure and deformation in highly discontinuous media

Large‐scale simulations of flow in deformable porous media require efficient iterative methods for solving the involved systems of linear algebraic equations. Construction of efficient iterative methods is particularly challenging in problems with large jumps in material properties, which is often the case in geological applications, such as basin evolution at regional scales. The success of iterative methods for this type of problems depends strongly on finding effective preconditioners. This paper investigates how the block‐structured matrix system arising from single‐phase flow in elastic porous media should be preconditioned, in particular for highly discontinuous permeability and significant jumps in elastic properties. The most promising preconditioner combines algebraic multigrid with a Schur complement‐based exact block decomposition. The paper compares numerous block preconditioners with the aim of providing guidelines on how to formulate efficient preconditioners. Copyright © 2010 John Wiley & Sons, Ltd.     

Zur Mechanik der nordamerikanischen Uplifts

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Simulating stochastically excited oscillations: The mode lifetime of ξ Hya

The discovery of solar-like oscillations in the giant star ξ Hya (G7 III) was reported by Frandsen et al. (2002). Their frequency analysis was very limited due to alias problems in the data set (caused by single-site observations). The extent to which the aliasing affected their analysis was unclear due to the unknown damping time of the stellar oscillation modes. In this paper we describe a simulator created to generate time series of stochastically excited oscillations, which takes as input an arbitrary window function and includes both white and non-white noise. We also outline a new method to compare a large number of simulated time series with an observed time series to determine the damping time, amplitude, and limited information on the degree of the stochastically excited modes. For ξ Hya we find the most likely amplitude to be ∼ 2 m s⁻¹, in good agreement with theory (Houdek and Gough, 2002), and the most likely damping time to be ∼ 2 days, which is much shorter than the theoretical value of 15–20 days calculated by Houdek and Gough (2002).     

The influence of central black holes on gravitational lenses

Recent observations indicate that many if not all galaxies host massive central black holes. In this paper we explore the influence of black holes on the lensing properties. We model the lens as an isothermal ellipsoid with a finite core radius plus a central black hole. We show that the presence of the black hole substantially changes the critical curves and caustics. If the black hole mass is above a critical value, then it will completely suppress the central images for all source positions. Realistic central black holes are likely to have masses below this critical value. Even in such subcritical cases, the black hole can suppress the central image when the source is inside a zone of influence, which depends on the core radius and black hole mass. In the subcritical cases, an additional image may be created by the black hole in some regions, which for some radio lenses may be detectable with high-resolution and large dynamic range VLBI maps. The presence of central black holes should also be taken into account when one constrains the core radius from the lack of central images in gravitational lenses.