The COPAS’08 expedition to the Patagonian Shelf: Physical and environmental conditions during the 2008 coccolithophore bloom

Here we present observations of the hydrography of the Patagonian Shelf, shelf break and offshore waters, with reference to the environmental conditions present during the period of peak coccolithophore abundance. Analysis of a hydrographic dataset collected in December 2008 (austral spring/summer), as part of the Coccolithophores of the Patagonian Shelf (COPAS) research cruise, identified 5 distinct surface water masses in the region between 37°S and 55°S. These water masses, identified through salinity gradients, displayed varying mixed layer depths, macronutrient inventories and chlorophyll-a fluorescence. Subantarctic Shelf Water (SSW), located to the north of the Falkland Islands and extending north along the shelf break, was also host to a large coccolithophore bloom. The similarities between the distribution of calcite, as seen in remote sensing data, and SSW indicate that the coccolithophore bloom encountered conditions conducive to bloom development within this water mass. Analysis of chemical and environmental data also collected during the COPAS cruise revealed that many of the commonly cited conditions for coccolithophore bloom development were present within SSW (e.g. low N:P ratio, high N:Si ratio, shallow mixed layer depth). In the other water masses present on the Patagonian Shelf greater variability in these same parameters may explain the more diffuse concentration of calcite, and the smaller size of possible coccolithophore blooms. The distribution of SSW is strongly influenced by the latitudinal variation in shelf break frontal width, which varies from 20 to 200 km, and consequently strong hydrographic controls underlie the position of the coccolithophore bloom during austral summer.     

Subsea uplifts origin of the Rugozerskaya bay and the Great Salma channel (Kandalaksha Bay)

The origin of the subsea uplifts of the Rugozerskaya bay and the Great Salma strait is discussed in this article. It was found that the present-day bottom surface of the investigation area imitates the post-glacial terrain. This was determined by accumulative glacial formations that were emulated with post-glacial sedimentation processes. All modern bottom uplifts are similar to the ancient post-glacial terrain. Most presentday bottom surface depressions are similar to post-glacial surface inequalities, but the configuration of modern closed kettles could be changed via glacial–marine sedimentation and other processes.     

Assessment of coastal communities’ vulnerability to floods using indicator-based approach: a case study of Greater Accra Metropolitan Area,Ghana

Coastal towns along the coast of Africa are among the most vulnerable to climate change impacts such as flooding and sea level rise. Yet, because coastal conditions in many parts of the region are poorly understood, knowledge on which population groups are at the most risk is less known, particularly in the Greater Accra Metropolitan Area (GAMA) of Ghana, where the capital city Accra is located. Without adequate information about the risk levels and why, the implementation of locally appropriate adaptation plans may be less effective. This study enriches our understanding of the levels of flood risks along the coast of GAMA and contributes knowledge to improve understanding of place-specific adaptation plans. The study uses data from a 300-household survey, stakeholder meetings, and interviews with local community leaders to construct an integrated vulnerability index. The index includes seven components made up of: dwelling type; house and house environment; household socioeconomic characteristics; experience and perception of flood risk; household and community flood adaptation strategies; house location, and physical characteristics. Our findings show that exposure to floods, particularly from local flash floods is relatively high in all communities. However, significant differences in sensitivity and adaptive capacity of the communities were observed due to differences in location, socioeconomic characteristics, and perception of risks to flooding and sea level rise. The complexity of factors involved in the determination of local-level vulnerability requires that the implementation of adaptation strategies needs to involve cross-sectorial partnerships, involving local communities, in building a comprehensive multi-risk adaptation strategy.     

Kinematics and dynamics of the southeastern margin of the Tibetan Plateau

On the southeastern margin of the Tibetan Plateau lies a large region which seismicity and GPS data show to be actively deforming. This paper describes the active faulting in the region, and how it relates to the velocity field observed with GPS. In places the velocity field is accommodated by rotations about vertical axes, and most or all of the strain at the surface in the region appears to be released seismically. GPS velocities are then compared to velocities calculated using a model for deformation driven by gravitational driving forces. Using rheologies estimated from experimentally derived mineral flow laws, the model provides velocities that are in good agreement with observed GPS velocities. It is not possible to uniquely determine the rheology or flow velocity at depth, and there are two forms of model solution which match the observed horizontal surface velocities. In one of these, vertical planes deform by pure shear, and in the other vertical gradients of horizontal velocity are present within the crust. Two distinct regions of normal-faulting earthquakes are present in the region, and have mechanisms which are most easily explained by gravity-driven deformation.     

A predictive model for space-based X-ray ccd degradation

The first generation of X-ray telescopes to use Charge-Coupled Devices (CCDs) is being launched this decade. With a read noise of a few electrons, CCDs provide Fano-limited spectral resolution across the soft X-ray band (0.1 – 10 keV). However, degradation of resolution due to charge transfer losses becomes noticeable as Charge Transfer Inefficiency (CTI) increases to 10^–5. In this paper, we present a model which calculates the effects of radiation damage in low Earth orbit in order to predict CCD lifetimes over which good charge transfer is maintained. The model presented here considers damage mechanisms within the CCD, environmental conditions in which the CCD operates, and experiment shielding. We find that the predicted CTI approaches 10^–5 after a one to two year mission for the flight instruments considered here.     

Long-term cyclicity of the Herbig Ae star BF Ori: Giant protocomets and accretion from a protoplanetary disk

Having analyzed the light curve for the Herbig Ae star BF Ori, we justify the hypothesis of a giant protocomet, GPC I BF Ori, with a period of 6.3 years and semimajor axis a = 10 ± 3 AU. Passing through periastron, such a giant protocomet partially breaks up. During each passage through periastron, the protocomet and the fragments that follow it supply dust to circumstellar space for a certain period of time. This hypothesis can account for the entire complex of observable phenomena of cyclic Algol-like activity in Herbig Ae/Be and T Tauri stars. Conditions in a protoplanetary disk after cocoon breakup are discussed. We adduce arguments for the absence of a dust disk and for the weak effect of objects other than comets on cyclic large-scale variability.     

Observations of fuors. II. Light curve of V 1515 Cyg and fourier analysis of the short-period component

Astronomical Institute, Uzbek Academy of Sciences. Translated from Astrofizika, Vol. 32, No. 2, pp. 221–230, March–April, 1990.     

Asteroid observations at low phase angles. I. 50 Virginia, 91 Aegina and 102 Miriam

We present observations of magnitude-phase dependences of three low-albedo asteroids down to phase angles of 0.1–0.2°. Data were obtained during 40 nights from 1994 to 1995 within the joint observational program at ESO and Kharkiv Astronomical Observatories with the aim to reach as low phase angles as possible. All three low-albedo asteroids may display a small nonlinear increase in magnitude-phase dependence at subdegree phase angles. The phase curves of 50 Virginia and 102 Miriam are poorly approximated by the HG function. Rotation periods of the asteroids were also determined: 14.310±0.010 hours for 50 Virginia, 6.030±0.001 h for 91 Aegina and 15.789± 0.003 h for 102 Miriam.     

A perturbation method and some applications

For differential equations with one fast variable, a perturbation method is introduced that transforms a solution valid over only a short time interval to a new solution composed of averaged variables plus a periodic function of the averaged variables. The averaged variables are governed by a set of differential equations where the fast variable has been removed and thus can be numerically integrated quickly or solved directly. This method is applied to a perturbed harmonic oscillator with a cubic perturbation, van der Pol's equation, coorbital motion in the restricted three-body problem, and to nearly circular motion of a particle near one of the primaries in the restricted three-body problem.