Glaciers in Svalbard: mass balance, runoff and freshwater flux

Gain or loss of the freshwater stored in Svalbard glaciers has both global implications for sea level and, on a more local scale, impacts upon the hydrology of rivers and the freshwater flux to fjords. This paper gives an overview of the potential runoff from the Svalbard glaciers. The freshwater flux from basins of different scales is quantified. In small basins (A < 10 km²), the extra runoff due to the negative mass balance of the glaciers is related to the proportion of glacier cover and can at present yield more than 20% higher runoff than if the glaciers were in equilibrium with the present climate. This does not apply generally to the ice masses of Svalbard, which are mostly much closer to being in balance. The total surface runoff from Svalbard glaciers due to melting of snow and ice is roughly 25 ± 5 km³ a⁻¹, which corresponds to a specific runoff of 680 ± 140 mm a⁻¹, only slightly more than the annual snow accumulation. Calving of icebergs from Svalbard glaciers currently contributes significantly to the freshwater flux and is estimated to be 4 ± 1 km³ a⁻¹ or about 110 mm a⁻¹.     

The use of assumed displacement fields in finite-element analysis to calculate the gravity effect of crustal deformation

An expression is derived which relates a displacement field u defined on a continuum to the change in gravity (Δg_D) brought about by deformation:

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where GG is the gravitational constant; ρ_R is the pre-deformation density function; V_R is the volume occupied by the continuum before deformation; T_D is a transformation which represents the one-to-one mapping of V_R onto the volume V_A occupied by the continuum after deformation: A₁ = R₁ + U₁(R₁, R₂, R₃)T_D: A₂ = R₂ + U₂ (R₁, R₂, R₃)A₃ = R₃ + U₃ ( R₁, R₂, R₃) where A₁, a₂, A₃, are the Cartesian coordinates of a point in V_A; R₁, R₂, R₃ are the Cartesian coordinates of a point in V_R; U₁, U₂, U₃, are the components of u; and α is the distance from the field point (x, y, z) to a general point in V_A or V_R. The derivation is based on the principle of conservation of mass as stated in continuum mechanics. The formulation of the finite-element procedure for problems in linear elasticity typically involves the selection of an assumed function for u within each element. Unknown constants which characterize the function are determined in terms of nodal displacements. The integral in the first equation above may therefore be evaluated for each element, and the results summed to obtain Δg_D. Convergence to the exact solution for Δg_D depends on the convergence of the finite-element solution for u. The procedure is demonstrated for axisymmetric, torsion-free deformation of a solid of revolution in which the elements are tori of triangular cross-section. These results may be useful in the analysis of gravity change associated with tectonic deformation of the earth's crust.     

Devensian organic interstadial deposits and ice sheet extent in Buchan,Scotland

Pre-Late Devensian organic deposits in the Buchan area of northeast Scotland were investigated for their geomorphological and palaeoecological (pollen, plant macrofossils, coleoptera) properties. Close ecological agreement exists between fossil indicators and allows the inference that the environment in the vicinity of the deposits was a dwarf shrub tundra of the type met today in high latitude areas of Scandinavia and arctic Russia. The latest in a series of radiocarbon dates from the site produced determinations beyond the limits of the method, although the geomorphological and fossil evidence appears to point to an interstadial date within Oxygen Isotope Stages 5a or 5c. The site has special significance for arguments concerning the much-debated concept of ‘Moraineless Buchan’; indeed, evidence is presented which supports the concept of extensive ice sheet glaciation during the Late Devensian for this crucial geographical area. If Buchan is to be seen as a further casualty amongst other disputed ice-free enclaves, then a return to earlier models of extensive ice sheet glaciation in the Late Devensian of Scotland would seem to be necessary. © 1998 John Wiley & Sons, Ltd.     

Comparison of spawning seasons,age, growth rates,and food of two sympatric species of searobins,Prionotus carolinus and Prionotus evolans,from Long Island Sound

Prionotus carolinus and Prionotus evolans were collected from many locations within Long Island Sound in 1971–1973, and in 1976–1977. Data from earlier collections in Block Island Sound (1943–1945) were also included. A total of 1751 specimens, 960 P. carolinus and 791 P. evolans was examined within these two time periods. Both species entered the Sound in April and spawned during June and July. P. evolans appeared to spawn slightly earlier in summer than P. carolinus. Adults began to leave the Sound after spawning and were usually absent after November. Young-of-the-year were taken regularly from August to November and, occasionally in water over 20 m deep, into February when the bottom water temperature was 1.4°C. At the end of the first growing seasons both species exhibited large variations in standard lengths. Back-calculations from scale annuli measurements indicated that linear growth rates during the juvenile years were similar in both species. However, P. evolans was considerably heavier than P. carolinus. During adulthood P. evolans was not only longer and heavier than P. carolinus, but lived longer. Growth rates are described by the following equations: P. carolinus L_t+1=9.60+0.68 (L_t), and p. evolans L_t+1=7.70+0.80 (L_t). Both species were opportunistic feeders, and crustaceans were clearly the dominant group of prey. Young-of-the-year, between 3–6 cm, ate copepods. As they grew they ate larger prey, such as Neomysis americana, Diastylis quadrispinosus, various species of amphipods of small sizes, and juvenile Crangon septemspinosus. Older fish ate larger sizes of these same prey, a number of species of crabs, juvenile Homarus americanus, and Squilla empusa. Occasionally they ate polychaetes, molluscs, and juvenile fish. Partitioning of the resources of Long Island Sound by these two species appeared to be by prey size. P. evolans ate prey that, on the average, were slightly larger than those eaten by P. carolinus. Furthermore, P. evolans ate a greater amount of nektonic species than P. carolinus, which appeared to prefer benthonic invertebrates.     

TIGRE: A new robotic spectroscopy telescope at Guanajuato,Mexico

TIGRE is a new robotic spectroscopy telescope located in central Mexico at the La Luz Observatory of the University of Guanajuato. The 1.2 m telescope is fiber‐coupled to an ´echelle spectrograph with a spectral resolving power exceeding 20000 over most of the covered spectral range between 3800 Å and 8800 Å, with a small gap of 130 Å around 5800 Å. TIGRE operates robotically, i.e. it (normally) carries out all observations without any human intervention, including, in particular, the target selection in any given observing night. In this paper we describe the properties of the TIGRE instrumentation and its technical realization, as well as our first operational experience with the performance and efficiency of the overall system. Finally, we present some examples of recent TIGRE observations. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Meteorite transport—Revisited

Meteorites are delivered from the asteroid belt by way of chaotic zones (Wisdom 1985a). The dominant sources are believed to be the chaotic zones associated with the ν₆ secular resonance, the 3:1 mean motion resonance, and the 5:2 mean motion resonance. Though the meteorite transport process has been previously studied, those studies have limitations. Here I reassess the meteorite transport process with fewer limitations. Prior studies have not been able to reproduce the afternoon excess (the fact that approximately twice as many meteorites fall in the afternoon as in the morning) and suggested that the afternoon excess is an observational artifact; here it is shown that the afternoon excess is in fact consistent with the transport of meteorites by way of chaotic zones in the asteroid belt. By studying models with and without the inner planets it is found that the inner planets significantly speed up the transport of meteorites.     

Tidal evolution of Mimas, Enceladus, and Dione

The tidal evolution through several resonances involving Mimas, Enceladus, and/or Dione is studied numerically with an averaged resonance model. We find that, in the Enceladus-Dione 2:1 e-Enceladus type resonance, Enceladus evolves chaotically in the future for some values of k₂/Q. Past evolution of the system is marked by temporary capture into the Enceladus-Dione 4:2 ee^′-mixed resonance. We find that the free libration of the Enceladus-Dione 2:1 e-Enceladus resonance angle of 1.5° can be explained by a recent passage of the system through a secondary resonance. In simulations with passage through the secondary resonance, the system enters the current Enceladus-Dione resonance close to tidal equilibrium and thus the equilibrium value of tidal heating of 1.1(18,000/QS) GW applies. We find that the current anomalously large eccentricity of Mimas can be explained by passage through several past resonances. In all cases, escape from the resonance occurs by unstable growth of the libration angle, sometimes with the help of a secondary resonance. Explanation of the current eccentricity of Mimas by evolution through these resonances implies that the Q of Saturn is below 100,000. Though the eccentricity of Enceladus can be excited to moderate values by capture in the Mimas-Enceladus 3:2 e-Enceladus resonance, the libration amplitude damps and the system does not escape. Thus past occupancy of this resonance and consequent tidal heating of Enceladus is excluded. The construction of a coherent history places constraints on the allowed values of k₂/Q for the satellites.     

Perihelion evolution of observed new comets implies the dominance of the galactic tide in making Oort cloud comets discernable

For an Oort cloud comet to be seen as a new comet, its perihelion must be moved from a point exterior to the loss cylinder boundary to a point interior to observable limits in a single orbit. The galactic tide can do this continuously, in a non-impulsive manner. Near-parabolic comets, with specific angular momentum , will most easily be made observable. Therefore, to reduce the perihelion distance H must decrease. Since weakly perturbed comets are, in general, more numerous than strongly perturbed comets, we can anticipate that new comets made observable by a weak tidal torque will more likely be first observed when their slowly changing perihelion distances are approaching their minimum osculating values under the action of the tide, rather than receding from their minimum values. That is, defining ΔH_tide as the vector change due to the galactic tidal torque during the prior orbit, and H_obs as the observed vector, the sign S≡Sign(H_obs·ΔH_tide) will more likely be −1 than +1 if a weak galactic tidal perturbation indeed dominates in making comets observable. Using comet data of the highest quality class (1A) for new comets (a>10,000 AU), we find that 49 comets have S=−1 and 22 have S=+1. The binomial probability that as many or more would exhibit this characteristic if in fact S=?1 were equally likely is only 0.0009. This characteristic also persists in other long-period comet populations, lending support to the notion that they are dominated by comets recently arrived from the outer Oort cloud. The preponderance of S=−1 also correlates with weakly perturbed (i.e., smaller semimajor axis) new comets in a statistically significant manner. This is strong evidence that the data are of sufficiently high quality and sufficiently free of observational selection effects to detect this unique imprint of the tide.     

Solar and planetary destabilization of the Earth-Moon triangular Lagrangian points

In the restricted circular three-body problem, two massive bodies travel on circular orbits about their mutual center of mass and gravitationally perturb the motion of a massless particle. The triangular Lagrange points, L₄ and L₅, form equilateral triangles with the two massive bodies and lie in their orbital plane. Provided the primary is at least 27 times as massive as the secondary, orbits near L₄ and L₅ can remain close to these locations indefinitely. More than 2200 cataloged asteroids librate about the L₄ and L₅ points of the Sun-Jupiter system, and five bodies have been discovered around the L₄ point of the Sun-Neptune system. Small satellites have also been found librating about the L₄ and L₅ points of two of Saturn's moons. However, no objects have been discovered around the Earth-Moon L₄ and L₅ points. Using numerical integrations, we show that orbits near the Earth-Moon L₄ and L₅ points can survive for over a billion years even when solar perturbations are included, but the further addition of the far smaller perturbations from other planets destabilize these orbits within several million years. Thus, the lack of observed objects in these regions cannot be used as a constraint on Solar System formation, nor on the tidal evolution of the Moon's orbit.