Numerical study on wave dynamics and wave-induced bed erosion characteristics in Potter Cove,Antarctica

Wave generation, propagation, and transformation from deep ocean over complex bathymetric terrains to coastal waters around Potter Cove (King George Island, South Shetland Islands, Antarctica) have been simulated for an austral summer month using the Simulating Waves Nearshore (SWAN) wave model. This study aims to examine and understand the wave patterns, energy fluxes, and dissipations in Potter Cove. Bed shear stress due to waves is also calculated to provide a general insight on the bed sediment erosion characteristics in Potter Cove.A nesting approach has been implemented from an oceanic scale to a high-resolution coastal scale around Potter Cove. The results of the simulations were compared with buoy observations obtained from the National Data Buoy Center, the WAVEWATCH III model results, and GlobWave altimeter data. The quality of the modelling results has been assessed using two statistical parameters, namely the Willmott’s index of agreement D and the bias index. Under various wave conditions, the significant wave heights at the inner cove were found to be about 40–50 % smaller than the ones near the mouth of Potter Cove. The wave power in Potter Cove is generally low. The spatial distributions of the wave-induced bed shear stress and active energy dissipation were found to be following the pattern of the bathymetry, and waves were identified as a potential major driving force for bed sediment erosion in Potter Cove, especially in shallow water regions. This study also gives some results on global ocean applications of SWAN.

     

U‐Pb zircon dating of metaigneous rocks from the Nordbreen Nappe of Svalbard’s Ny‐Friesland suggests their affinity to Northeast Greenland

SIMS U‐Pb zircon dating of metaigneous rocks of the Nordbreen Nappe from the West Ny‐Friesland terrane (Eastern Basement Province of Svalbard) yields crystallization ages of 1,761 ± 4 Ma for a felsic metatuff and 1,373 ± 4 Ma for a metagabbro dyke. The Palaeoproterozoic age of the metatuff is similar to previously obtained ages for various felsic rocks from the study area, whereas the Mesoproterozoic age of the metagabbro has not been thus far documented on Svalbard. However, a similar age pattern has been reported from Northeast Greenland. Therefore, we conclude that the West Ny‐Friesland terrane can be correlated with age equivalent units of Northeast Greenland. We also explore similarities and dissimilarities between the study area and other terranes of Svalbard and speculate on regional‐scale correlations. Together, the presented new ages provide critical piercing points in palaeogeographic reconstructions of the relatively poorly understood circum‐Arctic region.     

Simulating Martian regolith in the laboratory

Regolith and dust cover the surfaces of the Solar Systems solid bodies, and thus constitute the visible surface of these objects. The topmost layers also interact with space or the atmosphere in the case of Mars, Venus and Titan. Surface probes have been proposed, studied and flown to some of these worlds. Landers and some of the mechanisms they carry, e.g. sampling devices, drills and subsurface probes (“moles”) will interact with the porous surface layer. The absence of true extraterrestrial test materials in ample quantities restricts experiments to the use of soil or regolith analogue materials. Several standardized soil simulants have been developed and produced and are commonly used for a variety of laboratory experiments. In this paper we intend to give an overview of some of the most important soil simulants, and describe experiments (penetrometry, thermal conductivity, aeolian transport, goniometry, spectroscopy and exobiology) made in various European laboratory facilities.     

Ion microprobe studies of water in silicate melts. Concentration-dependent water diffusion in obsidian

The ion microprobe at Johnson Space Center has been calibrated for in situ water determinations on a 10-μm scale over the range 0.2 wt.% H₂O to 1.8, 6.8, and 3.7 wt.%, for basaltic, albitic, and rhyolitic glasses, respectively. The basalt glass calibration curve differs substantially from those of albite and rhyolite glasses, indicating a need to carefully match composition and/or melt structure between H₂O standards and unknowns.A value for the diffusivity of water as a function of concentration and time has been calculated from water diffusion profiles measured in rhyolite glasses prepared at 850°C and 700 barsP_t(H₂O) [1]. Transient diffusion into a semi-infinite medium is described by the equation:?(φ/2)?¸/?φ=?(D_w?¸/?φ)/?φ #x003B8;=1, φ=0, θ→ 0, θ→∞, wherex =distance from the cylinder edge,t =time,C₀ =initial concentration,C_s =concentration at the edge,C =concentration at x,θ = C ? C₀/C_s ? C₀,φ = x/t^1/2, andD_w =diffusivity of water. An iterative technique has been used to calculate solutions to the diffusion equation as a function ofD_w [2]. Comparison of these solutions with the ion probe data indicate that, for0.2wt.% ≤ C ≤ 3.7wt.%H₂O,D_w can be described by an exponential function of θ, of the formD_w = D₀exp(bθ), withD₀ (i.e.,D_w at 0.2%) = (0.8?2.2) × 10^?8 cm²/s and2 ≤ b ≤ 4.     

Ion microprobe studies of water in silicate melts: Temperature-dependent water diffusion in obsidian

The temperature dependence of water diffusivity in rhyolite melts over the range 650–950°C and [P_T(H₂O] = 700 bars is evaluated from water concentration-distance profiles measured in glass with an ion microprobe. Diffusivities are exponentially dependent on concentration over this temperature range and vary from about 10^?8 cm²/s at 650°C to about 10^?7 cm²/s at 950°C at 2 wt.% water. Water solubility also varies with temperature at a rate of ?0.14 wt. per 100°C increase. The avtivation energy (E_a) appears to be constant at 19 ± 1kal/mole for 1, 2,and 3 wt.% H₂O. Comparison of these data with results for cation diffusion indicates that this value is a minimum E_a for diffusion of any species in a rhyolite melt.Compensation plots of log₁₀D₀ (the frequency factor) versus E_a indicate that hydrous rhyolite melts follow the same trend as anhydrous basalts. D₀ increases for H₂O and Ca²⁺ [1] as E_a decreases. This suggests that these molecules may diffuse by different mechanisms than do monovalent cations, and that hydration of the melt affects diffusion of Ca²⁺ and H₂O differently than it does monovalent cation diffusion. The results imply that dramatic increases in cation diffusivities by hydration [1] may occur with additions of less than 1 wt.% H₂O.     

Crystal field transitions in Co2[Al4Si5]O18 cordierite and CoAl2O4 spinel determined by neutron spectroscopy

Inelastic magnetic neutron scattering has been used to determine the energy of the ⁴ A ₂→⁴ T ₂ transition in CoAl₂O₄ spinel and the δ₁ transition in Co₂[Al₄Si₅]O₁₈ cordierite. The observed crystal field splitting in Co-spinel is 485 meV (3900 cm⁻¹), which corresponds to a crystal field stabilization energy of 56.2 kJmol⁻¹. The transition energy of the δ₁ transition in Co-cordierite has been determined to be 21 meV (170 cm⁻¹). The present data demonstrate that magnetic neutron scattering can be used to measure crystal field transitions at energies of interest in the study of 3d-containing silicates. It may be used to measure transition energies when the use of optical spectroscopy is inappropriate. Received: 30 January 1997 / Accepted: 5 July 1997