Scientific information model for deepsea mapping and sampling

The Vents Program of the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory is an interdisciplinary research initiative that brings together scientists from a wide range of disciplines, including geophysics, geology, physical oceanography, chemistry, and biology. Each discipline collects a variety of data types of varying structures and requiring intercomparison. The challenge of scientific information management is thus approached with a view of supporting data from multiple survey, mapping, and sampling tools and subject to multiple levels of interpretation. The ultimate objective is a system that integrates the functions of data storage, selective retrieval, display, and archiving. The results of our ongoing efforts in scientific information modeling and management have produced a relational database in which marine geological, geophysical, chemical, and biological observations can be accessed by any investigator.     

Synthesis, characterization and thermochemistry of a Pb-jarosite

The enthalpy of formation from the elements of a well-characterized synthetic Pb-jarosite sample corresponding to the chemical formula (H₃O)_0.74Pb_0.13Fe_2.92(SO₄)₂(OH)_5.76(H₂O)_0.24 was measured by high temperature oxide melt solution calorimetry. This value ( = −3695.9 ± 9.7 kJ/mol) is the first direct measurement of the heat of formation for a lead-containing jarosite. Comparison to the thermochemical properties of hydronium jarosite and plumbojarosite end-members strongly suggests the existence of a negative enthalpy of mixing possibly related to the nonrandom distribution of Pb²⁺ ions within the jarosite structure. Based on these considerations, the following thermodynamic data are proposed as the recommended values for the enthalpy of formation from the elements of the ideal stoichiometric plumbojarosite Pb_0.5Fe₃(SO₄)₂(OH)₆:  = −3118.1 ± 4.6 kJ/mol,  = −3603.6 ± 4.6 kJ/mol and S° = 376.6 ± 4.5 J/(mol K). These data should prove helpful for the calculation of phase diagrams of the Pb-Fe-SO₄-H₂O system and for estimating the solubility product of pure plumbojarosite. For illustration, the evolution of the estimated solubility product of ideal plumbojarosite as a function of temperature in the range 5-45 °C was computed (Log(K_sp) ranging from −24.3 to −26.2). An Eh-pH diagram is also presented.     

Coupled (H, M) substitutions in forsterite

Coupled substitutions involving hydrogen plus trivalent elements (Al, Eu, Fe, Ga, Gd, Lu, Mn, Nd, Pu, Sc, Y and Yb) in forsterite (Mg₂SiO₄) are studied using atomistic simulation methods. Incorporation of hydrogen is energetically favourable when included in the forsterite lattice as hydroxyl groups (OH⁻) at O3 sites while the trivalent cations replace either magnesium or silicon. Our calculations show a strong dependence on the ionic radius of the impurity species and some variation with pressure. There are also significant structural distortions around the impurity defects. At low pressure (0 GPa), the smaller trivalent cations, (e.g. Al, Fe, Mn and Ga) substitute into forsterite by replacing Si as: . The larger trivalent cations (e.g. Eu, Gd, Lu, Nd, Pu, Y and Yb) however, replace Mg at the M2 site coupled with an Mg1 vacancy as described by . At 12 GPa, the large cations are more stable at Mg1 relative to Mg2, but both are predicted to be less stable than configurations associated with Si vacancies. The trivalent ionic radius has a significant effect on the H incorporation mechanism, however, the high formation energy of Si vacancies suggests that the presence of H in forsterite could inhibit incorporation of these elements, particularly at high pressure.     

The Adaptation of the Atmospheric Boundary Layer to a Change in Surface Roughness

The adaptation of the atmospheric boundary layer to a change in the underlying surface roughness is an interesting problem and hence much research, theoretical, experimental, and numerical, has been undertaken. Within the atmospheric boundary layer an accurate numerical model for the turbulent properties of the atmospheric boundary layer needs to be implemented if physically realistic results are to be obtained. Here, the adaptation of the atmospheric boundary layer to a change in surface roughness is investigated using a first-order turbulence closure model, a one-and-a-half-order turbulence closure model and a second-order turbulence closure model. Perturbations to the geostrophic wind and the pressure gradients are included and it is shown that the second-order turbulence closure model, namely the standard k - model, is inferior to a lower-order closure model if a modification to limit the turbulent eddy size within the atmospheric boundary layer is not included within the model.     

Large tectonic rotation of part of New Zealand in the last 5 Ma

Detailed paleomagnetic data from the Wairoa Syncline, a middle Miocene to the present forearc basin on the East Coast of the North Island, New Zealand, show that the rate of clockwise rotation for the last 5 Ma has been 7–8°/Ma of which less than 1.5°/Ma can be explained by apparent polar wander due to motion of the Australian or Pacific plates. This rotation is similar to a present-day rate of 7°/Ma determined from geodetic data. Between 5 and 20 Ma ago the rate of tectonic rotation is poorly determined and may be between 0° and 2°/Ma.

The change in the rate of rotation of the Wairoa Syncline around 5 Ma is probably related to a markedly different tectonic style in the New Zealand region within the last 5 Ma, associated with a change in position of the Euler poles of rotation for the Pacific-Australian plates.     

Fabrics,facies control and diagenesis of lacustrine ooids and associated grains from the Upper Triassic,southwest England

Petrographic analysis of ooids from the Upper Triassic (Mercia Mudstone Group) of southwest England provides an opportunity to assess in detail the origins, transport pathways and diagenesis of an ancient oolite. The Clevedon Oolite is dolomitized and contains a variety of dissolved ooids (oomoulds) and associated grains. The oomoulds occur in well‐sorted, planar and cross‐stratified grainstones, packstones, sandstones and conglomerates associated with shoreface, intershoal, foreshore, beachrock and littoral strandplain deposits. The ooids grew in suspension in the shoreface zone and developed a radial aragonite microstructure. The ooids grew to 0.80 mm in diameter, after which they fractured or ceased growing. Broken grains deposited on or near mobile shoals were rapidly recoated, while other grains, deposited in less agitated, intershoal and lower foreshore areas, were micritized or microbially bound into grapestone aggregates. Locally peloids, intraclasts, quartz grains and micritized grains from intershoal areas supplied nuclei for ooids on nearby shoals. Grains deposited in foreshore areas were rapidly cemented into beachrock and reworked into conglomerates. Soon after deposition, the ooids were subjected to widespread aragonite dissolution followed by dolomitization. The lack of pre‐dolomitization calcite, together with the abundance of early (pre‐compaction) dolospar cements and fabric‐selective dolomitization of micritic fabrics, suggest aragonite dissolution by dolomitizing fluids. Copyright © 2002 John Wiley & Sons, Ltd.