A sensitivity study of the dense shelf water formation in the Okhotsk Sea
[1] Sensitivity of Dense Shelf Water (DSW) formation to tidal mixing around the Kuril Straits, wind stress, and river runoff in the Okhotsk Sea is examined by an ice-ocean coupled model. Horizontal resolution of the model is set to 3–8 km in the northern Okhotsk Sea for well resolving the coastal polynyas which is believed to be the principal region of DSW formation. The model shows a good performance in terms of sea ice production and the consequent DSW formation. DSW is also found to be formed in the offshore region apart from the coastal polynya. DSW is defined independently for each experiment such that it identifies the water influenced by brine. By introducing such definition the sensitivity of the DSW formation is assessed separately for change of density and that of formation rate. The density of DSW exhibits high sensitivity to all the elements considered herein, while its formation rate is sensitive only to winds. Winds affect the DSW formation rate mainly by influencing that occurs in the offshore region.
Reevaluation of the Takano–Oonishi Scheme for Momentum Advection on Bottom Relief in Ocean Models
Abstract In the Takano and Oonishi models the finite-difference analog of the nonlinear momentum advection contains the concept of diagonally upward/downward mass and momentum fluxes along the bottom slope, and the generalized Arakawa scheme for the horizontal advection, modified to be fit to arbitrary coastal shape. It has been said to have a good performance, but is not widely used, largely because of its complicated expression. The purpose of this paper is to reevaluate the Takano–Oonishi scheme for the momentum advection to put it to more practical use by using the redefinition of it in a simple, generalized form and the confirmation of its good performance through a comparison with other schemes. Based on the definition of mass continuity for a momentum cell (U cell) in terms of that for tracer cells (T cell), the vertical and horizontal mass and momentum fluxes for the U cell are generalized on arbitrary bottom relief in simple forms. Although the grid spacing of the present model is different from ...
Igneous Rock Associations 23. The Bushveld Complex, South Africa: New Insights and Paradigms
SUMMARYThe Bushveld Complex has continued to serve as the basis for study into the fundamental nature of petrological processes for layered intrusion formation and for oxide and sulphide hosted Platinum Group Element (PGE)–Cu–Ni ore deposits. These studies have included discoveries in terms of the physical extent of Bushveld magmatism, both laterally and internally. Lateral variations in the mafic to ultramafic Rustenburg Layered Suite of the Northern Lobe of the complex have also revealed petrologically distinctive Upper Critical Zone equivalent rocks (the so-called Flatreef) with enhanced contamination and mineralization traits that reflect a transition between Eastern and Western Lobe equivalent stratigraphy and Platreef-style complexity. Traditional magma mixing models have been re-examined in light of radiogenic isotopic evidence for crustal involvement early in the chromite precipitation or formation process, combined with evidence for associated heterogeneous fluid contents, cryptic layering profiles, and textural evidence. A wide variety of alternative ore-genesis models have been proposed as a consequence. The fundamental mechanics of magma chamber processes and the existence of the magma chamber as an entity have been called into question through various lines of evidence which have promoted the concept of progressive emplacement of the complex as a stack of not-necessarily-quite-sequentially intruded sills (with or without significant quantities of transported phenocrysts), emplaced into variably crystallized and compacted crystal-liquid mush mixtures, modified by compaction-driven late magmatic fluid (silicate and aqueous) activity. Alternatively, petrological and geochemical observations have been used to discount these interpretations in favour of more conventional cooling and gravity-driven accumulation of silicate and ore minerals in a large, liquid-dominated system.RÉSUMÉLe complexe de Bushveld a demeuré à la base d’études sur la nature fondamentale des processus pétrologiques de formation d’intrusions litées et des gîtes des éléments du groupe platine (ÉGP)-Cu-Ni hébergés dans les oxydes et les sulfures. Ces études ont comporté des découvertes sur l’étendue physique, à la fois latérale et interne, du magmatisme de Bushveld. Les variations latérales de la suite stratifiée et mafique à ultramafique Rustenburg du lobe nord du complexe ont également révélé des roches équivalentes pétrologiquement distinctes de la zone critique supérieure (le communément désigné Flatreef) avec des traits de contamination et de minéralisation accrus qui reflètent une transition entre la stratigraphie équivalente des lobes est et ouest et la complexité de type Platreef. Les modèles traditionnels de mélanges magmatiques ont été réexaminés à la lumière de preuves isotopiques radiogéniques indiquant une implication de la croûte au début du processus de précipitation ou de formation de la chromite, combinées à des preuves de contenu fluide hétérogène associé, de profils de litage cryptique et de preuves texturales. Ainsi, une grande variété de modèles alternatifs de genèse de minerai a été proposée. La mécanique fondamentale des processus de la chambre magmatique et l'existence de la chambre magmatique en tant qu'entité ont été remises en question au moyen de divers éléments de preuve qui ont mis en avant le concept de mise en place progressive du complexe sous forme d'un empilement non-nécessairement séquentiel de sills injectés (avec ou sans quantités significatives de phénocristaux transportés) mis en place dans des mélanges de bouillie cristaux/liquide à cristallisation et compaction variable, modifiés par une activité tardive de fluide magmatique (silicaté et aqueux) induite par la compaction. Alternativement, des observations pétrologiques et géochimiques ont été utilisées pour écarter ces interprétations en faveur d'un processus plus conventionnel de refroidissement et d’accumulation de minérais silicatés et minéralisés induite par la gravité dans un vaste système à dominance liquide.