http://hdl.handle.net/10204/936 2013-05-19T11:33:56Z http://hdl.handle.net/10204/6636 Title: Development of a compressive surface capturing formulation for modelling free-surface flow by using the volume-of-fluid approach Authors: Heyns, JA; Malan, AG; Harms, TM; Oxtoby, OF Abstract: With the aim of accurately modelling free-surface flow of two immiscible fluids, this study presents the development of a new volume-of-fluid free-surface capturing formulation. By building on existing volume-of-fluid approaches, the new formulation combines a blended higher resolution scheme with the addition of an artificial compressive term to the volume-of-fluid equation. This reduces the numerical smearing of the interface associated with explicit higher resolution schemes while limiting the contribution of the artificial compressive term to ensure the integrity of the interface shape is maintained. Furthermore, the computational efficiency of the the higher resolution scheme is improved through the reformulation of the normalised variable approach and the implementation of a new higher resolution blending function. The volume-of-fluid equation is discretised via an unstructured vertex-centred finite volume method and solved via a Jacobian-type dual time-stepping approach. Description: Copyright: 2012 Wiley-Blackwell. This is the pre/post print version of the work. The definitive version is published in International Journal for Numerical Methods in Fluids, vol. 71(6), pp 788-804 2012-06-01T00:00:00Z http://hdl.handle.net/10204/6572 Title: The Benguela Current: An ecosystem of four components Authors: Hutchings, L; Van der Lingen, CD; Shannon, LJ; Crawford, RJM; Verheye, HMS; Bartholomae, CH; Van der Plas, AK; Louw, D; Kreiner, A; Ostrowski, M; Fidel, Q; Barlow, RG; Lamont, T; Coetzee, J; Shillington, F; Veitch, J; Currie, JC; Monteiro, PMS Abstract: The Benguela system is one of the four major eastern boundary upwelling systems of the world. It is unusual as there are two stratified subtropical or warm temperate boundary regions, on either side of the major wind-driven upwelling region(19–34_S), which itself is subdivided at 26_S by the powerful Luderitz upwelling cell. Important biological components cross the boundary areas at different stages to complete the life-history cycle. While the ‘‘Bakun triad” of factors responsible for the development of large pelagic fish populations (enrichment, concentration and retention) provide an important unifying principle for understanding the compromise implicit in adaptation to upwelling systems, the role of predation has been neglected, as has the fish yield relative to photosynthesis. The role global climate change will have in the Benguela in terms of shifting boundaries or weakening or intensifying gradients is being explored. The interannual and decadal signals are so strong in the region that long term trends are difficult to distinguish. Intensive resource utilisation and the collapse of several fish stocks occurred in the Benguela region during the 1960s and 1970s, with different recovery trajectories in the north and the south. The Angolan subsystem can be described as a subtropical transition zone between the wind-driven upwelling system and the Equatorial Atlantic, with gentle upwelling-favourable winds, well-defined seasons, intermediate productivity and moderate, declining fisheries. It is separated from the Namibian subsystem by the Angola-Benguela front. The northern Benguela shelf is a typical coastal upwelling system with equatorward winds, cool water, high plankton biomass and moderate to high fish biomass, which is currently in a depleted state. A shift from sardines to horse mackerel occurred during the period 1970–1990, while hake have never fully recovered from intensive fishing pressure up to 1990. Widespread oxygen-depleted waters and sulphur eruptions result from local and remote forcing, restricting the habitat available for pelagic and demersal fish species. The Luderitz–Orange River Cone is an intensive perennial upwelling cell where strong winds, high turbulence and strong offshore transport constitute a partial barrier to epipelagic fish species. Upwelling source water alters in salinity and oxygen, across this boundary zone. A decline in upwelling-favourable winds occurred between 1990 and 2005. The southern Benguela region is characterised by a pulsed, seasonal, wind-driven upwelling at discrete centres and warm Agulhas water offshore. High primary productivity forms a belt of enrichment along the coast, constrained by a front. Low-oxygen water, which only occurs close inshore, may adversely affect some resources. The west coast is primarily a nursery ground for several fish species which spawn on the Agulhas Bank and are transported by alongshore jet currents to the west coast. The Agulhas Bank forms the southern boundary of the Benguela system and it displays characteristics of both an upwelling and a temperate shallow shelf system, with seasonal stratification and mixing, coastal, shelf-edge and dynamic upwelling, moderate productivity and a well oxygenated shelf. A largebiomass of fish occupies the Bank during the summer season, with some evidence for tight coupling between trophic levels. A cool ridge of upwelled water, with links to coastal upwelling and to the Agulhas Current, appears to play an important but poorly understood role affecting the distribution and productivity of pelagic fish. A boom in sardine and anchovy populations was accompanied by an eastward shift, followed by 5 years of poor recruitment by sardine but successful recruitment of anchovy, indicating changes in the early life-history patterns of these two species. Description: Copyright: 2009 Elsevier. This is an ABSTRACT ONLY. The definitive version is published in Progress in Oceanography, vol. 83(1-4), pp 15-32 2009-12-01T00:00:00Z http://hdl.handle.net/10204/6538 Title: How supportive are existing national legal regimes for multi-use marine spatial planning?—The South African case Authors: Taljaard, S; Van Niekerk, L Abstract: Over the past six years international interest in multi-use marine spatial planning (MSP), as a practical process to launch integrated coastal management (ICM), exploded. This paper explores the extent to which existing national legal frameworks can support this process, focusing on the coastal marine environment. First the characteristics of an appropriate legal regime for multi-use MSP are explored by interrogating secondary data sourced from literature reviews and case studies. Key paradigms are distilled as a means of dissecting this complex process into a suite of characteristic determinants that disclose the underpinning environmental management approaches or principles. These criteria are then used to assess the compatibility of national legal regimes for multi-use MSP—in this instance the South African legal framework. Although multi-use MSP has not been explicitly adopted as a process within South Africa's broader ICM implementation, existing legislation does reveal support. The department responsible for the environment is viewed as the most appropriate agency to house the statutory mechanism for multi-use MSP at national and provincial levels, but delegating local multi-use MSP processes to local government agencies. The political will to deploy and dedicate duties and resources to effective implementation of multi-use MSP, however, remains critical. Finally, the approach adopted here is proposed as a means to assess the compatibility of other national legal regimes for multi-use MSP, although the suite of characteristic determinants may need to be reviewed from time to time, as new learning emerges from practice. Description: Copyright: Elsevier 2013. This is the Pre/Post print version of he work. The definitive version is published in Marine Policy, vol. 38, pp 72-79 2013-03-01T00:00:00Z http://hdl.handle.net/10204/6522 Title: Satellite observations of an annual cycle in the Agulhas Current Authors: Krug, M; Tournadre, J Abstract: Ocean models show an annual cycle in the Agulhas Current transport which has not yet been confirmed in analyses of in-situ or satellite observations. A cross-stream coordinate approach is used to study the variability of the Agulhas Current from 18 years of along-track altimetry and merged altimetry and close to 7 years of high frequency Sea Surface Temperature (SST) observations. While the position and width of the Agulhas Current’s dynamical core do not display an annual cycle, the geostrophic current speed at the current’s core exhibits distinct seasonal variations, with a stronger flow observed in austral summer. The annual cycle dominates the frequency spectra of the current’s core geostrophic velocities. Description: Copyright: 2012 American Geophysical Union. 2012-08-01T00:00:00Z