Browsing by Subject "marine"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Open Access
    Ice - ocean - atmosphere interactions in the Southern Ocean and implications for phytoplankton phenology
    (2021) Hague, Mark; Vichi, Marcello
    The annual advance and retreat of sea ice in the Southern Ocean is recognised as one of the largest seasonal events on Earth. Such considerable physical changes have profound effects on the vertical structure of the water column, and hence controls the availability of both light and nutrients to phytoplankton. This means that in the region seasonally covered by sea ice (the SSIZ), the timing of the growth and decline (phenology) of phytoplankton is determined to a large degree by the dynamic interactions between ice, ocean and atmosphere. However, this region is simultaneously one of the most poorly observed in the global ocean, and one of the most complex. This has led to significant gaps in our understanding of how sea ice modulates the exchanges of heat and momentum between atmosphere and ocean, as well as the implications this has for phytoplankton phenology in the SSIZ. This study seeks to address these gaps by combining both model and observationallybased methods. The lack of observational data are directly tackled through an analysis of BGC-Argo float data sampling under ice. Such data reveal high growth rates in the presence of near full ice cover and deep mixed layers, conditions previously thought to prevent growth. These results suggest a revision of our current understanding of the drivers of under ice phytoplankton phenology, which should take into account the unique character of Antarctic sea ice and its effect on the under ice light environment. In addition, results obtained from several numerical process studies indicates that phytoplankton may have a higher affinity for low light conditions than previously thought. From a modelling perspective, an analysis and intercomparison of 11 Earth System Models (ESMs) and their representation of vertical mixing and phenology is presented. This revealed that misrepresentations in phenology where driven by model biases in sea ice cover and vertical mixing. That is, only models with either too much or too little ice cover were able to simulate phenology close to observations. Furthermore, a strong correlation between the location of the ice edge and the extent of vertical mixing suggested that ESMs overly dampen ocean-atmosphere fluxes as mediated by sea ice. This led to the development of a regional ocean-sea ice model of the Atlantic sector of the Southern Ocean, from which experiments enhancing both heat and momentum fluxes could be conducted. It was found that the model responded more uniformly to enhanced heat flux, generally deepening the mixed layer closer to observations in winter. On the other hand, the effects of enhanced momentum flux (implemented by increased air-ice drag) where more complex and spatially heterogeneous, with contrasting responses depending on the initial vertical density structure of the water column. Overall, the argument is made that the unique features of Antarctic sea ice should be included in models if we are to improve the representation of the SSIZ mixed layer, and hence phenology
  • No Thumbnail Available
    Item
    Open Access
    Legislative reform of warranties in South African marine insurance law
    (2010) Brown, Gavin; Hare, John
    In South Africa, because of its historical connection with England, it is English law that has come to be applied in the context of insurance. One aspect of English insurance law that has come to be particularly criticised over time is the approach to warranties as specific and unique clauses in insurance contracts. The vociferous nature of the calls for change and the fact that their inequity • has been identified by both courts and commentators for over a hundred years is an indication of the need for change. This paper takes this need for change as its starting point, going on to consider what legislative reform is needed in South Africa to restore order to a particularly untidy area of insurance law. To do this, this paper will set out the application of warranties in South African insurance law by following their development in English law and their complicated reception into our own.
  • Thumbnail Image
    Item
    Open Access
    Seasonality of the Agulhas Current with respect to near- and far-field winds
    (2018) Hutchinson, Katherine; Penven, Pierrick; Beal, Lisa; Ansorge, Isabel; Hermes, Juliet
    The Agulhas Current plays a critical role in both local and global ocean circulation and climate regulation, yet the mechanisms that determine the seasonal cycle of the current remain poorly understood. Model studies predict an austral winter-spring maximum in poleward volume transport, whilst observations reveal an austral summertime (February-March) maximum. Here, the role of winds on Agulhas Current seasonality is investigated using shallow water models, satellite measurements, and a 23-year transport proxy based on observations. A one-and-a-half layer reduced gravity model is shown to successfully reproduce the seasonal phasing of the current. This seasonality is found to be highly sensitive to the propagation speed of Rossby waves, which determines the arrival time of the wind stress signal at the western boundary. By matching Rossby wave speeds to those observed using altimetry, an Agulhas Current with a maximum flow in February and a minimum flow in July is simulated, agreeing well with observations. Near-field winds, to the west of 35◦E, dominate this seasonality, as signals from more remote wind forcing dissipate due to destructive interference while crossing the basin. Local winds driving coastal upwelling/downwelling directly over the Agulhas cannot, alone, account for the observed seasonal phasing, as they force a NovemberDecember maximum and June minimum in flow. The seasonal response to Indian Ocean winds is also investigated using a barotropic (single layer) model with realistic topography. A barotropic adjustment cannot explain the observed Agulhas Current seasonality, predicting a wintertime maximum in transport. The results from the barotropic simulation are similar to previous model studies, where seasonality is dominated by a southward propagation of signals via the Mozambique Channel, suggesting that these models are too barotopic in their response to the winds. Findings from this study elucidate the role of near-field winds and baroclinic processes in determining the seasonality of the Agulhas Current.
  • No Thumbnail Available
    Item
    Open Access
    The impact of offshore and gas exploitation on the marine environment and its regulations under selected national regimes
    (2013) Fombang, Humphrey; Hare, John
    Despite the numerous advantages accrued from the exploitation of oil and gas worldwide, the repercussion of its activities on the marine environment has put the entire world under panic about the future of our beloved planet. Political leaders from both developed and developing countries through Conventions, Conferences, national policies and legislation, have been seeking various ways to regulate the exploitation of oil and gas on the continental shelf and Exclusive Economic Zone in order to protect the marine environment that is at the brink of losing its socio-economic values. With the present trend of events threatening the planet such as climate change and the call for sustainable development, the regulation of oil and gas exploitation on the marine environment remains a dilemma. It is now crystal clear that the principle of 'Common but Differentiated Responsibilities' as advocated by both the Rio and Johannesburg world summits on sustainable development, with regard to the regulations of oil and gas exploitation, which have already been put in place, must be strengthened.