Browsing by Subject "False Bay"

Now showing 1 - 8 of 8
  • Thumbnail Image
    Item
    Open Access
    A preliminary account of investigations into the False Bay sublittoral by the use of a diving helmet
    (1950) Jackson,Peter Brian Neville
    A great deal of work has been done on the ecology of the intertidal some of South African by the Zoology Department of the University of Cape Town under the direction of Professor T.A. Stephenon. As a result of this a number of valuable papers have been published dealing with the plants and animals of the zone, their ecology, lateral and vertical distribution and so on. Stephenon has, in three papers (1939, 1944,1947), dealt with general results and conclusions drawn from this survey. This work dealt entirely with the biotic between tidelevels, i.e., from the sublittoral fringe upward. it did not take into account the sublittoral, that part of the shallow coast which is perpetually submerged at all tides.
  • No Thumbnail Available
    Item
    Open Access
    A preliminary account of investigations into the False Bay sublittoral by the use of a diving helmet
    (1950) Jackson, P B N (Peter Brian Neville), 1923-
    A great deal of work has been done on the ecology of the intertidal some of South African by the Zoology Department of the University of Cape Town under the direction of Professor T.A. Stephenon. As a result of this a number of valuable papers have been published dealing with the plants and animals of the zone, their ecology, lateral and vertical distribution and so on. Stephenon has, in three papers (1939, 1944,1947), dealt with general results and conclusions drawn from this survey. This work dealt entirely with the biotic between tidelevels, i.e., from the sublittoral fringe upward. it did not take into account the sublittoral, that part of the shallow coast which is perpetually submerged at all tides.
  • Thumbnail Image
    Item
    Restricted
    A prominent colour front in False Bay, South Africa: Cross-frontal structure, composition and origin
    (Elsevier, 2008) Waldron, H N; Wainman, C K; Waldron, M E; Whittle, C; Brundrit, G B
    Colour fronts are a frequent occurrence in False Bay, South Africa, and their occurrence has been the subject of previous study and anecdotal conjecture. The opportunity arose to make a cross-frontal study of this feature in November 2005. Photographs were taken and, subsequently, satellite imagery was obtained. Measurements were made of temperature, salinity, turbidity, dissolved oxygen, suspended solids, plant nutrients and chlorophyll a. Cross-frontal comparisons were also made on particulate material using a scanning electron microscope (SEM) and elemental dispersive x-ray (EDX) analysis. Frontal waters were milky white-green in colour, in stark contrast to the adjacent clearer, green-blue waters. The milky white-green water (MW-GW) was found to be warmer, (apparently) less saline, more turbid, richer in nitrate and silicate and had a higher chlorophyll a concentration. The dissolved oxygen signal was less pronounced, both water types being supersaturated. Paradoxically, in spite of the higher turbidity in the MW-GW, both water types had similar weights of suspended solids, although the MW-GW material was found to be more abundant and fragmentary when compared with its green-blue water (G-BW) counterpart. The MW-GW was rich in calcium whereas the G-BW was silicon enriched. The central findings of this study are that the strong southerly, onshore wind conditions prior to MW-GW formation introduced calcium-rich, fine particulates into the waters of the surf-zone. The sources of these particulates are thought to be the sea bed sediments and the sea/land interface. The particulates are close to neutral buoyancy enabling the MW-GW to persist over the time-scale of days. A mechanism reinforced by the warming of this water in the nearshore zone. The water was then advected by windforcing and subsequently, its own inertia around the north-west corner of False Bay, at which stage it was easily observed and sampled. It is suggested that the eventual collapse of the front was due to the slowing down of inertial movement in combination with the passive sinking of fine particulates and evaporative cooling resulting in downward convection.
  • No Thumbnail Available
    Item
    Open Access
    Sedimentology of the Cape Town boulder beds
    (University of Cape Town, 2024) Akkaş, Tuğçe; Bordy, Maria Emese
    Gravelly sediment layers in fossil beaches around the Cape Peninsula and False Bay in South Africa are assumed to be Pliocene in age and are essential for reconstructing the ancient sedimentary dynamics along the shoreline in the greater Cape Town region. The cobble- to boulder-size clasts in these fossil beaches point to a genesis that can be linked to the erosion of local rocky shores during hurricanes and “super storms”. This mode of formation seems similar to the Pliocene fossil beaches located at different elevations around the world (aka 'the Pliocene sea-level paradox'). Although mapped c. 100 years ago, to date, no modern sedimentological study has been conducted on Cape Town's fossil beaches. Clast characteristics (e.g., clast size, sorting, roundness, composition) of the gravelly layers had been quantified in the field and by the processing of field images using ImageJ software. Our results show that the fossil beaches are dominated by cobble-sized orthoquartzite clasts and display a variety of percussion marks. Originating locally from the Ordovician Peninsula Formation, these clast-supported, rounded clasts decrease in size from east to west, with the maximum clast diameter of >3.2m being recorded at Kogel Bay in False Bay. While this sedimentological study of Cape Town's fossil beaches elucidates the ancient marine dynamics during their genesis, linking them with other Pliocene fossil beaches requires further investigation through their age assessment. Irrespective of their age, the sedimentological properties and stratigraphic position of the fossil beaches above the modern sea level show that during sedimentation not only was the relative sea level higher by up to 30 m, but also that these deposits formed in powerful marine events that are often associated with rising global temperatures.
  • Thumbnail Image
    Item
    Open Access
    Summer at the beach: spatio-temporal patterns of white shark occurrence along the inshore areas of False Bay, South Africa
    (BioMed Central, 2018-05-22) Kock, Alison A; Photopoulou, Theoni; Durbach, Ian; Mauff, Katya; Meÿer, Michael; Kotze, Deon; Griffiths, Charles L; O’Riain, M Justin
    Background Understanding white shark (Carcharodon carcharias) habitat use in coastal areas adjacent to large cities, is an important step when formulating potential solutions to the conservation conflict that exists between humans and large predatory sharks. In this study, we present the findings of a 2.5-year study of white shark occurrence and movement patterns adjacent to the City of Cape Town in False Bay, South Africa, with a focus on spring and summer months. Fifty-one white sharks were monitored annually at three offshore and twelve inshore sites by VR2 acoustic receivers, over 975 days from 1 May 2005 to 31 December 2007. Results Occurrence patterns at inshore sites during spring and summer were analysed using a generalized additive mixed model (GAMM) with a spatial term (longitude, latitude), time of day and year included as explanatory variables for site use. We found that sharks occurred more frequently at inshore sites along the northern and northwestern shores, compared to the rest of the bay, and they transitioned most frequently between four adjacent beach sites that encompass the most popular recreational water use areas in Cape Town. There was significant diel variation, with higher shark occurrence around midday, and a peak in shark occurrence in 2005, when human-shark interactions also peaked. However, we found no effect of shark size on occurrence patterns at inshore sites. Conclusions White sharks showed the highest levels of occurrence at specific inshore sites between Muizenberg and Strandfontein beach, and thus inclusion of these sites within False Bay’s marine protected area (MPA) network or recognition as Ecological or Biological Significant Areas (EBSAs) should be a future consideration. These insights into white shark habitat use at inshore sites in False Bay are important for successfully applying the principles of marine spatial planning (MSP) and for making science-based policy decisions. Furthermore, this information can be used to reduce potential shark-human conflict by incorporating it into future shark safety education campaigns.
  • No Thumbnail Available
    Item
    Open Access
    The circulation and thermal structure of False Bay: a process-oriented numerical modelling and observational study
    (2012) Nicholson, Sarah-Anne; Shillington, Frank; Waldron, Howard; Vietch, Jennifer
    False Bay, the largest bay in South Africa, lies between two of the world's most in-fluential current systems: the Agulhas and Benguela Current Systems. False Bay is situated at a biogeographic break (Pitcher et al., 2010), belonging to both the South-ern Benguela upwelling system and the Western Agulhas Bank. The oceanography of Southern Africa, particularly this region, is some of the most complex and highly variable in the world (Roberts, 2005). Owing to the surrounding steep orography and its position, the meteorology of the False Bay region is also complex, having wind con-ditions that are unique when compared to other regions of South Africa (Jury, 1991). It is under these special conditions that the circulation of False Bay is regarded as highly complex.
  • No Thumbnail Available
    Item
    Open Access
    The marine geology of False Bay
    (1966) Bowie, D K; Fuller, A O
    The marine geology of False Bay, lying in the southwestern extremity of the Southern African continent, has been investigated, The object of the study was to elucidate certain problems associated with marine terracing developed in the area and to describe the nature and distribution of sediments occurring on the floor of the bay with emphasis on the distribution as related to both bottom and surf current patterns. In past literature reference has been made to raised beaches at elavations of 50 to 60 ft; 20 to 25 ft; and 10 to 14 ft. The writer has surveyed certain of these features and has shown that erroneous elevations have been quoted, resulting in inaccurate age designations. Global dating of terraces, exposed and submerged1 is discussed and applied to the features in the Bay, in an attempt to record their history. The oldest feature, the Gordons Bay boulder beach at approximately 100 ft. above mean sea-level, is dated by the writer as of Great Interglacial age. It is pointed out that the Stellenbosch river terraces, dated by A. Krige (1927) as Last Interglacial, can in no way be related to this period. Evidence is presented which suggests that the 50 to 60 ft., 20 to 25 ft. and 10 to 14 ft. terraces formed during the Main, Intra and Late Monastrian periods respectively.
  • Thumbnail Image
    Item
    Open Access