Browsing by Author "Waldron, H N"

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    Evidence of carbon transport between shelf and slope waters in the Benguela upwelling system
    (2007) Swart, N; Waldron, H N; Hutchings, L
    The world ocean is pivotal in the global carbon cycle and, subsequent to anthropogenic loading of the atmosphere with CO2, its ability to sequestrate photosynthetically-fixed carbon is important with respect to our ability to predict climate change. A study of the Benguela Edge Exchange Processes was carried out to better understand the transfer of organic material between the continental shelf and slope environments in the southern Benguela upwelling system off the south-western coast of South Africa. Data were collected during three hydrographic surveys in which particulate organic carbon (POC) and nitrogen (PON) were measured to assess the distribution of organic matter across the shelf–slope interface. Results indicate that significant concentrations of organic material (POC > 80μg l−1 and PON > 13μg l−1) were found near the shelf break, providing evidence that shelf-derived primary production may be transported into deep waters offshore and sequestrated in the long-term. The findings of the survey data are supported by a carbon budget calculation. This study contributes to the Joint Global Ocean Flux Study and to an understanding of the extent to which slope environments act as carbon sinks.
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    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.