Evidence of carbon transport between shelf and slope waters in the Benguela upwelling system

Abstract

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.