The Benguela: Large Scale Features and Processes and System Variability

Shannon, L. V.; Nelson, G.

doi:10.1007/978-3-642-80353-6_9

Cited by 257 publications

(365 citation statements)

References 60 publications

Supporting

Mentioning

353

Contrasting

Unclassified

Order By: Relevance

“…Both locations are relatively close to deserts, known to release dust into the adjacent ocean. Both positions are close to a zone of coastal upwelling (Krauss, 1996;Shannon and Nelson, 1996). However, the northern position is closer to the coast and is thus more likely to receive organic-rich water from the coastal upwelling.…”

Section: Surface Samples From the Transectmentioning

confidence: 90%

The influence of solar ultraviolet radiation on the photochemical production of H2O2 in the equatorial Atlantic Ocean

Gerringa

Rijkenberg

Timmermans

et al. 2004

Journal of Sea Research

View full text Add to dashboard Cite

Hydrogen peroxide (H 2 O 2 ) was measured in marine surface waters of the eastern Atlantic Ocean between 25jN and 25jS. H 2 O 2 concentrations decreased from 80 nM in the north to 20 nM in the south, in agreement with earlier observations. A diel cycle of H 2 O 2 production as a function of sunlight in surface waters was followed twice whilst the ship steamed southward. Around 23jN a distinct diel cycle could be measured which correlated well with irradiance conditions. The wavelength dependency of H 2 O 2 formation was studied near the equator. For 16 hours, water samples were incubated with wavelength bands of the solar spectrum, i.e. visible (VIS: 400 -700 nm), VIS and ultraviolet A radiation (UVAR: 320 -400 nm) and VIS, UVAR and ultraviolet B radiation (UVBR: 280 -320 nm). A significant relationship was found between wavelength band and the production of H 2 O 2 . In addition, a clear positive relationship between intensity and production was found. UVAR was 6.5 times more efficient than VIS in producing 1 nM of H 2 O 2 , whereas UVBR was 228 times more efficient than VIS. When these data were weighted with respect to the energy of the solar spectrum at zenith hour, 28% of the H 2 O 2 was formed by VIS, 23% was formed by UVAR and 48% was formed by UVBR. Considering the strong attenuation of UVBR in marine waters as compared with UVAR and VIS radiation, the role of UVAR deeper in the water column is recognised. Furthermore results of this research emphasise the importance of VIS radiation in the formation of H 2 O 2 .

show abstract

Section: Surface Samples From the Transectmentioning

confidence: 90%

The influence of solar ultraviolet radiation on the photochemical production of H2O2 in the equatorial Atlantic Ocean

Gerringa

Rijkenberg

Timmermans

et al. 2004

Journal of Sea Research

View full text Add to dashboard Cite

show abstract

“…Boebel et al (2003) suggested that the cyclones could be related to interaction of Agulhas rings with the shelf, or to local upwelling along the shelf (Shannon and Nelson, 1996), or to an intermediate eastern boundary current along the shelf (Shannon and Hunter, 1988). Movies of sea level anomaly (MODAS) indicate energetic fluctuations starting near the retroflection and propagating up the west coast, with some fluctuations moving offshore , implying that the Agulhas is the source of energy.…”

Section: Ring Leakage Transportmentioning

confidence: 99%

Agulhas leakage into the Atlantic estimated with subsurface floats and surface drifters

Richardson

2007

Deep Sea Research Part I: Oceanographic Research Papers

158

View full text Add to dashboard Cite

show abstract

“…A comprehensive review of the circulation in the SE Atlantic Ocean and the Benguela System is given in Shannon and Nelson (1996). The northward component of the SET is responsible for offshore transport of water in near-surface layers.…”

Section: Atmospheric and Oceanic Circulationmentioning

confidence: 99%

“…In coastal zones south of *33°S, relatively warm surface water originates from the Indian Ocean and its equatorward spreading forms a highly variable frontal zone which separates cold upwelling water in the North from relative warm water in the South (Shannon and Nelson 1996). The Benguela upwelling regime thus is the only Eastern Boundary Current system with a poleward border of warm water.…”

Section: Atmospheric and Oceanic Circulationmentioning

confidence: 99%

Variability in upwelling intensity and nutrient regime in the coastal upwelling system offshore Namibia: results from sediment archives

Emeis

Struck

Leipe

et al. 2007

Int J Earth Sci (Geol Rundsch)

View full text Add to dashboard Cite

The coastal upwelling system offshore Namibia is ideally suited to address a focal question of the Integrated Marine Biogeochemistry and Ecosystem Research Programme: what are the mechanisms that drive long-term changes in ecosystems? Considerable interannual variability in climatic forcing is indicated by long time series of meteorological and remote sensing observation; these accompany considerable interannual to interdecadal changes in the upwelling intensity over the last 100 years, as well as a centennial trend. On longer time scales, the only archives available are sediment records spanning the late Holocene. To decipher the sediment record, we mapped surface-sediment patterns of proxies for physical (sea surface temperature/SST from alkenone unsaturation indexes) and nutrient (d 15 N on bulk sedimentary N) variables. Their present-day surface-sediment patterns outline the coastal upwelling cells and filaments and associated high productivity area. Analysed in an array of dated sediment cores, the spatial patterns of SST suggest long-term ([100 years) variability in the location and intensity of individual upwelling cells. The patterns of d 15 N outline an area of intense denitrification near the coast, and advection of water with low-oxygen concentrations in the undercurrent from the North. d 15 N exhibits considerable downcore variability, in particular over the last 50 years. The variability appears to be governed by differences in extent of denitrification and thus of the shelf oxygen balance, which appears to have deteriorated in the last 50 years. Together, the data suggest that SST and denitrification conditions have remained in the narrow bounds outlined by today's patterns in surface sediments, but that spatially small variability in upwelling intensity and make-up of upwelling feed waters induced considerable changes in the lower trophic levels of the coastal upwelling ecosystem over the last 6,000 years. Attempts to correlate proxy records from sediments with observational time series and regional climate reconstructions were not successful, possibly because annual to interannual environmental signals are erased in the process of sediment formation.

show abstract

The Benguela: Large Scale Features and Processes and System Variability

Cited by 257 publications

References 60 publications

The influence of solar ultraviolet radiation on the photochemical production of H2O2 in the equatorial Atlantic Ocean

The influence of solar ultraviolet radiation on the photochemical production of H2O2 in the equatorial Atlantic Ocean

Agulhas leakage into the Atlantic estimated with subsurface floats and surface drifters

Variability in upwelling intensity and nutrient regime in the coastal upwelling system offshore Namibia: results from sediment archives

Contact Info

Product

Resources

About