Chapter 9
The Upwelling Area Off Namibia, the Northern
Part of the Benguela Current System
Herbert Siegel, Thomas Ohde and Monika Gerth
Abstract In the area off Namibia satellite remote sensing data of the visible and
infrared spectral range were used to investigate the upwelling processes and the biological response. Satellite derived Sea Surface Temperature was applied to study
upwelling processes in relation to the driving trade winds. The investigations were
focussed on the intensity and horizontal extent, the temporal and spatial variability
including inter-annual and climate scales. Ocean colour satellite data allow investigation of the response of surface water to the nutrient input into the euphotic zone
by upwelling processes. Observations in the area revealed, that the phytoplankton
development starts with species absorbing light in the visible spectral range (diatoms and dinoflagellates) and may end in persistent shallow surface filaments with
light scattering algae blooms. These blooms of coccolithophores identified by different in situ methods changed the water colour by strong particle scattering to milky
turquoise discolorations. Further milky turquoise discolorations were identified as
sulphur plumes. Low wind periods support the degradation of organic matter and the
development of hydrogen sulphide in the bottom layer. After the onset of the trade
winds and the offshore transport of surface water hydrogen sulphide enriched waters
reaches with the near-bottom counter current the coast. Upwelling transports the water to the surface where the hydrogen sulphide will be oxidised to elemental sulphur.
An algorithm was developed to identify and separate the sulphur plumes from algae
blooms and other features on the basis of highly spectrally resolved satellite data
from the MERIS sensor. The algorithm identified only coastal plumes as sulphur
and that offshore plumes are formed by coccolithophores. The sulphur season is the
boreal spring starting in February and reaching the maximum in April.
9.1 Introduction
The Namibian coastal waters are hydrographically highly variable. Upwelling processes, plankton blooms and sulphur events are characteristics of the region which
have been intensively investigated by satellite remote sensing methods. This chapter
H. Siegel () · T. Ohde · M. Gerth
Leibniz Institut für Ostseeforschung Warnemünde, Rostock, Germany
e-mail: herbert.siegel@io-warnemuende.de
V. Barale, M. Gade (eds.), Remote Sensing of the African Seas,
167
DOI 10.1007/978-94-017-8008-7_9,
© Springer Science+Business Media Dordrecht 2014
The Upwelling Area Off Namibia, the Northern
Part of the Benguela Current System
Herbert Siegel, Thomas Ohde and Monika Gerth
Abstract In the area off Namibia satellite remote sensing data of the visible and
infrared spectral range were used to investigate the upwelling processes and the biological response. Satellite derived Sea Surface Temperature was applied to study
upwelling processes in relation to the driving trade winds. The investigations were
focussed on the intensity and horizontal extent, the temporal and spatial variability
including inter-annual and climate scales. Ocean colour satellite data allow investigation of the response of surface water to the nutrient input into the euphotic zone
by upwelling processes. Observations in the area revealed, that the phytoplankton
development starts with species absorbing light in the visible spectral range (diatoms and dinoflagellates) and may end in persistent shallow surface filaments with
light scattering algae blooms. These blooms of coccolithophores identified by different in situ methods changed the water colour by strong particle scattering to milky
turquoise discolorations. Further milky turquoise discolorations were identified as
sulphur plumes. Low wind periods support the degradation of organic matter and the
development of hydrogen sulphide in the bottom layer. After the onset of the trade
winds and the offshore transport of surface water hydrogen sulphide enriched waters
reaches with the near-bottom counter current the coast. Upwelling transports the water to the surface where the hydrogen sulphide will be oxidised to elemental sulphur.
An algorithm was developed to identify and separate the sulphur plumes from algae
blooms and other features on the basis of highly spectrally resolved satellite data
from the MERIS sensor. The algorithm identified only coastal plumes as sulphur
and that offshore plumes are formed by coccolithophores. The sulphur season is the
boreal spring starting in February and reaching the maximum in April.
9.1 Introduction
The Namibian coastal waters are hydrographically highly variable. Upwelling processes, plankton blooms and sulphur events are characteristics of the region which
have been intensively investigated by satellite remote sensing methods. This chapter
H. Siegel () · T. Ohde · M. Gerth
Leibniz Institut für Ostseeforschung Warnemünde, Rostock, Germany
e-mail: herbert.siegel@io-warnemuende.de
V. Barale, M. Gade (eds.), Remote Sensing of the African Seas,
167
DOI 10.1007/978-94-017-8008-7_9,
© Springer Science+Business Media Dordrecht 2014