Remotely sensed variability of temperature and chlorophyll in the southern Benguela: Upwelling frequency and phytoplankton response

Weeks, S. J., Barlow, R., Roy, C. and Shillington, F. A. (2006) Remotely sensed variability of temperature and chlorophyll in the southern Benguela: Upwelling frequency and phytoplankton response. African Journal of Marine Science, 28 3-4: 493-509. doi:10.2989/18142320609504201

Author Weeks, S. J.
Barlow, R.
Roy, C.
Shillington, F. A.
Title Remotely sensed variability of temperature and chlorophyll in the southern Benguela: Upwelling frequency and phytoplankton response
Journal name African Journal of Marine Science   Check publisher's open access policy
ISSN 1814-232X
Publication date 2006-11-01
Sub-type Article (original research)
DOI 10.2989/18142320609504201
Volume 28
Issue 3-4
Start page 493
End page 509
Total pages 17
Editor Stan C. Pillar
Place of publication Pretoria, South Africa
Publisher National Inquiry Services Centre
Language eng
Subject C1
260499 Oceanography not elsewhere classified
780104 Earth sciences
Formatted abstract
High-resolution (1km) satellite data from the NOAA AVHRR (Advanced Very High Resolution Radiometer) and OrbView-2 SeaWiFS (Sea-viewing Wide Field-of-view Sensor) are used to investigate the upper layer dynamics of the southern Benguela ecosystem in more detailed space and time scales than previously undertaken. A consistent time-series of daily sea surface temperature (SST) and chlorophyll a concentration images is generated for the period July 1998-June 2003, and a quantitative analysis undertaken. The variability in SST, upwelling and phytoplankton biomass is explored for selected biogeographic regions, with particular focus on intra-seasonal time scales. The location and emergence of upwelling cells are clearly identified along the length of the southern Benguela, being distinct on the narrow inner and the mid-continental shelves. Most notable is the rapidly pulsating nature of the upwelling, with intense warm/cold events clearly distinguished. The phytoplankton response to this physical forcing is described. Chlorophyll concentration on the inner shelf largely mirrors the pattern of SST variability, similarly dominated by event-scale processes. Over the mid-shelf, higher chlorophyll is observed throughout all seasons, although low biomass occurs during winter. The variability of the offshore extent of SST and chlorophyll is identified at locations of differing shelf width. Cooler upwelled water is confined primarily to the narrow inner-shelf, with event-scale pulses extending considerable distances offshore. Agulhas Current influences are readily observed, even on the Cape Peninsula inner-shelf. Chlorophyll concentrations vary considerably between the locations of differing shelf width. SST, upwelling and phytoplankton indices are derived for selected locations to quantify the intraseasonal variations. The SST indices show marked temperature changes associated with rapid pulsation on the event scale. No strong seasonal signal is evident. In contrast, the upwelling indices display a strong seasonal signal, with most intense upwelling occurring in spring/summer in the south. The phytoplankton response to the seasonal upwelling index differs between the selected locations. This study concludes that, although low-resolution SST and chlorophyll data may be useful for investigating general patterns over large scales, higher resolution data are necessary to identify finer scale spatial and temporal variability, especially in the inshore coastal zones.
Copyright © NISC Pty Ltd.
Keyword Marine & freshwater biology
Sea surface temperature (SST)
Eastern Boundary
Interannual variability
Pigment concentrations
Satellite imagery
Current systems
Q-Index Code C1

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Created: Wed, 15 Aug 2007, 20:59:36 EST