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Investigaciones marinas

versión On-line ISSN 0717-7178

Investig. mar. v.30 n.1 supl.Symp Valparaíso ago. 2002 

Warm Water Events in the Northern
Benguela: A Local Perspective

Bronwen Currie1, Chris Barthoamae1,
Kathie Noli-Peard2, Jens-Otto
Krakstad1, Anja Kreiner1

1 National Marine Information and Research Centre,
Ministry of Fisheries and Marine Resources,
P.O. Box 912, Swakopmund, Namibia,
2 Luderitz Research Station, Ministry of Fisheries and
Marine Resources, P.O. Box 394, Luderitz, Namibia

Associated with a slackening in upwelling, the intrusion of warm surface water along Namibia's northern coast is a regular annual occurrence. The intensity varies from year to year. Whilst the timing is always mid- to late summer, the southern coastal extent varies between 220 S to as far as 250 S. The term "Benguela Nino" is often loosely applied to this intrusion, with no stringent definition regarding timing, extent, origin or properties of this water.

In an environment as dynamically variable as the Northern Benguela upwelling system, increased temperature in the upper water column, and sometimes only in surface water, is unlikely to impact drastically on a marine community which is already adapted to a substantial swing in the annual temperature cycle. The origin of the warm water, together with the driving wind force and other water column parameters, should be examined before "warm events" are blamed for fish stock misbehaviour.

Using available time series for the period 1980 to 2001, this presentation looks at the annual surface temperature trends, the extent of both timing and intensity of warm water intrusion, as well as wind stress along the coast, and incidence of hypoxia and anoxia in the water column. In addition, the origin of the warm water is assessed using biotic markers, and trends in pelagic fish stocks are presented. Of special interest are the conditions over the last decade.

We suggest that intrusion of warm water from the north ("Angolan water") presents a vastly different oceanographic situation to intrusion of wind-driven oceanic water from the west, even though the superficial surface temperature regimes may be similar.

Included in the presentation will be:

• anomalies of SST over the past 20+ years, including time-series of latitudinal intrusions of warm surface water along the Namibian coast;

• graphed analyses of wind stress anomalies from both the southern and northern upwelling cells of the Namibian coast;

• comparison of these series to the available water column dissolved oxygen trends;

• a comparison with fish recruitment.

Data used is drawn from the few published records on the "Benguela-Nino" phenomenon, from satellite imagery data and from unpublished data from cruises carried out in Namibian waters.

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