Environmental Engineering Reference
In-Depth Information
vected northward by the surface current and causes a northward displacement
of the most productive area by a few degrees latitude. This displacement is
associated with a northward shift of the area of the most extreme subsurface
oxygen depletion produced by the respiration of sinking organic matter to the
area around 24
◦
S (Fig. 2).
Figure 3.
Averaged alongshore (a) and cross-shore (b) current velocity at the mooring (22
◦
59.7' S, 14
◦
02.8' E, 131 m water depth) located in the mud belt off Walvis Bay. The mooring
was deployed from December 9, 2002 until April 1, 2003, and from January 7, 2004 until May
5, 2004.
Data from the mooring in 130 m water depth at 23
◦
S indicate interannual
variations in the strength of the poleward undercurrent located below 20 m
water depth (Fig. 3a, b). In the period December 2002 until April 2003, the
meridional (southward) component had average current speeds of 4 cm s
−
1
,but
for the period January 2004 until May 2004, the current speed was averaging
only 2 cm s
−
1
(Fig. 3a). Similarly, the cross-shelf circulation represented by
the zonal component of the current varied between the two observation periods
(Fig. 3b). On-shore transport was weaker in 2004 compared to 2003 indicating
that the ventilation by ESACW in the intermediate layer was weaker in the
austral fall of 2004.
