The shelf edge system - Introduction to the Physical and Biological Oceanography of Shelf Seas - page 330

10.6.1 Wind-driven upwelling and biological response

Nutrient supply and the phytoplankton response
In clear sky conditions, the elevated chlorophyll concentrations arising from
upwelling-favourable winds are often apparent in satellite images. For instance,
comparison of concurrent images of sea surface temperature and sea surface
chlorophyll, off the Iberian Peninsula ( Fig. 10.17a ), illustrates the clear link between
the cool upwelled water and the enhanced phytoplankton concentration along the
entire Portuguese shelf. Looking in more detail at the southern Portuguese shelf,
shown in Fig. 10.17b , we can see a filament and eddy of upwelled water containing
elevated chlorophyll. Such eddies and filaments, which, as we noted in 10.3.1, are
correlated with topographic irregularities along the coastline (Haynes et al., 1993 ),
are known to be important for the export of material off the shelf (Alvarez-Salgado
et al., 2001 ). Figure 10.18 shows a cross-slope section off the Iberian Peninsula

(a)

44ºN

40ºN

Atlantic
Ocean

Atlantic
Ocean

36ºN

14ºW 10ºW 6ºW 14ºW 10ºW 6ºW

(b)

mg m -3

ºC

17 25

0.05 0.1 1 5 20

Figure 10.17 See colour plates version. (a) Satellite images of sea surface temperature (left) and
sea surface chlorophyll (right) off the Iberian Peninsula. Both images are composites taken
over July 25-27, 2007; (b) Detail of the boxes marked in (a) showing two large filaments of
upwelled water containing chlorophyll extending off-shelf. Images from NEODAAS,
Plymouth Marine Laboratory, UK.