Life in the shelf seas - Introduction to the Physical and Biological Oceanography of Shelf Seas - page 144

Figure 5.8 A CTD profile from the
Celtic Sea, July 2003. The solid line
is the temperature profile. Symbols
are the nutrient concentrations,
all mmol m 3 .

Temperature ( C)

10 12 14 16 18

0

20

-

- 40

- 60

- 80

0 2 4 6 8

Nitrate

0 0.2 0.4 0.6 0.8

Phosphate

0 2 4 6

Silicate

the diatoms. The dissolved inorganic nutrient compounds that provide these (e.g.
nitrate, ammonium, phosphate and silicate) are referred to as macronutrients.In
addition, a number of other nutrients are required in small quantities. The role of
iron in controlling phytoplankton growth has received particular attention (e.g.
(Martin and Fitzwater, 1988 ; Coale et al., 1996 ; Boyd et al., 2000 )), but copper,
nickel and zinc are also known to be important (Morel et al., 1991 ). These are the
micronutrients. Our focus is on the inorganic macronutrients, mainly because in
coastal and shelf seas the combination of river inputs and suspension of material
from the seabed mean that an adequate supply of micronutrients is almost always
available.

The limiting nutrient in shelf seas
In Fig. 5.8 you can see a typical vertical profile of the macronutrients from our work
in the Celtic Sea. The samples shown in Fig. 5.8 were collected in a thermally