Seasonal stratification and the spring bloom - Introduction to the Physical and Biological Oceanography of Shelf Seas - page 199

(a)

30

20

10

0

Nov 29 Dec 3 Dec 7

(b)

-10

-50

-90

Nov 29 Dec 3 Dec 7

(c)

2.0

1.6

1.2

0.8

0.4

0

Nov 29 Dec 3 Dec 7

Date 1998

Figure 6.13 Data from a mooring off the northeast shelf of New Zealand. (a) Wind speed;
(b) The vertical temperature structure on the shelf, with horizontal dotted lines marking the
positions of the temperature loggers on the mooring; (c) Near-surface nitrate concentration
recorded by a nitrate analyser on the mooring. The analyser was situated 25 metres below the sea
surface. [Adapted from Sharples et al., 2001a , courtesy of the American Geophysical Union.]

residence time is greater than the cell doubling time scale, there is the potential for
biomass accumulation in the surface waters. The magnitude of the critical mixing could
be raised if cells were buoyant and able to offset some level of turbulence. The important
message here is that the growth of phytoplankton is a response to the turbulent environ-
ment. A vertical profile of temperature or density is an often-used proxy for providing
some insight into the distribution of turbulence, but it is not completely reliable.

6.4.2 Phytoplankton growth in turbulent water

Strong tides and turbulent mixing produce high concentrations of suspended par-
ticulate material, thus increasing the attenuation of light and severely limiting the