Interior mixing and phytoplankton survival in stratified environments - Introduction to the Physical and Biological Oceanography of Shelf Seas - page 220

(a)

54

52

C

B

50

Celtic
Sea

A

48

9
Longitude

6 3

o

W

A B C

(b)

-100

0 1 2

Chlorophyll (mg m -3 )

-200

0 100 200 300 400 500

Distance (km)

Figure 7.8 See colour plates version. The map shows the course followed by the research vessel
RRS James Clark Ross in August 2003, towing the Seasoar undulating vehicle (see Fig. 1.5 ).
The contoured image shows temperature (lines, every 2 C) and chlorophyll concentration
(shaded) along the transect. The dark grey region is the seabed, showing the dropoff at the
shelf edge (60 km) and gradually shallowing towards the entrance to the Irish Sea (550 km).
Data were collected between the surface and a depth of 100 metres. Vertical white bands
indicate regions where there was a communication failure with the instrument. The arrows
labeled along the top axis show the positions of the course changes marked on the map.

or more of the three interior mixing processes described in Section 7.2.2 . Can we find
evidence to indicate whether, or not, each of the three key thermocline mixing pro-
cesses has a significant impact on the biochemistry of the thermocline?
Looking for such evidence is challenging; we need vertically well resolved time
series of the SCM. The subsurface nature of these layers rules out satellite remote
sensing as a convenient means to construct such time series. Cost and problems with
biofouling usually mean that moored instrumentation does not have the vertical
resolution to identify the evolution of the structure of subsurface chlorophyll layers.
However, we do have some useful observational evidence, and can gain further
information/insight by using numerical models.
Consider first the biochemical response to topographically generated internal
waves. The clearest examples occur at the shelf edge (see Chapter 10 ), but there is
some evidence of effects over the slopes of large banks on the shelf, as shown in
Fig. 7.9 . Stratified regions of the NW European shelf receive a typical daily-mean