Regions of freshwater influence (ROFIs) - Introduction to the Physical and Biological Oceanography of Shelf Seas - page 277

(a)

R.Kent

26.2 25.8

R.Lune

54°N

25.4

R.Wye

R.Ribble

Irish Sea

25

Liverpool

R.Mersey

R.Dee

North Wales

20 km

53°N

5°W 3°W

(b)

3

2

1

0

180

0 60 120 240 300 360

(c)

3

2

1

0

180

0 60 120 240 300 360

Time (Julian days)

Figure 9.6 (a) A typical map of the distribution of surface isolines of s t (kg m 3 ) in the
Liverpool Bay ROFI, (Sharples and Simpson, 1993 ) courtesy of the Estuarine Research
Federation. (b) A year-long time series of the difference between the near-bed and surface
density, D r(kg m -3 ), measured by a mooring in Liverpool Bay. The position of the mooring
is marked as in (a) (from Verspecht et al. , 2009 , courtesy of Springer). (c) The typical annual
progression of D r in the nearby Celtic Sea, where stratification is attributable to seasonal
changes in surface heat fluxes. Based on the model of Sharples, 2008 . In (a)

▲

marks the

mooring position for the data in Fig. 9.7 .

Much of the variation of the stratification in the Liverpool Bay ROFI is due to
irregular changes in runoff from the rivers and in wind stirring, but closer inspection
reveals that there is also an important periodic component associated with changes in
tidal stirring. Remember how we saw in Chapter 8 that the position of the tidal