748 EIGHTH PACIFIC SCIENCE CONGRESS 



It is apparent therefore that whilst land drainage can modify the 

 Cl°/oo structure of coastal waters, its role in the gradual increase in 

 phosphate levels at coastal stations since 1945 cannot be a direct one. 



(b) Lateral movement of slope waters into the coastal region. 



During 1940-42 F.R.V. "Warreen" was able to sample simultaneous 

 coastal and shelf stations at frequent intervals off Port Hacking. Fig. 

 10 shows the relationship between inorganic phosphates and Cl°/oo for 

 slope waters and Fig. 11 for the bottom coastal waters sampled during 

 this period. The regression line for the slope data above 10/xg/L PO4P 

 has been calculated and superimposed on the coastal water diagram. 

 The coastal data fits this regression line fairly well and it is highly 

 probable that slope waters of varying depths have periodically invaded 

 these coastal regions during this period. 



Since that time, the systematic collection of data at the Port Hack- 

 ing coastal station has revealed that these slope water invasions of the 

 coastal region are a common feature of the summer period, particularly 

 during the period of high vertical stability. These slope waters are 

 comparatively rich in phosphates with lower Cl°/oo. temperature and 

 dissolved O2 than the coastal bottom waters. Could the rise in in- 

 organic phosphates and the decrease in Cl°/oo in the bottom waters at 

 the Port Hacking station during 1943-1952 be an effect of more frequent 

 invasion and more effective assimilation of such slope Avaters into the 

 structure of coastal waters? 



Whilst lack of information about the dynamical continuity between 

 slope and coastal regions makes the examination of such a possibility 

 very difficult, there are certain significant features in the trend curves 

 at the Port Hacking station which favour such a theory. 



Referring again to Fig. 3, it can be seen that the mean summer 

 bottom temperatures have decreased fairly consistently from 1943 to 

 1949, and risen rather rapidly since that year. This trend is paralleled 

 by the Cl°/oo of these waters and, whilst the surface dilution of these 

 waters during the 1949 period and onward, may have contributed in 

 some measure to the later portion of this trend, the fact that this de- 

 crease commenced in 1944 would indicate some more fundamental cause 

 of the phenomenon. Assuming then that the decrease in summer bottom 

 temperature and chlorinity has been little influenced by the rainfall 

 cycles during the period, there seems good evidence to support the 

 theory of more effective assimilation of low temperatures and chlorinity 

 slope waters into the structure of the Port Hacking bottom coastal waters 

 during 1943-1949. 



(c) Increase in phosphate content of slope waters. 



