750 EIGHTH PACIFIC SCIENCE CONGRESS 



and chlorinity, associated with high total phosphorus characteristics is 

 difficuh to decide exactly, although such characteristics are more typi- 

 cal of deeper offshore waters of New South Wales than of east Tasma- 

 nia. 



Without sufficient knowledge of the dynamics of the New South 

 Wales Tasman Sea, however, it is impossible to demonstrate how such 

 a water mass could have influenced the Tasmanian coastal region. 



V. Meteorological and Dynamical Changes Associated 



WITH THESE TRENDS 



If we accept the proposition that the secular trends at the Port 

 Hacking coastal station are due in large measure to variations in the 

 amount of slope water influence, then a study of the possible factors 

 controlling such slope Water variation might eventually enable the 

 oceanographer to predict by study of the variation in the principal con- 

 trolling factors, oceanographical conditions in future seasons. For the 

 past 10 years the C.S.I.R.O. Fisheries Division has been studying the 

 montlily and annual variations in mean sea level at a station representa- 

 tive of coastal conditions off Port Hacking. 



If we examine the mean summer and winter mean sea levels varia- 

 tions at this station during the period 1942-1952, Fig. 15, the existence 

 of a secular trend is evident. Moreover, the magnitude of the cycle has 

 been much greater during the summer than the winter period. The 

 period of minimum summer mean sea levels from 1946 to 1949, cor- 

 responds to the period of lowest mean summer bottom temperatures 

 at the Port Hacking station. There is evidence from the New South 

 Wales coastal station of the development of a covmter current flowing 

 north, at distances of about 5 miles offshore, during the later part of 

 the summer. The high mean sea levels normally experienced in March- 

 April are considered to be an effect of this current along the coast. 

 Presumably then during seasons when this counter current is strongly 

 developed, the intrusion of slope waters is retarded because the isen- 

 tropic layers are tilted down towards the coast and oppose the lateral 

 movement of deep slope waters into the coastal region. 



In Fig. 16 the relationship between mean monthly sea level and 

 bottom temperatures at the Port Hacking station during December over 

 the period 1942-1952 is shown. For those years when high sea levels 

 prevailed during December and are indicative according to the theory 

 outlined above of weak slope water influence, the mean monthly bottom 

 temperatures are higher. 



It seems dear then that the ultimate answer to both variation in 

 slope water intrusion and the coastal mean sea level at the Port Hacking 



