SECULAR TRENDS AT E. AUSTRALIAN COASTAL STATIONS :1942-52 749 



Fig. 12 shows the relationship between total phosphorus and oxy- 

 gen saturation values of the Port Hacking summer bottom waters during 

 1943-1952. 



By differentiating the data into years, ic is possible to see clearly 

 that these bottom waters have changed their O^-total phosphorus rela- 

 tionship quite considerably during the period. 



To better illustrate this, two envelopes have been entered, one 

 labelled A, containing a majority of the data subsequent to and the 

 other labelled B, prior to that year. At any given oxygen saturation 

 level it is clear that the total phosphorus content has increased over the 

 period. Unfortunately one cannot assume from this that the parent 

 slope waters have also changed their total phosphorus and dissolved O, 

 content in a similar fashion at the depth of origin of these coastal in- 

 trusions. There would, however be no reason to suppose that the east 

 Australian slope waters would not undergo long term changes in hydro- 

 logical properties, and it is quite possible that an increase in the nu- 

 trient level of the parent slope waters themselves has contributed to 

 these coastal water trends. 



(d) Replacement of local coastal w^aters by a foreign water mass of 

 higher nutrient content. 



Along the east Tasmanian coast the evidence from coastal observa- 

 tions suggests that lateral movement of deep offshore waters into 

 coastal regions is extremely rare, largely because it is suspected that a 

 slope current is only weakly developed. One cannot assume therefore 

 that the same processes have contributed to the secular trends at the 

 Maria Island station, as have been considered responsible in more 

 northern latitudes. It is significant too that the rise in phosphates and 

 total phosphorus has been accompanied by an increase in Cl°/oo and 

 temperature during the winter period, particularly from 1947 to 1951. 

 On the evidence it was considered probable that in this region the 

 secular changes were due to a gradual displacement of the original east 

 Tasmanian water mass of 1945 by a new water mass of higher Cl°/oo> 

 temperature and nutrient content. 



In Fig. 13 the total phosphorus-chlorinity relationship of the mean 

 summer bottom data for east Australian coastal stations is shown. It 

 seems clear from this slide that all of the data can be developed by 

 mixing between three primary water masses with distinct total phos- 

 phorus-CP/oo relationship. If we examine the chlorinity-temperature 

 relationship. Fig. 14, three primary water masses can be distinguished. 

 It is possible to identify a New South Wales coastal and an east Tasma- 

 nian coastal water mass on their temperature, chlorinity, total phos- 

 phorus relationships, but the genesis of the third with low temperature 



