SECULAR TRENDS AT EAST AUSTRALIAN COASTAL 

 STATIONS: 1942-1952 



By D. J. RocHFORD 



Marine Biological Laboratory, Cronulla 

 N. S. W., Australia 



I. Introduction 



A phenomenon of extreme importance to the oceanographer work- 

 ing upon fisheries problems is the occurrence of long term trends in 

 hydrological conditions at any region. 



As part of its coastal oceanographical programme the C.S.I.R.O. 

 Fisheries Division has, since 1942, maintained monthly to fortnightly 

 sampling at a number of stations situated some five miles offshore in 

 about 60-70 metres of water. (Fig. 1.) 



At each of these stations samples for temperature, chlorinity, dis- 

 solved O2, pH, inorganic phosphates, organic phosphorus and nitrate 

 nitrogen have been collected at 10-metre depth intervals to 50 metres. 



Within the time limits of this paper it is proposed to demonstrate 

 long term trends in hydrological properties at a number of these sta- 

 tions, and to discuss possible causes of such trends. 



II. Data and Methods 



The data and the methods used in their collection and analysis 

 have been given in Oceanographical Station Lists of the C.S.I.R.O. 

 Vols. 4 and 14. 



In order to simplify the presentation of the trends, the data have 

 been divided into a summer period, October to April inclusive, and 

 a winter period. May to September, on the basis of the annual tem- 

 perature cycle in these waters. During the summer period the water 

 temperature increases or remains at a stationary maximum value, 

 whilst during the winter it decreases or remains stationary at a minimal 

 value. 



The vertical water column at each station has been subdivided into 

 a surface zone, in which sampling at 0, 10 and 20 metres depth are 

 included and a bottom zone in which sampling at 30, 40 and 50 metres 

 depth are included. Surface or bottom values of any hydrological prop- 

 erty are thus the A.M. of the 0, 10 and 20 or the 30, 40 and 50 metre 

 values respectively. 



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