An Estuarine Model of the Sub-Arctic 

 Pacific Ocean* 



J. p. TULLY and F. G. BARBER 



Fisheries Research Board of Canada, Nanaimo, British Columbia 



Features of an Estuarinef System 



THE basic requirement for the establishment of an estuarine 

 system in any region is the presence of a supply of fresh water 

 which exceeds the losses by evaporation or freezing. 



Tully (1958) considered such conditions in coastal embayments 

 (Fig. 1). He observed that the fresh water moved persistently 

 outward from the embayment over the surface, entraining sea 

 water from below to form a transition zonel in which there is a 

 halocline. The upper part of the halocline is usually isohaline, 

 because of mixing. It is called the upper zone, although it is 

 considered to be part of the halocline. Both of these zones become 

 progressively more saline along the path of outward flow, unless 

 they are continually refreshed. Below the halocline is a lower zone 

 in which the vertical and horizontal salinity gradients are small. 

 Here, the motion is inward toward the source region. 



Transport and Entroinment 



From his studies Tully concluded that fresh water entering the 

 surface accumulates locally over the denser (salt) sea water, until 

 a surface pressure gradient is established sufficient to move the 



* Previously published under title "An Estuarine Analogy in the Sub-Arctic 

 Pacific Ocean," in the Journal of the Fisheries Research Board of Canada, 17, 

 91-112 (1960). 



t The term "estuarine" is used in the same sense as Ketchum (1951) and Tully 

 (1958) to refer to a region in which sea water is measurably diluted with fresh water. 



t Tully (1949) introduced the term "zone" to designate a layer of consistent 

 structure or properties in the sea. "Structure" denotes the disposition of sea water 

 properties in a region, primarily in the vertical sense. 



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