CAXADIAX FlSlli:iiIi:S EXPEDiriOy, lOl.'rlo 481 



banks, with water of low salinity (under o3"/oo) and very low temperature (down to 

 1-5° C.) except at the surface in summer; (2) a Northern Oceanic zone (boreal) along 

 the southern side of the Grand Banks, with water of moderately high salinity (33- 

 35Voo) and moderately low temperature (3°-8° C), which connects with the bott(jm 

 water of the Atlantic; and (3) a Southern Oceanic zone (tropical) farther to the south 

 in the Gulf Stream, with water of high salinity (over SS^oo) and high temperature 

 (10°-25° C). 



The nortliern coastal water owes its low salinity to the fresh water poured in by 

 the rivers and to tlie melting of the icebergs from the north, and its low temix-rature 

 to the cooling effect of the rigorous winters and to floating ice. 



The southern oceanic water is brought up from the tropics by the Gulf Stream. 

 This accounts for its high temperature and salinity. 



The northern oceanic water may be derived in part from a mixture of the two pre- 

 ceding kinds. It is essentially an intermediate water, and in its circulation will, on 

 the one hand, have its temperature and salinity reduced by mixture with the coast 

 water and, on the other hand, have its temperature and salinity increased by mixture 

 with the Gulf Stream water. As it is heavier than they, it will be found beneath them 

 and, particularly toward the south, where it is less extensive, it will permit of their 

 mixing together above it. It is continuous around the south side of the Grand Banks 

 with the open water of the northwestern Atlantic, where is found the Labrador current. 

 The latter doubtless contributes along this course (around the banks) to our northern 

 oceanic water, but for the most part only at some depth and not on the surface. 



To these may be added a fourth, the Southern Coastal zone existing in the 'Mag- 

 dalen bay, to which certain southern coastal forms, e.g., the oyster, are restricted. It 

 is characterized by water of very low salinity and very high summer temeprature. and 

 is therefore similar to the upper layers of the northern coastal water. Its low salinity 

 is due to the large amount of fresh water poured into it by the St. Lawrence and other 

 rivers. Its high summer temperature is due to the same cause and to the shallowness 

 of this part of the gulf. In a negative way the absence of heavy tides contributes 

 to both the low salinity and the high temperature. 



In the Southern Oceanic zone we have at the surface Sagitta eJiflata, S. hipundata, 

 small 8. serratodentata, and Pterosagitta draco. In the depths there are iS^. hexaptera, 

 S. lyra, and KhronUta suhtilis. The extent of this zone in July-August is shown in ' 

 fig. 1. Surface species are indicated by horizontal lines, deep-water species by vertical 

 lines. The further extension landwards of the surface forms in the southwest part 

 of the region and of the deep-water forms in the northern part is noteworthy. This 

 is corroborated by the distribution of small S. serratodentata as shown in fig. G. The 

 nearness of the zone to the continental shelf on the south as compared with the north 

 is also important, indicating a turning of the Gulf Stream to the east. 



On the May-June cruise only the northern part of the area was investigated. 

 Only deep-water species were obtained. The records show that the surface Gulf 

 Stream forms, which were not found, must have been farther out than the deep-water 

 forms, and that both were at that time farther from the continental shelf than in July- 

 August. 



There is the question as to what part the Gulf Stream plays in mixing with either 

 the coastal or the boreal oceanic waters. The sharp inner mar^ns of the areas of 

 distribution of most of the Gulf Stream species is against the view that the Gulf 

 Stream by any back eddies remains as a distinguishable part of our waters. In the 

 upper layers the most abundant species (S. enflata) decreases in abundance toward the 

 inner side of the stream, and may even be lacking, showing that this inner margin is 

 mixed water going with the stream. A solitary individual was found inside the 

 stream, far in on the Scotian bank off Halifax. Its ability to survive in the water of 

 interrnediate salinity and temperature indicates that there can be little water of Gulf 

 Stream origin in the intermediate boreal oceanic zone, otherwise individuals of this 

 species would have been obtained at some of the nine intervening stations. S. serra- 



