The Stratospheric Circulation 



681 



bottom current.'''' This sub-arctic bottom water comes mainly from two source 

 regions: 



(1) from the north-western Labrador Basin where the colder bottom water with a 

 temperature of less than 1-2°C is formed (Wattenberg, 1938; Smith, Soule 

 and MosBY, 1937) and 



(2) from a region of formation extending all along the 3000 m depth of the south- 

 east Greenland continental slope into the inner angle of a bay; this source was 

 already referred to by Nansen (1912). 



From these two main centres the sub-Arctic bottom water spreads out towards more 

 southern regions. Influenced by the bottom topography, this spread, however, keeps 

 close to the western side along the foot of the continental shelf off the Labrador coast 

 as far as 50° N. A Labrador submarine rise here prevents its further southward spread. 

 The second centre of formation in the Irminger Sea is obviously less productive; since 

 already in about 55° N. this water type has mixed with warmer waters and has lost its 

 characteristic cold temperature. 



A small Arctic bottom current also occurs in the Pacific; cold bottom water in 

 moderate amounts penetrates over the boundary rises of the Okhotsk Sea into the 

 open ocean. However, this is likewise only of sub-Arctic origin and its productiveness 

 remains small. 



The ratio [exchange: velocity] can also be derived from the analysis of meridionally 

 oriented temperature and salinity sections (see Pt. I, p. 153) and stream lines of the 

 water transport can be constructed in order to obtain a representation of the current 

 course in its core (Fig. 321). The stream lines follow closely the bottom topography. 

 Over the crests of the ridges values of the above ratio lie between 2 and 3, in the depres- 

 sion between 5 and 6. For the same values of exchange the current intensity shows a 

 proportion of about 2-5:1. Wattenberg (1935) by keeping track of chemical processes 

 at the sea bottom and in the layers just above it found an exchange of about 

 4 cm~^ g sec"^. With this value, the velocity of the bottom current on the western side 



Brasilian Basin 



9000 10000 



Guyana-Basin 



14 000 15000 16000 



3000- 



D 5000 



40» S 3 



Fig. 321. Stream lines and values of the ratio between exchange and velocity in the core of 



the Antarctic Bottom Current in the Atlantic Ocean (evaluated from the temperature and 



salinity distribution in a longitudinal section of the Western Atlantic Trough). 



