THREE GENERAL STATIC CONDITIONS 



There are three general static conditions revealed by vertical sec- 

 tions of the ocean arranged in accordance with a grouping of rela- 

 tive positions of the isosteric surfaces, and with reference strictly to 

 the vertical. (1) The water may be found to have the same density 

 throughout its column when compression is disregarded — i. e., 

 homogeneous as to temperature and salinity. The specific volume 

 in such cases, due to pressure, will necessarily decrease downward, 

 thus it follows that the isosteric surfaces will be arranged solely in 

 dependence with pressure. Such conditions may prevail at the end 

 of winter when vertical convection has attained a maximum in- 

 fluence, or in the cases of strong winds which mix the surface layers, 

 sometimes to a considerable depth. Such a water mass is homo- 

 thermal and homohaline, and thus presents a consequent neutral 



Fig. 1. — A type of stratified water mass found over the Grand Banks south of Newfoundland. 

 The boundary of discontinuity between the two distinct layers is shown by the closely spaced 

 parallel lines 



equilibrium verticallj". (2) When one homogeneous mass of water 

 lies over another, then the water is in layers and is said to be stratified; 

 it will be found that there are few isosteric surfaces in each layer 

 compared \vith the number between two adjacent layers. An ex- 

 ample of stratification often occurs in the column lying over the 

 Grand Banks, when a cover of heavy water from the slopes is spread 

 over the bottom; above this, and extending to the surface, is a layer 

 of lighter, coastal water, maintained more or less homogeneous by 

 the turbulent effect of the winds. (3) But the most common dis- 

 tribution in the sea is where the density increases proportionally 

 and more or less regularly with the depth. The water in such cases 

 is characterized by numerous isosteric surfaces lying in greater 

 abundance at those levels where transitions of density occur; and 

 this condition is termed stable. A direct measure of the stability of 

 any water column is to be found in the number of isosteric surfaces 

 in excess of that contained in homogeneous water per unit increase 

 71321— 26t 2 



