3 
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 
ae 
“ot 
mer 
GRAND BANKS 
CAPE RACE TO TAIL. 
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 vertically. (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 with 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—26}——2 
