Part 1 



Chapter I 



The Ocean 



A. THE HORIZONTAL EXTENT AND THE STRUCTURE OF 



THE OCEAN 



1. Introduction, Vertical Structure of the Total Earth 



The total Earth system can be subdivided into three parts. The solid rock forms the 

 Lithosphere and is the solid core on which the other two layers rest. If the rock layer 

 was freed from all its characteristic irregularities it would be in the geodetic sense 

 "flat" (a simple rotational ellipsoid). The water forming the layer next in density, the 

 Hydrosphere, would cover as a single ocean the entire surface of the Earth. This is not 

 the case. The lithosphere is very uneven, and large depressions and elevations disturb 

 its regular shape. There is not suflScient water to cover all these irregularities entirely, 

 but it fills the depressions between the continental plateaus and leaves uncovered the 

 upper parts as continents. This outlines the form of the lithosphere and gives the Earth 

 its characteristic appearance. 



The third major part of the total Earth, the Atmosphere, lies as a gaseous envelope 

 above the hydrosphere and touches the lithosphere only over the continents. It should 

 be remembered that this is in fact exceptional, occurring over little more than a quarter 

 of the surface of the Earth. Normally, the lithosphere, the hydrosphere and the at- 

 mosphere are arranged one above the other with the diff'erent strata of each layer 

 arranged in order of density by the force of gravity. This is a necessary condition for 

 the static stability of the three parts of the total Earth, 



The transition from one layer to another is finite and rather abrupt. The water 

 masses of the ocean are bounded by two main surfaces (Fig. 1, Defant, 1940). 



(a) The interface between the lithosphere and the hydrosphere is the sea bottom: 

 across it there is a density change from approximately 2-5 to 1 -06 g/cm^. The investiga- 

 tion of the morphology of the sea bottom is one of the main tasks of oceanography. 



{b) The interface between the ocean and the atmosphere is the sea surface; here the 

 density change is from about 1-03 to 0-0013 g/cm'^. All phenomena affecting both, 

 ocean as well as atmosphere, take their origin from this surface. An accurate knowledge 

 of its form is of the greatest importance to oceanography. 



The water masses of the ocean lie entirely within these surfaces, forming a single con- 

 tinuous mass. All the energy absorbed by the ocean or given off by it must pass through 

 these boundaries, and this energy entering or leaving the ocean is the basic cause of all 

 the phenomena and changes of state in the water mass. 



2. The Horizontal Extent of the Ocean and its Boundaries 



The incomplete covering of the surface of the Earth by the ocean separates it into 



1 



