PHYSICAL CHEMISTRY OF THE DEEP OCEAN ENVIRONMENT 



by 



R. A. Home 

 Arthur D. Little, Inc., Cambridge, Massachusetts 02140 



INTRODUCTION 



Naval operations occur above, on, and in a medium which is easily one of 

 the most complex and ill-understood substances known to man - sea water. The 

 concurrence of relatively low temperatures (-1 to +4°C) and high hydrostatic 

 pressures (up to about 15,000 lbs/in"^) in the ocean depths further complicates 

 the situation and makes the deep ocean perhaps the most extraordinary environ- 

 ment in our universe. This paper reviews the results of some simple experi- 

 ments which we have performed in our laboratory over recent years in a 

 simulated deep ocean environment (Fig 1) , 



THE STRUCTURE OF SEA WATER* 



There are several theories of the structure of water. There is also a 

 minority opinion which insists that water has no structure at all. But at 

 the present time in the United States the most popular model for the state of 

 affairs in pure water appears to be that of Frank and Wen (1957), who proposed 

 that water consists of transient "clusters" of more-or-less ordered, H-bonded 

 water (sometimes, perhaps unfortunately, referred to as "ice-like") swimming 

 in and in equilibrium with "free", monomeric water (Fig 2). Nemethy and 

 Scheraga (1962) have calculated the size and concentration of these clusters 

 as a function of temperature. The application of pressure or the addition 

 of an electrolyte also affect the extent of water structure. 



Roughly speaking sea water is an 0.5M NaCl solution with a trace of MgS04. 

 The addition of electrolytes further complicates the structure of the system. 

 If an ion, such as Na"*", is placed in water the coulombic attraction between 

 the ion's charge and the partial charges of opposite sign of the water 

 dipoles results in a crowding or "electrostriction" of the water molecules 

 about the ion and an overall volume decrease (Fig 3). If the spacial dis- 

 tribution of water molecules in the first solvation sheath of an ion is sym- 

 metrical, such as Na(H„0), , the ion will be a structure -maker and will tend 

 to make the surrounding water more ordered as reflected in an increase in 



* 



For a more detailed discussion of the physical chemistry and structure 



of sea water see R. A. Home, J. Water Resources Res ., in press, 1965. 



223 



