618 CYCLES OF ORGANIC AND INORGANIC SUBSTANCES 



Biological Consequences 



It is likely to be difficult for any kind of suspended matter with 

 compressibility similar to water to remain long in a stratum of 

 water in neutral adiabatic equilibrium. Such matter will tend to 

 fall to the discontinuity below or to rise to the one above. This 

 means that water masses in neutral adiabatic equilibrium may be 

 very transparent and would carry no food for anything to live on. 

 They may be biological deserts. 



At the discontinuities in strong contrast, some of the "rain of 

 food from above" will tend to come to rest. The descent of boluses 

 from the more productive upper layers and their lateral spread at 

 the end of their journey should also intercalate suspended matter 

 into the "zones of conflict" which may be identified with the dis- 

 continuity layers. Thus both by vertical and horizontal processes, 

 food is likely to be introduced and held at the discontinuities. 

 It is here that one might expect all deep-sea living organisms to 

 m.ake their living. 



An obser\'er descending in a bathyscaphe would pass through a 

 succession of wide transparent, almost azoic layers and, inter- 

 calated with these, a succession of thin, relatively turbid water 

 layers rich in animals living on the food chain initiated on the basis 

 of the suspended matter. Bernard (1955), indeed, observed some- 

 thing very like this. 



It is more than likely that each discontinuity may provide a 

 rather difi^erent biological habitat from the others. It would not be 

 surprising to learn that an observer in a bathyscaphe could identify 

 biological indicator species for each main discontinuity. Many 

 deep-sea pelagic animals are weakly calcified and ill adapted for 

 strong swimming. Many may well spend their whole lives and 

 their offspring may be maintained at one of the discontinuities, 

 never to visit those abo\'e and below. The inter\-ening deserts may 

 curb ambition to travel. 



On the Age of Water Masses 



It seems that the time lapse between birth of a bolus on the 

 ridges between Greenland and Faeroe and its arri^'al on its ap- 

 propriate density platform may be a matter only of months. The 



