1. N'^/N^"* natural variations may provide valuable insight into the 

 marine nitrogen cycle. 



2. C^^IO^ ratios can suggest the kind of processes that put organic 

 matter into marine sediments now and especially during the last two 

 ice ages. These ratios can also help to demonstrate that different types 

 of photosynthesis (at least two) are going on. 



3. O'^/O^^ data on dissolved O2 can help explain the oxygen cycle in 

 the sea. 



Radionuclides in seawater are characterized by their extremely high 

 dilutions, and when higher concentrations are encountered, it should 

 always be suspected (and frequently is demonstrated) that life processes 

 have been involved. Some of the most spectacular examples of trace- 

 element accumulations have been demonstrated by following the uptake 

 of radionuclides of certain metals by living systems. For example, the 

 living interfacial region between seawater and certain brown algae ac- 

 cumulates concentrations of both natural polonium and artificial pluton- 

 ium by orders of magnitude above ambient water; polonium-210 by 

 90,000-fold, and plutonium-239 by 3,000-fold (Wong et al. 1972). (See 

 p. 65) 



In the case of polonium, additional buildup occurs in specific organs 

 of animals high in the tropic level. An extreme case is the 2.2 x 10^- 

 fold buildup (over seawater) of polonium-210 in one organ of a tuna fish 

 (Folsomet al. 1972). 



Life processes may afford powerful tools for understanding the dis- 

 tributions certain trace elements in the ocean. Even information on 

 major currents, and also information concerning mixing rates, can come 

 from chemical and radiochemical inspections of concentration buildup 

 in living systems. These often are most conveniently followed through 

 their radioactive properties (Folsom et al. 1968, 1970, Hodge et al. 

 1972). 



References 



Anikouchine, W.A., 1967, Dissolved chemical substances in compact- 

 ing marine sediment, J. Geophys. Res. 72(2), 505-509. 



Apollonio, S., 1961, The chlorophyll content of Arctic sea-ice, Arctic 

 14, 197-200. 



Apollonio, S., 1965, Chlorophyll in Arctic sea ice, Arctic 18, 118-122. 



Assur, A., 1958, Composition of sea ice and its tensile strength, in: 

 HAS-HRC. publ. 698, Arctic Sea Ice, pp. 106-138. 



67 



