302 EMERY, ORR, RITTENBERG 



these are typical of river waters, the average, 0.32 mg/L, w^ould cor- 

 respond to 8.4 X 10^ tons of dissolved organic nitrogen contributed by 

 rivers to the ocean each year. The ammonia-nitrogen of river water is 

 very uncertain, but may be the same order of magnitude as nitrate- 

 nitrogen (Conway, 1942, Note to Table 5), or about 5.5 x 10^ tons 

 per year. Summing the nitrate, organic, and ammonia-nitrogen, the total 

 dissolved nitrogen transported to the ocean each year by rivers is 19 x 10^ 

 tons. 



Fixed nitrogen is also contributed directly to the ocean in rain. Much 

 lower concentrations of total nitrogen appear to be present in rain water 

 falling on oceanic islands than on continental areas (Clarke, 1924, p. 55). 

 The average of the scanty measurements from islands is 0.20 mg/L 

 (Eriksson, 1952). If this value is a good average for the 297 x 10^^ L 

 of rain water falling on the ocean, the total contribution of fixed nitrogen 

 by rain is 59 x 10*^ tons annually. Only a negligible percentage of the 

 fixed nitrogen in the rain can have been derived directly from the ocean 

 because of the low concentration in the surface sea water (Hutchinson, 

 1944; Eriksson, 1952). On the basis of these estimates the total nitrogen 

 contributed by rivers and rain is 78 x lO'' tons, or only 0.8% of the 

 annual use by phytoplankton. The only remaining source for new growth 

 is nitrogen regenerated during the life and after the death of the plants, 

 and this must be the chief source. Riley (1951) estimated that 90% of 

 the organic matter annually produced is regenerated in the upper 200 m. 



Organic debris falling from the surface serves as food for many 

 scavengers living in the water and on the bottom so that little debris 

 becomes buried in an unaltered condition. The fact that some organic 

 matter, though altered, escapes complete oxidation during burial is 

 shown by its presence deep in the sediments and in sedimentary rocks. 

 Trask (1939) reported that nearshore sediments contain about 2.5% 

 organic matter and pelagic sediments about 1%, and Kuenen (1941) 

 estimated the average speed of oceanic sedimentation to be 1 cm of solid 

 material in 6000 years. Assuming that nearshore sediments are deposited 

 40 times as fast as pelagic ones (Trask, 1939), using an average ratio 

 of nitrogen to organic matter in sediments of 0.05, weighting the near- 

 shore and pelagic sediments by area (74,000,000 km^ for nearshore sedi- 

 ments and 287,000,000 km^ for pelagic sediments), and subtracting 50% 

 for losses of nitrogen during diagenesis (Emery and Rittenberg, 1952), 

 we find that about 8.6 x 10® tons of nitrogen is permanently deposited 

 annually. This is an order of magnitude less than the 78 x 10® tons of 

 annual contribution by rivers and rain. The lack of correspondence of 

 these figures indicates that other losses such as denitrification must be 



