Papers in Marine Biology and Oceanography, Suppl. to vol. 3 of Deep-Sea Research, pp. 12-14. 



Dissolved organic matter in the sea* 



By Mary Alys PLUNKEXTf and Norris W. Rakestraw 

 Scripps Institution of Oceanography, La Jolla 



We havb little real information about the nature and amount of dissolved organic 

 matter in the sea, especially in deep water. Among the few recorded determinations 

 of dissolved organic carbon the limited number made by Krogh (1934) have seemed 

 to us to be perhaps the most reliable. We are but slightly better off in our knowledge 

 about dissolved organic nitrogen. In addition to a few determinations made by 

 Krogh (1934), some results reported by von Brand and Rakestraw (1941), using 

 the same methods, may perhaps be regarded with confidence. On the basis of these 

 limited data it would appear that the concentration of dissolved organic matter in 

 the open sea is fairly constant at about 5 mg per litre. 



Krogh's work, just referred to, was carried out with the extreme care and attention 

 to detail which was characteristic of all his microchemical analyses, but because of 

 its limited extent (his carbon results were obtained from six samples collected from a 

 single station) it has long seemed to us highly necessary to corroborate and extend it. 

 His methods have never been used again until very recently, when Kay (1954) used a 

 modification to obtain results in the shallow waters of the Kielerbucht. 



Accordingly, in the spring of 1953, we assembled apparatus essentially similar to 

 Krogh's and carried out the analyses shown in Table I, on samples from three stations 

 off the coast of Southern and Lower California. The results are shown graphically 

 in Figure 1, along with curves for temperature and for oxygen at Station 1 10.70. Two 

 important conclusions emerge: 



The general level of concentration of dissolved organic carbon which Krogh 

 reported (two to three milligrams per litre) was confirmed at these stations. However, 

 instead of being homogeneously distributed it is definitely less at intermediate depths. 

 The significance of this fact is not clear; the data are too limited to conclude that it is 

 related to the location of the oxygen-poor layer. In any event, it throws some doubt 

 upon certain of Krogh's conclusions. 



In the fall of 1953, samples were obtained from two stations on the " Transpac " 

 expedition in the north-western Pacific. The results from these are tabulated in Table II 

 and graphically shown in Fig. 1. It will be seen that these are rather more irregular 

 in the upper layers and that the general level of concentration is distinctly lower than 

 at the earlier stations. All samples except that from 506 m at Station T-P 99 were 

 analyzed in duplicate. The samples from these two stations were frozen immediately 

 and kept in this condition until analyzed several months later. While this introduces 

 some uncertainty it nevertheless seems unlikely that significant oxidation took place 

 in the meantime. Deep-sea water has been preserved for much longer times and at 

 higher temperatures without appreciable consumption of oxygen (Rakestraw 1947). 

 Keys, Christensen and Krogh (1935) have also shown that the dissolved organic 



* Contribution of the Scripps Institution of Oceanography, New Series No. 802. 

 t Present address: Vassar College, Poughkeepsie, New York. 



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