282 E- Steemann Nielsen 



found by using light and dark bottle experiments of long duration in tropical oceanic 

 water must be considered almost entirely due to the increased bacterial activities. 

 They do not tell anything about the rate of respiration under natural conditions in 

 the sea. The smaller oxygen consumption in the light bottles as compared with the 

 dark bottles (no oxygen production is ever observed) might of course be due to 

 photosynthesis. A reduction of the bacterial respiration directly or indirectly due to 

 light can, however, as well explain the fact. Originally (Steemann Nielsen, 1952) 

 the idea of a direct bactericidal effect of sunlight was suggested. In the 1954 article 

 it was, however, suggested instead that antibiotics produced by the plankton algae 

 in light reduce the bacterial activity. It was shown first by Pratt et al. (1944) that 

 antibiotics are produced by plankton algae. 



Ryther (1954) suggests that the disagreement between the light and dark bottle technique and the 

 14C technique in tropical oceanic water is possibly due to (1) the supposition that plankton algae 

 nearly exclusively respire the newly formed products of their photosynthesis and (2) the supposition 

 that the rate of algae respiration is about equal to the photosynthetic rate in these waters. 



Experiments presented by Ryther in order to give his suggestions an experimental background 

 have now been repeated in this laboratory (Steemann Nielsen and Al Kholy, in press). No corro- 

 boration of his results could, however, be obtained. These seem obviously to be the result of an un- 

 satisfactory experimental technique. It is further shown that his suggestions would lead to some 

 fantastic and quite unrealistic assumptions of what is going on in the oceans. 



Ryther's suggestion that the algae nearly exclusively respire the newly formed products of their 

 photosynthesis seems to be contradicted by the work of the Berkeley Group. According to Calvin 

 and Massini (1952), algae in light respire, to a slight degree only, newly formed products. There is, 

 however, as will be shown in a subsequent paper, really a connection between photosynthesis and 

 respiration, although not of the extent supposed by Ryther. It has some influence on the measure- 

 ment of the organic production by the 14C technique. Under very unfortunate conditions in nature 

 the results from using this technique may possibly be up to about 15 % too low. Normally, however, 

 the influence is negligible. 



DISSOLVED ORGANIC MATTER IN SEA WATER AND ITS DECOMPOSITION 



One of the most amazing statements about the sea is that by far the largest amount 

 of the organic matter existing anywhere on this globe is found dissolved in the oceans. 

 According to Keys, Christensen and Krogh (1935) the dissolved organic matter in 

 water from all depths of the oceans corresponds to about 1 •2-2-0 mg C and 0-2 mg N 

 per Utre. About 15 kg organic matter is thus found below every m- ocean surface. 

 In comparison, the average annual net production per m^ by the phytoplankton is 

 only about 1% of this (Steemann Nielsen, 1952). 



Most of the organic matter produced by the plankton algae is presumably used 

 rather soon for respiration in some organism or other. The magnitude of animal life 

 in the sea could otherwise scarcely be explained. The organic matter dissolved in 

 ocean water must therefore on an average be rather old, presumably several thousand 

 years. 



The nature of the organic matter in question has not yet been investigated. If the 

 water is in situ, an extremely slow decomposition of the organic matter takes place. 

 About 25-50 % is, however, readily decomposed by bacteria, if the water is stored in 

 glass bottles (Keys, Christensen and Krogh, 1935; Waksman and Carey, 1935). 



It has been shown by ZoBell and Anderson (1936) that the presence of solid 

 surfaces is the factor which makes the bacterial decomposition of dissolved organic 

 matter in ocean water possible. Small bottles in which the ratio — inner surface of 



