104
E. D. S. CORNER AND ANTHONY 0 . DAVIES
B. Physico-chemical reactions
Most of the fixcd nitrogen in thc sca is iiivolvcd in a continuous
cycle in which plankton organisms play an important part. The
biological processes involved arc tlic subjects of later sections, but it is
worth noting a t this point that interchange between the inorganic
forms of nitrogen may also result from physico-chemical reactions.
Thus, Vaccaro (1962) found that the oxidation of ammonia to nitrite
in aerated sea water kcpt in the dark occurred within 48 hours. The
rate of oxidation was higher in water enriched with ammonia or to
which mixed plankton had been added, so that whereas a ten-fold
increase in nitrite took about 2 days in an unenriched sample, it required
only 0.52 days in one that was enriched. Although the possibility that
this oxidation had been caused by bacteria could not be excluded, the
numbers of microorganisms present were thought t o be too small to
explain the relatively fast reaction.
The photo-oxidation of ammonia in sea water has also been described (e.g. Rakestraw and Hollaender, 1936), but Hamilton (1964)
was unable t o confirm this finding. The absence of a catalytic surface
from the water used in Hamilton’s experiments may have caused the
difference, but he concluded that, even with catalysis, photo-oxidation
was unlikely t o play an important role in the marine nitrogen cycle.
On the other hand, he found that photo-reduction of nitrate t o nitrite
took place in sea water, 0.60 pg-atoms NO;-N/l appearing in a sample
containing 15 pg-atoms NO;-N/1 after one day’s exposure t o sunlight.
C. Organic nitrogen
Organicslly-bound nitrogen, present in particulate form (e.g. phytoplankton or zooplankton) is eventually released into the sea by processes such as excretion by zooplankton, and the decomposition of
marine organisms in general. The most important group of dissolved
nitrogen-containing organic compounds are the amino-acids and
Degens et al. (1964) identified 17 of these in the Pacific Ocean off
California. Concentrations of the individual acids in the surface waters
ranged between 0.7 and 12-Opg/l and increased slightly with depth. The
spectrum of acids varied little throughout the water column, the predominant members being serine (29.5y0), glycine ( 16-4y0), ornithine
(14.5%) and a-alanine (10.7%). Chau and Riley (1966) found somewhat
higher concentrations in the Irish Sea (individual values lying in the
range 2 to 16 pg/l), and some differences in the acid spectrum were also
apparent. Thus, Chau and Riley did not detect ornithine or histidine
in their samples, but did find mcthionine which was not reported by
Degens el al (1964).
E. D. S. CORNER AND ANTHONY 0 . DAVIES
B. Physico-chemical reactions
Most of the fixcd nitrogen in thc sca is iiivolvcd in a continuous
cycle in which plankton organisms play an important part. The
biological processes involved arc tlic subjects of later sections, but it is
worth noting a t this point that interchange between the inorganic
forms of nitrogen may also result from physico-chemical reactions.
Thus, Vaccaro (1962) found that the oxidation of ammonia to nitrite
in aerated sea water kcpt in the dark occurred within 48 hours. The
rate of oxidation was higher in water enriched with ammonia or to
which mixed plankton had been added, so that whereas a ten-fold
increase in nitrite took about 2 days in an unenriched sample, it required
only 0.52 days in one that was enriched. Although the possibility that
this oxidation had been caused by bacteria could not be excluded, the
numbers of microorganisms present were thought t o be too small to
explain the relatively fast reaction.
The photo-oxidation of ammonia in sea water has also been described (e.g. Rakestraw and Hollaender, 1936), but Hamilton (1964)
was unable t o confirm this finding. The absence of a catalytic surface
from the water used in Hamilton’s experiments may have caused the
difference, but he concluded that, even with catalysis, photo-oxidation
was unlikely t o play an important role in the marine nitrogen cycle.
On the other hand, he found that photo-reduction of nitrate t o nitrite
took place in sea water, 0.60 pg-atoms NO;-N/l appearing in a sample
containing 15 pg-atoms NO;-N/1 after one day’s exposure t o sunlight.
C. Organic nitrogen
Organicslly-bound nitrogen, present in particulate form (e.g. phytoplankton or zooplankton) is eventually released into the sea by processes such as excretion by zooplankton, and the decomposition of
marine organisms in general. The most important group of dissolved
nitrogen-containing organic compounds are the amino-acids and
Degens et al. (1964) identified 17 of these in the Pacific Ocean off
California. Concentrations of the individual acids in the surface waters
ranged between 0.7 and 12-Opg/l and increased slightly with depth. The
spectrum of acids varied little throughout the water column, the predominant members being serine (29.5y0), glycine ( 16-4y0), ornithine
(14.5%) and a-alanine (10.7%). Chau and Riley (1966) found somewhat
higher concentrations in the Irish Sea (individual values lying in the
range 2 to 16 pg/l), and some differences in the acid spectrum were also
apparent. Thus, Chau and Riley did not detect ornithine or histidine
in their samples, but did find mcthionine which was not reported by
Degens el al (1964).