Microbiomass and Detritus in the Upper 50 m of the Arabian Sea
237
but this relationship is not seen off the African coast. The distribution of N03 - -N and
SiOj--Si is similar to that of P01--Po
III. Hydrography
From the hydrographical data of the expedition DOING (1967) calculated higher
vertical velocities between 100 and 200 m south of Socotra, in the African waters near
the Equator and in the northern region off the Indian coast. These areas are characterized
by a slight uplift of the pycnocline combined with lower values of stability. Mixing is
higher in areas of reduced stability, which improves the supply of nutrients. We suggest
that this is the reason for the higher amounts of plankton in the northern Indian waters
and in the equatorial region near the African coast. Negative effects of mixing because of
bad light conditions did not seem to be effective during the time of the investigations. This
holds even for the Indian coastal waters, where according to DOING and KOSKE (1967)
stability in general is lower as compared with the coast of Africa. But winds were weaker
off the Indian coast (Beaufort 4 from NW was characteristic, while Beaufort 6 from NE
prevailed off the African coast), so that this may offset the effect of lower stability.
IV. Discussion
HAGMEIER (1964 a) and NELLEN (1967) reported values of microbiomass for the
same latitude of the tropical Atlantic. Our lowest concentrations correspond to the
results for the open tropical Atlantic, while these authors found values as high as most
of our data only in the region of the African shelf. HAGMEIER (1964 b) gives values for
the eastern Indian Ocean, which are comparable to our results.
It seems that in tropical and subtropical waters the amounts of microbiomass and
detritus are similar (HAGMEIER 1964 a and b; NELLEN, 1967, our data). The situation
is different in the more northern parts of the ocean, where detritus seems to prevail
(KREY,1964).
Certainly the quantity of microbiomass will be much higher in some parts of the
Arabian Sea when upwelling occurs. Our results show that even during the time of the
NE monsoon the amount of plankton is not as low as one would expect. As R YrHER
and MENZEL (1965) point out, one can characterize the Arabian Sea by "the high levels
of nutrients and their proximity to the surface", and therefore increased mixing will
lead to higher productivity.
237
but this relationship is not seen off the African coast. The distribution of N03 - -N and
SiOj--Si is similar to that of P01--Po
III. Hydrography
From the hydrographical data of the expedition DOING (1967) calculated higher
vertical velocities between 100 and 200 m south of Socotra, in the African waters near
the Equator and in the northern region off the Indian coast. These areas are characterized
by a slight uplift of the pycnocline combined with lower values of stability. Mixing is
higher in areas of reduced stability, which improves the supply of nutrients. We suggest
that this is the reason for the higher amounts of plankton in the northern Indian waters
and in the equatorial region near the African coast. Negative effects of mixing because of
bad light conditions did not seem to be effective during the time of the investigations. This
holds even for the Indian coastal waters, where according to DOING and KOSKE (1967)
stability in general is lower as compared with the coast of Africa. But winds were weaker
off the Indian coast (Beaufort 4 from NW was characteristic, while Beaufort 6 from NE
prevailed off the African coast), so that this may offset the effect of lower stability.
IV. Discussion
HAGMEIER (1964 a) and NELLEN (1967) reported values of microbiomass for the
same latitude of the tropical Atlantic. Our lowest concentrations correspond to the
results for the open tropical Atlantic, while these authors found values as high as most
of our data only in the region of the African shelf. HAGMEIER (1964 b) gives values for
the eastern Indian Ocean, which are comparable to our results.
It seems that in tropical and subtropical waters the amounts of microbiomass and
detritus are similar (HAGMEIER 1964 a and b; NELLEN, 1967, our data). The situation
is different in the more northern parts of the ocean, where detritus seems to prevail
(KREY,1964).
Certainly the quantity of microbiomass will be much higher in some parts of the
Arabian Sea when upwelling occurs. Our results show that even during the time of the
NE monsoon the amount of plankton is not as low as one would expect. As R YrHER
and MENZEL (1965) point out, one can characterize the Arabian Sea by "the high levels
of nutrients and their proximity to the surface", and therefore increased mixing will
lead to higher productivity.