46
R. I. CURRIE, A. E. FISHER and P. M. HARGREAVES:
are clearly shown on all except the first section which lay somewhat west of the main
part of the upwelling region and was probably partly under the influence of events
within the Gulf of Aden. The highest values occurred consistently close to the coast,
falling to levels of about 1.0 mg-at m -3 offshore.
Chlorophyll a values also tended to be high close to the coast and fall rather more
rapidly seawards than the P04 3 --P did; the zooplankton biomass follows a similar
pattern. Neither chlorophyll a nor zooplankton show an exceptional abundance. Only
in one solitary bloom of Gonyaulax polyhedra were cell numbers of the order of 10 7 per I
encountered. More generally counts ranged from 10 5 per I inshore to 10 3 per I offshore.
Streptotheca sp. was one of the most abundant diatoms of the coastal belt, along with
other chain-forming species of Chaetoceros and Fragillaria.
These facts again seem to point to the very active state of the circulation, but how
far they represent "steady state" levels during the upwelling period remains to be seen.
In so far as they can be compared, the repetitions of section 3 may be considered
to present the progression of the development of upwelling in the region of the Kuria
Muria Islands. Rather than a continuous progression, however, they must be looked
upon as representative phases of this development.
The contrast is most marked in the levels of dissolved inorganic P04 3 --P, but in the
algal stock and zooplankton biomass, also, a significantly greater amount was found at
the time of upwelling than in the premonsoon period. The "Anton Bruun" observations
in October 1963 include measurements of PO/--P and chlorophyll a. These have not
been plotted, since only three stations were sited within 200 miles of the coast, but the
values for these stations are shown in Table I and will be seen to differ little from the
March 1964 values of "Discovery".
Table 1. Average values of dissolved inorganic phosphate (mg-at m- 3 ) and chlorophyll a (mg m- 3 )
for the 0-100 m layer from" Anton Bruun" stations in October, 1963
Station
Distance offshore in miles
PO/- -P
Chlorophyll a
175
36
0.68
0.41
2. Somali Coast
a) Hydrographic Observations
176
104
0.75
0.30
177
171
0.51
0.69
The RRS "Discovery" and RV "Argo" conducted a survey of the Somali Current in
August-September, 1964 and the pattern of stations (Royal Society, 1965) was set out
in such a way as to make it possible to examine the upwelling area in the vicinity of Ras
Hafun, reported by PUFF (1890). WARREN, SrOMMEL and SWALLOW (1966) and SWALLOW
and BRUCE (1966) have described the water masses observed and the currents measured
on these surveys.
Fig. 10 shows the distribution of surface temperature in the area where upwelling
water was present and it is clear that the latter corresponds closely in distribution with
that described by PuFF (1890) in the Ras Hafun area; PuFF, however, also describes the
R. I. CURRIE, A. E. FISHER and P. M. HARGREAVES:
are clearly shown on all except the first section which lay somewhat west of the main
part of the upwelling region and was probably partly under the influence of events
within the Gulf of Aden. The highest values occurred consistently close to the coast,
falling to levels of about 1.0 mg-at m -3 offshore.
Chlorophyll a values also tended to be high close to the coast and fall rather more
rapidly seawards than the P04 3 --P did; the zooplankton biomass follows a similar
pattern. Neither chlorophyll a nor zooplankton show an exceptional abundance. Only
in one solitary bloom of Gonyaulax polyhedra were cell numbers of the order of 10 7 per I
encountered. More generally counts ranged from 10 5 per I inshore to 10 3 per I offshore.
Streptotheca sp. was one of the most abundant diatoms of the coastal belt, along with
other chain-forming species of Chaetoceros and Fragillaria.
These facts again seem to point to the very active state of the circulation, but how
far they represent "steady state" levels during the upwelling period remains to be seen.
In so far as they can be compared, the repetitions of section 3 may be considered
to present the progression of the development of upwelling in the region of the Kuria
Muria Islands. Rather than a continuous progression, however, they must be looked
upon as representative phases of this development.
The contrast is most marked in the levels of dissolved inorganic P04 3 --P, but in the
algal stock and zooplankton biomass, also, a significantly greater amount was found at
the time of upwelling than in the premonsoon period. The "Anton Bruun" observations
in October 1963 include measurements of PO/--P and chlorophyll a. These have not
been plotted, since only three stations were sited within 200 miles of the coast, but the
values for these stations are shown in Table I and will be seen to differ little from the
March 1964 values of "Discovery".
Table 1. Average values of dissolved inorganic phosphate (mg-at m- 3 ) and chlorophyll a (mg m- 3 )
for the 0-100 m layer from" Anton Bruun" stations in October, 1963
Station
Distance offshore in miles
PO/- -P
Chlorophyll a
175
36
0.68
0.41
2. Somali Coast
a) Hydrographic Observations
176
104
0.75
0.30
177
171
0.51
0.69
The RRS "Discovery" and RV "Argo" conducted a survey of the Somali Current in
August-September, 1964 and the pattern of stations (Royal Society, 1965) was set out
in such a way as to make it possible to examine the upwelling area in the vicinity of Ras
Hafun, reported by PUFF (1890). WARREN, SrOMMEL and SWALLOW (1966) and SWALLOW
and BRUCE (1966) have described the water masses observed and the currents measured
on these surveys.
Fig. 10 shows the distribution of surface temperature in the area where upwelling
water was present and it is clear that the latter corresponds closely in distribution with
that described by PuFF (1890) in the Ras Hafun area; PuFF, however, also describes the