Arabian Sea Upwelling
39
I. The Monsoon Regime
DOING (1970) has summarized the regime of surface winds (Fig. 2) and currents (see
Fig. 1, WYRTKI 1973, this volume) prevailing in the Arabian Sea. The SW monsoon
commences in May- June, and develops as a strong wind from the SW, blowing more
or less parallel to the Somali and Arabian coasts. It reaches its peak in July - August and
fades away in September-October. The winter months show a reversal of wind as the
weaker NE monsoon sets in.
During the SW monsoon a strong western boundary current develops flowing
northwards on the Somali coast (SWALLOW and BRUCE, 1966) and likewise a pronounced
flow to the north-east is evident off the Arabian coast (Royal Society, 1963).
1. Southeast Arabian Coast
a) Hydrographic Observations
SERYI and KHIMITSA (1963) show from their Masira section that in December 1961
there was a south-westerly flow of highly saline surface water along the Arabian coast
from the Gulf of Oman, which would be consistent with the sinking of water rather
Fig. 3. The vertical distribution of dissolved inorganic phosphate on a section normal to the SE
Arabian coast, from observations by RRS "Discovery" a in March, 1964, b in May, 1964 and
c in July, 1963, showing stages in the development of upwelling. Concentrations are expressed
in I1g-at 1- 1 or mg-at m- 3
than upwelling in the proximity of the coast. They also noted the comparatively low
P0 4 3 --P concentrations in this water, a feature which is also evident in the "Discovery"
section of March, 1964 off the Kuria Muria Islands (Fig. 3 a). Both these sets of
observations bear out the absence of upwelling in these months.
In May, 1964, however, the "Discovery" repeated the same section off the Kuria
Muria Islands and the results show a marked weakening and seawards displacement of
the south-westerly surface flow, while along the coast the isotherms of the upper layers
39
I. The Monsoon Regime
DOING (1970) has summarized the regime of surface winds (Fig. 2) and currents (see
Fig. 1, WYRTKI 1973, this volume) prevailing in the Arabian Sea. The SW monsoon
commences in May- June, and develops as a strong wind from the SW, blowing more
or less parallel to the Somali and Arabian coasts. It reaches its peak in July - August and
fades away in September-October. The winter months show a reversal of wind as the
weaker NE monsoon sets in.
During the SW monsoon a strong western boundary current develops flowing
northwards on the Somali coast (SWALLOW and BRUCE, 1966) and likewise a pronounced
flow to the north-east is evident off the Arabian coast (Royal Society, 1963).
1. Southeast Arabian Coast
a) Hydrographic Observations
SERYI and KHIMITSA (1963) show from their Masira section that in December 1961
there was a south-westerly flow of highly saline surface water along the Arabian coast
from the Gulf of Oman, which would be consistent with the sinking of water rather
Fig. 3. The vertical distribution of dissolved inorganic phosphate on a section normal to the SE
Arabian coast, from observations by RRS "Discovery" a in March, 1964, b in May, 1964 and
c in July, 1963, showing stages in the development of upwelling. Concentrations are expressed
in I1g-at 1- 1 or mg-at m- 3
than upwelling in the proximity of the coast. They also noted the comparatively low
P0 4 3 --P concentrations in this water, a feature which is also evident in the "Discovery"
section of March, 1964 off the Kuria Muria Islands (Fig. 3 a). Both these sets of
observations bear out the absence of upwelling in these months.
In May, 1964, however, the "Discovery" repeated the same section off the Kuria
Muria Islands and the results show a marked weakening and seawards displacement of
the south-westerly surface flow, while along the coast the isotherms of the upper layers