Question

Salinity patterns in Indian ocean

Answer 1

Salinity at the sea surface (Figure 2) resembles the evapo-
ration–precipitation pattern, with some differences due to
runoff, ocean currents and ice melt. The total salinity range
of the open ocean is about 30–40 parts per thousand or ‰
(see Salinity, Volume 1). The international convention is
that salinity has no units; its value is approximately grams
salt per kilogram of sea water. Many authors continue to use
the practical salinity unit (psu) rather than leaving the quan-
tity unitless. While salinity in coastal estuaries can be much
lower, it does not affect large oceanic-scale patterns. Low-
est salinities occur in the Arctic and Antarctic where there is
both net precipitation and seasonal ice melt. Highest salin-
ities occur in the Red Sea and Persian Gulf, both located
in the northwestern Indian Ocean, where net evaporation is
high. High salinity is also found in the Mediterranean Sea.
In the open ocean, high salinity occurs in the subtropical
areas of net evaporation seen in Figure 1. A band of low
salinity underlies the ITCZ at 10 °N.
The effect of continental runoff is apparent in lowered
surface salinity near the mouths of major rivers such as the
Amazon and the Congo and the numerous large rivers that
empty into the Bay of Bengal, east of India, including the
Ganges and Brahmaputra. Runoff from many rivers around
the Gulf of Alaska in the northeastern Pacific and around
the Arctic Ocean is important in the lowered salinities of
high-latitude ocean regions.