L - Cochin University of Science and Technology

3.2.2.3. Dissolved oxygen (DO)
Distribution of bottom water DO in the study area is presented in figurs 8k-o.
Generally DO showed a sharp decrease towards deeper depths in the study area.
Along Monnugao transect DO showed a decrease to deeper stations. Off Ratnagiri,
high DO values were observed at all stations and the pattern of distribution was same
as that observed off Monnugao. OLT Mumbai, a general trend of decrease was
observed except at 75 m depth where a slight increase was noticed. OfT Veraval and
Dwaraka also, the decreasing trend was observed towards deeper depths. Generally
higher values were observed up to 75 m and the gradient increased from shallow to
deeper depths.
Transect wise variation of DO distribution in various depth zones (Fig. 7a-f)
showed that at 30 m, 50 m and 75 m zones, a gradual increase was observed from
south to north. At 100 m zone, a fluctuating trend was noticed with low value off
Vcraval and high value off Dwaraka. At 150 m zone generally low values were
observed and as an exception from the previous depth zones here DO showed a
decreasing trend towards north. Beyond 150 m, 2 observations were made and off
Mumbai recorded high DO (0.6ml/l) and off veraval recorded low value (0.16ml/l).
Generally in the shallow depth zones of 30 to 75 m there was a northward increase in
DO values while at 150 m zone, a reverse trend was observed.
3.2.3. Seasonal comparison
Seasonal variations were very conspicuous in the study area. Temperature
during post-monsoon decreased to deeper depth stations in all transects while during
pre-monsoon it increased initially and then decreased to deeper depths. During post­
monsoon, temperature increased to north while during pre-monsoon a northward
decrease was noticed and the average temperature in the whole study area was high
during pre-monsoon compared to post-monsoon. Salinity distribution, during post­
monsoon period showed an increasing trend towards deeper depths only ofT
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