Pragnya IAS · Chapter 7 of 15 · Oceans & marine processes
Ocean salinity: evaporation, rain & rivers map study
Compare saline subtropical seas with rainfall- and river-diluted surface waters.
STUDY NOTE 1
A balance of water fluxes
Evaporation removes freshwater and tends to increase salinity. Precipitation, river runoff and ice melt generally dilute surface water. Circulation mixes these effects, so salinity cannot be predicted from latitude alone.
STUDY NOTE 2
Subtropical versus equatorial
Dry subtropical ocean regions often have higher surface salinity than rainy equatorial waters. Polar processes include dilution from melting ice and salt rejection during sea-ice formation; the two should not be confused.
STUDY NOTE 3
Arabian Sea and Bay of Bengal
Large river input and rainfall contribute to lower surface salinity in the Bay of Bengal compared with much of the Arabian Sea. Values vary seasonally and vertically; this is a broad comparison, not a universal fixed number.
STUDY NOTE 4
Enclosed seas differ
The Red Sea has high evaporation and limited freshwater inflow. The Baltic receives substantial freshwater and restricted ocean exchange. The Mediterranean loses water through net evaporation and exchanges through Gibraltar.
Map reading activity
Compare Red Sea, Baltic, Bay of Bengal and Arabian Sea. For each, identify evaporation, rainfall, runoff or restricted exchange as a leading explanation rather than assigning an unsupported exact value.
What does this ocean salinity: evaporation, rain & rivers lesson explain?
Evaporation removes freshwater and tends to increase salinity. Precipitation, river runoff and ice melt generally dilute surface water. Circulation mixes these effects, so salinity cannot be predicted from latitude alone.
UPSC map practice & Geography Optional connection
For UPSC GS I and Geography Optional physical geography revision, connect the spatial pattern with the process in the study notes. Draw a small labelled sketch, explain the mechanism and distinguish conceptual models from observed datasets. These are Pragnya-authored exercises, not official UPSC previous-year questions.
References & original artwork
This lesson covers chapter 7 of the supplied reference curriculum. Pragnya IAS notes, activities and questions are independently authored; source PDF pages, branding, personal watermarks and unverified PYQs are not republished. Earth image: NASA Blue Marble, distributed via WebGL Earth; resized and compressed for this lesson. World coastlines: Natural Earth public-domain 1:110m land, simplified. These are educational concept views, not legal boundaries, forecasts or navigation maps.