Water (Oceans)

We are tied to the ocean. And when we go back to the sea, we are going back from whence we came. — John F. Kennedy

12.1 Relief of the Ocean Floor

Major features:

The continental shelf off India's west coast supports fisheries; the Arabian Sea and Bay of Bengal flank the peninsula.

12.2 Temperature and Salinity

Ocean temperature decreases with depth. The thermocline is the layer of rapid temperature change.

Salinity — dissolved salts, mainly NaCl. Average ocean salinity ~35‰ (parts per thousand).

Factors affecting salinity:

• Evaporation increases it; precipitation and river inflow decrease it
• Enclosed seas (Red Sea) are highly saline; Baltic Sea is brackish

Indian Ocean salinity is lower near the Bay of Bengal (river discharge) and higher in the Arabian Sea (evaporation).

12.3 Ocean Deposits

Terrigenous — from land (sand, mud, silt)

Biogenous — shells and skeletons (ooze)

Hydrogenous — precipitated minerals (manganese nodules)

Cosmogenous — meteoric debris

Coral reefs — built by organisms in warm, shallow seas (Lakshadweep, Andaman reefs).

12.4 Importance of Oceans

• Climate regulation — heat reservoir; drives monsoon
• Trade and transport — Mumbai, Chennai, Kochi, Visakhapatnam are major ports
• Resources — fish, minerals, oil, tidal energy
• Biodiversity — marine ecosystems

India's Exclusive Economic Zone (EEZ) extends 200 nautical miles, offering vast marine resources.

Chapter Summary

• Ocean floor: shelf, slope, abyssal plain, ridges, trenches
• Temperature and salinity vary by depth, latitude, and evaporation
• Ocean deposits: terrigenous, biogenous, hydrogenous
• Oceans regulate climate, support trade, and provide resources
• India bordered by Arabian Sea, Indian Ocean, and Bay of Bengal

Exercises (NCERT)

• Exercise 1 — relief features of the ocean floor
• Exercise 2 — factors affecting temperature and salinity
• Exercise 3 — importance of oceans for India