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Temperature, Salinity, and Other Characteristics of Ocean Water – UPSC Geography Notes
Overview: The physical properties of ocean water such as temperature, salinity, and density determine the nature of marine life, ocean currents, and climatic systems. Understanding these characteristics is essential for UPSC Geography and Climatology, as they influence weather, rainfall, and the distribution of life in oceans.
Table of Contents
- 1. Introduction
- 2. Temperature of Ocean Water
- 3. Factors Affecting Ocean Temperature
- 4. Vertical and Horizontal Distribution of Temperature
- 5. Salinity of Ocean Water
- 6. Factors Affecting Salinity
- 7. Distribution of Salinity
- 8. Density and Other Characteristics
- 9. Relationship Between Temperature, Salinity, and Density
- 10. UPSC Quick Revision Notes
- 11. Previous Year Question
1. Introduction
Ocean water is not uniform throughout. It varies in temperature, salinity, and density depending on location, depth, and circulation. These properties play a crucial role in the movement of ocean currents and global climate regulation.
2. Temperature of Ocean Water
Temperature refers to the degree of hotness or coldness of ocean water. It varies both horizontally (from equator to poles) and vertically (from surface to depth).
- Average surface temperature of oceans: around 27°C.
- Highest temperatures: near the equator.
- Lowest temperatures: near the poles and deep ocean basins.
3. Factors Affecting Ocean Temperature
- Latitude: Temperature decreases from the equator towards the poles.
- Solar Radiation: Areas with direct solar rays receive more heat.
- Ocean Currents: Warm currents raise temperature; cold currents lower it.
- Prevailing Winds: Winds moving from land to sea or sea to land affect surface temperature.
- Cloud Cover: Clouds reduce heating during day and cooling at night.
- Upwelling: Cold, nutrient-rich water rises from the depths and cools the surface.
4. Vertical and Horizontal Distribution of Temperature
(a) Horizontal Distribution
- Highest temperatures are recorded between 10°N and 10°S latitudes.
- Temperature decreases towards the poles.
- Western parts of oceans are warmer due to warm ocean currents (e.g., Gulf Stream).
- Eastern margins are cooler due to cold currents (e.g., California Current).
(b) Vertical Distribution
Temperature decreases rapidly with increasing depth. The vertical profile is divided into three layers:
- Surface Layer (0–200 m): Warmest layer due to direct solar heating.
- Thermocline (200–1,000 m): Rapid decrease in temperature with depth.
- Deep Zone (>1,000 m): Uniformly cold (near 0°C), dark, and dense water.
5. Salinity of Ocean Water
Salinity refers to the total amount of dissolved salts in 1,000 grams of seawater. It is expressed in parts per thousand (‰ or ppt).
Average salinity of ocean water = 35‰ (3.5%), meaning 35 grams of salt per kilogram of seawater.
6. Factors Affecting Salinity
- Evaporation: Increases salinity by removing water.
- Precipitation: Decreases salinity by adding freshwater.
- River Discharge: Reduces salinity near river mouths.
- Temperature: High temperature → more evaporation → higher salinity.
- Ocean Currents: Warm currents increase salinity; cold currents decrease it.
- Ice Formation: In polar areas, freezing of seawater increases salinity of surrounding water.
7. Distribution of Salinity
(a) Horizontal Distribution
- Highest salinity: Subtropical regions (20°–30° latitudes) due to high evaporation.
- Lowest salinity: Near equator (due to heavy rainfall) and poles (due to ice melting).
- Red Sea and Persian Gulf have salinity above 40‰ (very high).
- Baltic Sea and Arctic Ocean have salinity below 10–15‰ (low).
(b) Vertical Distribution
- At the surface → salinity is higher due to evaporation.
- At greater depths → salinity is more uniform.
- In polar regions → salinity increases with depth.
8. Density and Other Characteristics
(a) Density
Density of ocean water is the mass per unit volume, usually expressed in grams per cubic centimeter (g/cm³).
- Average density: 1.025 g/cm³.
- Increases with higher salinity and lower temperature.
(b) Pressure
- Increases with depth due to the weight of overlying water.
- At 1,000 m depth → pressure is about 100 times that at the surface.
(c) Colour and Transparency
- Pure water is colorless, but seawater appears blue or green due to sunlight scattering and reflection from algae and sediments.
- Transparency decreases in coastal regions due to suspended sediments.
(d) Waves and Tides
- Surface movement of water is caused by wind (waves) and gravitational forces (tides).
- Both are influenced by the temperature, density, and salinity of water masses.
9. Relationship Between Temperature, Salinity, and Density
- Temperature ↑ → Density ↓ (warm water is lighter).
- Salinity ↑ → Density ↑ (salty water is heavier).
- Cold and saline water sinks, while warm and less saline water rises → causes vertical circulation and ocean currents.
10. UPSC Quick Revision Notes
Layers → Surface, Thermocline, Deep zone.
Average salinity = 35‰; highest in subtropics, lowest near poles/equator.
Density = 1.025 g/cm³; increases with salinity, decreases with temperature.
Warm currents → raise temperature & salinity.
Cold currents → lower temperature & salinity.
Red Sea → highest salinity; Baltic Sea → lowest.
Interrelation → Temp ↓ + Salinity ↑ → Density ↑ → Sinking of water masses.
11. Previous Year Question
Q. Which of the following factors decreases the salinity of seawater?
(a) Evaporation
(b) Precipitation
(c) Ocean Currents
(d) Solar Radiation
Answer: (b) Precipitation
Related Keywords
Temperature and Salinity of Oceans UPSC Notes, Ocean Water Characteristics, Oceanography UPSC, Salinity Distribution, Ocean Density, Physical Geography Notes, Marine Geography.
Sources: NCERT Class XI – Fundamentals of Physical Geography, Goh Cheng Leong (Certificate Physical and Human Geography), NOAA Ocean Data (simplified for UPSC aspirants).
Next Topic → Ocean Currents and Tides – UPSC Geography Notes
