Physical Properties of Ocean Water

I. Temperature Variations in Oceans

a. Horizontal Distribution of Temperature

• Equatorial regions receive high insolation → high surface temperatures (up to 30°C).
• Polar regions receive little solar radiation → surface temperatures fall below 0°C.
• Warm ocean currents (e.g., Gulf Stream) raise surface temperatures along eastern margins of continents in higher latitudes.
• Cold currents (e.g., California Current) lower temperatures along western coasts in subtropics.

b. Vertical Temperature Profiles

• Ocean water temperature decreases with depth.
• Three layers:
  1. Surface Layer (Mixed Layer) – well-mixed by wind and waves; uniform temperature (up to ~200m).
  2. Thermocline Layer – sharp decrease in temperature with depth (200m–1000m).
  3. Deep Zone – stable, uniformly cold (~2°C to 4°C), extends below 1000m.

c. Thermocline Zone

• A transition zone between warm upper layer and cold deep layer.
• Acts as a barrier to vertical mixing of water.
• Strongly developed in tropical oceans; weak or absent in polar regions.
• Important in ocean circulation and biological productivity.

II. Density of Ocean Water

a. Factors Affecting Density

1. Temperature: Inversely proportional – colder water is denser.
2. Salinity: Directly proportional – more saline water is denser.
3. Pressure: Increases density slightly at great depths.

b. Density Stratification in the Ocean

• Ocean water is stratified into layers based on density:
  • Upper Layer – low density, well-mixed, less saline and warmer.
  • Pycnocline – zone of rapid density increase with depth.
  • Deep Layer – high density, cold and saline water.
• Thermohaline Circulation is driven by these differences in density (temperature + salinity).

III. Oceanic Pressure and Its Impact

• Increases with depth due to the weight of overlying water.
• At 10m depth, pressure increases by 1 atmosphere.
• Affects:
  • Movement and mixing of water masses.
  • Adaptation of deep-sea organisms.
  • Design of submersibles and underwater infrastructure.

IV. Ocean Waves and Tides

a. Types of Ocean Waves

1. Wind-generated waves – most common, caused by friction of wind over surface.
2. Tsunami – seismic sea waves caused by undersea earthquakes or volcanic eruptions.
3. Tidal Waves – large waves associated with the gravitational pull of the moon and sun (not to be confused with tsunami).
4. Internal Waves – occur along pycnocline (density gradient) in deeper ocean layers.

b. Formation and Characteristics of Tides

• Tides are periodic rise and fall of sea level due to gravitational forces of the moon and sun.
• Types of tides:
  • Spring Tide – highest tidal range; occurs during new moon & full moon (sun, moon, and earth aligned).
  • Neap Tide – lowest tidal range; occurs during first and third quarters of the moon (sun and moon at right angles).
• Diurnal Tide – one high and one low tide daily.
• Semi-diurnal Tide – two high and two low tides daily.
• Mixed Tide – varying heights of tides each day.

Significance:

• Tides influence navigation, fishing, tidal power generation, and coastal processes.