Water (Oceans)

Learning Objectives

• Understand the processes involved in the hydrological cycle, including evaporation, condensation, precipitation, and runoff, and their significance in the earth's hydrosphere.
• Analyze the major and minor oceanic relief features, such as continental shelves, slopes, deep sea plains, ridges, seamounts, and trenches, and their formation processes.
• Examine the factors affecting temperature distribution in oceans, including latitude, land-water distribution, winds, and ocean currents, and understand the concept of the thermocline.
• Investigate the factors influencing the salinity of ocean waters, its horizontal and vertical distribution, and the interrelationship between salinity, temperature, and water density.

Chapter Notes

Hydrological Cycle

• Definition: The hydrological cycle describes the continuous movement and exchange of water within the earth's hydrosphere.
• Processes Involved:
  • Evaporation: Water is converted from liquid to vapor and rises into the atmosphere.
  • Condensation: Water vapor cools and changes back into liquid droplets.
  • Precipitation: Water falls from the atmosphere to the earth's surface as rain, snow, etc.
  • Runoff: Water flows over the land surface and returns to bodies of water.
• Components:
  • Water storage in oceans, atmosphere, ice, snow, and groundwater.
  • Processes like evapotranspiration, sublimation, and infiltration.

Oceanic Relief Features

• Major Divisions:
  • Continental Shelf: Extended margins of continents, shallow with an average width of 80 km.
  • Continental Slope: Steep slope connecting the shelf to the ocean basin, depth varies between 200 and 3,000 m.
  • Deep Sea Plain: Flat and smooth regions, depths between 3,000 and 6,000 m.
  • Oceanic Deeps/Trenches: Deepest parts, associated with tectonic activity.
• Minor Features:
  • Mid-Oceanic Ridges: Mountain ranges under the ocean.
  • Seamounts: Volcanic mountains rising from the seafloor.
  • Submarine Canyons: Deep valleys cutting across continental shelves.
  • Guyots: Flat-topped seamounts.
  • Atolls: Coral reefs surrounding a lagoon.

Temperature Distribution in Oceans

• Factors Affecting Temperature:
  • Latitude: Temperature decreases from the equator to poles.
  • Land-Water Distribution: Oceans in the northern hemisphere are warmer.
  • Winds: Influence temperature by moving warm or cold water.
  • Ocean Currents: Warm currents raise temperatures; cold currents lower them.
• Vertical Distribution:
  • Thermocline: A layer with a rapid temperature decrease, found between 100-400 m depth.
  • Three-Layer System: Surface warm layer, thermocline, and deep cold layer.

Salinity of Ocean Waters

• Definition: Salinity is the total content of dissolved salts in seawater, expressed in parts per thousand (ppt).
• Factors Affecting Salinity:
  • Evaporation and Precipitation: Influence surface salinity.
  • River Influx and Ice Processes: Affect coastal and polar salinity.
  • Winds and Currents: Distribute salinity across regions.
• Distribution:
  • Horizontal: Varies from 33 to 37 ppt in open oceans, higher in enclosed seas.
  • Vertical: Salinity increases with depth, forming a halocline where changes are sharp.