world of water chapter 3

3 The World of Water

3.1 The Water Planet

  • Earth's Water Coverage:

    • Over 70% of Earth's surface is covered by water, earning it the nickname "water planet."

    • Major oceanic divisions:

      • Atlantic Ocean

      • Pacific Ocean

      • Indian Ocean

      • Arctic Ocean

    • Smaller bodies of water, such as seas, exist between continents; e.g., the Caribbean Sea connects to the Atlantic Ocean.

  • Geographic Measurement:

    • Latitude: Lines parallel to the equator (0°). Examples:

      • Galápagos Islands: 0° latitude.

    • Longitude: Lines from the North to South Pole, intersecting latitude lines. The prime meridian (0° longitude) runs through Greenwich, England.

3.2 The Water Budget

  • Definition: Earth's water budget is the total volume of water contained on the planet.

    • Distribution:

      • Oceans: 97% of Earth's water.

      • Freshwater: 3%, mostly in glaciers and ice, with a third as liquid in rivers, lakes, and underground sources.

  • Sea Level Changes Over Time:

    • Sea level was lower during the last Ice Age, possibly by up to 100 meters due to water being frozen.

    • Climate warming since the Ice Age has contributed to rising sea levels.

  • Water Cycle Overview:

    • Water transitions between liquid, vapor, and solid through:

      • Evaporation: Water changes to gas and rises.

      • Condensation: Water vapor cools to form clouds.

      • Precipitation: Water falls as rain, snow, etc.

3.3 Water as a Solvent

  • Dissolution in Water: Water's chemical properties allow it to be an effective solvent, often referred to as the universal solvent.

    • Ocean water composition:

      • Approximately 96.5% water + 3.5% dissolved salts (mainly NaCl).

    • Solute vs. Solvent:

      • Solute: Substance dissolved (e.g., salt).

      • Solvent: Substance dissolving (e.g., water).

  • Water's Molecular Structure:

    • Water molecules (H2O) consist of one oxygen atom and two hydrogen atoms, resulting in polar properties where one side is slightly positive and the other negative, allowing for electrostatic interactions with ions.

  • Impact on Ocean Chemistry:

    • Sodium and chloride ions dissociate in water, leading to the properties that define saline water.

    • pH in Water:

      • pH measures acidity or alkalinity from 0 to 14.

      • Ocean water typically has a pH around 8 (slightly basic).

      • Acid rain can lower the pH of freshwater systems more significantly than ocean water due to buffering capacity.

3.4 The Salty Sea

  • Salinity Definition: Salinity refers to the amount of dissolved salts in water, with ocean average salinity at approximately 3.5%.

  • Sources of Seawater Salinity:

    • Rivers: Carry salts from land into the ocean.

    • Ocean Floors: Hydrothermal vents release minerals into seawater contributing to salinity.

  • Salinity Variations:

    • Varies with evaporation and freshwater influx (from rain or rivers). Higher salinity is often observed in enclosed seas (like the Red Sea) due to higher evaporation compared to open ocean areas.

    • Salinity changes with depth due to thermoclines, haloclines, and temperature effects on molecules.

  • Scientific Measurements:

    • Testing Salinity: Using an indicator solution can determine salt presence more effectively than taste.

Chapter Review Questions

  • Vocabulary Terms:

    • Key terms include: acid, base, dissolved oxygen (DO), evaporation, halocline, pH, precipitation, solvent, etc.

  • Understanding the Water Cycle:

    • Essential questions about sea level changes, sources of salts, and the relationship between salinity, freshwater inputs, and evaporation cycles.