Hydropshere is small - 1/4500 of the mass of the earth

• Mass of hydrosphere -1.3x10²⁴ g
• Components and the mass of hydrosphere
  • Oceans - 97.2%
  • Ice sheets and glaciers -2.15%
  • Streams, Lakes, ground water and atmosphere - 0.65%
  • Atmosphere - 0.001%
• Freshwater resources:
  • Ice sheets and glaciers - 84.95%
  • Groundwater - 14.16%; when ice is excluded, 94%
  • Lakes, Rivers etc - 0. 55%

Water on the planet is roughly a closed system: fixed quantity

• Loss of hydrogen by dissociation at top of atmosphere (small)
• Addition of water by magmas during the plate tectonic cycle (small)
• ocean level changes (~100 m)due to locking up water in glacial periods
• Hydrosphere has existed for as long back as 3.95 billion years.

The Hydrologic cycle

• Cycle that involves water, lithosphere,atmosphere and biosphere
• Evaporation from the oceans and continents: solar radiation energy
• Precipitation on oceans and land: conversion to potential energy
• Run off and sediment transport: gravitational and kinetic energy
• Groundwater: gravity
• Annual Water balance in the hydrologic cycle
• Driving forces - solar radiation and gravity

Energy transfer in the hydrologic cycle: the three states of water

• Changes state invove either absorption or release of energy
• Latent heat: energy involved in change of state
  • ordered to less ordered requires energy
  • Liquid water to vapor (evaporation): 2260 J/g
  • melting of Ice to liquid water: 330 J/g
  • sublimation of ice to water vapor: 2590 J/g
  • less ordered to more ordered releases energy
  • Water vapor liquid water: 2260 J/g released
  • liquid water to ice: 330 J/g released
  • precipitation of vapor as snow: 2590 J/g
• Evaporation and condensation are the most important in energy transfers
• ~ 30% of all incoming solar energy is used to drive the hydrologic cycle

The oceans:

• About 71% of the earths surface is covered by oceans.
• Average depth is about 4.0 Km.
• More than half of ocean water is in the Pacific ocean
• Volume of the oceans is 18 times that of continents -"Water Planet"
• 97.2 % of all the mass of hydrosphere is in the oceans
• Unequal distribution of land and oceans - most land is in the N. Hemisphere

The composition of ocean water

• Water is a powerful polar solvent - ocean water contains nearly all the elements
• Average Ocean water contains about 3.5% by weight of dissolved salts
• Most important salts are: NaCl, MgCl₂, Na₂SO₄, CaCl₂, KCl (over 99% all)
• Major ions are: (Cl)^-, (Na)⁺, (Mg)²⁺, (SO₄)^2- (sulfate), (Ca)²⁺, (K)⁺,
• Dissolved gases: Carbon dioxide (CO₂) (most abundant): > 60 times in the atmosphere, Nitrogen (N₂), and Oxygen (O₂)
• Biologically important ions - Nitrate (NO₃)^-, Nitrite (NO₂)^-, and Phosphate (PO₄)^- : all a few ppm
• Trace elements - toxic as well as those essential to life
  • Essential: I, Fe, Cu, Mn, etc
  • Toxic: Pb, Hg etc
• More than 90% of all biota in the oceans

Why is the ocean salty?

• Sources of ocean salt:
  • Continents - via river discharge: Ca²⁺, (CO3)^2-, (SO4)^2-,
  • From the interior volcanic exhalations at spreading centers- Na⁺ and Cl^- ions
• Salinity of surface waters is related to latitude
  • Evaporation: in mid latitudes
  • Precipitation: high in equatorial regions,
  • Inflow of large rivers: Amazon. Niger etc
  • Freezing and melting of ice in cold regions
  • Salinity remains constant becasue salts are added to and removed from the oceans.

Heat capacity of the oceans

• Temperature distribution of surface water - bands parallel to equator
• Large exchanges of energy due to the hydrologic cycle
• Temperature does not change much because of high heat capacity of water

Physical characteristics of ocean water:

• Salinity: about 3.5 % (per hundred) usually expressed as 35 per mil (per thousand)
• Temperature: varies from ~ 21-26° C to 3-4° C with depth
• Density controlled by salinity and temperature

Layered structure of oceans, based on salinity and temperature

• Vertical stratification of ocean water: based on density
  • 2% by mass- Surface waters : 50 - 200 meters, well mixed, 21-26° C
  • 18% by mass- Thermocline above 1500 m- Layer of rapidly dropping temperature
  • 80% by mass- Deep water - cold 3-4° C, with uniform salinity, denser