Properties of Water Ocean motions governed by fundamental physical laws of conservation of mass, momentum and energy Water’s truly unique property as related to Earth System Science: At standard pressure, water changes from a liquid to a solid at 0° C (32°F) and from a liquid to a gas at 100°C (212°F). Only substance that can exist in all three phases within the Earth’s range of temperatures. Other properties of water (additional properties in Table 7.2): - great heat storage ability - little internal friction - dissolves solids and gases readily (“universal solvent”) - changes phase in atmosphere and in ocean - solid form floats - transparent to some wavelengths of light, nearly opaque to others - high surface tension Geography “Physical Geography of the World’s Oceans”

Question: Why does water behave the way it does? Answer: Water’s properties are due to its unique molecular structure.

Chemistry protons, electrons and (usually) neutrons form atoms - atoms, building blocks of matter, bond to form molecules - hydrogen (H) and oxygen (O) bond to form water (H 2 O) Chemical bonding involves electrons - ionic bond involves transfer of electrons - covalent bond involves sharing of electrons

water molecule covalent bonds between oxygen and two hydrogen atoms oxygen attracts electrons more strongly than hydrogen, resulting in a net positive charge on the hydrogen atoms, and a net negative charge on the oxygen atom.

hydrogen bonds Electrical attraction between molecules

freshwater density vs. temperature

surface tension

Physical implications of surface tension: - capillary waves - viscosity (thickness or internal friction) - molecular diffusion

day-night temperature differences on earth’s surface

Energy is necessary to drive ocean processes. Forms of energy important to oceanographers (Table 7.1) - solar energy - thermal energy - kinetic energy - potential energy - chemical energy How does water store and exchange thermal energy or heat? - heat capacity - relationship between heat and temperature - temperature - measure of average kinetic energy of molecules - heat - spontaneous transfer of energy from a high temperature system to a lower temperature system specific heat - (C p ) amount of heat necessary to change the temperature of a unit mass by 1 °C

James Joule (1818 – 1889) heat gain equivalent to potential energy loss joule (J) – energy from a force of 1 Newton moving through distance of 1 meter

specific heat values water = C p (T,P) ~4180 J kg -1 °C -1 seawater = C p (T,S,P) ~4000 J kg -1 °C -1 silicon (sand) = ~710 J kg -1 °C -1 concrete = ~752 J kg -1 °C -1 air = ~1000 J kg -1 °C -1 ice = ~2050 J kg -1 °C -1

sea breeze – as land warms to temperature greater than ocean during day land breeze – as land cools to temperature lower than ocean during night specific heat differences between ocean and land influences local weather

water structure and phase transitions Heat must be added/removed to alter hydrogen bonds and change state of water. This heat not expressed in a change of temperature.

2. / energy and phase transitions Figure 7-11 in text; another error 3. / 0. Energy to heat 1 gm ice by 1 °C = 2.05 J/g

Readings for next time (thermodynamics of water): Read first part of Chapter 7 (pgs 113 – 122)