Chapter 3: Physical and Chemical Features of Seawater and the World Oceans
Why Study this?
Part One: The Waters of the Ocean
Water makes up 80% of most marine organisms.
95 % in jellyfish!
Makes life possible!
Water: Three States
 Water is the only substance that occurs in all 3 states within the range of surface temperatures on Earth.
 Solid(Ice), Liquid (Water), Gas (Water Vapor)
The Unique Nature of Pure Water
 H2O
 Covalent bonds
 Water is polar
 Allows for weak hydrogen bonds to form between different water molecules.
 Reason for many of waters unique properties
The Unique Nature of Pure Water
 Molecules heated, move quicker, bonds break until evaporation.
 Molecules cool, move slower
 Water becomes denser as it cools, molecules closer, same mass, less volume.
 Freezes when molecules locked into a fixed crystal by hydrogen bonds.
Water and Ice
 Solid water is less dense than liquid water.
 Insulates the water below so that it doesn’t freeze.
 Ice forms on top allowing organisms to live underneath the ice
Heat Capacity
 Hydrogen bonds must be broken before molecules can begin to move around
 Water melts at higher temperature & absorbs a lot of heat when it melts and great deal of heat must be
removed to freeze it = high heat capacity.
 In melting ice, added heat breaks more hydrogen bonds than increasing molecular motion, so the temp of icewater mixture remains at 0°
 Adding heat goes into melting the ice not raising temperature. Ex: Ice keeping drinks cold
 Therefore marine organisms not affected by temperature changes in atmosphere
Heat and Water
 Molecular structure changes with temp.
 1) In ice, H bonds hold molecules in a hexagonal pattern, in a crystal
 2) Heat added, ice warms up, molecules move quicker until break free of crystal structure. Ice melting
 3) While ice is melting, added heat absorbed by H bonds, not by increasing the temp.
 4) When ice completely melted, additional heat causes temp to rise.
 5) Some molecules fast enough to break all bonds and evaporate.
 At 100 degrees C, all H bonds broken, water boils and evaporates.
Water as a Solvent
 Dissolves more things than any other natural substance, esp. salts
 Called the universal solvent
 Salts made of opposite charged particles (ions) and conduct electricity
 In water, strong ion charges attract water molecule, water molecules surround the ions and pull them
apart =dissociation
Water as a Solvent -Seawater
 Characteristics of seawater due to nature of pure water and materials dissolved in it
 Dissolved solids due to weathering of rocks on land & hydrothermal vents
 Rain and snow
Water as a Solvent-Seawater
 Sodium chloride account for 85% of all solids dissolved, Na and Cl
 Salinity is total salt dissolved in seawater
 Measurement
 Parts per thousand, 30-35 OR g/mL, 1.020-1.025
Challenger Expedition
 William Dittmar
o Wrote papers on composition of seawater
 Rule of constant proportions
o Salinity varies, but not percent composition of ions
Seawater
 Removal and addition of water, changes salinity.
 How?
 Avg. 35 ppt and between 33-37 ppt in open ocean.

Salinity fluctuations
• Oceans well mixed, salinity varies as a result of addition/removal of fresh water, rather than
removal/addition of salt.
Salinity, temperature, and density
 Get denser as it gets saltier, colder, or both
 Ocean temp varies -2° to 30°C (28-86°F)
 Temps below 0°C possible because saltwater freezes at colder temps.
 Density controlled more by temperature than salinity
 Are exceptions therefore salinity & temp need to be measured to determine density
Trace Elements and Dissolved gases
 Trace elements: Nitrogen Phosphorus, and Iron
 Needed to make amino acids, nucleic acids (DNA)
 Sulfate, Magnesium, Calcium, Potassium, Bromide, Bicarbonate, Fluoride
 O2, CO2 and N2 in atmosphere and sea surface
 Gas exchange happens between the surface and atmosphere
 Oxygen
o Necessary for respiration
o Most oxygen is released into the atmosphere
 Carbon Dioxide
o Necessary for photosynthesis
o 80% of gasses is carbon dioxide
o 50 times more CO2 stored in oceans than in atmos.
o Important topic in global climate change
 Gas dissolves better in colder water
Transparency
 Sunlight can penetrate, but it’s affected by the material
suspended in the water
 Important to the photosynthetic organisms
 Seawater is transparent, but not all colors penetrate as well.
 blue is best, red is worst
Transparency
 Runoff --makes coastal waters less transparent than
open ocean.
 Plankton and algae blooms can affect water transparency
 Simple instrument to test water clarity, Secchi disk
Pressure
 Sea level = 1 atm or 14.7 pounds per square inch (psi)
 On land, organisms are under 1 atm.
 Marine organism have the pressure of the atmosphere
and water
Added weight of water column
Each 10 meters (33 ft) = another atmosphere
Ex: 33 ft down = _____ atm of pressure.
Ex: 66 ft down =______atm of pressure.
Pressure Effects
 Increase pressure/depth, gases compress.
 Causes gas-filled structures to shrink or collapse
 Decrease pressure/depth, gases expand