CHEMICAL OCEANOGRAPHY

Aquatic Science

*** The ocean is the largest repository of organisms on the planet, with representatives from all phylums.

*** Seawater surrounds all marine organisms, composes the greater bulk of their bodies, and is the medium by which various chemical reactions take place, both inside and outside their bodies.

seawater: pure water (solvent) plus dissolved solids and gases ((96.5% H2O and 3.5% solute)

• Dissolved solids come from the weathering processes of

continental rock • Gases come from the atmosphere• 97.2% of all water on Earth is ocean water (over 285 million

cubic miles of water)• salts: the solid compound substances in sea water made up

of positive and negative ions

salinity: the total amount of solid substances (solute) in the water in ppt (34 to 37 ppt), or ~3.5% salt.

Chemical composition of the ocean is divided into four parts:

1. Dissolved Inorganic Matter (chlorine, sodium, magnesium, sulfur)

- concentrations of elements can vary with location, time or season, and biological activity

- inorganic salts compose most of the solid matter (99.28%) with chloride at ~55% and sodium at ~31%, and includes 11 additional and necessary salts (required for photosynthesis, shell construction, etc)

salinity in ppt. = (1.80655)(chlorinity in ppt) because the proportion of chlorinity to salinity is constant

2. Dissolved Gas (48% nitrogen, 36% oxygen,15% CO2) - the solubility of the gas depends on temperature of the gas and solution (seasonal), atmospheric pressure of the gas, and salt content of the solution. - oxygen concentrations decrease

with depth - two sources of oxygen (atmosphere and ocean

plants) - anaerobic organisms live in depths with no oxygen - pH decreases with depth (decrease in plants to remove CO2 which keeps pH stable

3. Dissolved Organic Matter (small and variable amounts)

4. Particulate Matter (organic and non-organic materials, including fine-grained minerals)***There are between 100 and 1.000.000 bacteria cells per cubic centimeter in just one spoonful of ocean water***

Factors that control or influence the chemical composition of the ocean:

• exchange with the atmosphere• solubility of different compounds• reduction by anaerobic bacteria• precipitation and exchange with the ocean bottom• inflow of fresh water (also bringing in salts)• freezing and melting of sea ice• chemical reactions that control or influence the concentrations of different elements• biological processes (including decomposition)• temperature (evaporation)

Three unique properties of water:1. dissolving power : makes ocean water

nature’s “rich soup” - Water is a MOLECULE (2 hydrogen atoms

and one oxygen) A. the hydrogen atoms bond to the oxygen

atom by SHARING electrons (COVALENT BONDING). This makes water a

stable molecule. B. Water is a POLAR MOLECULE: (contains

both charges) The electrical charges of the atoms do not

completely cancel each other out. The bigger oxygen atom draws the

electrons from the hydrogen closer to its nucleus, making the oxygen slightly

negative and the hydrogen end slightly positive.

C. As a result of POLARITY, water molecules cluster (cohesion) as the hydrogen (positive) end of one molecule is attracted to the oxygen (negative) end of another and weak HYDROGEN BONDS are formed between molecules.

D. Due to its POLARITY, water is the UNIVERSAL SOLVENT. Any particles that have charges on them (metals +/non-metals ) will be attracted to the oppositely charged ends of the water molecules (adhesion), dissolving.

2. surface tension (surface “skin”): Due to COHESION of water molecules water is very DENSE (800X the density of air). This allows organisms to float along effortlessly and lightweight insects to skim across the surface.

3. colligative properties (slow but large capacity for absorbing heat):

- these properties vary because of the amount of elements in solution and not because of the TYPE of element.

Examples:A.boiling point elevation or heat capacity: a rise in salt levels

decreases the amount of heat necessary to raise temperature 1 degree

B. freezing point depression: a rise in salt levels lowers the freezing point of water

C. vapor pressure lowering: ocean water evaporates more slowly than water without salts

D. osmotic pressure: a rise in salt levels increases osmotic pressure to equalize salinity inside and outside a cell membrane

Important People in the Study of Ocean Water Chemistry:

1. Robert Boyle: attributed with the first scientific study of ocean water

2. Lavoisier: discovered that water is a compound of hydrogen and oxygen

3. Forchhammer: Principle of Constant Proportions A. The RATIO of major dissolved components in ocean water

is constant. B. Steady State Condition: the amount of an element

introduced into the ocean per unit time equals the amount deposited out as sediment per unit time on the ocean floor.

C. Residence Time: the amount of an element present divided by the rate the element is added (average length of time an element spends in the ocean)

4. Dittmar Challenger Expedition: 3 important findings A. The quantity of one major component in seawater can

be used to determine the salinity of seawater B. Oxygen content decreased with water depth C. Carbon dioxide levels are lower at the surface than in

deeper waters.

Focuses of Chemical Oceanographers:

1. Increased presence of pollutants in ocean

2.Acid rain3.Effects of animals and

plants on the composition of ocean water

4.The effects of increased amounts of carbon dioxide released into the atmosphere and ocean

5. Mineral deposits on the ocean floor (manganese nodules, etc)