Physical and Chemical Oceanography Part I: CHEMICAL COMPOSITION

Salinity salt concentration in parts per thousand (ppt) Variance: ocean average: 35 ppt (350/00) Variance: Sea diluted with freshwater by: River Melting glaciers Units=ppt

Chemical (salt) Composition fairly constant for millions of years Salinity Mainly: sodium, chloride ions Smaller: sulfate, magnesium, hydrogencarbonate, potassium So what percent on average is pure water—96.5% ,and 3.5% is salts Remember hydrogencarbonate=bicarbonate Potassium-1% CSSMCPB-acronym??? Rule of constant proportion=fixed proportion From Section 4 Nutrient Cycles

Chemical Composition local changes can occur Volcanic activity- Runoff Atmospheric dissolution

1. Volcanic Activity Gases: CO2, Sulfur, hydrogen sulfide, hydrogen chloride dissolve in atmospheric H2O enter sea by precipitation Submerged volcanoes at plate boundaries emit gases (chlorine) Major source of chloride ions in sea Salinity can change

2. Runoff *Flow of water from land Rain, melted snow & ice Drains to oceans directly or from rivers Passes through soil Urban runoff into drains Bringing freshwater which will change salinity but this is known as freshwater inflow/glacial/iceberg melting Runoff is dealing with bringing pollutants from the land into the water

2. Runoff Picks up pollutants – pesticides, fertilizers and oil-derived substances food chains and webs increasing concentration at each trophic level Example: industrial wastewater with mercury Minamata Bay 1932- 1968 Shellfish & organisms Human consumption – neurological disorders, paralysis and death So in this case salinity is not changed

3. Atmospheric Dissolution Gases dissolved are at equilibrium with atmosphere Concentration of it depends on relative solubility, temperature and salinity of sea Dissolved gases: Nitrogen (N) nitrogen-fixing microorganisms make products for other organisms Carbon Dioxide (CO2) Photosynthesis Oxygen (O) Respiration Adding other chemicals into the water. In this case salinity is not changed

Salinity Evaporation – salt stays behind hydrometer Hypersaline (increased amount of salt) Ex: lagoon – high temp. Evaporation Ex: Dead Sea – extreme Accumulation of solutes 10x saltier than ocean

Precipitation rain, snow Dilutes sea water, decreases salinity Estuaries Melting glaciers

Salinity is variable across the ocean High salt concentrations are usually in the middle of the ocean basins away from the mouths of rivers, which input fresh water. High concentrations are also in sub-tropical regions because evaporation rates are high and in landlocked seas in arid (no rain) regions. At high latitudes, salinity is low because the melting of ice dilutes seawater. As a general rule, salinity is low where precipitation is greater than evaporation, mainly in coastal or equatorial regions.

A closer look Relatively LOW salinity Relatively HIGH salinity Teacher’s Note: Low salinity areas are circled in blue, high salinity areas in black. Salinity will increase with distance from land

WHY IS SALINITY IMPORTANT? SALINITY IS ONE FACTOR THAT CONTROLS THE DENSITY OF OCEAN WATER

Density temperature salinity Warm on top of cold, dense water Temperature gradient WHEN WATER AT DIFFERENT DEPTH HAVE DIFFERENT DENSITIES --LAYERS OF WATER WILL FORM=OCEAN CURRENTS

Density If temp. abruptly as depth = thermocline Shallow layer of warm on deep layer of cold depth temperature

Density salinity density halocline – abrupt change in salinity as depth Lower salinity (lower density) on top of higher salinity (higher density) Mixing occurs by wind blowing at the surface down to ~200 m Turbulence and currents Temperature changes

Pycnocline- rapid change in density with depth Pycnocline- rapid change in density with depth. Is a function of the thermocline and halocline. B/c density is a function of temp and salinity. Temp. is the dominant factor influencing density Show video—12 minutes

Dissolved Oxygen (DO) temperature Oxygen solubility General rule:

Dissolved Oxygen Temp of H2O O2 slightly less soluble in salt than fresh Temp of H2O Dissolved Oxygen Concentration Freshwater 0⁰C 14.6 mg/dm3 5⁰C 12.8 mg/dm3 10⁰C 11.3 mg/dm3 15⁰C 10.2 mg/dm3 20⁰C 9.2 mg/dm3 25⁰C 8.4 mg/dm3 Show overhead table comparing salt and freshwater What is the pattern?

D.O. surface layer = high D.O. D.O. removed by respiration of marine Can be supersaturated by 2 processes: Turbulence & mixing by waves causing atmospheric O2 to dissolve Photosynthesis by algae O2 as byproduct D.O. removed by respiration of marine organisms

D.O. decreases to minimum as depth increases Increases again as depth increases Oxygen minimum layer – depth that concentration of DO is lowest Between 100m and 1000m