WEEK 2: Major Determinants of Environments

• Covers almost 71% of Earth’s surface. • Comprises diverse marine environments. • Plays a major role in determining climate, and thus influences terrestrial surface environments.

first section

• Sea surface temperature is largely determined by insolation pattern.

• The ocean is warmed by insolation from above. • Seawater temperature decreases with depth. • Steepest part of temperature gradient is called thermocline.

• 96.5% water (H2O) • 3.5% salt ions (e.g., Na+, c1-, Ca2+, Mg2+)

• Salts and minerals are eroded from continental rocks and carried by rivers to the ocean. • When seawater evaporates, salt ions are left behind. - Higher salt concentration in areas of high evaporation rate. • Ocean salinity averages 35 parts per thousand (3.5%). - Varies spatially depending on evaporation rate.

• Seawater salinity changes with depth. - Steepest part of salinity gradient is called halocline.

• A function of temperature and salinity. - Colder water is denser. - Saltier water is denser.

• The density profile of ocean water is determined by temperature and (to a lesser extent) salinity profiles. - Steepest part of density gradient is called pycnocline.

• The ocean is vertically zoned (stratified) into layers based on vertical gradients in temperature and salinity (and thus density). - Circulation patterns and concentrations of nutrients and oxygen can differ between these decoupled layers.

• Water absorbs light energy. • Depth to which sunlight penetrates defines the base of the photic zone. • Below this depth the ocean is dark (aphotic zone). - Photosynthesis cannot take place. • Depth of photic zone depends on season, latitude, time of day, water clarity, and weather. - Typically less than 200 meters below sea surface.

• Oceans occupy the oceanic basins that surround continents. • Sea level is higher than the continental margins. • The flooded portion of a continental margin is called the continental shelf. • An epicontinental (= epeiric; = inland) sea is a shallow sea covering the central area of a continent. - Only a few present-day examples (e.g., Hudson Bay, Baltic Sea, Caspian Sea). • Seafloor profile consists of three parts: - Continental shelf (0 meters to c. 200 meters deep). - Continental slope. - Abyssal plain (ocean basin; 4,000 meters to 6,000 meters deep).

• Waves are driven by the wind blowing over a fluid surface (“wind waves”). • Size depends on wind speed, time and distance (fetch) over which wind blows, and water depth. • Depth to which water is agitated depends on size of wave. - Wave base is deeper during storms than during fair weather conditions. • Affects area of shelf disturbed by wave action.

• Gravitational pull of the Moon on Earth produces high tide in the ocean. [Interesting that this isn’t just some mystical occurrence.] • Earth’s rotation results in each location experiencing two high tides per day. • The Sun also exerts a (weaker) gravitational pull on the oceans. • High tide is even higher when the Moon and Sun align. [An eclipse?] - New and full moons. - Two spring tides per month.

second section

• Pelagic realm (within the water column): - Neritic province (above the continental shelf). - Oceanic province (above the continental slope and ocean basin). • Benthic realm (at the seafloor): - Shelf zone (on the continental shelf). - Bathyal zone (on the continental slope). - Abyssal zone (on the abyssal plain [deep ocean floor]).

• Photic zone (above depth to which light can penetrate). • Aphotic zone (below depth to which light can penetrate).

third section

• Oceans affect climate through their different thermal and physical properties compared to land.

• Water surfaces evaporate, land surfaces do not. - Evaporation is primary source of water vapor to the atmosphere. - During evaporation, water molecules absorb energy and store it as latent heat. - Has cooling effect on adjacent environment. • Water has a higher specific heat capacity than land. - It takes about four times as much energy to warm 1 gram of water by 1°C than it does to warm 1 gram of rock or soil by 1°C. - Water warms (and cools) more slowly than a land surface. • Water is fluid and can flow; land cannot. - Flow results in mixing of cooler and warmer waters, spreading available energy over a greater volume. - Water redistributes heat internally, so warms and cools less rapidly than land.

• Land surface warms (and cools) more quickly and to more extreme temperatures than does a body of water. - Bodies of water exhibit less extreme seasonal temperature swings than adjacent land masses. - “Maritime effect”.

• Seasonal temperature variation is moderated on and near water masses. • Maritime versus continental effect is clear in global annual temperature ranges.

fourth section

• Imbalance of energy drives vast global circulation of energy and mass. • Poleward transfer of energy and mass is achieved by: - Global winds. - Ocean currents. - Dynamic weather systems.