Chapter 4 Water, Waves, and Tides

71% of Earths surface is covered with water 97% salt water 3% fresh water

Nature of Water Marine organisms are 70 – 80% water by mass. Terrestrial organisms are approximately 66% water by mass! Physical properties of water excellent solvent high boiling point and freezing point denser in its liquid form than in its solid form supports marine organisms through buoyancy provides a medium for chemical reactions necessary for life

Nature of Water Structure of a water molecule 2 H atoms bonded to 1 O atom polar - different parts of the molecule have different electrical charges: the oxygen atom carries a slight negative charge; the hydrogen atoms carry a slight positive charge

Figure 4-1 (a) Water Molecules.

Figure 4-1 (b) Water Molecules.

Figure 4-1 (c) Water Molecules.

Nature of Water Specific heat (Thermal capacity) Water and light ocean can maintain relatively constant temperature Water and light much light reflected into the atmosphere different wavelengths (colors) of light penetrate to different depths

Nature of Water Chemical properties of water pH scale measures acidity/alkalinity ocean’s pH is slightly alkaline (average 8) organisms’ internal and external pH affect life processes such as metabolism and growth

Salt Water Salinity seawater = 3.5% salt, 96.5% water expressed as in g per kg water or parts per thousand (ppt) salinity of surface water varies as a result of evaporation, precipitation, freezing, thawing, and freshwater runoff from land areas around 30o N and 30o S = high salinity (evaporation > precipitation) poles = high salinity (freezing – removes water from sea)

Hydrogen sulfide (H2S) Chlorine (Cl2) Sulfur Chloride (Cl–) Precipitation Chloride (Cl–) Sulfate (SO42–) Hydrogen sulfide (H2S) Chlorine (Cl2) Volcano Sulfur Sea spray removes salts Salts removed when organisms are caught for food River discharge Carbonate (CO32–) Calcium (Ca2+) Sulfate (SO42–) Sodium (Na+) Magnesium (Mg2+) Calcium (Ca2+) Magnesium (Mg2+) Potassium (K+) Rock on the seafloor Clay particles adsorb Organisms die Bottom sediments Precipitation Stepped Art Fig. 4-6, p. 75

Salt Water Gases in seawater gases from biological processes oxygen is a by-product of photosynthesis release of CO2 from respiration oxygen-minimum zone – located just below sunlit surface waters solubility of gases in seawater seawater has more O and CO2 but less N than the atmosphere affected by temperature, salinity and pressure

Table 4-3 Gases Found in Seawater

Figure 4-8 Distribution of Solar Energy.

Ocean Heating and Cooling Sea temperature temperature varies daily and seasonally affected by energy absorption at the surface, loss by evaporation, transfer by currents, warming/cooling of atmosphere, heat loss through radiation seasonal variations in the amount of solar radiation reaching the earth, occur especially between 40o and 60o N and S because angle of sun’s rays change dramatically at these latitudes seasonally

Figure 4-10 Average Surface Temperatures Of The World Ocean.

Winds and Currents Winds result from horizontal air movements caused by temperature, density, etc. as air heats, its density decreases and it rises; as it cools, density increases and it falls toward earth wind patterns: upper air flow from the equator towards the north and south

Figure 4-11 North-South Air Flow.

Winds and Currents Winds Coriolis effect Apparent force on moving particles resulting from the earth’s rotation path of air mass appears to curve relative to the earth’s surface—to the right in the Northern Hemisphere, left in the Southern

Figure 4-12 (c) The Coriolis Effect.

Winds and Currents Surface wind patterns 3 convection cells in each hemisphere: northeast & southeast trade winds westerlies polar easterlies areas of vertical air movement between wind belts Doldrums (at equator) horse latitudes (at 30o N & S)

Figure 4-13 Surface Wind Patterns.

Winds and Currents Ocean currents surface currents driven mainly by trade winds (easterlies and westerlies) in each hemisphere Coriolis effect deflection can be as much as 45-degree angle from wind direction gyres—water flow in a circular pattern around the edge of an ocean basin

Figure 4-14 (a) Gyres.

Figure 4-14 (b) Gyres.

Winds and Currents Classification of currents western-boundary currents: fastest, deepest currents that move warm water toward the poles in each gyre (e.g. Gulf Stream) eastern-boundary currents: slow moving, carry cold water toward the equator transverse currents: connect eastern- and western-boundary currents in each gyre biological impact western-boundary currents not productive, carry little nutrients, but increase oxygen mixed in water eastern-boundary currents productive, nutrient-rich

Figure 4-15 Major Ocean Currents.

Winds and Currents Currents below the surface energy transferred from winds to surface water is transferred to deeper water deeper-water currents are deflected by the Coriolis effect, down to about 100 m friction causes loss of energy, so each layer moves at an angle to and more slowly than the layer above, creating an Ekman spiral Ekman transport—net movement of water to the 100-m depth

Figure 4-16 Ekman Spiral.

Ocean Layers and Ocean Mixing Density increases when salinity increases Density increases when temperature decreases

Ocean Layers and Ocean Mixing Characteristics of ocean layers depth 0-100 m (330 feet): warmed by solar radiation, well mixed 100-1,000 m: temperature decreases thermocline – zone of rapid temperature change halocline: salinity increases 0-1,000 m pycnocline: 100-1,000 m, where changes in temperature and salinity create rapid increases in density seasonal thermoclines

Figure 4-18 (a) Changes In Temperature, Salinity, And Density Of Seawater With Depth.

Figure 4-18 (b) Changes In Temperature, Salinity, And Density Of Seawater With Depth.

Figure 4-18 (c) Changes In Temperature, Salinity, And Density Of Seawater With Depth.

Ocean Layers and Ocean Mixing Horizontal mixing winter temperatures and increased salinity owing to freezing result in very dense water at the poles, which sinks toward the ocean floor

Ocean Layers and Ocean Mixing Vertical mixing isopycnal—stable water column that has the same density from top to bottom vertical mixing allows water exchange between surface and deep waters nutrient-rich bottom water is exchanged for oxygen-rich surface water

Ocean Layers and Ocean Mixing Upwelling and downwelling equatorial upwelling water from currents on either side of the equator is deflected toward the poles, pulling surface water away to be replaced by deeper, nutrient-rich water coastal upwelling Ekman transport moves water offshore, to be replaced by deeper, nutrient-rich water coastal downwelling coastal winds force oxygen-rich surface waters downward and along the continental shelf

Ocean Layers and Ocean Mixing Deepwater circulation differences in density, not wind energy, cause water movement in deep oceans dense Antarctic water sinks to the bottom and moves slowly toward the Arctic

Waves Wave formation wave: a flow of energy or motion, not a flow of water generating force: a force that disturbs the water’s surface, e.g., wind, geological events, falling objects, ships

Figure 4-22 Characteristics Of Waves.

Waves Types of waves Progressive (forced) waves are generated by wind and restored by gravity, progress in a particular direction forced waves are formed by storms, which determine their size and speed free waves, no longer affected by the generating force, move at speeds determined by the wave’s length and period swells are long-period, uniform free waves which carry considerable energy and can travel for thousands of km

Waves Types of Waves (con’t) deepwater and shallow-water waves deepwater waves—waves that occur in water that is deeper than ½ of a wave’s wavelength breakers deepwater waves become shallow-water waves when they move into shallow water surf zone—area along a coast where waves slow down, become steeper, break, and disappear breakers form when the wave’s bottom slows but its crest continues at a faster speed

Figure 4-23 Breakers.

Waves Types of Waves (con’t) Tsunamis (large seismic sea waves) seismic sea waves are formed by earthquakes tsunamis have long wavelengths, long periods and low height compression of the wave’s energy into a smaller volume upon approaching a coast or island causes a dramatic increase in height

Figure 4-24 Tsunami.

Tides Tides: periodic changes in water level occurring along coastlines Why tides occur tides result from the gravitational pull of the moon and the sun though smaller, the moon is closer to earth, so its gravitational pull is greater water moves toward the moon, forming a bulge at the point directly under it the centrifugal force opposite the moon forms another bulge areas of low water form between bulges

Figure 4-25 Tides.

Tides Spring and neap tides during spring tides, the times of highest and lowest tides, the earth, moon and sun are in a line and act together creating highest and lowest tides when the sun and moon are at right angles, the sun’s pull offsets the moon’s, resulting in neap tides, which have the smallest change between high and low tide

Figure 4-26 Spring And Neap Tides.

Tides Tidal range diurnal tide: one high tide and one low tide each day semidiurnal tide: two high tides and two low tides each day (most common) mixed semidiurnal tide: high and low tides are at different levels flood tides are rising; ebb tides are falling tidal currents are associated with tidal cycle slack water occurs during the change of tides

Figure 4-27 (a, b & c) Tidal Patterns.

Figure 4-27 (d) Tidal Patterns.

Climate and the Ocean Ocean is a great modifier of temperature Hydrologic cycle Convection, evaporation, and precipitation

Weather Front - when cold air mass collides with a warm air mass Fronts are marked by stormy weather

Monsoons Seasonal wind pattern changes caused by heating or cooling on the continents Summers - significant rainfall and winters - very little Common on the west coast of India and in Southeast Asia

Cyclones Large rotating storm systems of low-pressure air Forms over warm oceans near Equator Typhoons – Pacific Ocean Hurricanes – Atlantic Ocean Strong rotating winds At least 74 miles per hour Thunder and Lightning Winds rotate in a counterclockwise direction around a central, calm eye

When it moves over land (or cold water) the storm begins to weaken quickly Storm is fueled by warm water Average 100 cyclones worldwide each year

Weather symbol for a hurricane is: Marine flags that warn of a hurricane

Hurricane Structure Eye – relatively calm roughly 20 to 30 miles wide Smaller the eye – stronger the winds Right side generally has the fastest winds Left side usually has the most rain

Hurricane Classification 5 categories based on current maximum wind speed Saffir-Simpson Hurricane Scale Category 1 – Winds 74-95 mph Category 2 – Winds 96-11 mph Category 3 – Winds 111-130 mph Category 4 – Winds 131-155 mph Category 5 – Winds over 155 mph Very rare, status for a short time

Storm Surges Becoming more dangerous due to increase in coastal population

Waterspouts Tornado over water May carry water as high as 328 ft Very short-lived Not particularly dangerous Most often occur during the summer months Florida Keys have the most in the U.S.