© 2006 Thomson-Brooks Cole Chapter 4 Water, Waves, and Tides.

© 2006 Thomson-Brooks Cole Key Concepts The polar nature of water accounts for many of its physical properties. Seawater contains a number of salts, the most abundant being sodium chloride. Salts are constantly being added to and removed from the oceans. The exchange of energy between oceans and the atmosphere produces winds that drive ocean currents and weather patterns.

© 2006 Thomson-Brooks Cole Key Concepts The density of seawater is mainly determined by temperature and salinity. Vertical mixing of seawater carries oxygen to the deep and nutrients to the surface. Waves are the result of forces acting on the surface of the water. The gravitational pull of the moon and the sun on the oceans produces tides.

Nature of Water 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 Freezing point and boiling point –hydrogen bonds—weak attractive forces between slightly positive H atoms of one molecule and slightly negative O ends of nearby molecules –responsible for high freezing/boiling points

Nature of Water Water as a solvent –polar nature keeps solute’s ions in solution –water cannot dissolve non-polar molecules

Nature of Water Cohesion, adhesion, and capillary action –cohesive H bonds = high surface tension –adhesion—attraction of water to surfaces of objects that carry electrical charges, which allows it to make things wet –capillary action—the ability of water to rise in narrow spaces, owing to adhesion

Nature of Water Specific heat –water has a high specific heat (amount of heat energy needed to raise 1 g 1 o C) –ocean can maintain relatively constant temperature Water and light –much light reflected into the atmosphere –different wavelengths (colors) of light penetrate to different depths

© 2006 Thomson-Brooks Cole Nature of Water Chemical properties of water –acids release H + atoms in water –bases bind H ions and remove them from solution –pH scale measures acidity/alkalinity –ocean’s pH is slightly alkaline (average 8) owing to bicarbonate and carbonate ions –organisms’ internal and external pH affect life processes such as metabolism and growth

Salt Water Composition of seawater –6 ions make up 99% of dissolved salts in the ocean: sodium (Na + ) magnesium (Mg 2+ ) calcium (Ca 2+ ) potassium (K + ) chloride (Cl - ) sulfate (SO 4 2- ) –trace elements—present in concentrations of less than 1 part per million

Salt Water Salinity –seawater = 3.5% salt, 96.5% water –expressed as in g per kg water or parts per thousand –salinity of surface water varies as a result of evaporation, precipitation, freezing, thawing, and freshwater runoff from land –10 o N-10 o S = low salinity (heavy rainfall) –areas around 30 o N and 30 o S = high salinity (evaporation) –from 50 o = low salinity (heavy rainfall) –poles = high salinity (freezing)

Salt Water Cycling of sea salts –sea salt originally from earth’s crust –ocean composition has remained the same owing to balance between addition through runoff and removal –salts removed in many ways: sinking or depositing on land by sea spray evaporites concentration in tissues of organisms harvested for food adsorption—process of ions sticking to surface of fine particles, which sink into sediments

Salt Water Gases in seawater –gases from biological processes oxygen is a by-product of photosynthesis most organisms use O, release CO 2 just below sunlit surface waters is the oxygen- minimum zone –solubility of gases in seawater seawater has more O and CO 2 but less N than the atmosphere solubility: CO 2 > O > N affected by temperature, salinity and pressure

Salt Water –role of bicarbonate as a buffer bicarbonate formed from the solution of CO 2 buffer—a substance that can maintain the pH of a solution at a relatively constant point bicarbonate’s buffering action helps maintain a stable environment for marine organisms

Ocean Heating and Cooling Earth’s energy budget –energy input sun’s radiant energy heats earth’s surface spherical shape + presence of the atmosphere cause the amount of radiant energy reaching earth’s surface to decrease with increasing latitude

Ocean Heating and Cooling Earth’s energy budget –energy output excess energy absorbed by the earth is transferred to the atmosphere by evaporation and radiation accumulation of greenhouse gases can prevent heat energy from radiating back to space

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, especially between 40 o and 60 o N and S

Winds and Currents Winds –result of horizontal air movements caused by temperature, density, etc. –wind patterns: upper air flow from the equator towards the north and south

Winds and Currents Winds –Coriolis effect a point rotating at the equator moves faster than a point at a higher latitude path of air mass appears to curve relative to the earth’s surface—to the right in the Northern Hemisphere, left in the Southern

Winds and Currents –surface wind patterns 3 convection cells in each hemisphere winds are designated by the direction from which they are coming –northeast trade winds –southeast trade winds –westerlies –polar easterlies areas of vertical air movement between wind belts –doldrums –horse latitudes

Winds and Currents Ocean currents –surface currents driven mainly by trade winds (easterlies and westerlies) in each hemisphere Coriolis effect –currents deflected to the right of the prevailing wind direction in the Northern Hemisphere, to the left in the Southern Hemisphere gyres—water flow in a circular pattern around the edge of an ocean basin

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—carry cold water toward the equator transverse currents—connect eastern- and western-boundary currents in each gyre biological impact –western-boundary currents carry little nutrients but increase oxygen mixed in water—not productive –eastern-boundary currents productive, nutrient-rich

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

Ocean Layers and Ocean Mixing Density—the mass of a substance in a given volume, usually in g/cm 3 –pure water’s density = 1 g/cm 3 –salt water’s density = 1.0270 g/cm 3 Density increases when salinity increases Density increases when temperature decreases

Ocean Layers and Ocean Mixing Characteristics of ocean layers –depth 0-100 m: warmed by solar radiation and well mixed –100-1,000 m: thermocline (decreasing temperatures create increasing density) –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

Ocean Layers and Ocean Mixing Horizontal mixing –higher density causes water at 30 o N to form a curved layer that sinks below less- dense equatorial surface water and then rises to rejoin the surface at 30 o S –even denser water curves from 60 o N to 60 o S below other surface waters –winter temperatures and increased salinity owing to freezing result in very dense water at the poles, which sinks toward the ocean floor 0

© 2006 Thomson-Brooks Cole Ocean Layers and Ocean Mixing Vertical mixing –vertical overturn results when denser water at the top of the water column sinks while less-dense water rises –isopycnal—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 –densest water of all is Antarctic Bottom Water, mostly formed in winter in the Weddell Sea –dense Antarctic water sinks to the bottom and creeps very slowly toward the Arctic –some North Atlantic Deep Water moves into the North Atlantic via a channel east of Greenland –high-salinity Mediterranean Deep Water flows through the Strait of Gibraltar into the Atlantic Ocean

© 2006 Thomson-Brooks Cole 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 most common = wind also geological events, falling objects, ships –restoring force—the force that causes the water to return to the undisturbed level = surface tension for capillary waves = gravity for gravity waves

Waves Types of waves –progressive waves are generated by wind and restored by gravity, and they progress in a particular direction forced waves are formed by storms, which determine their size and speed speed of free waves, no longer affected by the generating force, is 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

© 2006 Thomson-Brooks Cole Waves –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 –plungers form when the beach slope is steep –spillers are found on flatter beaches

Waves wave refraction—bending of waves as the portion that reaches shallow water first slows, but the portion still in deeper water continues at the original speed –tsunamis 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 pr island causes a dramatic increase in height

Tides 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

Tides Spring and neap tides –during spring tides, the times of highest and lowest tides, the earth, moon and sun are in a line, combining the pull of the sun and moon –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

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 tide ranges from high water to low water flood tides are rising; ebb tides are falling tidal currents are associated with tidal cycle slack water occurs during the change of tides

© 2006 Thomson-Brooks Cole Chapter 4 Water, Waves, and Tides.

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© 2006 Thomson-Brooks Cole Chapter 4 Water, Waves, and Tides.

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