Chemical and physical features of seawater and the


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Chemical and physical features of seawater and the

  1. 1. The Waters of the Ocean
  2. 2. A. The Unique Nature of Pure Water All matter is made of atoms Elements are make from one kind of atom A molecule is two or more different atoms combined Water is a polar molecule; one end is positively charged and the other is negatively charged
  3. 3. 1. The Three States of Water Only substance on Earth to naturally exist in three states Weak hydrogen bonds form between to the positive end and the negative end of different water molecules Solid water molecules pack close together & locked in fixed three dimensional pattern Becomes more dense until about 4°C (get less dense) & expands When water freezes in fresh and marine water the ice forms on top allowing organisms to live underneath the ice When marine water freezes it acts like an insulator to stop freezing all the water
  4. 4. 2. Heat and Water Bonds must be broken before molecules can begin to move around Melts at higher temperature & absorbs a lot of heat when it melts (high latent heart of melting) and great deal of heat must be removed to freeze it Melting ice, added heat breaks more hydrogen bonds than increasing molecular motion Mixture of ice & water is 0°-adding heat goes into melting the ice not raising temperature High heat capacity therefore marine organisms not affect by temperature changes in atmosphere & latent heat of evaporation
  5. 5. 3. Water as a Solvent Dissolve more things than any other natural substance (universal solvent) especially salts Salts made of opposite charged particles and conducts electricitySingle atoms or groups of atoms In water, strong ion charges attract water molecule, water molecules surround the ions and pull them apart (dissociation)
  6. 6. B. Seawater Characteristics due to nature of pure water & materials dissolved in it Dissolved solids due to chemical weathering of rocks on land & hydrothermal vents
  7. 7. 1. Salt Composition Sodium chloride account for 85% of all solids dissolved Salinity is total salt dissolved in seawater number of grams left behind when 1000 grams evaporated if 35 grams left then 35 parts per thousand or 350/00 or 35 psu (practical salinity units) Rule of constant proportions states that the relative amounts of various ions in seawater are always the same Differences in salinity results from removal (evaporation) and addition (precipitation) of water Rarely have to deal with changes in ratio of ions as result easier to control salt & water balance Average salinity is 35 psu and between 33-37 psu in open ocean Red Sea is 40 psu 7 & Baltic Sea is 7 psu Why is Red Sea salinity so high and the Baltic Sea so low?
  8. 8. 2. Salinity, Temperature, and Density Get denser as it gets saltier, colder, or both -2° to 30°C temps. below zero possible because saltwater freezes at colder temps. Density controlled more by temperature than salinity There are exceptions therefore salinity & temp need to be measured to determine density
  9. 9. 3. Dissolved Gases O2, CO2 and N2 in atmosphere & sea surface Gas exchange happens between the surface & atmosphere Dissolved gas concentration higher in cold water, lower in warm water Amount of oxygen in water is affected by photosynthesis & respiration Most oxygen is released into the atmosphere More susceptible to oxygen depletion than atmosphere 80% of gasses is carbon dioxide
  10. 10. 4. Transparency Sunlight can penetrate, but it’s affected by the material suspended in the water Important to the photosynthetic organisms Runoff makes coastal waters less transparent than deep blue waters of open ocean
  11. 11. 5. Pressure On land, organisms are under 1 atm at sea level Marine organism have the pressure of the atmosphere & water With every 10m increase depth another atm is added As atms increase gases are compressed Organism have air bladders, floats and lungs that shrink and collapse Limits depth range, some organism are injured when brought to the surface Submarines & housing must be specially engineered to withstand pressure
  12. 12. Ocean Circulation Throughout depths currents move and mix ocean waters and transport heat nutrients, pollutants and organisms
  13. 13. A. Surface circulation Driven by the wind
  14. 14. 1. The Coriolis Effect Because Earth is rotating anything that moves over the surface tends to turn a little rather in a straight line Deflects large-scale motions like winds and currents to the right in Northern Hemisphere and to the left in Southern Hemisphere
  15. 15. 2. Wind Patterns Winds driven by heat energy from sun Trade winds warmer at equator wind at equator becomes less dense and air from adjacent areas gets sucked in to replace it creating winds wind bent by Coriolis Effect approach equator at 45° angle where there is no land steadiest winds Westerlies at middle latitudes move in opposite direction Polar easterlies at high latitudes most variable winds
  16. 16. 3. Surface Currents Winds push the sea surface creating currents Surface current moves off 45° Top layer pushes on layer below & again Coriolis Effect come into play Second layer moves slightly to right and slower and is repeated down the water column (Ekman spiral) lower waters move progressively at greater angles from wind effect of wind decrease with depth 100 m no wind is felt produces Ekman transport upper part of water column moves perpendicular to wind direction to right N. Hemisphere & left in S. Hemisphere
  17. 17.  trade winds move toward equator the equatorial current move parallel currents combine into huge gyres west side of gyres carry warm water to higher latitudes while cold current flow on eastern sides giant thermostat warming the poles & cooling tropics tropical organisms like corals tend to extend into high latitudes on the west sides of the oceans cold loving organisms like kelp grow closest to equator on eastern shores
  18. 18.  large-scale fluctuations can cause conditions like El Nino current shift with season and weather near the continental shelf currents are effect by the shape of the bottom & coastline
  19. 19. B. Thermohaline Circulation and the Great Ocean Conveyor Ocean water stratified Cold more dense on the bottom & warmer less dense on top1. The Three-layered Ocean Surface layer or mixed layer 100 to 200m thick Mixed by wind, waves and currents Sometimes in summer & spring in temperate & polar waters sharp transition to cooler water (theromoclines) noticed by divers Intermediate layer depth of 1000 to 1500m Main thermocline rarely breaks down & in open ocean Deep or bottom layers Below 1500 m typically less than 4°C
  20. 20. 2. Stability and Overturn Water column with less dense water on top and dense water on bottom with no mixing is stable Depends on the difference in densities between layers If difference is small not much energy is needed to mix the water Downwelling occurs when top layers become more dense & sinks The sinking water displaces and mixes with deeper water (overturn) Density & temperature profiles are straight-lined Temperate and polar during winter
  21. 21.  Mixing layers extends greater into water column Important to productivity In intense downwelling, large volume of water may leave without mixing Changes in salinity at surfacePrecipitation, evaporation, freezing, and temp. Once water sunk it does not change in salinity and temp. (water mass) Oceanographers can follow the circulation over large distances Because it is driven by density (determined by temp and salinity) the circulation is called thermohaline circulation
  22. 22. 3. The Great Ocean Conveyer Only places where surface overturn reaches the bottom is Atlantic south of Greenland & north of Antartica The sinking water spreads though the Atlantic & other ocean basins then eventually rise to surface and flows back Recycles about every 4000 years Regulates climate and alterations have produced rapid climate changes (ie ice ages) Bring dissolved oxygen to deep sea
  23. 23. 3.3 Waves and TidesA. Waves Caused by wind Wave crest moves up & forward Trough moves down and back Water particles do not go anywhere Moves in a circle Faster the longer the wind the bigger the waves Fetch-span of open water Larger the fetch the bigger the wave Seas Sharp peaks stretch over trough Move away get faster than speed of wind
  24. 24.  Swells Once waves settle Surf Bottom forces water to move elongated ellipses Wavelength get shorter Waves “pile up” becoming higher & steeper until they fall forward Water affected by mixture of waves Two crest adding to make a higher wave (wave reinforcement)As high as ten stories Trough & crest combine & cancel out the wave
  25. 25. B. Tides Influence marine organisms Organisms are exposed & submerged on shore Drive circulation of bays and estuaries, trigger spawning
  26. 26. 1. Why Are There Tides? (if water covered completely by water) Gravitational pull of sun & moon & rotation of Earth, moon, & sun Moon’s influence gravity strongest on side of earth closest - pulls water in ocean toward it Opposite side furthest from moon - pull is weakest earth’s rotation is like unbalanced tire (wooble) creates a centrifugal force - makes the oceans bulge out toward the moon & away from moon 2 high tides and 2 low tides in 24 hours and 50 minutes extra 50 min because for earth to catch up to moon
  27. 27.  Sun ½ as strong as moon because so far away Full & new moon (sun moon in line) Tidal range (difference between high and low tide) is largeSpring tides First and third quarter Sun & moon at right angles partially cancel each other out – tidal range small Neap tides
  28. 28. 2. Tides in the Real World Tides vary depending on location and the shape and depth of the basin East coast of N. America & most of Europe & Africa have semidiur West coast of USA & Canada mixed semidiurnal tide- successive tides of different height Diurnal ( 1 high and 1 low) rare on Antarctica and parts of Gulf of Mexico, Caribbean, & Pacific Tide tables give predicted time and height of high and low tides Determined by local geology Weather like strong winds can cause water to pile on the shore creating higher tide than predictednal tides (2 highs and 2 lows)