Ch. 3: Chemical and Physical Features of Seawater and the World Ocean

1. Ch. 3: Chemical and Physical Features of Seawater and theWorld Ocean

2. 3.1 The Waters of the Ocean • 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. 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. 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

5. Heat and Water, Cont. • 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

6. 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)

7. 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

8. Seawater Cont. • 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)

9. Seawater Cont. • 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& Baltic Sea is 7 psu • Why is Red Sea salinity so high and the Baltic Sea so low?

10. 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 a colder temps. • Density controlled more by temperature than salinity • There are exceptions therefore salinity & temp need to be measured to determine density

11. 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

12. 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

13. 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

15. 3.2 Ocean Circulation • Throughout depths currents move and mix ocean waters and transport heat nutrients, pollutants and organisms

16. A. Surface circulation • Driven by the wind

17. 1. The Coriolis Effect • Because Earth is rotating anything that moves over the surface tends to turn a little rather than 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

18. 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

19. Global Trade Winds

20. 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

21. Surface Current Cont. • 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 (Coriolis) • trade winds move toward equator the equatorial current • move parallel • currents combine into huge gyres (large systems of circulating currents

23. 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

24. El Nino • large-scale fluctuations can cause conditions like El Nino • current shift with season and weather • near the continental shelf currents are effected by the shape of the bottom & coastline

25. B. Thermohaline • Circulation and the Great Ocean Conveyor • Ocean water stratified • Cold more dense on the bottom & warmer less dense on top

26. 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

27. 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

28. 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

29. 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

31. 3.3 Waves and Tides • A. Waves • Caused by wind • Parts of a wave • Wave crest: moves up & forward • Trough: moves down and back • Water particles do not go anywhere!! • Move in a circle • Faster (the longer the wind the bigger the waves) • Fetch-span of open water • Larger the fetch, the bigger the wave

32. Waves and tides cont. • Seas • Sharp peaks stretch over trough • Move away and get faster than speed of wind • 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

33. 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

34. Tides • Influence marine organisms • Organisms are exposed & submerged on shore • Drive circulation of bays and estuaries, trigger spawning

35. 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

36. 2 high tides and 2 low tides in 24 hours and 50 minutes • extra 50 min because for earth to catch up to moon • 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

37. 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 semidiurnal • tides (2 highs and 2 lows) • 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