Chemical and physical features of seawater and the
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Chemical and physical features of seawater and the

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according to the owner of this ppt he took some of the facts from various sources.

according to the owner of this ppt he took some of the facts from various sources.

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    Chemical and physical features of seawater and the Chemical and physical features of seawater and the Presentation Transcript

    • 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
    • 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
    • 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
    • 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)
    • 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
    • 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?
    • 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
    • 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
    • 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
    • 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
    • Ocean Circulation Throughout depths currents move and mix ocean waters and transport heat nutrients, pollutants and organisms
    • A. Surface circulation Driven by the wind
    • 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
    • 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
    • 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
    •  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
    •  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
    • 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
    • 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
    •  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
    • 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
    • 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
    •  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