Chemical and Physical Features of Seawater and the World Ocean: Chemical and Physical Features of Seawater and the World Ocean


The “Weather” of the Marine Environment: The “Weather” of the Marine Environment Wind Waves Tides Currents Temperature Salt


Slide3: Where organisms are found in the marine environment is determined by the chemical and physical factors To understand the biology of marine organisms, we must know something about the environment in which they live


The Waters of the Ocean: The Waters of the Ocean


Slide5: Marine organisms are mostly made of water 80% or more by weight in most cases Jellyfish – 95% Water makes life possible


The Unique Nature of Pure Water: The Unique Nature of Pure Water All matter is made of atoms Elements – made of a single kind of element Molecules – two or more atoms joined together – ex. Water Water molecules stick together because of their polarity These weak bonds are known as hydrogen bonds


Slide7: Hydrogen bonds make water different from any other substance on earth


Three States of Matter: Three States of Matter Solid, liquid, gas Water is the only substance that naturally occurs in all three states on earth


Special Characteristics of Water: Special Characteristics of Water In liquid water hydrogen bonds hold most of the molecules together in small groups Temperature is a reflection of the average speed of the molecules – faster they move the higher the temperature When the molecules move fast enough they escape the hydrogen bonds and enter the gaseous phase (evaporation)


Slide11: In water vapor the molecules are not held together by hydrogen bonds As water cools the molecules pack closer together and take up less space Therefore the density of water increases as water cools until it reaches 4oC Below 4oC water becomes less dense Cool seawater will sink since it is denser


Slide12: Once water cools hydrogen bonds reform Ice crystals (solid made of regular patterns of molecules) Water molecules are spaced farther apart than in liquid water making ice less dense than water Ice will float on top of water – special property that makes life in the water possible – insulates water below


Heat and Water: Heat and Water It takes a large amount of heat to melt ice As heat energy is added and the temperature of ice rises, the molecules vibrate faster, breaking some of the hydrogen bonds that hold the crystal together


Latent Heat of Melting: Latent Heat of Melting Amount of heat required to melt a substance


Melting Ice: Melting Ice Once ice begins to melt added heat breaks more hydrogen bonds rather than increasing the speed of molecular motion Any heat put in goes into melting the ice, not into raising the temperature


Heat Capacity: Heat Capacity Amount of heat needed to raise a substance’s temperature by a given amount How much heat a substance can absorb Water has one of the highest heat capacities of any substance


Importance of Water’s High Heat Capacity: Importance of Water’s High Heat Capacity Most marine organisms are not subjected to the rapid and sometimes drastic temperature changes that occur on land


Latent Heat of Evaporation: Latent Heat of Evaporation The amount of heat energy that is needed to evaporate a substance Change from a liquid to a gas Water absorbs a great deal of heat when it evaporates


Water as a Solvent: Water as a Solvent Universal solvent Especially good at dissolving salts Salts are made of combinations of particles that have opposite electrical charges The polarity of water allows it to break down the salts


Slide21: Ion – electrically charged particles Ions have stronger charges than the ends of water molecules When a salt enters water the ions break apart and become surround by water molecules which break there hydrogen bonds to surround the ion Ions pull apart or dissociate and the salt dissolves


Seawater: Seawater Characteristics of seawater are due both to the nature of the pure water and to the material dissolved in it


Solids Dissolved in Seawater: Solids Dissolved in Seawater Come from the chemical weathering of rocks on land and are carried to the sea by rivers Earth’s interior Hydrothermal vents Volcanoes


Salt Composition: Salt Composition Solutes – dissolved materials 6 ions compose over 99% of the solids dissolved in seawater Na and Cl account for 85% of the dissolved solids in seawater


Salinity: Salinity Total amount of salt dissolved in seawater Usually expressed as the number of grams of salt left behind when 1,000 grams of seawater are evaporated 1 = dissolved trace elements


Slide26: Ions are good conductors of electricity Electrical conductivity of seawater therefore reflects the concentration of dissolved ions Practical Salinity Units – psu – measurement of salinity determined from conductivity measurements


Importance of Salinity: Importance of Salinity Salinity of water greatly affects the organisms that in it


Rule of Constant Proportions: Rule of Constant Proportions Percentage of various ions in seawater remains constant even though the total amount of salt in the water can vary slightly


Slide29: Oceans are chemically well mixed and ocean salinity varies almost entirely as a result of the addition or removal of pure water rather than the addition or removal of salt


Addition and Removal of Water: Addition and Removal of Water Water is removed from the ocean primarily by evaporation and to a lesser extent by freezing Water is added to the ocean by precipitation


Average Salinity of the Ocean: Average Salinity of the Ocean 35 ppt (parts per thousand) Red Sea 40 ppt Baltic Sea 7 ppt (from river runoff)


Salinity, Temperature and Density: Salinity, Temperature and Density The saltier the water the denser it is The density of seawater therefore depends on its temperature and its salinity


Measuring Temperature and Salinity: Measuring Temperature and Salinity Can be measured by lowering specially designed bottles and thermometers on a wire to the desired depth A weight called a messenger is released to slide down the wire, triggering the bottles to snap shut and trap a water sample


Temperature Profile: Temperature Profile A graph that shows the temperature at different depths in the ocean Water column – vertical shaft of water


Modern Technology: Modern Technology Oceanographers usually use electronic sensors to quickly and accurately record salinity, temperature and depth throughout the water column, rather than at certain depths CTDs – Conductivity Temperature Depth meters XBTs – Expendable bathythermographs – measure temperature


Problem: Problem Measurements can only be made at one place at one time – difficult to get information over a large area Ship had to move to a new place to make more measurements Conditions change because of currents or weather Many ships would help but it is expensive


Part Solution: Part Solution Make measurements with automated instruments that are left in the ocean Satellites can measure surface conditions


Dissolved Gases: Dissolved Gases Gases are dissolved in seawater as well as solid materials The 3 most important gases are: oxygen, carbon dioxide and nitrogen Found in the atmosphere and dissolve at the sea surface


Gas Exchange: Gas Exchange movement of gases between the atmosphere and the ocean surface


Slide41: Gases dissolve better in cold than warm water Dissolved gas concentrations are higher in polar waters than in the tropics


Oxygen: Oxygen Not very soluble 0 to 8 milliliters per liter of seawater On average 4 to 6 ml/L Air has 210 ml/L


Carbon Dioxide: Carbon Dioxide More soluble than oxygen because it reacts chemically when it dissolves 80% of the dissolved gas in the ocean .04% in air Stores more than 50 times as much total CO2 as the atmosphere


Transparency: Transparency Biologically important property Sunlight can penetrate into the ocean Allows for photosynthesis Not all colors penetrate seawater equally well Water is most transparent to blue light


Slide47: As depth increases more colors are filtered out Red is the first to be filtered out Something that is red at the surface looks black or gray at depth because there is no red light to reflect off them and be seen At depths of 1000 m or 3300 ft there is total darkness


Turbidity: Turbidity Transparency of water is strongly affected by material that is suspended and dissolved in the water Ex. Muddy water, lots of plankton


Pressure: Pressure Factor that changes dramatically with depth On land – 1 atm of pressure With each 10m (33 ft) of increased depth another atmosphere of pressure is added As the pressure increases the gases are compressed – limits range of orgs – ex. Swim bladder


Water Density and the Three Layered Ocean: Water Density and the Three Layered Ocean


Slide54: Much of the three dimensional structure of the sea, especially in relation to depth is controlled by the density of the water


Stability and Overturn: Stability and Overturn Densest water sinks so the ocean is usually layered or stratified Deep water – cold and dense Surface water – warm and light


Water Column Stability: Water Column Stability Stable Water Column - Less dense on top, dense on bottom Low stability – surface water is only slightly less dense Highly stable – large density difference Unstable – surface water more dense than bottom water


Slide57: Downwelling – when surface water sinks Overturn – when dense surface water displaces deeper water Temperature and density profiles are vertical straight lines for water columns experiencing overturn


Slide59: Overturn usually occurs in temperate and polar regions during the winter when the surface water cools The water descends to a depth determined by its density


Slide60: The processes that change salinity in the open ocean (precipitation, evaporation and freezing) occur only at the surface Temperature changes occur only at the surface


Water Mass: Water Mass Once surface water has sunk its properties do not change The volume of water has a “fingerprint”, a characteristic combination of temperature and salinity Oceanographers can tract the movement or circulation of water masses


Thermohaline Circulation: Thermohaline Circulation Circulation driven by changes in density which in turn is determined by temperature and salinity Extend throughout the ocean depths Important in regulating earth’s climate and chemically mixing the oceans Brings dissolved oxygen to the deep sea Helps determine the abundance of life in the deep sea


The Three-Layered Ocean: The Three-Layered Ocean


Surface Layer: Surface Layer 100 to 200 m thick (330 to 660 ft) Mixed by wind, waves and currents Also known as the mixed layer


Thermocline: Thermocline Sudden changes in temperature over small depth intervals seasonal


Intermediate Layer: Intermediate Layer Below the surface layer of around 1500 m (5000 ft) Contains the main thermocline


Main Thermocline: Main Thermocline zone of transition between warm surface water and cold water below lies in the intermediate layer rarely breaks down feature of the open ocean


Deep and bottom layers: Deep and bottom layers Below 1,500 m or (5,000 ft) Uniformly cold Typically less than 4oC (39 oF)


Motion in the Ocean: Motion in the Ocean


Surface Circulation: Surface Circulation Most intense motion of the ocean occurs at the surface in the form of surface currents and waves Driven by wind which is driven by heat from the sun Coriolis effect also strongly influences


Coriolis Effect: Coriolis Effect Earth is round and rotating so anything that moves over its surface tends to turn a little rather than moving in a single straight line Mostly effects winds and ocean currents that move over large distances


Slide73: Northern Hemisphere – deflects things to the right Southern Hemisphere – deflects things to the left


Winds Patterns: Winds Patterns Winds in our atmosphere are driven by heat energy from the sun Most of the solar energy is absorbed near the equator Warm air rises at the equator Air from adjacent areas gets sucked in to replace the rising equatorial air creating wind


Slide75: The wind does not move straight to the equator but are bent by the Coriolis effect – approach at a 45 angle


Trade Winds: Trade Winds winds near the equator (northeast and the southeast) steadiest winds on earth between 0 and 30 degrees


Westerlies: Westerlies driven by solar energy more variable between 30 and 60 degrees move in the opposite direction to the trade winds


Polar Easterlies: Polar Easterlies Most variable Between 60 and 90 degrees


Surface Currents: Surface Currents The major wind fields of the atmosphere push the sea surface creating currents All major surface currents of the open ocean are driven by the wind


Slide81: When pushed by the wind the uppermost layer of water begins to move The water does not move in the same direction as the wind but at a 45o angle because of the Coriolis effect The top layer pushes the water below but at a 45o angle and so on


Ekman Spiral: Ekman Spiral Spiral change in the movement in the water column when the water is pushed by the wind At a depth of a few hundred meters the wind in not felt at all Ekman Layer – upper part of the water column that is affected by the wind


Slide84: Ekman transport – taken as a whole the Ekman layer moves at 90o from the wind direction


Consequence of the Coriolis Effect: Consequence of the Coriolis Effect Trade winds move towards the equator the equatorial currents that these winds produce move parallel to the equator


Gyres: Gyres Wind driven surface currents combined into huge more less circular systems Under the influence of the Coriolis Effect


Transportation of Solar Heat: Transportation of Solar Heat Warm currents on the western sides of the gyres carry vast amounts of solar heat from the equator to higher latitudes Cold currents flow in opposite direction on the eastern sides Ocean currents act as a giant thermostat warming the poles and cooling the tropics


Slide89: Large scale fluctuations in current patterns can dramatically effect weather around the world - El Nino


Role of Surface Currents: Role of Surface Currents Surface water temperatures are higher on the western sides of the oceans where currents carry warm water away from the equator


Waves: Waves


Waves: Waves Wind causes Most familiar of all ocean phenomena Affect the organisms that live on the shore


Wave Parts: Wave Parts Crest – highest part of a wave Trough – lowest part of a wave Wave Height – vertical distance between trough and crest Wavelength – distance between two successive crests or troughs Period – time a waves takes to go by any given point


Water Movement: Water Movement In a wave crest, water moves up and forward In a wave trough, water moves down and back On the whole water particles do not go anywhere at all – just move in circles Waves carry energy across the surface, not water


Formation of waves: Formation of waves Begins when the wind starts to blow The faster and longer the wind blows the larger the waves get Fetch – span of open water over which the wind blows – determines size of waves


Seas: Seas waves that have sharp peaks and relatively flat wave troughs


Swells: Swells Waves with smooth rounded crests and troughs Similar to ideal waves


Surf: Surf Waves that becomes so high and steep as it approaches the shoreline that it breaks Waves become closer together Energy is released on the shoreline when the wave breaks


Tsunamis: Tsunamis Deadly waves Japanese word for “harbor wave” Produced by earthquakes, landslides, volcanoes, and other disturbances of the sea floor Tidal waves – properly called – seismic sea waves


Slide102: Long fast moving waves Wavelengths of 240 km (150 mi) Travel 700 km/hr (435 mi/hr) – as fast as a jet plane Open ocean – not very high – 1 m


Warning: Warning Worldwide network of seismic monitoring stations that provide instant notice of an earthquake or other seismic disturbance System has saved lives but is far from perfect Can’t predict which earthquakes produce killer tsunamis Also many people in developing countries do not get the warnings


Tides: Tides


Tides: Tides Dominant influence on near shore sea life Expose and submerge organisms on the shore Drive the circulation of bays and estuaries Triggers spawning


Causes of the Tides: Causes of the Tides Caused by the gravitational pull of the moon and sun by rotations of the earth moon and sun Earth and the moon rotate around a common point (their combined center of mass) This rotation produces a centrifugal force


Slide107: The centrifugal force just balances the gravitational attraction between earth and the moon The centrifugal force and the moon’s gravity are not in perfect balance everywhere on earth’s surface


Slide108: On the side nearest the moon, the moon’s gravity is stronger and pulls the water toward the moon On the side away from the moon the centrifugal force dominates and pushes the water away from the moon


Slide109: If earth were completely covered with water, the water would form two bulges on opposite sides of the planet Water would be deep under the bulges and shallower away from the bulges


Slide110: Earth is spinning like a top on its own axis As it does this any given point would be under the bulge and then away from the bulge High tide occurs when a point is under a bulge and low tide occurs when it is away from a bulge


Slide111: The earth rotates on its axis every 24 hours so a point will have two high tides and two low tides The moon advances on it orbit each day so a full tidal cycle takes 24 hours and 50 minutes


The Sun’s Bulge: The Sun’s Bulge Sun produces a bulge like the moon but is it smaller When the sun and the moon are in line there bulges add up and when they are at right angle to one another they cancel each other out


Tidal Range: Tidal Range Difference in water level between successive high and low tides


Spring Tide: Spring Tide When the sun and moon bulge add together High high tides and low low tides Named because they seem to surge up like spring water Occur when there is a full or new moon


Neap Tide: Neap Tide Occur when sun and moon are at right angles to one another Moon is in the 1st and 3rd quarters Average tides Low high tide and a high low tide


Variations in Tides: Variations in Tides Tides vary from place to place depending on the location and on the shape and depth of the basin


Bay of Fundy, Canada: Bay of Fundy, Canada


Tide Terms: Tide Terms Semidiurnal tides – two high and two low tides Mixed semidiurnal tides- successive high tides of different height Diurnal Tides – one high and one low - uncommon


Tide Tables: Tide Tables Give the predicted time and height of high and low tides Very accurate


The End: The End