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Seawater and the World Ocean. Chemical and Physical Properties.
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Seawater and the World Ocean Chemical and Physical Properties
All matter is made of atoms!1. Elements are made of one kind of atom2. Compounds are elements that are combined.A. Ionic compounds are made of ions (ionic bonding )B. Molecular compounds are made of atoms that share electrons (covalent bonding)Water is a compound, whose molecules are held together by hydrogen bonds.
A hydrogen bond is formed when a charged part of a molecule having polar covalent bonds forms an electrostatic (charge, as in positive attracted to negative) interaction with a substance of opposite charge.
States of Water • Solid (ice) - definite volume and shape, little molecular movement, only vibration • Liquid - definite volume, take the shape of the container. Molecules role over each other • Gas (water vapor) - indefinite volume, fills its container. Molecules are in constant movement.
Why it’s so important that ice can float on water • Allows ample liquid habitat for organisms • Acts as an insulator • By floating on the surface, it prevents lakes from freezing completely.
Heat Capacity of Water - the amount of heat needed to raise the temperature of water 1 degree Celsius High heat capacity means that organisms are not subject to huge changes in temperature.
Latent Heat of Evaporation is the amount of heat that water must absorb in order to evaporate.Hydrogen bonding makes evaporation difficult and keeps water a liquid which allows life to exist on earth.
Solvent Properties • Called the universal solvent because most things dissolve in it • Water easily dissolves salts • - ions are surrounded by polar water molecules • - molecular substances will not dissolve in water • Like dissolves like!
SEA WATER is a mixture of dissolved solids - some material comes from the weathering of rocks - other material from hydrothermal vents - much material is emitted by volcanoes • Composition of Seawater • 99% of solids in seawater are ions • 85% of ions are Na and Cl • Salinity is given in grams/1000 grams of water, ranges from 33 to 37%, averaging at 35% • enclosed seas, such as the Dead Sea, may be as high as 40% in salinity • seas fed by run off from glaciers or other • ice, such as the Baltic Sea, are only 7%
Salinity is tested by a conductivity meter Units are PSUs: practical salinity units The Rule of Constant Proportions states that the percentages of various ions in sea water remains constant. The proportions vary only due to the introduction of pure water from streams, rivers or melting glaciers. Most oceans are chemically well mixed having a constant composition of ions in solution.
Density of Seawater is dependent upon temperature - as temperature increases, density density decreases salinity - as salinity increases, density increases Since temperature varies more than salinity in the ocean, density is more dependent upon temperature. A CTD (Conductivity, Temperature, and depth) is a device with electronic sensors that scientists use to detect conductivity, temperature and depth (CTD) within a column of water.
A temperature profile can be obtained with a CTD or with a Niskin bottle which records temperature and salinity within a water column.
Dissolved Gases in Seawater O2 and N2 and CO2 are dissolved or released to the environment at the surface. Gases dissolve to a greater extent in cold water. Polar regions have more gases dissolved. 0 to 8 ml/L of O2 is dissolved in seawater 210 ml/L of O2 is dissolved in the atmosphere The amount of O2 is affected by photosynthesis and respiration. O2 in the sea is subject to depletion by respiration much more than in the atmosphere.
Carbon Dioxide CO2 is more soluble because it reacts with water. CO2 makes up > 80% of all gases in the sea and < .04% of all gases in the air The ocean stores 50 times as much CO2 as is in the atmosphere.
Transparency Measured with a secchi disk. Important because light must penetrate the water for photosynthesis to take place. Clear ocean water is most transparent to blue light. As depth increases, other colors are absorbed. At 1000ft, there is only darkness.
Pressure Changes dramatically with depth. Sea level - 1 atm 10 meters - 2 atm 20 meters - 3 atm 30 meters - 4 atm As gases compress, air bladders, floats and lungs collapse. Pressure limits the depth of many marine organisms.
This grouper has a swim bladder which blows up ike a balloon if brought to the surface too quickly because of decreased pressure.
Circulation It is most intense near the surface, driven by winds and the Coriolis Effect. Because the earth turns, anything that moves across the surface winds up moving in a curved line. The Coriolis Effect deflects winds in the Northern Hemisphere to the right and in the Southern Hemisphere to the left.
A missle fired from the center (equator) appears to move upward (Pole) because it maintains its speed as the ground below moves slower. It appears to curve relative to the earth’s surface.
WINDS -are driven by heat energy from the sun - less dense air rises at the equator and air from adjacent areas gets drawn in to replace the air that moved upward. (It is bent by the Coriolis Effect and approaches the equator at a 45 degree angle) - these winds are called Trade Winds - they are the steadiest winds on the surface of the sea
Other Winds Westerlies - move in opposite directions to trade winds at middle latitudes Polar Easterlies - most variable winds, occur at high latitudes
Surface Currents The major wind fields of the earth push the surface of the sea and create currents. The uppermost layer of the water moves in a direction that is a 450 angle because of the Coriolis Effect. The top layer pushes on the next layer which moves slightly to the right of it. Each layer in succession does the same thing until a spiral is created - called the Eckman Spiral.
Definitions Ekman layer - the uppermost part of the water column that isaffected by the wind.Equatorial currents - those produced by winds that move parallel to the equator.Gyres - huge circular systems made up of wind driven currents
(a) Salinity profile (b) deepwater temp. and salinity profile (c) thermocline
The Three Layered Ocean • Oceans are stratified because the densest layer sinks. • The water column remains stable if there is a significant difference in density. • When the surface water is denser than lower layers, it will sink in a process called overturn. • Changes in salinity and temperature occur primarily on the surface layer
Three Layers • Surface layer – 100 to 200 meters, mixed by wind waves and currents • Intermediate layer – to a depth of 1500 meters, contains the main thermocline • Deep and bottom layers - below 1500 meters
Waves • In general, water particles allow a wave to pass through them. They are the medium through which energy is transferred. • Waves form when the wind blows • 1. “fetch” is the span of open water over which the wind blows • 2. When the wind blows it pushes up crests into peaks and stretches out the troughs creating waves called “seas”. • 3. When the waves have moved away from the wind, they become “swells” • 4. When waves approach the shore they feel the bottom, slow down and pile up creating “surf”
Wind has blown over this bay for an entire day. On the top side of the bay, wind is blowing over a longer stretch of water. The fetch is longer on the top side and waves are bigger here.
Water particles move in circles as a wave passes through them.
Storm winds generate seas, peaked waves with relatively flat troughs. When they move out of the storm area, they become swells with rounded crests and troughs. In shallow water they get closer together, become unstable and break.
TIDES • Tides are a major influence on nearshore life, drive bay circulation and trigger spawning. • Tides are caused by the gravitational pull of the moon and sun and by rotations of earth, moon and sun.
