51 terms

Oceanography unit 4

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What makes the water molecule so special?
Covalent Bonding, Electronegativity differences, Polar Molecule, Hydrogen Bonding, Very high Specific Heat, compared to other molecules same size, States of Matter found on planet Earth, Effect of Salt on Water's Melting Point and Boiling Point
Properties of water:
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Water Molecule
Covalent bond, 104.5 degree angle between the hydrogens (bent molecular geometry), neutral: no overall charge but the sharing of electrons is unequal because of the angle of the hydrogens (unequal distribution of the electrons, Oxygen is highly electronegative and Hydrogen is electro positive, one oxygen molecule can be attracted to up to 4 hydrogen molecules, relatively weak to covalent bond (1/10th the strength), constantly forming and breaking
Covalent bond
Sharing of the valence electrons
Hydrogen bonds
formed in water when the partially positive side on a hydrogen molecule is attracted to the partially negative side of a oxygen molecule, more energy is needed to break a hydrogen bond during melting or boiling, more hydrogen bonds when in solid state, hydrogen bonds last only a few trillionths of a second in water, but immediately bond to another molecule. At any given moment a substantial % of H2O molecules are bonded to their neighbors giving H2O more structure than other liquids.
Changes of state
Changes in hydrogen bonding due to addition or losses of heat, pure water has no suspending particles, freezes and melts at 0 degrees celsius, takes energy to break hydrogen bonds, water boils at 100 degrees celsius
Liquid to gas
evaporation
solid to gas
sublimation
gas to liquid
condensation
Heat
measure of total kinetic energy of the molecules and atoms in a substance. measured in calories.
Temperature
Average kinetic energy, the measurement of the gain/loss of heat that occurs in a body as heat energy is added or removed. Measured in degrees, Fahrenheit, Celsius and Kelvins, as temperature the calories decrease: require slightly less heat energy
Calorie with a little c
the amount of heat needed to raise 1g of water 1 degrees C
Calorie with a capital c
kilocalorie = one thousand calories.
Latent heat of fusion
heat necessary to change the state of H2O between a solid and a liquid, 80 calories, water in ocean or lakes takes longer to freeze or thaw: Latent means slowly
Latent heat of vaporization
140 calories, from liquid to gas
ice to water (Change in molecular state of matter)
heat energy increases speed of motion of molecules, heat energy needed to break H bonds; (becomes liquid), broken bonds allow molecules to move faster; but water molecules still stay close together because of polarity; H bonds short term, if molecules move fast enough, then they overcome attraction to become a gas, When cooled, energy is released so attractions can form, Salt added to water the boiling point raises and lowers its freezing point, sea water freezes at -2 degrees celsius
Heat capacity
how much heat is needed to raise the temperature of 1g of a substance by 1 degrees C. (copper pan: low HC, water is very high), Temperature changes very little for water, much heat is needed to raise or lower temperature due to H bonds, The heat capacity of water is 1 calorie to raise the temperature of 1g 1 degrees C, higher than most any liquid, Water's high specific heat allow the world's oceans to change temp slowly, helping to keep Earth's temp. stable. (Chart 5.2)
Cohesion
how united a body is, depends on bonding of molecules.
Surface tension
tendency of liquid surface to contract owing to bonding forces between molecules or how difficult it is to stretch or break the surface of a liquid, Water has a high surface tension; overfill a cup but won't overflow, breeze can stretch and wrinkle water surface, water striders, addition of salt or decreasing water temp: increases surface tension of water. *High surface tension in oceans is important in early formation of waves
Viscosity
property of a fluid to resist flowing, water has little resistance to flowing or stirring, therefore a low viscosity, Viscosity is affected by temperature, motor oil is highly viscous when cold, low viscosity when hot, Water near the equator is less viscous than Arctic water
Compressibility
water and seawater are nearly incompressible, Pressure comes from overlying water and air, pressure increases 1 atm (14.7 lb/in2) every 10m, surface water will lose 1.7% of volume at 4000m, pressure acting on world's oceans reduce water level by 37m, So pressure increases the density of water
Density
mass per unit volume of a substance; measured grams of matter/cm3, water has density of one gram at 4CSeawater has density of 1.0278 at 4 degrees C sea water is more dense than freshwater, Warm water is less dense than cold water, At 4 degrees C, water is the most dense; each molecule can form 4 H-bonds with 4 other molecules. Curved hill shape w/apex at 4 degrees c, ice has molecules that are further apart; lattice work; takes up greater space than water; ice floats on water.
Density of salt water
salt increases the density of water, 24.7 g/kg (parts per thousand) of salt in water is a special number; this is where the freezing temperature and the temperature of maximum density coincide, Water with a salt content less than 24.7g/kg, acts like fresh water; reaches maximum density (before it freezes), cooling fresh water below 4C actually makes the water less dense and more buoyant, so it remains at surface & freezes, increase in temp leads to a decrease in density, Water with a salt content greater than 24.6 g/kg will never reach maximum density. It freezes before it reaches max density, Ocean water has an average salt content of 35 g/kg, seawater sinks continuously as it is cooled and its density increases continuously,
Salinity
near the equator the salinity is higher than in the poles, the salinity changes with the seasons: the winter has higher salinity than the summer because of the ice caps
Dissolving ability
Water is known as the universal solvent since so many solutes dissolve in water, Salt (NaCl) is easily dissolved since the polar molecules strongly attract the Na+ and the Cl-; water molecules forms spheres around each ion, Rainwater washing over land carries ions out to sea; how ocean received its salt content, salt rarely returns to land; water evaporation
Transmission of energy
Fresh water & salt water both transmit energy in the form of heat, light, or sound
conduction (heat energy)
transfer of heat energy from one molecule to another;
water is a fairly poor conductor; transfers heat slowly
convection (heat energy)
the transfer of heat energy by density-driven process. Water becomes less dense when heated and rises; sinks when loses heat and becomes more dense; convection cell.
radiation (heat energy)
heat energy transferred by waves or rays without the need of a substance to transfer the energy. Water receives and reflects solar energy; water absorbing the heat will make it less dense; warm water stays at the surface.
Electromagnetic Radiation
Light striking the earth is one form of it that the earth receives from the sun: Visible light- very narrow section of the spectrum. red is bottom and violet is top, red has longest wave length and violet is the shortest,
Light colors
seawater absorbs 60% of visible light in the 1st m; 80% of light is absorbed within 10 m; 1% of light reaches 100 m; no light after 1000 m, red is absorbed quickly within 10m (closest to infrared) and violet light goes deeper and absorbed the least, light is refracted by water; light is slower in denser water than in air, light hits suspended particles and scatters, Depth of light helps to estimate plant growth; helpful for fishing seasons and the size of catches
attenuation
the decrease in energy of an electromagnetic wave as it travels further from its source; decreased by absorption and scattering of light
Secchi disk*****
30cm black and white disk lowered into water to determine attentuation.
Sound in water
travels faster and further in water than it does in air, average velocity of sound in seawater: 1500 m/sec, average velocity of sound in air: 334 m/sec, speed of sound increases with increase in temp, pressure, and salt content; decreases with the opposite, Water dissipates high-frequency sounds quicker than low-frequency sounds, sound reflects back after striking objects; can be used to sense shape and determine distance of object,
Echo soundings
echo sounders are used by ships to determine depth; beam of sound sent perpendicular to sea floor, time it takes to echo helps determine depth, Sound can penetrate some layers on sea floor; helps determine properties of seafloor. For example basalt reflects stronger signal than other ocean sediments
Ocean salinity
average salt content in 1000g of seawater is 35 g, 86% of salt is NaCl, the rest is other salts, measured in parts per thousand (o/oo); average ocean salinity is 35 o/oo, salinity changes with temprature: variations in evaporation, precipitation, freezing, thawing, river runoff affect salinity, when seawater freezes, only the water (H2O) freezes; salt enters into the seawater and makes it saltier.
Figure 1.5
Low salinity in cool and rainy 40-50° N and S, High salinity at 25° N and S, Low salinity at near equator, Low salinity along coasts with high precipitation or river inflow (25o/oo at near Columbia River), Some seas have high salinity (Med Sea, Red Sea); high evaporation and low river inflow, Some seas have low salinity (Med Sea, Red Sea); high evaporation and low river inflow, Polar areas have high salinity in winter when ice freezes, low salinity when melts in summer.
Dissolved salts
salts break into up into ions when dissolved, 6 ions make up 99% of salts dissolved in seawater, cations: Na, Mg, Ca, K, anions: cl, SO4
Conservative constituents: table 5.1
Major constituents of seawater that do not change their ratios due to biological and chemical processes.
Principle of Constant Proportion
Regardless of salinity, the ratios of between the amounts of major ions in open-ocean water are constant, thorough mixing of water maintains constant ratios, Not true for water close to land, especially near river inflow
Trace elements
include all other elements found in seawater and are found at less than 1 part per million, non0conservative: their percentage will change depending on where they are found because they are used in chemical and biological process' in the ocean
Sources of Salts
crust and interior of E, rainwater carries cations from rock to ocean; anions came from gases from the mantle during E's early development, volcanic eruptions release hydrogen sulfide, sulfur dioxide, chlorine gases (anions) to form SO4 and Cl ions, Water entering cracks in oceanic crust, near mid-ocean ridges and hot spots, has average salinity; when water leaves from hydrothermal vents (smokers), the salt content is nearly doubled, seawater becomes hot from nearby magma, Hot water readily reacts with rocks to gather more cations, By convection where water enters the ridge system and exits out of smokers, the entire ocean volume may circulate through ridge system every 10 million years
The salt balance
last 1.5 billion years, salt has remained the same in oceans; means salt input from rivers equals salt output from oceans.
How is salt removed from water
by sea spray from waves, also removed when isolated seas evaporate off water and the salt is left behind to become land deposits known as evaporites, ions react and precipitate on ocean floor (CaCO3), animal excrement attracts ions and deposited on ocean floor, Ca2+ is incorporated into shells, Most salt is removed by attraction to fine clay particles, clay particles are sediments which become rocks (Adsorption: the adherence of ions and molecules to a particle's surface).
2 methods of discerning salinity
1st: measuring one ion can determine salinity because of principle of constant proportion, example: If I find water that has 18g of Cl, I can figure the rest of the weights of the other 5 ions which make the different salts. 2nd: Today most measurements are made with a salinometer, electrical device used to measure conductivity,
Gases in Seawater
The ocean and the atmosphere exchange gases constantly, Nitrogen, oxygen, carbon dioxide are most abundant in ocean and atm, Gases measured by mL/L of seawater.
Basic Principles of gases in seawater
Colder water holds more dissolved gas than warmer water, Less salty water holds more gas than saltier water, Water under greater pressure holds more gas than water under less pressure.
Distribution of Gases in Seawater
Photosynthesis: plants produce oxygen and use carbon dioxide to produce organic compounds; light is close to surface and O2 would be close to surface, The air above the ocean surface: O2 is readily abundant due to seawater mixing with atmosphere, Respiration: organisms break down organic compounds by using O2 and releasing CO2; respiration occurs at all depths in the ocean, decomposition
Decomposition (Distribution of Gases in Seawater)
bacterial breakdown of nonliving organic matter, uses O2 and releases CO2, Dissolved O2concentrations vary from 0 to 10 mL/L, CO2 concentrations are 45-54 mL/L; found throughout ocean since respiration and decomposition occur at all levels.
Slide 48-52: study slide show notes
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Eutrophic
More Oxygen gas and less carbon dioxide