OCE1001 Quiz Feb 19 Lecture 8 Seawater Density Water o Electrons negatively charged particles can be shared with or moved to another atom chemical bonds o Water molecules form when electrons are shared between two hydrogen atoms and one oxygen atom covalent bond o Oxygen is more electro negative than hydrogen o Water is a polar molecule Easily dissolves other compounds Attracts other water molecules o Liquid H2O o Gas H2S M34 o Hydrogen bonds Positive end H of 1 water molecule is attracted to the negative end O of another water molecule Electrostatic force Creates a loosely held frame work Cohesion holds the hydrogen bonded molecules together surface tension Adhesion allows water to stick to other substances o Water is a good solvent particularly for dissolving salts Types of Chemical bonds o Covalent share electrons but not equally 100 s of kcals o Ionic electrostatic attraction 10 s of kcals Holds salts together NaCl Anions are negative Cl Cat ions are positive Na CaCO3 limestone CO3 and SO4 are examples of compound ions Ions are charged particles SiO2 quartz sand SiO2 2H2O opal o H bonding weakest bonds kcals Heat o Heat is energy produced by the random vibrations of atoms or molecules o Temperature change is one response to input or removal of heat Measures how rapidly the molecules are vibrating o 2 ways water responds to heat input 1 Sensible heat transfer Temperature change 2 Latent heat transfer A phase change Liquid to vapor Only takes 80 cal g to go from ice to water Takes 540 cal g to go from water to vapor Water has a HIGH heat capacity Heat capacity is a measure of the heat required to raise the temperature of 1g of a substance by 1 degree C The strength and of hydrogen bonds between water molecules means water requires more heat energy to raise its temperature than most other substances This means water resist temperature when heat is added or removed Water humidity WATER MODERATES TEMPURATURE CHANGE o Thermal inertia Weather doesn t warm as much as land in the summer or cool as much in the winter X Y plots o Normally the independent variable goes on the x axis and the dependent variable goes on the y axis Sometimes we put the independent variable on the vertical axis An Example would be a plot of depth and temperature Density o Things that change density Temperature Hydrostatic Pressure Salinity Ocean Currents are controlled by three things o Density Density is inversely related to temperature Density is directly related to salinity Cold water is more dense than warm water o Wind o Gravity tides Stratified Water column o When warm water floats on top of cold water o Tropical water is most stratified Isopycnal constant density o Sinking and mixing of a body of water Density zones o Surface zone mixed layer Relatively constant temperature and salinity Pycnocline Density is increasing with depth Deep zone Below pycnocline little change in water density The Atlantic is the saltiest ocean People used to think that the deep ocean was azoic no life but because of the ocean conveyor belt O2 gets to the deep sea which allows for life The ocean conveyor belt o Subsurface currents Thermohaline circulation o Transports heat from the tropics to higher latitudes o 80 ocean water moved by subsurface currents o Density driven currents o Gravity is the driving force o Heavier denser H2O sinks due to gravity o Gases have retrograde solubility More dissolve in COLD water So polar sinking good conduit for oxygenation of the deep sea Lecture 9 Seawater salinity Ocean volume o Ocean formed early in earths history o Ocean volume is at a steady state Inputs outputs Sources sinks o The ocean is a way station o Inputs Rivers volcanism hydrothermic circulation MOR Sediment CaCO evaporate formation MOR o Outputs Residence time o Amount source or sink o Sodium Chloride have long residence time o Lead has short residence time Rivers carry salts to the ocean Vents add potassium calcium trace minerals and remove magnesium sulfate The components of salinity o Chloride the most abundant ions o HCO3 Ca Mg Na SO4 Cl o Ocean 35 salt per sea water Cl Na SO4 HCO3 o River 01 salt per sea water Very dilute 19 4 g kg o Halite NaCl sodium 10 8 g kg o Sulfate So4 2 Compound anion 2 4 g kg o Bicarbonate o Calcium o Potassium o Water 96 5 salts are the 4 Constant composition o Chance the salinity change the amount of all the ions in the same way o 35 salt salinity o 19 4 chlorinity The major constitutes of seawater are conservative o This means they have constant compositions their ratios do not change relative to each other o The principle of constant proportions although the salinity of carious samples of sea water may vary the ratio of major salts is constant Ca HO3 are used to form shells so their correlation can vary independent to salinity The salinity chlorinity ration is 10 35 1 Determining salinity o Salinity can be determined by measuring the chlorinity o Salinity is related to chlorinity by the linear relationship Salinity in parts per thousand 1 80655 x chlorinity in parts per thousand o Physical methods Refractometry relatively imprecise convenient Conductivity cells most commonly used requires temperature compensation Summary o Properties unique to water Good solvent for dissolving salts High heat capacity High boiling and freexing point o Things that very density of water Temperature Salinity Pressure Currents o Currents are caused by Winder DENSITY denser water sinks Decreases with temp increase Increase with salinity increase Increases with pressure increase This means Warm water is floating on cold and fresh water is floating on salty water Called Thermohaline circulation Iclicker questions o What is the unit that is equivalent to raising the temp of 1 gram of water by 1 degree centigrade Calorie o What is the time period for the global conveyor belt 1 000 years o In the oceans all of the following processes decrease local salinity EXCEPT for one Which process increases salinity Evaporation Coldest and saltiest waters are at the poles At the poles the water column is unstable Stable water column o Salinity increases with depth temp decreases with depth o Stratified Unstable water column o Salinity is uniform with depth temp uniform with depth o Not stratified mixed well o Dense water continually sinking North Atlantic deep water off the coast of Greenland Antarctic bottom water South pole off the coast of Antarctica o Densest water in the ocean GASES HAVE RETROGRADE SOLUBILITY o More
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