Stripers247.com Forums - View Single Post - The Thermocline.
View Single Post
  #18  
Old 12-01-2006, 09:14 PM
Striperjim's Avatar
Striperjim Striperjim is offline
Registered User
 
Join Date: Mar 2004
Location: Planet Earth
Posts: 4,316
Default Re: The Thermocline.

Update from the Lamont Earth Observatory

Saltwater.
oThe water column in the ocean can be divided into the surface layer, pycnocline, and deep layer
oThe surface layer is about 100 m thick, comprises about 2% of the ocean volume and is the most variable part of the ocean because it is in contact with the atmosphere
§ The surface layer is less dense because of lower salinity or higher temperature
o The pycnocline is transitional between the surface and deep layers and comprises 18% of the ocean basin
§ In the low latitudes the pycnocline coincides with the thermocline, but in the mid-latitudes it is the halocline
§ Tropical and subtropical oceans are permanently layered with warm, less dense surface water separated from the cold, dense deep water by a thermocline,a layer in which water temperature and density change rapidly
Tropical and subtropical oceans are permanently layered with warm, less dense surface water separated from the cold, dense deep water by a thermocline,a layer in which water temperature and density change rapidly
·
Temperate regions have a seasonal thermocline and polar regions have none
· Explain development and breakdown of seasonal thermocline
o Salinity displays a latitudinal relationship related to precipitation and evaporation
§ Highest ocean salinity is between 20-30o N and S or the equator
§ Low salinity at the equator and poleward of 30o results because evaporation decreases and precipitation increases
§ In some places surface water and deep water are separated by a halocline, a zone of rapid change in salinity
§ Water stratification (layering) within the ocean is more pronounced between 40oN and 40oS
o Density of sea water is a function of temperature, salinity and pressure
§ Density increases as temperature decreases
§ Salinity increases as pressure increases
§ Pressure increases regularly with depth, but temperature and salinity are more variable
§ Higher salinity water can rest above lower salinity water if the higher salinity water is sufficiently warm and the lower salinity water sufficiently cold
§ Pycnocline is a layer within the water column where water density changes rapidly with depth
o The water column in the ocean can be divided into the surface layer, pycnocline, and deep layer
o The surface layer is about 100 m thick, comprises about 2% of the ocean volume and is the most variable part of the ocean because it is in contact with the atmosphere
§ The surface layer is less dense because of lower salinity or higher temperature
o The pycnocline is transitional between the surface and deep layers and comprises 18% of the ocean basin
§ In the low latitudes the pycnocline coincides with the thermocline, but in the mid-latitudes it is the halocline
o The deep layer represents 80% of the ocean volume
§ Water in the deep layer originates at the surface in high latitudes (polar regions) where it cools, becomes dense, sinks to the sea floor and flows outward across the ocean basin


Chem 1103: Lecture 3: The Properties of Sea Water: Chap. 5

· Four types of oceanography
ogeological, chemical, physical, biological
· Basic Chemical Notions

o Atoms are the smallest units which display all of the properties of the material
o Molecules are chemically-combined compounds formed by two or more atoms H2O NaCl CO2
o Atoms are composed of:
§ Nucleus – the center of the atom consisting of positively charged particles called protons and neutrally charged particles called neutrons
§ Electrons – negatively charged particles which orbit the nucleus in discrete electron shells
o Periodic chart of elements
§ each has atomic number and that is the number of protons
o Electrically stable atoms have the same number of electrons as protons
o Ions are atoms with either more or fewer electrons than protons and are therefore electrically charged H+ Na+ Cl- OH-
§ Shells and atoms want to have shells filled
§ First shell 2; second shell 8
o Periodic chart
§ Noble gases have filled shells don’t react with much
§ Gases O2 and N2
§ Carbon not a gas – graphite and diamond - solids
o Isotopes are atoms which contain the same number of protons but different numbers of neutrons and therefore have different weights -1H 2H 3H 16O 18O 12C 14C
· Basic Physical Notions
o Heat results from the vibrations of atoms (kinetic energy) and can be measured with a thermometer
§ In solids the atoms or molecules vibrate weakly and are rigidly held in place by electrical bonds - example kids in high chairs or on bus with seat belts
§ In liquids the atoms or molecules vibrate more rapidly, move farther apart, and are free to move relative to each other – example kids who have to hold hands and stay in a room
§ In gases the atoms or molecules are highly energetic, move far apart, and are largely independent – example kids on the loose with the doors open
§ Evaporation (vaporization) is the transition from liquid to gas; condensation is the reverse
· Molecules with enough energy escape from liquid into gas
· Cold removes some energy and gas forms into liquid
§ Temperature controls density. As temperature increases, atoms or molecules move farther apart and density decreases because there is less mass (fewer atoms) in the same volume
· Warm air and warm water both rise and cold air and cold water sink
· The water molecule
o The water molecule is unique in structure and properties
§ H2O is the chemical formula for water
§ Unique properties of water include:
· Exists naturally as solid, liquid, and gas
· Higher melting and boiling point than other hydrogen compounds
· High heat capacity, amount of heat needed to raise the temperature of one gram of water 1oC
· Greater solvent power than any other substance
§ Water molecules are asymmetrical in shape with the two hydrogen molecules at one end separated by 105o when in the gaseous or liquid phase and 109.5o when ice
§ Asymmetry of a water molecule and distribution of electrons result in a dipole structure with the oxygen end of the molecule negatively charged and the hydrogen end of the molecule positively charged
§ Dipole structure of water molecule produces an electrostatic bond (hydrogen bond) between water molecule which cluster together in a hexagonal (six-sided) pattern
§ Ice floats in water because all of the molecules in ice are held in hexagons and the center of the hexagon is open space, making ice 8% less dense than water
§ Hydrogen bonding is responsible for many of the unique properties of water because more energy is required to break the hydrogen bonds and separate the water molecules
· High melting and boiling points due to more energy needed to break the Hydrogen bonds
§ Water dissolves salts by surrounding the atoms in the salt molecule and neutralizing the ionic bond holding the molecule together. Dissolved salts from cations (positively charged ions) Na+ and anions (negatively charged ions) Cl-
§ Fresh water reaches its maximum density at 3.98oC
· Below this temperature increasing numbers of water molecules form hexagonal polymers and decrease the density of the water
· Above this temperature, water molecules are increasingly energetic and move farther apart, thereby decreasing density
§ The process of water surrounding an ion is called hydration
o Sea water consists of water with various materials dissolved within it
§ The solvent is the material doing the dissolving and in sea water it is the water
§ The solute is the material being dissolved
§ Saturated solution can hold no more salt
§ Unsaturated solution can hold more
§ Supersaturated solution has more than it can hold
§ Salinity is the total amount of salts dissolved in the water
§ Salinity is measured in parts of salt per thousand parts of water and is expressed as ppt (parts per thousand0 or abbreviated o/oo
§ Now salinity really as psu (practical salinity units)
§ Average salinity of the ocean is about 35 o/oo or 3.5%
o Many chemicals in seawater
o Five groups
§ Major constituents
§ Nuturients
§ Gases
§ Trace elements
§ Organic compounds
o Major constituents are anions and cations – show table
§ 99% of all the salt ions in the sea are sodium (Na+), chlorine (Cl-), sulfate (SO4-2), Magnesium (Mg+2) calcium (Ca+2) and Potassium (K+)
§ sodium and chlorine alone comprise ~86% of the salt in the sea
§ the major constituents of salinity display little variation over time and are a conservative in sea water
o Nutrients are chemicals essential for life – like fertilizer
§ Major nutrients in the sea are compounds of nitrogen, phosphorus, and silicon
§ Because of usage, nutrients are scarce at the surface and their concentration is measured in parts per million (ppm)
§ Concentration of nutrients vary greatly over time and because of this they are considered a nonconservative in seawater
o Gases
§ In order of decreasing abundance, the major gases in the sea are nitrogen, oxygen, carbon dioxide, an the noble gases, argon (Ar), neon (Ne), and helium (He)
§ Nitrogen and the noble gases are considered to be inert because they are chemically non-reactive
§ Oxygen and carbon dioxide are not conservative since they are involved in photosynthesis and respiration by plants and animals
· Photosynthesis – CO2 in O2 out – plants
· Respiration - O2 in CO2 out – animals
§ Oxygen and carbon dioxide vary greatly in space and time due to these processes
o Trace elements
§ Manganese Mn, lead Pb, mercury Hg, gold Au, iodine I, iron Fe
§ [SIZE2]Occur in minute quantities and are usually measured in parts per million (ppm) or parts per billion (ppb)[/size]
§ Even in small quantities they are important in either promoting life or killing it
o Organic compounds
§ At this level, organic compounds are large complex molecules with carbon, except graphite and diamond - also not gases – CO2 but gasoline, oils, carbohydrates, fats, proteins, hormones, and vitamins
§ Marine organic compounds occur in low concentrations
§ Produced by organisms in metabolic reactions or through decay.

· Salinity
o Salinity is the total mass, expressed in grams, of all substances dissolved in one kilogram of sea water when all carbonate has been converted to oxide, all bromide and iodine has been replaced by chlorine, and all organic compounds have been oxidized at a temperature of 480oC
§ Principle of constant proportion states that the absolute amount of salt in sea water varies, but the relative proportions of the ions is constant
· Relative percentage of each salt is constant – ex. with % and $
· Because of this principle it is necessary to test for only one salt ion to determine the total amount of salt present
· Use chlorine because it is abundant and easy
§ Chlorinity is the amount of halogens (chlorinity, bromine, iodine, and fluorine) in the sea water and is expressed as grams/kilogram or o/oo
§ Salinity is equal to 1.8065 time chlorinity
§ Salinometers determine chlorinity from the electrical conductivity produced by the dissolved salts and get salinity from that
o Salinity in the ocean is in a steady-state condition because the amount of salt added to the ocean (input from source) equals the amount removed (output into sinks)
§ Steady state – condition of equilibrium, no net change, but things can be changing
§ Conservation of mass – what goes in, comes out
§ Salt sources include weathering of rocks on land and the reaction of lava with sea water
· Weathering mainly involves the chemical reaction between rock and acidic rainwater, produced by the interaction of carbon dioxide and rainwater forming carbonic acid
· Carbonic acid will be discussed later
· For now, acid eats the rock and weathers it
· Example, mineral orthoclase, a common feldspar of granite, decomposes to kaolinite in acidic solution
· 2KAlSi3O8 + 2H+ + H2O ® 2K+ + Al2Si2O5(OH) 4 + 4SiO2
· orthoclause - KAlSi3O8
· kaolinite - Al2Si2O5(OH) 4
· Dissolved silica - SiO2
§ Salt sinks include the following
· Evaporation removes only water molecules
o Remaining water becomes increasingly saline, eventually producing a salty brine
o If enough water evaporates, the brine becomes supersaturated and salt deposits begin to precipitate forming evaporite minerals
· Wind blown spray carries minute droplets of saltwater inland
· Adsorption of ions onto clays and some authigenic minerals
· Shell formation by organisms
§ Lack of similarity between relative composition of river water and the ocean is explained by residence time, average length of time that an ion remains in solution in the ocean
· Ions with long residence times tend to accumulate in the sea, whereas those with short residence times are removed
· Rapid mixing and long residence times explain constant composition of sea water
o Addition of salt modifies the properties of water
§ Pure water freezes at 0oC, adding salt lowers the freezing point because salt ions interfere with the formation of the hexagonal structure of ice
§ -1.91oC for 35 psu
§ Density of water increases as salinity increases
§ Vapor pressure is the pressure exerted by the gaseous phase on the liquid phase of a material. It is proportional to the amount of material in the gaseous phase.
· Vapor pressure decreases as salinity increases because salt ions reduce the evaporation of water molecules
· Chemical and Physical Structure of the Oceans
o Ocean surface temperature strongly correlates with latitude because insolation, the amount of sunlight striking Earth’s surface is directly related to latitude
§ Ocean isotherms, lines of equal temperature, generally trend east-west except where deflected by currents
· Ocean currents carry warm water poleward on the western side of the ocean basins and cooler water equatorward on the eastern side of the ocean
§ Insolation and ocean-surface temperature vary with the season
§ Ocean surface temperature is highest in the tropics (25oC) and decreases poleward
· El Nino
o Upwelling of deep, nutrient-rich water supports large populations of phytoplankton and fish
o The waters off the coast of Peru normal is an area of upwelling, supporting one of the world’s largest fisheries
o Every three to seven years, warm surface waters in the Pacific displace the cold, nutrient-rich water on Peru’s shelf in a phenomenon called El Niño
o
El Nino results in a major change in fauna on the shelf and a great reduction in fishes, which can lead to mass starvation in fishes
o El Nino starts with a shift in the wind in the Pacific, which changes the Ekman transport, reducing the pile up of water on the west side of the Pacific. The water moves east and shuts off the upwelling.
__________________
How inappropriate to call this planet Earth when it is quite clearly Ocean.
Arthur C. Clarke
Reply With Quote