Types of Oceanography So far – Geology

Types of Oceanography So far – Geology
Oceanography split generally into four sub disciplines We are now entering chemical oceanography, or what is more accurately termed geochemistry. Geochemistry, because much of the chemistry of seawater is influenced by rock and sediment interactions with water. So far – Geology Today – Chemistry (geochemistry)

Atoms are the smallest unit which display all of the properties of the material.
Subatomic particles are smaller, but do not retain materials characteristics. Let’s begin with a brief discussion of the properties of matter. The atom is the basic unit of matter. It is not the smallest unit of matter, but it is the smallest unit of matter that still retains the characteristics of the whole material.

The Atom and Electron Shells
Composed of Nucleus center; positive charge protons and neutrons Electrons – outside in shells; negative charge; orbit the nucleus in discrete shells Atomic numbers (number of protons) Hydrogen – 1 Oxygen - 8 The general structure of the atom Nucleus is the center of the atom. Contains neutrons (neutral charge) and protons (postive charge) Electons form a cloud of negative charge that surrounds the nucleus Electons said to be arranged in shells. Inner shell can contain up to 2 electrons. Outer shell can contain more.

168O Notation Mass number = #protons + # neutrons
Element symbol (oxygen) Atoms are defined as the smallest unit which display all the properties of the material Atoms are not the smallest particle (sub-atomic particles are smaller, but do not posess the properties of the whole substance). This is the periodic table of elements, the pure substances Atomic number (# of protons in nucleus)

Element Groups (Families)
Periodic Table of the Elements Element: pure substances that cannot be separated into constituent substances with unique properties. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Cs Ba * Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 55 56 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Fr Ra ** Rf Db Sg Bh Hs Mt Uun Uuu Uub 87 88 104 105 106 107 108 109 110 111 112 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 89 90 91 92 93 94 95 96 97 98 99 100 101 02 103 Element Groups (Families) Alkali Earth Alkaline Transition Metals Rare Other Metalloids Non- Halogens Noble Gases This is the periodic table of elements, the pure substances are called elements, and they are defined by their purity. Arranged in order of increasing atomic number. Atomic numbers appear on table. Also arranged into families which have similar characteristics.

Basic Chemical Notions
Electrically stable atoms: same number of electrons as protons, no charge. Examples: H, N, O Ions: atoms with either more or fewer electrons than protons and are therefore electrically charged. Example: H+, Na+ (cations); Cl-, Br- (anions). Atoms can have charge if there are unequal number of electrons and neutrons. Matter does not exist as single atoms withough charges. Always charged. Exception to this is the noble gasses (He, Ne,

Isotope: atoms of the same element that differ in weight due to variable numbers of neutrons. (all work almost the same way chemically). Example: 3H, 12C, 13C, 14C, 16O, 17O, 18O. Unstable (radioactive, e.g., 14C) and stable (e.g., 13C) isotopes. Isotope refers to atoms of the same type, but with different numbers of neutrons. Atomic mass is changed, but atomic number remains the same (same no. of protons) Isotopes have (almost) identicle chemical properties, but are heavier or lighter. Can be radioactive or stable.

Compound: a pure substance that can be resolved into two or more elements. Molecule : small group of atoms held together by relatively strong forces called chemical bonds. Example: CaCO3, H2O, CO32-, proteins, nucleic acids, carbohydrates, etc. Nearly interchangeable definitions.

Heat and State Heat results from the vibrations of atoms (kinetic energy) and can be measured with a thermometer. Three states of matter: Solids: atoms or molecules vibrate weakly and are rigidly held in place. Liquids: atoms or molecules vibrate more rapidly, move farther apart and are free to move relative to each other. Gases: atoms or molecules are highly energetic, move far apart and are largely independent. Atoms and molecules posess kinetic energy that is dissipated as movement (vibration, rotation and translation) and generates heat. Heat can be measured with a thermometer Matter can be in one of 3 states, solid, liquid or gas, depending on the amount of kinetic energy in the sytem.

Gas solid Changes of State
evaporation melting liquid condensation freezing One state and change to the other. This is called change of state. Melting: transition from solid to liquid. (freezing is opposite) Evaporation: liquid to gas (condensation is opposite) State transition where liquid phase is bypassed is sublimation. Gas directly to solid, or solid directly to gas. There fore temperatuere direclty controls density (mass/volume) by increasing or decreasing the number of atoms within a given volume. Temperature controls density. As temperature increases, atoms or molecules move farther apart and density (mass/volume) decreases because there is less mass (fewer atoms) in the same volume.

The water molecule is unique in structure and properties.
H2O is the chemical formula for water. Unique properties of water include: 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. THE WATER MOLECULE Structure of water molecule Two hydrogens attached to one oxygen. In liquid phase the angle of H’s is 105deg, but in solid phase this changes to 109deg. Share electrons to complete their outer shells (two for H, 8 for O). Water has unique properties that are related to its structure. High MP High Heat capacity Great solvent power.

The Water Molecule Dipole nature
If you compare water’s properties to other hydrogen containing molecules, it is different We a relationship between molecular wt and freezing point and melting point. But water falls off this trend. Water has higher FP and MP than that predicted by this trend. This difference is due to the dipole nature of the water molecule Dipole: due to molecule’s asymmetry, there is more positive charge on one end, and negative charge on the other. This sets up the molecule to act as dipole Size of clusters of water molecules decreases at higher temp, and this stickiness decreases with fewer clusters. Hydrogen bonds form between adjacent water molecules in liquid state, causing them to stick together more and vaporize at higher temp than predicted. Likewise, the H-bonds in ice, prevent it from melting until a higher temp than that predicted.

Hexagonal Crystal Structure of Ice
The Water Molecule 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. Ice is less dense than water, so it floats. This is unusual. When water freezes, the molecules become set in a crystalline lattice network that results in them being spaced further apart than in liquid state. If the water molecules are spaced further apart in ice than in liquid water, then it is LESS DENSE, therefore it floats. Hexagonal Crystal Structure of Ice

The Water Molecule Density changes of pure water with temperature
Water density is low at high temps: kinetic energy of molecules is causing them to move further apart- decrease density. As temperature decreases, the kinetic energy decreses, and molecules hydrogen bonds pull them closer in together, forming more and more clusters. At ~4C, water reaches its max density As temperatue decreases, the ice latticework sets up and density goes the other way.

Dissolution The Water Molecule Solvent is material doing dissolving
Solute is material being dissolved Water is universal solvent, dissolves many substances Dipole structure of water helps it to dissolve substances with charges NaCl = Sodium Chloride = table salt Dissolved NaCl = Na+ + Cl- Water is the universal solvent- it will dissolve many substances. This is very important because all the salts in the ocean are dissolved from solid rock on land. Definitions, solvent, solute Dissolves substances with charges. Dipoles arrange themselves to attach to anions and cations and pull them away from their solid matrices.

Seawater Seawater consists predominantly of water with various materials dissolved within it. 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 bromine and iodine has been replaced by chlorine and all organic compounds have been oxidized at a temperature of 480oC. ppt (parts per thousand) or o/oo Average salinity of the ocean is about 35 o/oo. Analytical methods: Weight of salts Chemical titration conductivity Seawater is water with lots of stuff dissolved in it. Salinity is a measure of saltiness of water, or the mass of dissolved substances. Units of salinity is sometimes ppt. (though not always.) Measurement methods Simplest method is to weigh salts dried up Measure concentration of one salt (principle of constant proportions) Modern method is to measure electrical conductivity. new units are unitless (conductivity ratio).

Five Groups of Solutes in Seawater
Major Constituents (the salts) Nutrients Gases Trace elements Organic compounds

Major Constituents Salt Ion Ions in Seawater % Chloride (Cl-) 18.980
55.04 Sodium (Na+) 10.556 30.61 Sulfate (So42-) 2.649 7.68 Magnesium ( Mg2+) 1.272 3.69 Calcium (Ca2+) 0.400 1.16 Potassium (K+) 0.480 1.10 Bicarbonate (HCO3-) 0.140 0.41 Bromide (Br-) 0.065 0.19 Boric acid (H3BO3-) 0.026 0.07 Strontium (Sr2+) 0.013 0.04 Floride (F-) 0.001 <0.01 Other ions <0.001 <0.01% List of major seawater constituents Chloride and sodium comprise ~85 percent of all MC’s

Nutrients are chemicals essential for life.
Major nutrients in the sea are compounds of nitrogen, phosphorus and silicon. Because of usage, nutrients are scarce at the surface and their concentrations are measured in parts per million (ppm). Concentration of nutrients vary greatly over time and because of this they are considered a nonconservative property of the sea. Nutrient element Nutrient compound Concentration [ppm] Phosphorus (P) Phosphate(PO43-) 0.07 Nitrogen (N) Nitrate (NO3-) 0.5 Silicon (Si) Silicate (SiO44-) 3 Nutrients are another category, Nutrients are for the growth of ocean plants that form the base of the food chain and upon which most of ocean’s food web is dependent. P, N, needed by all phytoplankton, Si needed by diatoms. Concentrations are much lower than MC’s, and are in the PPM range. Ppm = g/MT or g/1E6 g, or one part per million Because nutrients are used up by phytoplankton, and phytos live in surface waters, the nutrient level in surface waters is low, and increased with depth. Nutrients behave in a non-conservative fashion.

Gases In order of decreasing abundance the major gases in the sea are: -Nitrogen (N2) -Oxygen (O2) -Carbon dioxide (CO2) -Noble gases, argon (Ar), neon (Ne) & helium (He). The noble gases are considered to be inert because they are chemically non-reactive. Nitrogen (N2) is inert with the exception of nitrogen fixing cyanobacteria. Oxygen (O2) and Carbon dioxide (CO2) are biologically active. Gases, like other compounds, are dissolved in seawater. Major gases are N2, O2, CO2 and noble gases

Trace Elements Trace elements occur in minute quantities and are usually measured in parts per billion (ppb). -even in small quantities they can be important for either promoting or killing life. Trace element Concentration [ppb] Lithium (Li) 170 Iodine (I) 60 Molybdenum (Mo) 10 Zinc (Zn) Iron (Fe) Aluminum (Al) Copper (Cu) 3 Manganese (Mn) 2 Cobalt (Co) 0.1 Lead (Pb) 0.03 Mercury (Hg) Gold (Au) 0.004

Organic Compounds Marine organic compounds occur in low concentrations and consist of large complex molecules produced by organisms, such as: - -lipids (fats) -proteins -carbohydrates -nucleic acids (DNA, RNA) -hormones -vitamins

Principle of Constant Proportion
Principle of constant proportion –applies to salts that exhibit conservative properties in seawater (Cl-, Na+). states that the absolute amount of salt in sea water varies, but the relative proportions of the ions is constant. Salinity (o/oo) = x chlorinity (o/oo) Now let’s think about the major constituents again. We can apply a principle called constant proportion to apply to those salts that exhibit a conservative behavior in seawater examples chloride and sodium ions This principle states that for many salts in the sea, the absolute amount may vary from place to place, but the relative proportions of the ions will remain constant. This principle was exploited to measure salinity of seawater. We no longer have to dry a sample of SW and weigh the salts, now we can , through analytical chemical techniques, measure the concentration of a single ion (chloride, because its present in highest concentration) and then apply a constant to determine the total salinity. Because the analytical procedure could not distinguish between chloride ion and ions of theother halides (bromide, iodide, fluoride), theywere all lumped together as “chlorinity”. Chlorinity: concentration of chloride ion (Cl-), plus all other halide ions (Br-, Fl-).

Major Constituents Salt Ion Ions in Seawater % Chloride (Cl-) 18.980
55.04 Sodium (Na+) 10.556 30.61 Sulfate (So42-) 2.649 7.68 Magnesium ( Mg2+) 1.272 3.69 Calcium (Ca2+) 0.400 1.16 Potassium (K+) 0.480 1.10 Bicarbonate (HCO3-) 0.140 0.41 Bromide (Br-) 0.065 0.19 Boric acid (H3BO3-) 0.026 0.07 Strontium (Sr2+) 0.013 0.04 Floride (F-) 0.001 <0.01 Other ions <0.001 <0.01% List of major seawater constituents Chloride and sodium comprise ~85 percent of all MC’s

Steady-state Equilibrium
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). Ocean (salts constant) source sink Now, it turns out that over very long (geological) time periods, the salinity of the ocean has not changed. But we know that salts are continually being added to the ocean from rivers and land runoff. So, why isn’t ocean getting saltier? The answer is that the ocean is in steadystate equilibrium, i.e. , the amount of salts added in rivers is balanced by an equal amount of salt being removed. The ocean can be said to have sources and sinks. Source is ways that salts are added to ocean, sink is ways in which it is removed.

Salt Sources and Sinks Sources Sinks
Weathering of rocks on land (acid rainwater) Reaction of lava with seawater Sinks Precipitation due to evaporation (brine, evaporite minerals) Adsorption on clays Authigenic sedimentation- (i.e., ferromanganese nodules) Wind-blown spray Shell formation by organisms (CaCO3) Acid rainwater. CO2 added to water produced “acidic’ water that promotes weathering of land rocks to extract ions into river water that are eventually transported to ocean. CO2 +H2O = HCO3- +H+ more hydrogen ions, more acidic.

Residence time 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 (Cl- , Na+) have low chemical reactivity and tend to accumulate in the sea Ions with with short residence times (Ca2+, K+) have higher chemical reactivity, and are removed. Rapid mixing and long residence times explain constant composition of sea water. Salt Ion Residence Time in sea [106 y] Concentration in seawater [%] Concentration in river water [%] Chloride (Cl-) Inf. 55.04 6.5 Sodium (Na+) 260 30.61 5.2 Calcium (Ca2+) 8 1.16 12.4 Potassium (K+) 11 1.10 1.9 Why isn’t river water salty? To answer this we must consider the concept of residence time.

Residence time Ocean takes about 1000 y to completely mix.

Addition of salt modifies physical properties of water.
Freezing point Increase salt content lowers temperature to freeze. Density Increase salt content makes water more dense. Vapor pressure Increase salt content lowers the vapor pressure above the water.

How do temperature and salinity vary in the ocean? Daily (diurnal)
Chemical and Physical Structure of the Oceans How do temperature and salinity vary in the ocean? Daily (diurnal) Seasonally Vertically with depth Horizontally with latitude and longitude

Chemical and Physical Structure of the Oceans
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

Chemical and Physical Structure of the Oceans
Because solar insolation varies with latitude (greatest insolation at equator, least at poles), surface sea temperatures vary generally with this insolation, being highest at equators and lowest at poles. However, it is not a perfect parallel isopleths of temperature (isotherms). Major ocean currents are responsible for transporting heat. The major ocean gyres move ina clockwise fashion in northern hemisphere and anticlockwise fasion in SH. The major ocean currents transport warm equatorial water to nothern latitudes in NH along western border of oceans, and transport cold polar water southward along the eastern sides of the basins. Similarly, for the SH, the counterclockwise motion of the gyres transports warm equatorial waters southward along the western sides of the basins, and cold polar water northward along the eastern sides of basins.

Insolation and ocean-surface water temperature vary with the season.
Temperature also varies with season, due to changing insolation from winter to summer solstice. IN temperate waters where you see large changes in seasonal insolation, you find a predictable procession of thermal stratification in ocean surface waters. Winter to summer: lessening of wind strenght, increase of insolation andheating of surface. Summer to winter: increasing wind strength, net heat loss from surface waters. Heat is ventilated to atmosphere.

Temperate regions have a seasonal thermocline and polar regions have none.
This seasonal progression of thermocline is most pronounced in temperate regions. IN polar waters, there is no , or very little, thermocline. In tropical waters, there is a permanent thermocline, which, like the solar insolation, does not vary throughout the year. This layering can be disrupted by the passing of storms and other disturbances. Temperature Profiles

Tropical and subtropical oceans are permanently layered with warm, less dense surface water separated from cold, dense deep water by a thermocline. So, if we view the ocean across a latitudinal section from north to south, we see the diffs. Tropical and subtropical oceans permanently layered by less dense warm surface layer separating cold deep water by thermocline. At poles, no thermocline exists, and cold water is right to the top. Notice VE

-clines are depth intervals where there is rapid vertical changes in properties.
Now lets talk about –clines. I’ve been throwing around the term thermocline. A cline is the suffix used to denote change. A thermocline is the depth inteval over which there is sharp vertical changes in Temp. Likewise for salinity and density Halocline, pycnocline. In some cicumstances, a sharp temp gradient and a sharp salinity gradient can result in no change in density, if the direction of the temp and salinity offset one another, i.e., if increase in temperature (less dense) is accompanied by increase in salinity (more dense).

Salinity changes with latitude due to variations in precipitation and evaporation.
Like for temperature, the surface salinity across the globe is determined by the amount of insolation. This map shows the distributon of surface salinity. Isopleths of salinity are shown (isohalines). General patterns: In major ocean basins, there is maximal salinity fount between ca latitudes. Lower salinity is found at higher latitudes and at equator. What is responsible for this pattern?

Salinity changes with latitude due to variations in precipitation and evaporation.
It turns out this pattern is related to the balance between precipitation and evaporation, two processes that add or remove water molecules from the surface ocean (away from the influence of rivers) and dilute or increase salinity. Graph of surface salinity and evaporation minus precipitation. As seen on the global map, the highest salinities are between deg latitudes in both N and S hemispheres, and lowest S near equator.

Density of sea water is a function of temperature, salinity and pressure.
Density increases as temperature decreases and as salinity and pressure increase. 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.

Thermocline, Halocline, Pynocline

The water column in the ocean can be divided into the surface layer, pycnocline and deep layer.
The surface layer is about 100m 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 than the layers below because of its lower salinity or higher temperature. The pycnocline is transitional between the surface and deep layers and comprises 18% of the ocean basin.

The deep layer represents 80% of the ocean volume.
Water in the deep layer originates at the surface in high latitudes where it cools, becomes dense, sinks to the sea floor and flows equatorward across the ocean basin. Density Structure of the Oceans

Gases in Seawater Gas In dry air (%) In surface ocean water (%)
Nitrogen (N2) 78.03 47.5 Oxygen (O2) 20.99 36.0 Carbon Dioxide (CO2) 0.03 15.1 Ar, H2 ,Ne & He 0.95 1.4

Gas solubility and saturation
Solubility is a measure of a substance's tendency to dissolve and go into solution. Saturation value is the equilibrium amount of gas dissolved in water at an existing temperature, salinity and pressure. The surface layer is usually saturated in atmospheric gases because of direct gas exchange with the atmosphere. Below the surface layer, gas content reflects the relative importance of respiration, photosynthesis, decay and infusion from volcanic vents.

Gas solubility and saturation

Oxygen distribution Oxygen tends to be abundant in the water of the surface layer and deep layer, and lowest in the pycnocline. Surface layer is rich in oxygen because of photosynthesis and diffusion from the atmosphere layer. Oxygen minimum layer occurs at about 150 to 1500m below the surface and coincides with the pycnocline.

Oxygen distribution

Carbon Dioxide Carbon dioxide is of major importance in controlling the acidity of seawater. Major sources of carbon dioxide are respiration and decay. Major sinks are photosynthesis and construction of carbonate shells. Carbon dioxide controls the acidity of sea water. A solution is acidic if it has excess H+ (hydrogen) ions and is basic if it has excess OH- (hydroxyl) ions. pH measures how acid or base water is. - pH of 0 to 7 is acidic. - pH of 7 is neutral. - pH of 7 to 14 is basic.

The pH scale

Carbon dioxide species

Carbon Dioxide

5-6 Gases in Seawater Dissolved CO2 in water acts as a buffer, a substance that prevents large shifts in pH. Dissolution of carbonate shells in deep water results because cold water under great pressure has a high saturation value for CO2 and the additional CO2 releases more H+ ions making the water acid. Warm, shallow water is under low pressure, contains less dissolved CO2 and is less acidic than the deep water. Carbonate sediments are stable and do not dissolve.

Carbon dioxide species

Water is recycled continually between the ocean and the land.
The Ocean as a Physical System 5-7 Water is recycled continually between the ocean and the land. The reservoirs of water include: Oceans - cover 60% of the northern hemisphere and 80% of the southern hemisphere and contain 97% of Earth’s water. Rivers, lakes and glaciers. Groundwater - contains a larger volume of water than all of the combined water in lakes and rivers. The hydrologic cycle describes the exchange of water between ocean, land and atmosphere. On land precipitation exceeds evaporation. In the ocean evaporation exceeds precipitation.

The Hydrologic Cycle

The Ocean as a Physical System
5-7 The ocean is part of a vast biogeochemical system. Rocks on land undergo weathering and these weathered products are transported to the sea where they may be deposited directly or used by organisms and later deposited as organic remains or organic wastes. These sedimentary deposits are buried, lithified and recycled by plate tectonics into new land, which undergoes weathering repeating the cycle.

The Ocean Sciences: Chemical Techniques
Water samples must be collected in inert containers and isolated as they are recovered so as to prevent contamination. The Niskin bottle has valves at each end which are automatically closed when a weight, called a messenger, is sent down the cable and causes the bottle to flip over and seal itself. Sample depth can be determined from cable inclination and length or with a pulsating sound source.

The Ocean Sciences: Desalinization
Desalinization is the process of producing potable (drinkable) water from seawater using one of the following methods. Distillation is the evaporation of seawater and the condensation of the vapor. Freezing can produce salt-free ice which can be melted for water. Reverse osmosis is placing seawater under pressure and forcing water molecules through a semi-permeable membrane leaving a brine behind.

The Ocean Sciences: Desalinization
Electrodialysis is using electrically charged surfaces to attract cations and anions leaving behind freshwater. Salt absorption is using resins and charcoal to absorb ions from sea water.

The Ocean Sciences: Other Physical Properties of Water
Sea ice is ice that forms by the freezing of sea water; icebergs are detached parts of glaciers. As sea water freezes, needles of ice form and grow into platelets which gradually produce a slush at the sea surface. As ice forms, the salt remains in solution, increasing salinity and further lowering the freezing point of the water. Depending upon how quickly the ice freezes, some salt may be trapped within the ice mass, but is gradually released. Pancake ice are rounded sheets of flexible sea ice that become abraded as they collide.

Pressure ridges are the buckled edges of sea ice masses that have collided. Sea ice thickens with time as snow freezes to its surface and water to its bottom. Sheets of ice are broken by waves, currents and wind into irregular, mobile masses, called ice floes.

Amount of light entering the ocean depends upon the height of the sun above the horizon and the smoothness of the sea surface. 65% of light entering the ocean is absorbed within the first meter and converted into heat. Only 1% of light entering the ocean reaches 100m. Water displays the selective absorption of light with long wavelengths absorbed first and short wavelengths absorbed last. In the open ocean, blue light penetrates the deepest.

In turbid coastal waters light rarely penetrates deeper than 20m and the water appears yellow to green because particles reflect these wavelengths. The photic zone is the part of the water column penetrated by sunlight. The aphotic zone is the part of the water column below light penetration and permanently dark.

The speed of sound in water increases as salinity, temperature and pressure increase, but in the ocean, the speed of sound is mainly a function of temperature and pressure. Above the pycnocline increasing pressure with depth increases the speed of sound despite the gradual decrease in temperature. Within the pycnocline, the speed of sound decreases rapidly because of the rapid decrease in temperature and only slight increase in pressure.

Below the pycnocline the speed of sound gradually increases because pressure continues to increase, but temperature only declines slightly. SOFAR Channel is located where sound speed is at a minimum. Refraction of sound waves within the channel prevents dispersion of the sound energy and sound waves travel for 1000s of kilometers within the channel.

The Ocean Sciences: Sea Surface Microlayer
The sea surface microlayer is the water surface to a depth of a few hundred micrometers. It is critical for the exchange of gases, liquids, and solids between the atmosphere and the ocean.

Neuston layer is the habitat of the sea surface microlayer and is inhabited by the neuston, all organisms of the microlayer. Model of the Sea-Surface Microlayer

Profile of the Ocean

Processes that transport matter to the surface layer from below are: Diffusion - random movement of molecules. Convection - vertical circulation resulting in the transfer of heat and matter. Bubbles - the most important process because bubbles absorb material and inject it into the air as they bursts.

Processes within the microlayer can be divided into the: Biological - bacteria and plankton are more densely concentrated in the neuston layer than below. Photochemical effect - the interaction of ultraviolet light and organic compounds.

Types of Oceanography So far – Geology

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