WEEK 10

PROPERTIES OF SEA WATER

Water is a polar chemical compound composed of two hydrogen atoms and one oxygen atom (H2O).

The thermal properties of water are responsible for the mild conditions on Earths surface.

Water density is greatly affected by temperature (and salinity).

The chemical and physical properties of water make it ideal to support life.

A watermolecule iscomposed oftwo hydrogenatoms and oneoxygen atom.Water is a polarmolecule,having apositive and anegative side.Water occur in 3 states : liquid solid gas

What are two important properties ofwater molecules?

1. Cohesion - the ability of water molecules to stick to each other, creating surface tension.Surface Tension :Measures the strength of the water surface filmAttraction of water molecules creates strong film compared to common liquidsPermits water to hold substances heavier & denser than itself.

e.g. Surface tension allows insects to stand and walk on water surface

2. Adhesion the tendency of water molecules to stick to other substancesMolecules at edge sticks to molecules of glass just above them, at the same time pull other water mols along.E.g. Allows paper towel/ sponge to soak water

Cloud formation, plant physiology

Water And HeatWhat is the difference between heat and temperature?

Heat is energy produced by the random vibrations of atoms or molecules (cal).- is a measure of how many molecules are vibrating & how rapidly they are vibrating.

Temperature is an objects response to input or removal of heat (oC).- records only how rapidly the molecules of a substance are vibrating.

Heat Capacity is a measure of the heat required to raise the temperature of 1g of a substance by 1C.

Water has a very high heat capacity, which means it resists changing temperature when heat is added orremoved.

Prevents extreme range in earths temperaturewater bodies are more stable

SolventAbility to dissolve substances gases, nutrients, other chemicals e.g. acids, bases, salts influences water quality & properties

If not, life could not exist because water transfer nutrients vital to life in plants & animalsSolubility of gases Temperature A drop of water falling through airDissolves atmospheric gasesLANDAffects quality of land, lakes, rivers, other water bodies

DENSITY Pure water- freezes at 0C (soild)- boils at 100C (gas/vapor)

freezing point is lowered when substance is dissolved in water e.g. spreading salt on streets to prevent ice formation

unlike other substances which are densest in their solid state, ice is less dense than water

Water density = 775x greater than air

Max density of water = 1.000g/cm3 at 3.94C (not at freezing point) ice at 0C = 0.9168g/cm3

Density ionic content (e.g. salt) Importance :- prevents water bodies freeze from the bottom up- allows water stratificationICE :Expands when freezes by 8%Floats on water

Pressureat sea level, organisms are under the same pressure as we are, which is dependent of the weight of all the air above them (= 1 atmosphere or 14.7 lbs/in2)

every 10 m depth, increase another atmosphere of pressure

as pressure increases, gases compress, which restricts the vertical distribution of organisms

this gas compression and pressure increase has effects for animals who dive and who live at depth, but may be brought to the surface by human activities (i.e., fishing) ex: during net hauling fish swimbladders inflate more rapidly than the fish can compensate for

Chemical Properties of Seawater~ 97% of earths surface water is marine.By mass: seawater ~96.5% water & 3.5% dissolved substances (most of which form salts)

Salinity a measure of the dissolved solids in seawater, usually expressed in grams per kilogram or parts per thousand (ppt), practical salinity unit (psu) by weight.

Standard seawater has a salinity of 35 at 0C (32F) 1 kg of seawater contains ~35g of dissolved salts.

Away from coastal areas salinity varies within a narrow range ~33 - 37

Near shore salinity can be more variable

Major constituents of Seawater at 35 Salinity

A diagrammatic representation of the most abundant components of a kilogram of seawater at 35 salinity. Note that the specific ions are represented in grams per kilogram, equivalent to parts per thousand ()

Minor and Trace Elements in Seawater at 35 Salinity

Salinity varies depending on several factors: evaporation precipitation freshwater runoff

Most of the dissolved solids in seawater are salts that have been separated into ions. Most abundant Sodium (Na+) & Chloride (Cl-)

Salinity strongly affects what organisms are in seawater.

What are the dissolved substances? inorganic salts organic compounds (originally from organisms) dissolved gases

Sources of dissolved substancesChemical weathering of rocks on land, carried to sea by runoff & rivers (Na+ , Mg2+)Earths interior released through hydrothermal vents (Cl-, Sulfide)Atmosphere (volcanoes & other sources) enter in rain or snow

(previous figure)

Processes that regulate the major constituents in seawater.

Ions are added to seawater by rivers running off crustal rocks, volcanic activity, groundwater, hydrothermal vents and cold springs, and the decay of once-living organisms.

Ions are removed from the ocean by chemical entrapment as water percolates through the mid-ocean ridge systems, or by spray, uptake by living organisms, or incorporation into sediments (and ultimately by subduction).

Dissolved gasesRequired by plants & animals living in the ocean to survive

no marine animal has the ability to break down water molecules to obtain oxygen directly no marine plant can manufacture enough carbon dioxide to support its own metabolism

Major gases in seawater nitrogen (N2) oxygen (O2) carbon dioxide (CO2)

The lower the temperature (T ), the greater the solubility of gases(cold water has more oxygen)

The proportions of dissolved gases in the ocean differ from the atmosphere differences of solubility (lower in water)

Major Gases in the Atmosphere & Ocean

Gas% of Gas inAtmosphere, by Volume% of Dissolved Gas in Seawater, by VolumeConcentration in Seawaterin Parts per Million, by MassNitrogen (N2)78.08 %48%10-18 ppmOxygen (O2)20.95%36%0-13 ppmCarbon dioxide (CO2)0.035%15%64-107 ppm

Upper layers of ocean water are usually saturated additional nitrogen will not dissolve

Required by organisms to build up proteins & other biochemicals(but they cannot use the free nitrogen in the atmosphere and ocean directly)

It must first be fixed into usable chemical forms by specialized organisms

Some sp of bottom-dwelling bacteria can manufacture usable nitrates from the nitrogen dissolved in seawater

Most nitrogen compounds needed by living organisms must be recycled among the organisms themselves

Nitrogen

~ 6mg of oxygen is dissolved in each liter of seawater.(6 ppm)Vital resource for animals that extract oxygen with gillsSources : photosynthesis of plants/ plantlike organisms from atmosphereDissolved oxygen (DO) can be increased by: water movement lowering water temperature

Oxygen

Needed by photosynthetic plants for growth

Reacts with seawater to form bicarbonate & carbonate ions.

More CO2 store in the ocean than in on land. (is a common constituent of shells and sediments)

Affects pH buffering system (prevent broad swing of pH when acids/bases are introduced

pH of Seawater slightly alkaline due to the bicarbonate buffering system and to sodium, calcium & potassium.7.5 8.4 & fairly constant

Carbon Dioxide

How concentration of O2 & CO2 varies with depth

O2 is abundant near the surface because of the activity of marine photosynthesizers. O2 conc. Decreases below the sunlit layer because of the respiration of marine animals & bacteria & the O2 consumed by the decay of tiny dead organisms slowly sinking through the area.

Plants & plantlike organisms use CO2 during photosynthesis, so surface level of CO2 are low. P/sthesis cannot take place in dark, so CO2 given off by animals & bacteria tends to build up at depths below the sunlit layer. CO2 also increases with depth because its solubility increases as pressure increases and temperature decreases.

Temperature, salinity & water densityDensity of seawater is depends on temperature (T) salinity (S) pressure (p)

Ocean water form stable layers with the heaviest at the bottom density stratification

Evaporation can also produce salty, dense water that sinks to the bottom until it reaches a layer of water of equal density.

Warm freshwater entering the ocean at a river mouth is much less denser & floats for miles above the cooler, salty layer below.

Density structure of the oceanOcean 3 density zones

Surface zone mixed layer / upper layer of the ocean T & S relatively constant with depth (because wave action & current) water in contact with atmosphere & exposed to sunlight contains the oceans least dense water ( ~ 2% of total ocean volume) to a depth of 150 meters ( depending on local conditions, may extend up to 1,000m or be absent entirely)

2. PYCNOCLINE

Pycnocline = the middle zone of the ocean in which density increases rapidly with depth.

Temperature falls & salinity rises in this zone.Isolates surface water from the denser layer below.Contains ~ 18% of all ocean water. 3. DEEP ZONE

Lies below the pycnocline At depths below about 1,000 m. Little additional change in water density with increasing depth through this zone. Contains about 80% ocean waters.

Density stratification in the ocean. In most of the ocean, a surface zone (or mixed layer) of relatively warm, low-density water overlies a layer called the pycnocline. Density increases rapidly with depth in the pycnocline. Below the pycnocline lies the deep zone of cold, dense water about 80% of total ocean volume.

= The zone of the ocean in which temperature (T) decreases rapidly with depth.Pycnoclines rapid density increase with depth is due mainly to a decrease in water T.Thermoclines are not identical in form for all oceans or latitudes

Thermocline

A zone of rapid salinity (S) increase with depth.Low S can also contribute to the pycnocline , especially in cool regions where precipitation is high.

Halocline

Low S precipitation > evaporation

Tropics evaporation > precipitation

Polar & temperate precipitation > evaporation

The deep ocean at all latitudes are similar cold, salty, dense

Sunlight is scattered & absorbed once penetrates the ocean

Scattering occurs as light is bounced between air or water molecules, dust particles, water droplets or other objects before being absorbed.

Higher density (along with suspended & dissolved particles) makes scattering more prevalent in the water than air.

Absorption structure of water molecules it happens to strike when light is absorbed, molecules vibrate & lights electromagnetic energy is converted to heat.

Light & colours of the ocean

Light from the Sun:

effects the salinity of the ocean (heat) drives ocean currents & modifies our climate (heat) energy for photosynthesis

Ocean Euphotic ZoneProductivity of food by photosynthetic marine organisms Water is heated by sun, heat is transferred from ocean to atmosphere & space & gases are exchanged.Most of the oceans life is found here.Aphotic ZoneComplete blackness except for light generated by living organisms.Bioluminescence The production of light by living organisms

Water colors

Light energy of some colors is converted to heat nearer to the surface than others.

The table shows the percentage of light absorbed in the uppermost meter of the ocean, and the depths at which only 1% of the light of each wavelength remains.

The bar shows the depth of penetration of 1% of the light of each wavelength (as in the last column of the previous table)

Shorter wavelengths are bluer

Longer wavelengths are redder

The visible spectrum (wavelengths that human eyes can detect) is only a part of the entire electromagnetic spectrum.

Only green & blue wavelengths pass through water in any appreciable quantity or distance.Ocean colour

The top 1m of the ocean absorbs 71% of red light.

Light becomes bluer with depth because the red, yellow & orange wavelengths are being absorbed.

By ~300m, even the blue light has been converted to heat.

Clear ocean looks blue because blue light can travel far enough to be scattered back through the surface to our eyes. Water (and seawater) is a very good absorber of all wavelengths of light except blue.

Why does our ocean looks blue?

Changes in ocean color are primarily due to changes of:

the type and concentration of organisms suspended in the water, namely phytoplankton (which include photosynthetic bacteria, such as the cyanobacteria). Areas of river outflow, sewage outfall, or intense land runoff, near the coasts, may contain large amounts of suspended sediments, which give seawater a brownish or dirty color.

SOUND

Form of energy transmitted by rapid pressure changes in an elastic medium.Sound energy decreases as it travels through seawater because of spreading scattering absorption

Scattering occurs when sound bounces off bubbles, suspended particles, organisms, the surface, the bottom & other objects.

Sound waves can travel greater distances through water than light waves can before being absorbed. because sound travels through water so efficiently, marine animals use sound rather than light to see in the ocean.

Speed in seawater 5X of sound in air (~1,500m/ second)

Speed when :T & pressure

Sound travels faster in warm ocean surface than in deeper, cooler waters.

Speed decreases with depth minimum 1,000m

Below 1,000m, increasing pressure > increasing T, so speed increases again.The relationship between water depth and sound velocity

Sonar

Whales & other marine mammals use clicks & whistles to find food & avoid obstacles.

UK01902_2_Sem1_1213_FAFA*UY01102_3_Sem2_1011_FAFA*Precipitation rain, snow, river input from precipitation on landUY01102_3_Sem2_1011_FAFA*however, seawater can hold only a small fraction of the oxygen that is produced, so excess oxygen is diffused into the atmosphere (ocean provides 50% of the atmosphere's oxygen content) the amount of dissolved oxygen can be increased by turbulence (water movement) caused by waves and surface winds dissolved oxygen declines rapidly as depth increases because the rate of photosynthesis is slowed by decreasing light intensity UY01102_3_Sem2_1011_FAFA*Density is one of the most important parameters in the study of the oceans dynamic. Small horizontal density differences (caused for e.g. by differences in surface heating) can produce very strong currents.