Unit 4

4:12 a PHYSICAL PROPERTIES OF WATER

1. TEMPERATURE IS THE MOST IMPORTANT LIMITING FACTOR.

A change in temperature can alter many other parametersThus thermal pollution is a serious concern.Surface water is heated by the sun and changes seasonally.A narrow zone called the thermocline separates warm surface water from cool bottom water. Divers can feel temperature differences as they go through this zone. Whales use this zone for long distance communication.Most marine animals are ectothermic (cold-blooded). Warmer water temperature increase their metabolism.

However warm water hold less O2

so they tolerate cold Water at extremes better than water that is too warm.

Mammals and a few fishes are endothermic (cold-blooded)They can usually maintain a constant body temperature. But can suffer from hypothermia just as humans do.

Pollution, illness and other environmental stresses alter their ability to keep warm and maintain enzyme functions.

4:12 B Sea Surface Temperature

Evaporation and energy condensation provide to run the hydrologic cycle; this energy reduces the possibility of freezing in marine organisms’ tissue. Water also has high heat capacity that allows it to absorbor release large quantities of heat with little temperature change’ helps to moderate climate.

2. Salinity is the amount of dissolved solids in waterIncluding ions of chloride, sodium, sulfate, magnesium, Calcium and potassium.

The first four ions Listed are remarkablyConstant in seawater. IfThe chloride ion is measuredThen the other ions can beMeasured.Salinity can be measured by a hydrometer as

specific gravity, or by conductivity or chlorinity. Units are in parts per thousand(ppt).

Surface salinity is greatly influenced by temperature. HighTemperatures cause increased evaporation rates andIncreased salinity

4:12 CThe halocline is a place wherefluctuating surface salinityIs divided from the constantof deeper water.Stenohaline organisms can Not tolerate changes in salinity. Euryhaline organismscan adapt to mostfluctuations

Some properties of temperature are due to the unusual Nature of the water molecule.

4:12 C cont 3. Density is mass/volumeIt is affected by temperatureand salinity.

Water is 800 times more Dense than air. Sea waterIs more dense than fresh. This density causes buoyancy.

Above the freezing point, the density of water is 1g/cubic centimeterWhen water freezes, its density decreases because the volume Increases. Ex. Hose cracking when water freezes in it.

4:12 C cont.Ice has a density of.92 grams/cm3 soit floats in water.Any object willfloat in water if the density is less than the density of waterit is floating in.

In order to reduce an object’s density, the volume can be increased

1. The pH is a logarithmic function of the per cent of hydrogen ions in a solution

In sea water, the pH is closely associated with dissolved carbon dioxide and is usually between7.5 – 8.5

4”13 A cont.

CO2 is a reactant in photosynthesisAnd a product of respiration. It dissolves easily in sea water And is stored in marine shellsAnd sediments

H2 O + Co2 = H2 CO3

Water + Carbon Dioxide makes carbonic acid. that lowersthe pH.

4:13 A cont. H2CO3 = HCO3 +H Carbonic acid disassociateshydrogen which raisesthe pHThese reactions change thepH of the water. The pHis expressed on a scale from1 – 14. Each value is 10 foldincrease the previous number.

Enzyme activities and the shapes of vital proteins require a stable pH. Since Mollusk’s shells are calcium carbonate, a decrease in pH could dissolve shells.

4:13 B Dissolved Gases

Dissolved nitrogen is the most common gas in the oceanbecause it dissolves from the gas in the atmosphere where there is 78%

Nitrogen gas can’t be used by organisms until it is attached to oxygen in a process called nitrogen fixation

Nitrogen fixation occurs because blue-green algae convertnitrogen gas to a useable form that animals need for Building proteins and amino acids.

4:13 B cont

3. Dissolved oxygen primarilycomes from photosynthesis of marine plants and algae.They produce well over 50%Of the total atmosphericOxygen.

Oxygen is notOxygen gas is not very soluble so most of it diffusesInto the air. Marine animals need it for respiration.Below the thermocline there is very little oxygen

4:13 b cont. 4. Carbon dioxide is highly soluble in sea water whichcontains about 50 times moreCO2 than the atmosphere. It enters the water from the air as well as from respiration.

However it can be depleted at the surface due to useBy plants. It is also necessary for shell formation.Oceans remove and store carbon dioxide whichremain relatively constant between 45 and 54 mL/Lof sea water

The sun emits wavelengths of energy in the form oflight. Light is only 1 wavelength segment on theelectro-magnetic spectrum.

4:14 A cont

Marine plants (autotrophs))Make their own food by Photosynthesis. Heterotrophs can’t make make food so they eat plants.

Marine food webs depend on light that is eitherAbsorbed or reflected as it enters the water. About65% of the light energy is absorbed in the first fiveFeet and can’t be used by autotrophs.

Red light is absorbed first in most marine environments.Many marine bottom dwelling animals are red. Why?

4;14 A cont

Blue light is transmitted best. Why does the sky and water look blue?

Light is inversely proportionalto depth. As you descend itgets darker.

The lighted layer is called the photic zone: about 10%of the ocean. Dark layer is the aphotic zone: 90%of the ocean is dark.

4:14 B Turbidity

Turbidity is the measure of suspended and dissolvedSolids. The more sediment (solids), the less light Penetration and the poorer the visibility. Photosynthesis Is reduced by turbidity.

The compensation zone is the depth where the rate of photosynthesis = rate of respiration. Oxygen production = carbon dioxide consumption

4:14 B cont.

The zone’s depth depends on light/ turbidity raises thecompensation zone.

Turbidity can be measured with a secchi disk as visibilityDivide the depth of the secchi disk line by the water’s depth.

Turbidity is usually lower in areas of high productivity. Filter-feeders use some of the TSS (total suspended solids)for food.

4:15 A PressurePressure at sea level is the Weight of air (14.7 lbs/in2).

As you descend pressure results from the weight of theWater above you (hydrostatic pressure) as well asThe air pressure.

For every 33 feet = 1 atmosphere of pressure 14.7 lb/in2

At 100 feet = 4 atmospheres of pressure 58.8 lb/in2

The pressure in the Mariana Trench is 7 tons/2

This tremendous pressure lowers water’s freeing pointwithout affecting the volume.

SCUBA tanks contain air under pressure so that the internal pressure inside the lungs equals the pressureon the external surfaces exerted bythe water.

4:15 A Cont.

4:15 AWhen ascending, the airvolume in your lungsexpands. The lungscould be ruptured if youdo not continuously exhale

There is a limit to how much pressure a person canwithstand. It varies due to experience but saferecreational diving stops at 130 ft.

4:15 B Molecular Arrangement of Water

The shape of the water molecule gives it special propertiesthat effect marine organisms.

1. Viscosity is the resistance to flow; it provides buoyancyfor plankton while increasing the energy used by nekton to swim.

2. Surface tension is the attraction of surface watermolecules. They provide limited support for insects & larvae

3. Water is the universal solvent. Many substances will dissolve in water which helps dilute the harmful wasteproducts of animals.

Relationships of Parameters

The properties of waterare interconnected. their relationship toeach other demonstrateshow easily the delicate balance can be upset.

By examining relationships, the effect that one parameterhas on another can be predicted

4:15 B cont.

A direct relationship is when twoparameters both increases ordecreases at the same time

An inverse relationship is when 1 parameter increases while the other parameter decreases.

Generally, as you descend, the ocean becomes colder,denser, saltier, and more pressure, less light andfewer gases.

That’s all Folks!