Chemical Properties of Water

The basics and a little more than you wanted to know!

Temperature

The most important limiting factor

Changes can alter many other parameters (thermal pollution is a big problem)

Surface water that is heated by the sun goes through seasonal changes.

The Thermocline is a narrow band of water that separates warm surface water from cool bottom water

Cold water holds more oxygen than warm water.

Sea Surface Temperatures

A little More

Evaporation and condensation provide energy to run the hydrological cycle

This energy reduces the possibility of freezing in marine organisms’ tissue

Water also has a high heat capacity that allows it to absorb or release large quantities of heat with little temperature change

This helps in moderating climates

Salinity

The amount of dissolved solids in waterIncludes ions of chloride, sodium, sulfate, magnesium, calcium and potassium

Measured using a hydrometer to calculate specific gravity, or by conductivity. Units would be measured in ppt.Surface salinity is greatly influenced by temperature.

High temps cause increased evaporation rates and increased salinity.

The Halocline

Like the thermocline, only it is the zone dividing the surface (fluctuating) salinity with the constant salinity found in deep water.Stenohaline organisms can not tolerate changes in salinityEuryhaline organisms adapt to most fluctuations

Density

Affected by both temperature and salinity800x’s as dense as air.Density causes bouyancy

Thermocline + Halocline = Pycnocline

pH – logarithmic function of the % of hydrogen ions in a solution

In sea water, pH is between 7.5 –8.5Closely associated w/ dissolved CO2

CO2 is a reactant in photosynthesis and a product of respiration.

Dissolves easily in sea water and is stored in marine shells and sediments.

H2O + CO2 = H2CO3, Lowers pH

H2CO3 = HCO3+ H, raises pH

pH cont.

Both reactions change the pH of the water. Ph is expressed on a scale from 1-14. Each value is a ten fold increase over the previous.

The pH Scale

pH Cont.

Enzyme activities and the shapes of vital proteins require a stable pH. A decrease in pH could dissolve the calcium carbonate in mollusk shells.

Dissolved Gases

Dissolved N is the most common gas in the ocean. Dissolves from the atm. where it is 78%.

N gas can’t be used by organisms until it is attached to O in a process called nitrogen fixation.N fixation occurs because blue-green algae convert N gas to a useable form that animals need for building proteins and amino acids.

Dissolved Oxygen

primarily comes from photosynthesis of marine plants and algae. They produce over 50% of the total atmospheric Oxygen. (not to be confused with oxygen in the water molecule )O is not very soluble so most of it diffuses into the air.

Below the thermocline, there is very little O.

Carbon Dioxide

Carbon dioxide is highly soluble in sea water which contains about 50 x’s more CO2 than the atmosphere.

Enters the water from air as well as through respiration.

Can be depleted at surface by plants.Necessary for shell formation.Oceans remove and store CO2 which remain relatively constant at 45-54 ml/liter of sea water.

Transmission of Light

light in the sea comes from two sources: sun and organisms a large portion of the electromagnetic radiation from sun (or moon) is reflected back into atmosphere -- so only the upper kilometers of the water column are illuminated

Seeing the Light

light below the surface differs from that above in both quality and quantity because a major change occurs at the air-sea surface interface 

combined consequences of reflection from the surface and refraction into it reduce the angular distribution of light to a narrow cone of solid angle 97° 

so a fish looking upward only sees the surface above water in that cone -- or window (called Snell's window) -- outside of the window is back-scattered light from deeper water

Light Penetration

water absorption preferentially removes both long (red) and short (ultraviolet) wavelengths, rapidly resulting in near-monochromatic blue light, which is then reduced by 90% for every 70 m of depth 

in coastal waters material from plant decay can absorb additional short wavelengths, resulting in a greenish hue to the water turbidity allows green wavelengths to penetrate

Penetrating Light

since water selectively absorbs the reds and violets, blue penetrates to the lower limits of the photic zone (autotrophs use red and blue wavelengths) before being absorbed the intensity of light decreases with greater depth

thus autotrophs are restricted to the illuminated upper surfaces of the ocean, called the photic zone and are unable to live in the dark lower portion of the ocean called the aphotic zone

colors are seen differently in shallow vs. open ocean water: in shallow water there is a structural background of the shore or a reef which allows animals to hide in it; in open ocean, no refuge exists and the background is uniform

Light Cont.

Marine Plants (autotrophs) make their own food by photosynthesis. Heterotrophs can’t make food so they eat plants.The cycle depends on light entering the water which may be absorbed or reflected.

About 65% of light energy is absorbed in the first 5 feet and can’t be used by autotrophs.

More Light

Red light is absorbed first in most marine environments. Many marine bottom dwelling animals are red. Why?Blue is transmitted bestLight is inversely proportinal to depth. As you descend, it gets darker.The lighted layer is called the photic zone: about 10% of the ocean. The dark layer is the aphotic zone.

Turbidity

Turbidity is a measure of the suspended sediments.More sediments results in less light penetration and poor visibility. Photosynthesis is reduced.The compensation zone is the depth where the rate of photosynthesis = rate of respiration.

O production = rate of respiration

Turbidity cont.

Turbidity can be measured with a secchi disk as visibility.Divide the depth of the secchi line by the water’s depth.Turbidity is lower in areas of high productivity.

Pressure

Pressure at sea level is the weight of air (14.7 psi)As you descend, pressure results from the weight of the water above you (hydrostatic pressure) as well as air pressure.

Pressure going down

For every 33 feet = 1 atm of pressureAt 100 feet = 4 atm of pressure or ~58.8 psiThe pressure at the Mariana Trench is ~ 7 tons/in2

Increased pressure lowers water’s freezing point without affecting the volume.

More on Pressure

SCUBA tanks contain air under pressure so that the internal pressure inside the lungs equals the pressure on the external surfaces exerted by waterWhen ascending, the air volume in your lungs expands. The lungs could be ruptured if you do not continuously exhale.There is a limit to how much pressure a person can with stand. It varies due to experience but safe, recreational diving stops at 130 feet.

Molecular arrangement of water

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

Viscosity is the resistance to flow: it provides buoyancy for plankton while increasing the energy used by nekton to swim.Surface tension is the attraction of surface water molecules. Water is the universal solvent.

Relationships of Parameters

Properties of water are interconnected. Their relationship to each other demonstrates how easily the delicate balance can be disturbed.

Direct relationship = Two parameters both increase or decrease at the same timeInverse relationship = one parameter increase, while the other decreases.

In General

As you descend, the ocean becomes colder, denser, saltier, has more pressure, less light and has fewer gases.