Unformatted text preview: Water Properties
The cradle of life We will cover
We will cover
• Chemical structure of water
States of Water
Density of water with depth
Light in the ocean
Sound in the ocean
Waves Water’s unique properties
Water’s unique properties
• Water is an excellent solvent because each H2O molecule has a + & charge • The atoms of H & O share electrons in what is known as a covalent bond •Oxygen has 6 electrons, and wants 2 more
electrons for stability.
•Hydrogen has 1 electron and wants 1 more electron
for stability. A covalent bond
exists when two
electrons are shared
by two non-metallic
atoms. Dipolar. **Electron density higher around oxygen, giving that end a partial
negative charge. Hydrogen bond is a weak bond formed when a charged part of a molecule
having polar covalent bonds forms an electrostatic (charge, as in positive
attracted to negative) interaction with a substance of opposite charge. The weak
bonds are easily and rapidly formed and broken under normal biological
conditions. They are extremely important in biological systems and Their
presence explains many of the properties of water. Think of each water molecule as Think of each water molecule as being a little magnet
• Magnets have positive and a negative sides and if you place one magnet near another they will be attracted to each other Water cohesion causes surface tension & capillary action.
Water cohesion causes surface tension & capillary action. Water is a powerful solvent Ionic molecules dissolve well in water. Ethanol dissolves
well in water because
it is polar. On the other
hand, oil is
water because it
is non-polar, and
thus does not
dissolve well in
water. Water easily passes through three Water easily passes through three different states: solid, liquid & gas In water vapor the molecules are In water vapor the molecules are not held together by hydrogen bonds
• As liquid water temperature rises, the water molecules move faster and faster.
• Evaporation rate increases
• When water gets hot enough nearly all the bonds are broken and the water boils
• When liquid water cools, the molecules move closer together and the water becomes denser To go from 0 C to 100 C takes one calorie of To go from 0 C to 100 C takes one calorie of energy per degree per ml of water. • BUT to melt the same volume of ice at 0 C it takes 80 calories.
• AND to vaporize 1 ml of water at 100 C it takes 540 calories.
• This is called the “latent heat of melting or of vaporization”. This is the energy needed to go from one state to another. 0° 100° 0° 100° Freezing Temperature
• Freshwater freezes at 0 C (32 F) and seawater doesn’t freeze until about minus 1.5 C because the salts in seawater depress the freezing point (that is why they salt highways in winter). Freshwater has its highest density Freshwater has its highest density at 4oC
• Thus in a pond, warmer water at 4o C can be on the •
• bottom and colder, 1o C water on the surface.
BUT in seawater, water just gets denser and denser as it gets colder because of the effects of salt on the freezing point.
So the colder seawater is, the denser it is.
The denser water is on the bottom, lighter water on top
The higher seawater’s salt content, the denser it is
The colder seawater is, the denser it is. water Thermocline
• Water circulates freely in the •
• upper mixed layer of the ocean (upper 100 m or so)
Thermocline is a layer of rapid temperature change between the mixed layer and deep water
Once the phytoplankton use up the nutrients in the mixed layer, the thermocline is a barrier between the nutrient rich deep water and nutrient poor mixed layer Polar
Tropical In tropics
• Surface water is warmest, and thermocline is most pronounced.
• The tropics have a permanent thermocline which does not break down seasonally as it does in temperate areas. Seasonal changes in thermocline in Seasonal changes in thermocline in temperate regions
• In winter, water is vertically isothermal (same temperature) and mixes well from winter storms
• In spring it progressively warms near the surface and by summer a strong thermocline has formed
• In fall cooling occurs and the thermocline breaks down Warming Cycle:
4. August Cooling Cycle:
5. January Next, note warm surface waters in tropics which Next, note warm surface waters in tropics which prevent deep nutrient rich water from coming to the surface • Polar surface waters are cool allowing deep nutrient rich water to come to surface
• Can you identify any cool surface waters in tropics?
• Hint: look at coast of Chile & SW Africa Mixed Layer
• The mixed layer consists of water of the same density at the surface
• This water can mix vertically, particularly by wind blowing across its surface
• The thermocline is below the mixed layer The thermocline exists mainly in tropical and The thermocline exists mainly in tropical and sub tropical waters. Nearer the poles at latitudes higher than 50 N or S, it barely exists Salinity of seawater
Salinity of seawater
• 85% of the salts in seawater consist of ordinary table salt (sodium chloride)
• Six ions make up 99% of the salt content of seawater
• See next table Salt Ion
Salt Ion Ions in Seawater Ions by Weight (%) Cumulative (%) 55.04 55.04 Chloride (Cl ) (‰)
18.98 Sodium (Na+) 10.556 30.61 85.65 Sulfate (SO42) 2.649 7.68 93.33 Magnesium (Mg2+) 1.272 3.69 97.02 Calcium (Ca2+) 0.4 1.16 98.18 Potassium (K+) 0.38 1.1 99.28 Bicarbonate (HCO3) 0.14 0.41 99.69 Bromide (Br) 0.065 0.19 99.88 Boric Acid (H3BO3) 0.026 0.07 99.95 Strontium (Sr2+) 0.013 0.04 99.99 Fluoride (F) 0.001 0 99.99 Total 34.482 99.99 99.99 Salinity is defined as the total amount of salt Salinity is defined as the total amount of salt dissolved in seawater • Seawater has about 35 grams of salts in 1000 grams of water.
• 1000 grams of water = 1 Liter
• We define salinity in “Practical Salinity Units” or PSU
• 35 PSU = 35 grams of salts/Liter Proportions of salts (i.e. Na or Cl) Proportions of salts (i.e. Na or Cl) remain the same no matter what the salinity is
• If you make up aquarium water with “Instant Ocean” to a low or a high salinity, the ratio of each salt remains the same. This is exactly the same case in the ocean.
• This principal is called “The rule of constant proportions” Where is the ocean the most salty?
Where is the ocean the most salty?
• The water with the highest salt content is found where evaporation is greatest. This is in areas such as the Sargasso Sea in the North Atlantic where there is a pronounced high pressure system with lots of sunlight and little rain.
• There is more rain at the equator so the ocean is less salty there. Some Bays such as Laguna Madre in Texas may Some Bays such as Laguna Madre in Texas may
have twice the salinity of seawater salinity because of low freshwater input, high evaporation and restricted flushing This is a typical salinity profile from the Sargasso This is a typical salinity profile from the Sargasso Sea. High surface salinity because of high evaporation. Even though the higher salts make the surface water dense, the high temperature makes this water lighter. Sources of Salt. The salts in seawater Sources of Salt. The salts in seawater come from weathering of continents & volcanic activity over millions of years Seawater density
• Temperature and salinity together have a •
• major influence on seawater density.
As salinity increases, density increases.
As temperature increases, density decreases.
The halocline is a zone of rapid salinity change.
The pycnocline is zone of rapid density change (next slide) The pycnocline is a zone of rapid The pycnocline is a zone of rapid density change with depth
• When there is a strong pycnocline (produced by individual or combined effects of temperature and salinity) there is a barrier between lighter surface waters and colder deep waters
• This barrier acts to restrict circulation between these two layers Temperature and salinity together affect seawater density. Differences Temperature and salinity together affect seawater density. Differences in density from one place to another in the ocean drive ocean circulation. This is called thermohaline circulation. Nearer the poles, seawater cools and becomes more dense and it sinks. Gasses dissolve in seawater
Gasses dissolve in seawater
• Most important to life are oxygen, carbon dioxide and •
• nitrogen gasses
The colder the seawater, the more dissolved gasses it can hold
As soda water is taken out of the refrigerator, bubbles form as the water warms CO2 is only 0.04% of air but in CO
seawater it can be 80% of gasses • This is because it reacts chemically with water as it dissolves
• There is over 50X more CO2 in seawater compared with what is in air
• Since this is a greenhouse gas, it is very fortunate that it dissolves readily in seawater Visible light is between 400700 nm Visible light is between 400700 nm wavelength
• Short (~400nm) wavelengths are blues Long wavelengths (~650700 nm) are reds
In clear ocean water, blues penetrate deepest
• In coastal water there is a lot of dissolved organic matter (called Gelbstoffe or Gilvin) and this absorbs the blues, thus leaving green wavelengths (thus coastal water appears to be green). Light penetration
• About 50% of all light energy hitting the ocean is absorbed in the first meter…..most of this is the longer RED wavelengths. This warms surface waters.
• In clear open ocean water, there is sufficient light for photosynthesis by phytoplankton or macroalgae in the upper 100150 meters.
• This zone where there is enough light for photosynthesis is called the EUPHOTIC Secchi Disc
• Light penetration can be • •
• measured with a Secchi Disc
You lower the disc until it just disappears, record it, then lower it deeper and bring it up and record depth you first see it. Take the mean, and this is the Secchi depth.
Useful to compare the clarity or transparency of different waters
Depth at which it disappears is around 1% of light
This is roughly the bottom of the EUPHOTIC zone Secchi Disc invented by advisor to Secchi Disc invented by advisor to the Pope, Pietro Angelo Secchi
• In 1865 Light is refracted in water
Light is refracted in water
• When light goes from one medium to another (air to water) it is bent. Thus when you look in the water, objects aren’t where they appear to be. Refraction
• Light travels in a different direction when it leaves water and enters the air SOFAR (Sound Fixing And SOFAR (Sound Fixing And Ranging) Channel • Sound travels over 4 X faster in water than in air.
• Sound speed increases with increases in • • temperature, salinity & pressure (TSP)
At a depth of about 1000 m, TSP values result in slow sound speed. This is called the SOFAR Channel and sound can be trapped there (refracted into the channel) and travel long distances.
Theoretically, a whale off Africa can “talk to” a whale off S. America if in this channel. SOFAR Channel
SOFAR Channel Theoretically whales can Theoretically whales can communicate over thousands of miles
• Today with so much sonar and engine noise, probably not. Pressure increases 1 Atmosphere Pressure increases 1 Atmosphere every 10 m. i.e. 50 m = 6 ATM Water Pressure
• Deep water organisms do not have any gaseous voids (bladders) in • their tissues, thus they avoid any bad effects from water pressure.
SCUBA divers can get the bends if they come up to the surface too rapidly. This is due to the formation of bubbles in blood (much like opening a bottle of soda which was under pressure). To avoid the bends, divers must acclimate slowly at different depths as they come to the surface. Earth-Moon System
Earth-Moon Tides are caused
by two forces:
Centrifugal force. Gravitational attraction w/o any forces Centrifugal force The Moon takes 28 days to circle The Moon takes 28 days to circle the earth. • There are two Spring and two Neap tides every •
• 28 days
Spring tides occur at the Full and New Moon when the moon is lined up with the sun.
Spring Tides: Combined gravity from sun and moon aligned produce the highest high and lowest low tides
Neap tides occur at the Half Moon. Neap tides have the least amplitude Monthly
Tides b a&c
· The Moon and the Sun are in phase so
they reinforce each other
· They are said to be in conjunction (New
Moon) or in opposition (Full Moon)
· Spring tide (long tide) c a b&d
· The solar and lunar tides are out of phase
so the tidal range is smaller than average d · The Moon is said to be in quadrature
· Neap tide (short tide) Types of Tides Location of Tides Tides are caused by two forces:
Gravitational attraction and Centrifugal
Tidal Cycle : 24 hrs 50 min
The moon rises 50 min later each
day; thus high or low tide arrives 50
min later each day. Ocean Waves
Ocean Waves Wave base depth = ½ wavelength, where orbits do not Wave base
move at all. If you get deep you won’t get battered as a scuba diver. Deep water waves = occur where the orbits of water particles are near circular because the sea bottom (solid) is deeper that ½ wavelength.
Intermediate waves = occur where a wave can “feel” the bottom and the orbits of water particles are elliptical because the sea bottom (solid) is (½1/20) wavelength. Shallow water waves = occur where the depth is shallower than (1/20) wavelength. Examples 1) wind waves in shallow water
2) tsunamis (seismic) waves
3) tide waves As a wave approaches the beach
As a wave approaches the beach
• Wave speed decreases Wavelength (L) decreases Wave height (H) increases But wave energy remains the same At H:L of 1:7 or greater, wave breaks Mavericks in Half Moon Bay
Mavericks in Half Moon Bay Because of a shoal that juts out from shore, waves Because of a shoal that juts out from shore, waves squeeze together and build up height Tsunami
• Caused by sudden movement of earth’s •
• crust. Wave initially may be only 36 ft.
Incorrectly called a “tidal wave”
Have extremely long wavelengths (60120 miles), and travel very fast (50100 mph)
Are classified as a “shallow water wave”
When they come into shallower water, the wave height grows dramatically.
Wave height may be 20100 ft high! Swedish Mother runs into ocean to Swedish Mother runs into ocean to save her 3 kids from Tsunami
• All survived What is a Nautical Mile?
• A Statute Mile has 5280 ft. A Nautical Mile has • 6080 ft.
A KNOT is 1 Nautical Mile/hr. Remember that position on the earth is determined by latitude & longitude Remember that each degree of Remember that each degree of latitude has 60 minutes
• A Nautical Mile is equal to one minute of latitude (not Longitude!)
• There are 90 degrees from the Equator to each of the poles. There are 60 minutes in each degree. • How many Nautical miles from the Equator to the Pole?
• 90 x 60 = 5400 Naut. Miles Sailors measured ship speed by tying knots in a Sailors measured ship speed by tying knots in a rope and throwing a flat plate over the side • They counted the number of knots in the line that passed through their fingers in 28 seconds (measured with an “hourglass”). Each knot was 47’ 3” apart. This gave speed in Knots Who first discovered global Who first discovered global warming?
• Svante Arrhenius, Swedish chemist predicted that rising CO2 levels in atmosphere would lead to global warming 1896. Came up with theory of causes of ice ages. How do we measure ocean How do we measure ocean depth
• In old days, with a rope and a weight.
• Today use sound and time the distance from the “ping” to the echo
• Today use a “multibeam” system Next SF Earthquake?
Next SF Earthquake?
• Pretty high probability This Study Guide summarizes some of the This Study Guide summarizes some of the physical and chemical properties of seawater
• Water is excellent solvent because it has a + & charge. •
• Bonding between water molecules causes surface tension.
Constant proportion of salts in seawater
NaCl makes up 85% of salts in seawater
Saltiest water on surface N & S of equator. Why?
Thermocline seasonality in temperate areas, permanent in tropics. Little or no Thermocline in Polar waters
Thermocline separates nutrient rich deep water from low nutrient surface water Blue light penetrates deepest offshore, but green deepest in coastal areas because of presence of dissolved organic matter in coastal waters More
• The euphotic zone is the near surface region where there is enough •
• light for photosynthesis
Sound travels over 4X faster in water than air
SOFAR sound channel. What is it?
Water pressure increases 1 atm for every 10 m
Pressure is usually not a problem for deep dwelling organisms because they have no gaseous voids in their bodies
Know the causes of tides, what is typical daily tidal cycle. What kind of tidal cycle SF Bay has.
Why do the tides occur 50 min later each day. What is difference between “Spring” and “Neap” tides and why are they different More
• Know differences between Deep water, Intermediate, and Shallow water waves. Know the depth at which a wave starts to “feel” the bottom (1/2 the wavelength).
• Characteristics of a Tsunami Wave
• What is a Nautical Mile? How many in a degree of Latitude? What is a Knot? That’s all!
• Read Chapter 3 ...
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- Fall '08
- Seawater, Tide, Thermocline