Transcript Chemical and Physical Features of Seawater and the World Ocean

Chemical and Physical
Features of Seawater and the
World Ocean
“If there is magic on this planet, it is contained in water.”
Loren Eiseley
“Well, me don’t swim too tough so me don’t go in the water too deep.”
Bob Marley
What is Water ?
– the stuff covers 70% of the Earth
 Brainstorming activity
 Chemical & Physical Properties of Water
 Categorization activity
 Defend your categories
 If time permits… why the answer to life is
104.5º
 Introduction
Chemical & Physical Properties

Physical property – properties that describe a
substance without changing the identity of the
substance.


Physical change – change that does not result in the
production of a new substance, only the appearance
of the substance
Chemical property – properties that describe
how a substance changes into a completely
different substance

Chemical change – change that results in the
production of another substance
Common Properties of Water
Physical Properties
Chemical Properties
Cohesion/Surface tension
Found in all three states on the
earth
Universal Solvent – dissolves more
substances than any other
common liquid
Conduction of heat – highest of all
liquids (except for mercury)
pH – water dissociates into anions
(OH-) and cations (H+)
Latent heat of vaporization –
highest of all common substances
Polarity – water has positive and
negative ‘ends’
Latent heat of fusion – high for a
molecule of its size
(melting/freezing)
Hydrophobic effect
Heat capacity – highest of all
common solids & liquids
Density – max at 4ºC for pure
water
Viscosity –relatively low for a liquid
References
Castellano, A. (2006) “Victoria Beach”
Castro, P. & M.E. Huber (2005) Marine Biology, 5th ed. McGraw-Hill Higher
Education, Boston, MA.
“Chemical Properties of Water” PlanetWater.au.com Retrieved on Feb 3, 2007
from www.ozh2o.com/index.html
“floating water 5” (2006) wester
Lower, S. (2007) “H2O a gentle introduction to the structure of water.” Retrieved
on Feb 3, 2007 from http://www.chem1.com/acad/sci/aboutwater.html
Nybakken, J.W. & M.D. Bertness (2005) Marine Biology, An Ecological
Approach, 6th ed. Pearson Education, Inc., San Francisco.
Perlman, H. (2006) “Water properties” Water Science for Schools. USGS.
Retrieved on Feb 3, 2007 from
http://ga.water.usgs.gov/edu/waterproperties.html
Petrucci, R.H. (1982) General Chemistry Principles and Modern Applications,
Macmillan Publishing Co. Inc., New York.
The Water Molecule
 Two
hydrogen atoms,
one oxygen atom
 H atoms form 105º angle
 This angle produces an
asymmetrical dipole.
Slight (+) charge on the H
atoms and slight (-)
charge on the O atoms.
O
H
H
105º
The Water Molecule

O
H
H
These slight charges cause
the (+) H atoms of one water
molecule to attract the (-) O
atoms of other water
molecules.
 These weak bonds are
called hydrogen bonds.
 Water can hydrogen bond
with other substances aside
from itself.
Why does ice float?
Density-Temperature Relationship
Background
 Temperature is a measure of kinetic energy (KE). As
KE decreases, hydrogen bonds stay formed and
break less. Water molecules stay closer together
until…
Explanation
 As the temperature approaches 4ºC, less dense ice
clusters begin to form in the liquid.
 At 0ºC when all water molecules become locked in
the rigid ice lattice, the hydrogen bonds actually hold
molecules farther apart than at 4ºC. This creates
spaces making the water less dense.
Why does ice float?
Density-Temperature Relationship Graph
How can water bugs “stride” across
water without breaking the surface?
Surface tension and cohesion

The cohesion or mutual attraction of
water molecules creates a flexible
barrier on the surface of water.
www.nps.gov/olym/insect/gerridae.jpg

This helps support aquatic insects
such as water striders (Halobates sp.)
Why do fish not get electrocuted
when lightning strikes the ocean?
Conductivity
Explanation
 Conductivity is a property that measures the ability of
a substance to transmit heat, electricity, or sound.
 Pure water is not a good conductor of electricity. Its
conductivity is about 20 dS/m.
(Compare with silver – the highest conductivity with 63 x 106 S/m)

In addition, the electrical charge of lightning usually
spreads instantaneously along the surface of the
water from the location of the strike and to a lesser
degree below the surface at the strike site. Fish in
other areas are not affected.
Why do coastal areas have slower
temperature changes than inland
areas?
Heat capacity
Background
 Heat – energy of molecular motion
 Water can absorb or give up heat by
conduction (molecular exchange of
heat) or convection (mixing)
Explanation
 Water can hold heat longer and
release heat more slowly than land.
 Temperature differential between land
and ocean will cause uneven heating
of air masses which drive winds and
moderate any drastic temperature
changes.
Off-shore breeze
On-shore breeze
Why don’t fats and oils dissolve in
water?
Polarity

Fats and oils are nonpolar
molecules.


These compounds do not have slight
regions of charge like water does.
Therefore water molecules are not
attracted to nonpolar molecules and
actually can be repelled by them.

Basis for cell membranes and the water
repellency of marine mammals and
birds.
Why does water dissolve more
substances than any other common
liquid?
The Universal Solvent

Because water is polar, it dissolves
most substances, especially other
polar molecules and compounds
composed of ions, atoms or
molecules that carry an electrical
charge.
 These ionic compounds are often
called salts.
 NaCl (salt) most common dissolved
salt in ocean. There are many
others.
 Seawater is a solution of these salts.
Salt crystal
Seawater
Sources of salts and dissolved solids:
 Erosion of rocks and soil
 Breakdown of organisms
 Condensation of rain from the atmosphere
 Releases from hydrothermal vents
Seawater is
 96.5% water
 3.5% dissolved compounds
Salinity
• Total amount of
dissolved salts in
seawater.

Measured in parts per thousand (ppt)




Grams of salt left behind when 1000g of water evaporate
Average value 35 ppt or 35‰
Range from 0‰ near river mouths to 40% in the
dead sea.
Globally, seawater salinity remains constant. Rule
of constant proportions states that the percentage
of various ions in seawater remains constant.
Surface Salinities of the Oceans
Dissolved compounds in seawater
 Inorganic
substances (salts, nutrients)
 Dissolved gases
 Organic compounds (fats, oils, vitamins,
amino acids, proteins)
 Nitrates and phosphates (usually in
excess as pollution)
 Pollution (DDT, PCBs, chlorinated
hydrocarbons that are synthetic)
Dissolved Gases
 Primarily
nitrogen, carbon dioxide, oxygen
 N2 biologically inert.
 CO2 needed for photosynthesis and pH
buffering.
 O2 required for respiration.
www.abc.net.au/science/news/
stories/s269960.htm
Factors that Affect Salinity

Salinity increases due to…



freezing of seawater.
evaporation.
Salinity decreases due to…



melting of icebergs and sea ice.
precipitation.
run-off from rivers.
pH
 The
amount of hydrogen ions in a
substance is referred to as pH.



pH = (pondus hydrogeni or “power of
hydrogen”
pH = -log10 [H+]
Scales ranges from 0 to 14.
 Therefore,
a pH of 14 means that the
water is very alkaline (basic) while pH 1
means it is acidic. A pH of 7 is neutral.
Seawater pH


The carbonic acid – bicarbonate – carbonate system
keeps seawater at a pH value between 7.5 and 8.4.
The oceans are an enormous “sink” for atmosphere
CO2
The Carbon
Buffering System
 Seawater
has an unusually large
capacity to absorb CO2.
CO2 + H2O  H2CO3 (carbonic acid)
H2CO3  H+ + HCO3 – (bicarbonate ion)
HCO3 –  H+ +
CO32-
(carbonate ion)
Work Cited
Kreger, Chris. "Acid Mine Drainage: Alkalinity." Exploring the Environment: Water Quality.
2004. Wheeling Jesuit University. 2 Oct 2008
<http://www.cotf.edu/ete/modules/waterq/wqalkalinity.html>.
Lower, Stephen. "A gentle introduction to water and its structure." H2O. 2008. 1 Oct 2008
<http://www.chem1.com/acad/sci/aboutwater.html>.
"October 2006 Archives." [Weblog The Marine Electronics Weblog] Oct 2006. Panbo . 1
Oct 2008 <http://www.panbo.com/archives/2006_10.html>.
Water Conductivity. 2008. Lenntech Water Treatment & Purification B.V.. 1 Oct 2008
<http://www.lenntech.com/water-conductivity.htm>.
Woodruff, Steve W.. "Water & Weather." Los Angeles Pierce College Weather Station. 1
Oct 2008 <http://data.piercecollege.edu/weather/water.html>.
The Salinity-Temperature-Depth
Relationship in the World Oceans
Part One – Depth Profiles
Seawater – General Trends
 Temperature
and salinity determine the
density of seawater.



Colder water is more dense; therefore, it sinks.
Saltier water is more dense; therefore, it sinks.
Which is more variable on the earth? Temperature or salinity?
 Which would have a greater effect on the density of seawater? Temperature
or salinity?
Global Sea Surface Temperature

This image shows the temperature of the ocean water at the surface. Measurements were taken from August 6-11, 2001. The temperature scale is in Celsius. Cold temperatures are shown in pink
to purple, moderate temperatures in aqua to green and warm temperatures in yellow to red.

This particular data set was taken by the NOAA-16 satellite. NOAA-16 is part of the TIROS series of polar-orbiting, environmental satellites.
Image courtesy of The National Oceanic and Atmospheric Administration (NOAA)
Surface Salinities of the Oceans
Biogeographical Zones

Based on sea surface temperature, four major
biogeographical zones emerge:




Polar
Cold temperate
Warm temperate (subtropical)
Tropical (equatorial)
Global Sea Surface Salinity
Depth Profiles
Increasing variable 
Graph that shows a specific
ocean variable plotted against
depth.

Usually drawn “upside
down” with increasing depth
on the Y-axis and the
variable across a top X-axis
so that the graph represents
an “ocean profile.”

For any specific location, a
depth profile can be
understood as a vertical
‘snapshot’ of a column of
water or water column.
0
 Increasing depth (m)

Depth Profiles
Which one represents temperature? salinity?
© 2000-06 National Oceanic and Atmospheric Association (NOAA)
Depth Profiles
How do temperature and salinity contribute to density?
© 2000-06 National Oceanic and Atmospheric Association (NOAA)
Salinity-Temperature-Depth Profile
Thermocline – the
depth zone of the
most rapid
temperature decline
Pycnocline – the
depth zone of
rapid density
change
© Lamont-Doherty Earth
Observatory
Halocline – the
depth zone of the
most rapid salinity
change
Other Profiles
 What
might the depth profile look like for
the following variables?



Dissolved oxygen
Transparency of light
Pressure
Light Transparency
This diagram offers a basic illustration of the depth at which different colors of light penetrate
ocean waters. Water absorbs warm colors like reds and oranges (known as long wavelength
light) and scatters the cooler colors (known as short wavelength light). Image courtesy of Kyle
Carothers, NOAA-OE
Light Transparency
Sunlight is composed of colors with different wavelengths
 ROY G BIV
 Longer wavelengths (red/orange) have lower energy
than shorter wavelengths (violet/indigo)


E = hc/λ
where E = energy, h = Planck’s constant, c = speed of light, and λ = wavelength
Light Transparency
General trends:

Longer wavelengths are absorbed at the
surface. Shorter wavelengths can
penetrate to depths of approximately
1000m in clearest waters.
 Extent of light attenuation defines photic
zone

Euphotic zone – surface to approx.
200m max. – sufficient sunlight for
photosynthesis

Disphotic zone – variable 501000m, usually 200-600m –
insufficient sunlight for
photosynthesis (less than 1% of
sunlight penetrates)

Aphotic zone – below disphotic
zone – no light
Pattern can vary with suspended/dissolved
substances.
More suspended/dissolved substances 
less light penetration
Dissolved Oxygen
Oxygen
Change in dissolved oxygen with
depth in eastern tropical Pacific
Ocean (red line) and the tropical
Atlantic Ocean (orange line).
Modified from Oceanography: An
Introduction, D.E. Ingmanson &
W.J. Wallace, ©1973.
Oxygen (ml per L)
0
0
500
1000
Depth (m)
• non-conservative
• low solubility in seawater
• only 5.4 ml/L at 35 ppt
and 20ºC (8 ml/L at
0ºC)
• more soluble in colder
water
• less soluble in saltier
water
• oxygen minimum zone –
usually 500 to 1000m
depth
1500
2000
2500
3000
3500
4000
1
2
3
4
5
6
Dissolved Oxygen
Oxygen Minimum Zone
 depth in open ocean waters at which oxygen
concentration approaches zero
 usually between 200 and 1000m
 Why there?

Inputs of O2 to the oceans


wave action, storms, surface mixing, photosynthesis
Depletion of O2 from the oceans

respiration, decomposition
At this depth, consumption of O2 by organisms for respiration consumes all of
the oxygen, without suitable replacement by photosynthesis or surface
mixing.
Pressure
Surface
• 1 atmosphere of air
(1kg/cm3 or 14.7 lbs./in.2 or ≈
1 bar) pushing down at sea
level
What is significance for marine
organisms?
What is significance for marine
research and exploration?
0
0
500
1000
Depth (m)
With Depth
• water more dense than air
• each 10m of depth
increases pressure by an
additional atmosphere
• linear relationship
Pressure (atm)
1500
2000
2500
3000
3500
4000
4500
5000
100
200
300
400
500
References
Castro, Peter, and Michael E. Huber. Marine Biology. 5th. Boston: McGraw Hill Higher Education, 2005.
Davidson, M.A., Abramowitz, M., Olympus America, Inc., and Florida State University, (2003 Aug 1). Optical
Microscopy Primer. Retrieved February 21, 2007, from Molecular Expressions Web site:
http://micro.magnet.fsu.edu/primer/lightandcolor/lightsourcesintro.html
Enchanted Learning.com, (2007). Twilight Ocean (Disphotic) Zone Animal Printouts. Retrieved February 21, 2007, from
Biomes-Habitats Web site: http://www.zoomschool.com/biomes/ocean/twilight/
Naik, Naomi. "Plot the Temperature Profile." Climate Kids Corner. Lamont-Doherty Earth Observatory. 19 Feb 2007
National Oceanic and Atmospheric Association (NOAA) (2007 Feb 12). Deep Light. Retrieved February 21, 2007, from
Ocean Explorer Web site:
http://oceanexplorer.noaa.gov/explorations/04deepscope/background/deeplight/deeplight.html
National Oceanic and Atmospheric Association (NOAA). "NOAA/NESDIS Edge Image Display." Windows to the
Universe. 2000-06. LUniversity Corporation for Atmospheric Research (UCAR). 19 Feb 2007
<http://www.windows.ucar.edu/tour/link=/earth/Water/images/ocean_temp.html&edu=high>.
Nybakken, James W., and Mark D. Bertness. Marine Biology: An Ecological Approach. 6th. San Francisco: Pearson
Education, Inc., 2005.
photic zone. (2007). In Encyclopædia Britannica. Retrieved February 20, 2007, from Encyclopædia Britannica Online:
http://www.britannica.com/eb/article-9059790
Quiz Tomorrow


Salinity-Temperature-Depth Relationships
Depth Profiles










Thermocline
Halocline
Pycnocline
Light
DO
Pressure
Stratification (three layers)
Stability
Overturn
Global Thermohaline Circulation
The Salinity-Temperature-Depth
Relationship in the World Oceans
Part Two – The Three-Layered Ocean
and the Great Conveyor Belt
 The


oceans are three-dimensional
Horizontally from north to south/ east to west
(geographic changes)
Vertically – depth
Which dimension has the biggest influence on living conditions?
• DEPTH – this third dimension is controlled by density
What two variables have the greatest effect on density?
• TEMPERATURE & SALINITY
Stratification



Less dense water
(warmer/less salty/or
both) floats at the
surface
Denser water
(colder/saltier/or both)
tends to sink
Creates stratification


essentially causes
layers to form in the
ocean.
imparts vertical
stability to the ocean
The Three-Layered Ocean
Surface layer







surface to approx. 200m
also called the mixed layer, because it 200
is mixed by wind, waves, currents, &
storms
may be the only layer found in shallow
1500
coastal waters over the continental
shelf
seasonal thermoclines may form
here
Intermediate layer

0
Depth (m)

bottom of surface layer to approx.
1,500m
main thermocline can be found here
Deep & bottom layers


below 1,500m
uniformly cold (less than 4ºC)
5000
Surface layer
Intermediate layer
Deep
& bottom layers
Stability

Stability – likelihood that a water column in
the ocean will remain stratified.

High stability
• large density difference between deep and shallow
water
• keeps water column stratified

Low stability
• slight density difference between deep and shallow
water
• relatively easy to mix the two layers
Overturn

Instability (unstable)



surface layer becomes more dense than deep layer
surface water sinks resulting in downwelling
process known as overturn
• What might a depth profile look like when downwelling occurs?

Straight Line Profiles
• What climate conditions might cause downwelling?


Occurs in temperate/polar regions in winter when surface water cools
once water sinks, its temperature and salinity do not
change since the processes that change them are
surface phenomena
• becomes a “signature” for the water mass
• oceanographers can follow these water masses as
they circulate throughout the oceans
Global Thermohaline Circulation

Gets its name from fact that it is driven by density
differences in water masses which are in turn caused by
temperature and salinity differences.

It acts as a giant conveyor belt.

Importance:





Extends throughout ocean depths
Regulates the Earth’s climate
Transports heat and nutrients throughout globe
Chemically mixes the world’s oceans
Brings oxygen-rich surface water to the deep sea
Great Ocean Conveyor – A Critical Look
IPCC – Intergovernmental Panel on Climate Change
The Great Ocean Conveyor

Water sinks…

Main Currents in the North Atlantic
Norwegian Sea (North Atlantic
Deep Water – NADW)
• Forms due to heat loss and high
salinity

Labrador Sea
• Deep convection

Weddell Sea (Antarctic Bottom
Water – ABW) – densest
• Forms mostly because of low
temperature

…and returns to surface.


Indian Ocean
North Pacific Ocean
• Both due to warming by equatorial
temperatures and the parting of ocean
water by equatorial tradewinds.
An oceanic roundabout. As warm ocean currents in the
subpolar gyre gradually cool, they warm Europe and may
trigger seesaws in climate (McCartney et al., 1996,
Oceanus, 39, 19-23)
The thermohaline circulation "conveyor belt". Purple arrows indicate cold, deep ocean currents. Red arrows show shallow, warm water
circulation patterns.
Credit: Image courtesy CLIVAR (after W. Broecker, modified by E. Maier-Reimer)
Thermohaline Circulation in 3D!

http://www.youtube.com/watch?v=SdgUyLTUYkg&feature=fvwrel
 http://www.youtube.com/watch?v=3niR_-Kv4SM
 http://www.nodc.noaa.gov/cgi-bin/OC5/WOA05F/woa05f.pl?parameter=t
Role of THC in Climate Change

Brings warmth from the tropics
to higher latitudes


Particularly in the North Atlantic
Has “shut off” in recent geologic
past


(12,800 years ago - the Younger
Dryas)
Evidence
• Oxygen isotope and carbon dioxide
isotopes in ice cores
• Foraminifera and glacial deposits in
sediment cores
• Low latitude glaciology
• LDEO - Abrupt Climate Change Younger Dryas Explanation
SATELLITES SEE GULF STREAM WARM
WATERS
This is a NASA satellite image of the warm waters of
the Gulf Stream running up the U.S. eastern
seaboard. The Gulf Stream shows up as a winding
rope of orange and yellow (indicating warm waters)
against the cooler green and blue waters. Credit:
MODIS Ocean Group NASA/GSFC SST product by
U. Miami
References
Castro, Peter, & Michael E. Huber. Marine Biology. 5th. New York: The McGraw-Hill Companies, Inc.,
2005.
Hoffman, Jennifer. Science 101: Ocean Science. Irvington, NY: Harper Collins Publishers, Inc., 2007.
Kunzig, Robert. "In deep water." Discover Dec 1996: 86-96.
Naik, Naomi. "2: What scientific evidence do we have that abrupt climate change has happened
before?." Abrupt Climate Change. 2003. Lamont Doherty Earth Observatory of Columbia
University. 3 Mar 2008 <http://www.ldeo.columbia.edu/res/pi/arch/examples.shtml>.
Russell, Randy. "Transfer and Storage of Heat in the Oceans." Windows to the Universe. 6 June 2007.
The Regents of the University of Michigan. 3 Mar. 2008
<http://www.windows.ucar.edu/tour/link=/earth/Water/ocean_heat_storage_transfer.html