Introduction to Oceanography
Surtsey, Iceland.
Wikimedia Commons, NOAA
image, Public Domain, http://
commons.wikimedia.org/wiki/
File:Surtsey_eruption_2.jpg
Lecture 8: Seawater
Physical and chemical properties of Seawater
Periodic Table figure, NASA Science Education
Resource Center, Public Domain
Playa del Rey & LAX, CA,
E. Schauble, UCLA
1
Atoms
•  Atom: cannot be broken down into
simpler parts by chemical means
•  Nucleus:
–  Protons (+) & Neutrons (uncharged)
–  Massive
–  Small (~10–15 m)
•  Electrons (–)
–  Little mass
–  Most of the volume
(~10–10 m = 1 Å)
Svdmolen/Jeanot, Wikimedia Commons, Creative Commons
A S-A 3.0, http://commons.wikimedia.org/wiki/File:Atom.svg
Helium
Ions
•  Ions are atoms with net electrical charge
–  Anion: negative charge (Cl–) -- extra electrons
–  Cation: positive charge (Na+) -- electrons removed
–
–
–
–
–
11+
–
Na+: 11p+, 10e–
–
–
–
–
E. Schauble, UCLA
Elements on the left side of the periodic table of
elements tend to become positive (H, Na, Mg).
Elements near the right side of the periodic table
tend to become negative (O, F, Cl)
Molecules
•  Substances made up of chemically bonded
atoms
2
What kind of ions will an element form?
Tend to form
cations (+)
Tend to form
anions (–)
NASA image, Science Education Resource Center,
http://serc.carleton.edu/images/usingdata/nasaimages/periodic-table.gif, Public Domain
Chemical Bonds
e–
•  Covalent: shared between
atoms (i.e., H2O)
•  Ionic: Charges borrowed by
anions
e–
e–
e–
e– –
e
+
8+
e–
e–
e–
e–
e–
+
–  Like Na+Cl–
Na+
Cl–
•  Hydrogen Bonding: in water, H has slightly + charge,
which attracts negatively charged O.
H in water molecules also attracts anions like Cl–
O in water molecules also attracts cations like Na+
Bond Strength: Covalent > Ionic > H-bond
All images E. Schauble, UCLA
3
Water Molecule: H2O
Covalent bond between O and H
•  Polar Molecule
–  Positive “ears”-105o
–  Mickey Mouse
–  Polar structure
H
O
e–
e–
e–
+ e–
e–
e–
–  Effect of polarization
–  ~5% as strong as covalent
bonds
–  tends to make molecules
clump together –
i.e., condense
e–
e–
e–
e–
e–
8+
•  Hydrogen Bonding
e–
e– –
e
+
8+
H
+ e–
e–
e–
e–
e–
e–
+
E. Schauble, UCLA
ball & stick model rendered using MacMolPlt
Hydrogen bonding
•  Hydrogen Bonding
–  Each H2O: 4 possible
H-bonds
–  Makes liquid water
“clump” together
–  Accounts for many
peculiarities
•  Great solvent power
–  Saline ocean
water
•  Thermal and density
properties
Qwerter/Michal Maňas, Wikimedia Commons, Creative Commons A S-A 3.0,
http://en.wikipedia.org/wiki/File:3D_model_hydrogen_bonds_in_water.jpg
4
Heat Capacity
Substance Heat Capacity (cal/gram/oC)
Granite
0.20
Gasoline
0.50
Water
1.00
Ammonia
1.13
The only common
liquid with
higher heat
capacity than
water is
ammonia!
Photo by
..its.magic..,
Flickr, Creative
Commons 2.0,
http://
www.flickr.com/
photos/rizielde/
3373257326/
sizes/l/
Heat Capacity
Examples:
TV dinner: Aluminum
Foil vs. Gravy.
Both are at the
same temperature,
but gravy has
much higher heat
capacity – it hurts!
At the beach:
Sand vs.water
Photo by A. Lau, “are you gonna eat that”, http://www.flickr.com/photos/andreelau/186536202, Creative Commons
Attribution-NonCommercial-NoDerivs 2.0 Generic
5
Climate Comparison
LAX -- on coast.
Strong ocean
influence.
Little daily/seasonal
variation in Temp.
Omaha, NE –
middle of continent.
Weaker ocean
influence.
Variable Temp.
Pidwirny, M. (2006). "Climate Classification and
Climatic Regions of the World". Fundamentals of
Physical Geography, 2nd Edition. http://
www.physicalgeography.net/fundamentals/7v.html
Physical States of Matter
Solid: molecules bonded in a fixed lattice
–  Add energy (i.e., latent heat of fusion)…
Liquid: bonded molecules but in
no fixed lattice
–  Add energy (i.e., latent heat of
vaporization)…
Gas:
Free molecules
Zeitraffer, Wikimedia Commons, CC A S-A 3.0,
http://commons.wikimedia.org/wiki/File:Timelapse.GIF
NASA, Public Domain,
http://ksnn.larc.nasa.gov/videos/
poolboil.mov
6
Relationship between Heat and Temperature for H2O
steam
140
120
liquid boiling to steam
100
Latent heat of vaporization
80
id
60
liqu
Temp.
(ºC)
40
ice
melting
to liquid
20
-20
ice
0
Latent
heat of
melting
E. Schauble, UCLA
-40
0
500
1000
1500
2000
2500
3000
3500
Heat (Joules/gram)
Sensible Heat: measurable change in temperature when heat is added or
subtracted (sloping lines).
Latent Heat: no temperature change with added/subtracted heat (flat lines).
Density of Pure Water
•  Density of fresh liquid water ≈ 1 gm/cm3
Maximum density
of pure water
occurs at 4o C
(but at freezing
temperature in
salty water, i.e.
seawater)
Max density
(1.0) at 4ºC
1.02
1.00
Density
(gm/cm3)
liqu
0.98
id
0.96
0.94
0.92
Ice much
less dense
(0.92) at 0ºC
ice
0.90
-20
0
20
40
60
80
100
Temperature (ºC)
E. Schauble, UCLA
7
Density & Structure of Ice
Ice density 0.92 gm/cm3
8% less than liquid water
Molecular bond angle
increases to 109o
Allows H-bonds to form
solid, but widely
spaced, lattice
Ice is less dense than liquid!
Therefore: ice floats!
Unique property of water,
due to H-bonds.
Materialscientist, Wikimedia Commons, Creative Commons A S-A 3.0,
http://commons.wikimedia.org/wiki/File:Hex_ice.GIF
Thermal Convection in Water
•  Cold surface water
becomes more
dense
•  Sinks below
warmer
surrounding
waters
Where should this
occur in the
ocean?
Jberes87, YouTube,
http://www.youtube.com/watch_popup?v=QBVMm9i-pvo
8
es
Qu
tion
s?
GOES-9 movie, NASA Mesoscale
Atmospheric Processes, Public Domain,
http://rsd.gsfc.nasa.gov/rsd/movies/
preview.html
Chemical Properties of Seawater
Tend to form
cations (+)
Tend to form
anions (–)
NASA image, Public Domain, Science Education Resource Center,
http://serc.carleton.edu/images/usingdata/nasaimages/periodic-table.gif
9
Water: Universal solvent (almost)
Rule of solubility: like dissolves like
• Water is polar, so it
tends to dissolve polar
molecules and ionic salts
• Non-polar stuff like oil
not dissolved well
Oil-like (hydrophobic) parts
of molecules in our cell
membranes keep us from
turning into puddles of bone
soup.
Water dissolving salt, Liu and Michaelides, London
Centre for Nanotechnology, UCL,
http://www.ucl.ac.uk/news/ucl-views/0803/salt500
Water: great at dissolving stuff
•  H-bonding in H2O like ions & polar molecules
Water combining
with ions from
sodium chloride
Based on illustrations by Steve Berg, Winona State U. Free license
for educational use, http://course1.winona.edu/sberg/Illustr.htm
10
Salinity
Dissolved Salts: Mainly Na+
and Cl–
Constituents of table salt
No salt crystals in seawater
Ions separated in seawater,
recombine on evaporation
Average ocean salinity:
3.5% by mass
Seawater: 96.5% water, 3.5%
dissolved substances
4 x 1019kg dissolved salt
Enough to cover the planet with a
80 m thick layer
Saltwater evaporation ponds, San Francisco Bay, CA.
dro!d, Creative Commons A S-A 2.0, http://flickr.com/
photos/23688516@N00/364573572
Sources of Dissolved Salts
1) Weathering and alteration of
the crust
Seawater chemistry doesn’t quite
match river water
•  Na, K, Mg, Ca can be derived
from rock weathering
•  BUT not everything can be due to
crustal weathering alone
2) Mantle degassing
(volcanoes)
H2O, CO2, HCl, N2, H2S
released in volcanic gases
Top: Rio Tinto, Spain, Carol Stroker(?), NASA,
Public Domain, http://upload.wikimedia.org/
wikipedia/commons/b/b0/
Rio_tinto_river_CarolStoker_NASA_Ames_Res
earch_Center.jpg
Bottom: Halemaumau, Hawaii, Mila Zinkova,
Wikimedia Commons, Creative Commons A SA 3.0, http://upload.wikimedia.org/wikipedia/
commons/9/92/
Sulfur_dioxide_emissions_from_the_Halemaum
au_vent_04-14-08_1.jpg
11
Major Constituents
Most abundant dissolved elements & molecules:
Cl–, Chlorine
Na+, Sodium
SO42–, Sulfate
Mg2+, Magnesium
Ca2+, Calcium
K+, Potassium
Major dissolved species occur in constant
relative ratios in seawater
e.g., Cl/Mg mass ratio is usually 15 in seawater
Implication: the oceans are mixed & stirred
Figure by Hannes
Grobe, Alfred Wegener
Institute, Creative
Commons A S-A 2.5,
http://
commons.wikimedia.org
/wiki/File:Sea_salte_hg.svg
Chemical Residence Times
•  Residence Time: the average length of time an element spends in the ocean
Res. Time =
€
Amount of element in ocean
Element's rate of removal (or addition)
from the ocean
•  Residence time of chlorine…
•  Amount in ocean:
.02 kg/kg (concentration) * 1.4x1021kg (ocean mass) = ?? Kg
•  Rate of addition (from rivers):
~2.2x1011kg/yr
•  Residence time = amount/rate = ??
•  Assumes long-term steady-state
12
Chemical Residence Times
Residence Time: the average length of time an element spends in the ocean
Res. Time =
€
Amount of element in ocean
Element's rate of removal (or addition)
from the ocean
Constituent
Res. Time (yrs)
Chlorine (Cl–)
108
Sodium (Na+)
6.8 x 107
Silicon (Si)
2 x 104
Water (H2O)
4.1 x 103
Iron (Fe)
2 x 102
Chemical Residence Times
Elements with shorter times aren’t well
mixed, vary place-to-place
Fe, Si, CFC-11 input are examples
CFC-11
(CCl3F)
Non-Conservative
Shorter bio/geo/seasonal residence times
• Poorly soluble: Al, Ti, Fe
•  Biological nutrients/products:
Oxygen (respiration),
Fe and P (nutrients),
carbon dioxide (photosynthesis),
Si (shells)
•  Chemicals created by
recent human activity
CFC-11 vs. time, Plumbago, Wikimedia Commons, CC A S-A 3.0, http://
upload.wikimedia.org/wikipedia/commons/2/25/AYool_CFC-11_history.png.
CFC-11 vertical inventory, Plumbago, Wikimedia Commons, CC A S-A 3.0,
http://upload.wikimedia.org/wikipedia/commons/2/20/
GLODAP_invt_CFC11_AYool.png
CFC-11 vibration, E. Schauble, UCLA, http://www2.ess.ucla.edu/~schauble/
MoleculeHTML/CCl3F_html/CCl3F_page.html
13
Trace Elements
•  Some are conservative, often these are chemically similar to
abundant conservative elements (Li+ is like Na+, Br– like Cl–)
•  Many trace elements behave like nutrients
–  Some are necessary for life (i.e., Fe)
•  Some are toxic in high
concentrations
Hg is fat soluble, accumulates
up the food chain
From <1x10–9 g/g (seawater)
to 1x10–6 g/g (shark)
–  Top predators are most
likely to have high Hg:
•  Shark
•  Swordfish
•  King Mackerel
•  Tilefish
~ White (Albacore) Tuna
(list from EPA, 2004)
NASA image, Science Education Resource Center, Public Domain
Biological Nutrients
•  N, P, Fe, Si
•  More needed for organic processes or
skeletal growth than is easily available
•  Consumed in photic zone (lots of
biological growth)
–  Si used by diatoms for skeletal material
•  Enriched in deep waters due to
breakdown of organic matter
•  Upwelling flows transport nutrients
back up to shallower waters
Image from N. Carolina Dept. of Agriculture,
appears to be Public Domain,
http://www.ncagr.gov/cyber/kidswrld/plant/label.htm
14
Questions
Seasalt evaporation and harvesting, Tavira, Portugal, Nemracc, Wikimedia Commons, Creative Commons A 3.0
Unported, http://commons.wikimedia.org/wiki/File:Salt_evaporation_pond_near_Tavira_Portugal.JPG
What controls the density of Seawater?
In the ocean water density changes due to:
•  Temperature (Largest variability)
•  Salinity
(Modest variation
Max density
in ocean)
(1.0) at 4ºC
1.02
1.00
Density
(gm/cm3)
liqu
0.98
id
0.96
0.94
Ice much
less dense
(0.92) at 0ºC
ice
0.92
0.90
-20
0
20
40
60
80
100
Temperature (ºC)
E. Schauble,
UCLA
15
Effects of Temperature & Salinity
Water density at sea surface pressure, in grams/cm3
Least
dense
E. Schauble,
UCLA, based on
Fofonoff and
Millard (1983)
Algorithms for
computation of
fundamental
properties of
seawater. Unesco
Tech. Pap. in
Marine Sci. 44
Temp.
(ºC)
Antarctic
Intermediate
Water
Antarctic
Bottom Water
North Atlantic
Deep Water
Densest
% Salinity
(grams salt/100 grams seawater)
Physical Structure of the Oceans
•  Three Density Zones
–  1) Mixed Layer, 2) Pycnocline, 3) Deep Water
C
C’
American Meteorological Society, http://oceanmotion.org/images/
ocean-vertical-structure_clip_image002.jpg
16
The ocean is layered by density
Density (g/cm3)
1.0258
1.0266
1.0274
De
Sa
Temperature (ºC
lin
ity
(%
)
3)
cm
(g/
Depth (m)
)
ity
ns
2ºC
1.0282
6ºC
10ºC
3.44% 3.46% 3.48% 3.5%
T
S
Adapted from plot of S. Atlantic (45ºS, 50ºW) CTD data at U. Southampton
School of Ocean and Earth Science,
http://www.soes.soton.ac.uk/teaching/courses/oa631/ctd_plot.jpg
Ocean Water: Layered by density.
#1) The Mixed Layer
Top ~100 m
1.0258
1.0266
1.0274
De
Temperature (ºC
lin
ity
(%
)
3)
cm
(g/
Depth (m)
)
ity
2ºC
1.0282
Sa
ns
Variable thickness
0 m - 1000 m
2% of ocean volume
At surface, so is
strongly affected by
wind, gas exchange
with air
Sunlit
6ºC
10ºC
3.44% 3.46% 3.48% 3.5%
Adapted from plot of S. Atlantic (45ºS, 50ºW) CTD data at U.
Southampton School of Ocean and Earth Science,
http://www.soes.soton.ac.uk/teaching/courses/oa631/ctd_plot.jpg
17
Layer #2) The Pycnocline
1.0274
1.0282
Sa
ity
ns
lin
ity
(%
)
3)
cm
(g/
Depth (m)
1.0266
De
• 
1.0258
)
• 
• 
Density gradient between
Mixed Layer and Deep Water
18% ocean volume
Mostly due to temperature
change (deeper water is
colder)
At poles, surface water is
also cold, so pycnocline
caused mostly by change in
salinity
(I.e. halocline).
Temperature (ºC
• 
2ºC
6ºC
10ºC
3.44% 3.46% 3.48% 3.5%
Adapted from plot of S. Atlantic (45ºS, 50ºW) CTD data at U.
Southampton School of Ocean and Earth Science,
http://www.soes.soton.ac.uk/teaching/courses/oa631/ctd_plot.jpg
Layer #3) The Deep Layer
1.0258
1.0266
1.0274
De
Temperature (ºC
lin
ity
(%
)
3)
cm
(g/
Depth (m)
)
ity
2ºC
1.0282
Sa
ns
•  Water originates at
high latitude (cold)
•  Cold ~4o C waters
•  80% of ocean’s
volume
•  Completely dark
(aphotic) and
relatively unaffected
by surface
conditions
6ºC
10ºC
3.44% 3.46% 3.48% 3.5%
Adapted from plot of S. Atlantic (45ºS, 50ºW) CTD data at U.
Southampton School of Ocean and Earth Science,
http://www.soes.soton.ac.uk/teaching/courses/oa631/ctd_plot.jpg
18
•  Region where
temperature changes
with depth.
•  Typically ~100 - 1000 m
•  Strong near equator
(hot surface water)
•  Weak at poles (surface
water almost as cold as
deep water)
0
Polar (60ºS)
Thermocline
-100
)
ºN
34 ornia
)
alif
5ºN
s (1
pic
o
r
T
(C
-200
-300
-400
Depth
(m)
-500
-600
-700
-800
-900
-1000
Plot E. Schauble, UCLA
from NOAA CTD data.
0
5
10
15
20
Temperature (ºC)
Halocline
•  Changing salinity instead of temperature
–  Sharp gradient in salinity with depth
–  Strongest near river mouths, regions with high
rainfall. Why?
19
Pycnocline
1.0258
1.0266
1.0274
De
lin
ity
(%
)
3)
cm
(g/
Temperature (ºC
)
ity
Depth (m)
1.0282
Sa
ns
•  Depth interval
with strong
vertical density
gradient
•  Caused by
thermocline &
halocline
2ºC
6ºC
10ºC
3.44% 3.46% 3.48% 3.5%
Adapted from plot of S. Atlantic (45ºS, 50ºW) CTD data at U.
Southampton School of Ocean and Earth Science,
http://www.soes.soton.ac.uk/teaching/courses/oa631/ctd_plot.jpg
Questions
Temperature (ºC)
Pressure (104 kg/m/sec2) -roughly equivalent to meters depth
0
10
20
Salinity (g/103g)
30
34
34.5
35
Dissolved O2 (10–6moles/103g)
0
35.5
0
0
0
200
200
200
400
400
400
600
600
600
800
800
800
1000
1000
1200
1200
50
100
150
200
250
1000
1200
CTD data from ALOHA station, Hawaii, July 7, 1997
20
Dissolved Gases in the Ocean
•  Atmospheric gases
dissolved in seawater
–  Mainly N2, O2
–  CO2
•  Relative Solubilities:
–  Gases are most soluble in
COLD water
•  Polar waters: cold, rough
waters = gas rich
•  Less soluble in salty
water (“salting out”)
Photo by JD (Kinchan1), Creative
Commons Attribution-NonCommercialNoDerivs 2.0 Generic
http://www.flickr.com/photos/jdbaskin/
5334126513
•  Not quite the same process
as
Mentos+Diet Coke
Photo by Michael Murphy, Wikimedia Commons,
GFDL/Creative Commons-BY-SA 3.0, http://
commons.wikimedia.org/wiki/
File:Diet_Coke_Mentos.jpg
Dissolved Gases in the Ocean
Gas
Atmosphere Dissolved in
(Volume %) Ocean
(Volume %)
Nitrogen (N2)
78.08%
48%
Oxygen (O2)
20.95%
36%
Carbon dioxide (CO2) 0.039%
15%
21
Oxygen (O2)
•  Produced in the photic zone (top 200 m)
where photosynthesis occurs
Also dissolves from
atmosphere
Consumed below
photic zone by
Animal respiration
Bacterial oxidation
of organic
detrital matter
Mainly at sea floor
•  Oxygen minimum
in region below
photic zone
(200 - 1000 m)
–  Also depleted
bottom water zone
Plot from Station ALOHA, N. of Hawaii, from Dore et
al. (2009) PNAS doi: 10.1073/pnas.0906044106
Carbon Dioxide
•  Like N2 and O2, dissolves from the atmosphere
at the ocean surface
•  Also produced by respiration (digestion) of
organic matter
•  Consumed by photosynthesis
•  CO2 combines chemically with H2O
–  VERY soluble in seawater---1000x solubility of
nitrogen or oxygen
−
CO 2 + H 2O ⇔ H 2CO 3 ⇔ H + + HCO 3 ⇔ 2H + + CO 3
Carbonic Acid
Bicarbonate
ion
2–
Carbonate
ion
€
22
Carbon Dioxide
•  > 90% stored in bicarbonate ions, HCO3–  At 10o C, Salinity = 3.43% and pH = 8.0:
CO2
1%
(HCO3)–
94%
(CO3)2–
5%
•  Consumed in photic zone (photosynthesis)
•  Produced by respiration, decomposition of organic matter
Photosynthesis
•  Plants and phytoplankton make simple
organic compounds (sugars) from H2O,
CO2
CO2 and light energy
Light
–  Energy stored in compounds
–  O2 formed as byproduct
–  Occurs in the photic zone
O2
Sugar
PHOTOSYNTHESIS
6H 2O + 6CO 2 + sunlight ⇔ C 6H12O 6 + 6O 2
RESPIRATION
Photo by Wikiwatcher1, Wikimedia Commons, Creative Commons A S-A 3.0, http://commons.wikimedia.org/wiki/
File:Seaweed_Rocks2_wiki.jpg
€
23
Respiration
•  Plants and animals oxidize sugars to
release energy
–  Water and carbon dioxide are by products
–  Occurs throughout the water column
PHOTOSYNTHESIS
6H 2O + 6CO 2 + sunlight ⇔ C 6H12O 6 + 6O 2
RESPIRATION
O2 and CO2 vs. Depth
€
Photosynthesis
Respiration
ORGANIC LOW T, HIGH P:
HIGH CO2
DECAY
SOLUBILITY
Plot from Station ALOHA, N. of Hawaii, from Dore et al. (2009) PNAS doi: 10.1073/pnas.0906044106
24