Introduction to Oceanography
Lecture 9: Seawater 2
CO2 bubbles degassing from an underwater volcano.
Photo from Pacific Ring of Fire 2004 Expedition. NOAA Office of Ocean Exploration.
Public Domain. http://www.flickr.com/photos/51647007@N08/5015582382
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
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
2
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
3
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
4
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
5
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
6
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
7
•  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?
8
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
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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%
10
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
€
11
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
€
12
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
13
Acid-Base Balance
•  H2O occasionally splits into H+ and OH–  1 molecule in 5.5x108 dissociates at 25o C
H 2O ⇔ H + + OH _
€
J. W. Pang(?), UCLA Chemistry,
www.chem.ucla.edu/~gchemlab/ph-paper.jpg
pH Scale
•  pH scale = Logarithmic scale
pH = − log10 (H + )
•  Neutral (pure) water:
–  1/(5.5x108) water molecules is disassociated
–  there are about 55 moles of water per liter
€
Concentration of H+=
55/(5.5x108) = 10–7 moles/liter
–  Neutral water pH = 7
•  lower pH = acid, higher pH = base
14
pH Scale
Stephen Lower,
Wikimedia Commons,
CC A S-A 3.0, http://
en.wikipedia.org/wiki/
File:PH_scale.png
The Carbonate Buffer System
•  Seawater pH = ~8.0 (slightly basic)
•  Maintained by carbonate buffer system:
−
CO 2 + H 2O ⇔ H 2CO 3 ⇔ H + + HCO 3 ⇔ 2H + + CO 3
Carbonic Acid
€
Bicarbonate
ion
2–
Carbonate
ion
•  Increase CO2 in water, acidity increases
What happens to pH?
•  Add acid and CO2 is produced
15
The CO2 system and carbonate
•  Deep waters form at the poles: High
CO2 and therefore acidic
•  Acidity interacts to dissolve calcium
carbonate (CaCO3) deposits on the
deep sea floor
–  Acidity and temperature control carbonate
compensation depth (CCD)
Questions
Image from UNESCO, Presumed Public Domain, http://ioc3.unesco.org/oanet/FAQacidity.html
16
Wind
Wind sea, N. Pacific, Winter 1989, M/V
NOBLE STAR/NOAA, Public Domain,
http://commons.wikimedia.org/
wiki/File:Wea00816.jpg
•  Lecture 8: Atmospheric Circulation
Atmosphere-Ocean Coupling
•  Why study atmospheric circulation?
–  Atmosphere & ocean processes are
intertwined
–  Atmosphere-ocean interaction moderates
surface temperatures, weather & climate
•  Weather: local atmospheric conditions
•  Climate: regional long-term weather
–  Atmosphere drives most ocean surface
waves and currents (our next topic)
17
Composition of the Atmosphere
•  Dry Air: 78% Nitrogen, 21% Oxygen
•  BUT it is never completely dry
–  Typically contains about 1% water vapor
Chemical residence time of water vapor in the air is
about 10 days
(liquid water residence time in
ocean: 3x103 years!)
–  Liquid evaporates into the air,
then is removed as dew, rain,
or snow
–  Warm air holds much more
water vapor than cold air
Figure by Greg Benson, Wikimedia Commons
Creative Commons A S-A 3.0,
http://en.wikipedia.org/wiki/File:Dewpoint.jpg
Density of Air
•  Typical air density ~ 1 mg/cm3
12000
–  About 1/1000th the
density of water
–  Air is much easier to compress
than water
10000
Everest 8848m
8000
Elevation (m)
•  Temperature and pressure
affect the density of air
•  Temperature: Hot air is less
dense than cold air
•  Pressure: Air expands with
elevation above sea level
Passenger
jet 10-13km
6000
Mt. Whitney 4421m
4000
2000
Empire State Bldg. 450m
0
0
40000
80000
120000
Pressure (N/m2)
Figure by E. Schauble,
using NOAA Standard Atmosphere data.
18
Density & temperature of Air
•  Rising air expands
& cools
–  Vapor condenses
into clouds,
precipitation
•  Sinking air is
compressed and
warms
–  Clear air
Figure adapted from Nat’l Weather Service/
NOAA, Public Domain,
http://oceanservice.noaa.gov/education/yos/
resource/JetStream/synoptic/clouds.htm
2000 meters
15ºC
15ºC
1000 meters
24ºC
15ºC
34ºC
15ºC
(1.4% H2O)
Expanding Air Cools and Condenses
•  Like opening a pressurized bottle of soda
•  Air expands and cools
•  Water vapor condenses -- cloud formation
MMovies by J. Aurnou, E. Schauble, UCLA
mov1
19
s
on
sti
2000 meters
15ºC
15ºC
Qu
e
1000 meters
24ºC
15ºC
34ºC
Figure adapted from Nat’l Weather Service/
NOAA, Public Domain,
http://oceanservice.noaa.gov/education/yos/
resource/JetStream/synoptic/clouds.htm
15ºC
(1.4% H2O)
Solar Heating of the Earth
•  Solar energy absorbed unevenly over Earth’s surface
•  Energy absorbed / unit surface area varies with:
–  Angle of the sun
–  Reflectivity of the surface (i.e., ice v. ocean)
–  Transparency of the atmosphere (i.e., clouds)
23.5º
Przemyslaw "Blueshade" Idzkiewicz,
Creative Commons A S-A 2.0, http://
commons.wikimedia.org/wiki/
File:Earth-lighting-wintersolstice_EN.png
20
Solar Heating of the Earth
Sunlight heats the ground
more intensely in the
tropics than near poles
• 
file:///Users/schauble/ESS15_Oceanography/
Images_and_movies/Insolation2.swf Heilemann CCU/
NSF Flash
Sunlight
intensity (top of
atmosphere)
Sunlight
intensity
(ground)
Figure by William M. Connolley using
HadCM3 data, Wikimedia Commons, Creative
Commons A S-A 3.0,
http://commons.wikimedia.org/wiki/
File:Insolation.png
Solar Heating & the Seasons
June 20-21: N.
Pole tilted
towards Sun
Sept. 22-23: Sun
shines on both poles
equally
Not to scale!
Oct. 26: We
are here
March 20-21: Sun
shines on both poles
equally
Dec 21-22: N.
Pole tilted away
from Sun
Background image: Tauʻolunga, Creative Commons A S-A 2.5, http://en.wikipedia.org/wiki/File:North_season.jpg
•  Seasons are caused by Earth’s 23.5o tilt
•  Northern summer: north hemisphere points at sun
21