Primary Fields of Oceanography
Announcements:
First problem set due tonight at midnight
Weathering
Geology
Chemistry
Precipitation/
Dissolution
First exam in one week – Tuesday Oct 11th
Study questions posted on web page under “lecture notes”
Organic C
production &
degradation
Review for exam on Thursday – Come with questions
Nutrients
Contaminants
This week: Marine chemistry
Physics
Biology
Introduction to Chemical Oceanography
Part 1: Wacky water
What makes water climb celery stalks?
Why is the ocean blue? Why is it salty? What determines the
concentrations of salts and other chemicals in seawater? What is
the chemical structure (chemical geometry) of the ocean?
1
Properties of water
Polarity:
Results in
Hydrogen
bonding
Surface tension
cohesion > adhesion
(E.g, Hg and glass)
adhesion > cohesion
Water’s dipole moment
Properties of water compared to similar compounds
Water
(H2O)
H-sulfide
(H2S)
Ammonia
(NH3)
Methanol
(CH3OH)
Ethanol
(C2H5OH)
Ether
(C2H5OC2H5)
Molecular
Weight
18
Boiling Point °C
@ 760mm.Hg@20°C
100
Surface Tension
Dynes cm-1
73
34
-60
(a)
17
-33
(a)
32
65
22
46
78
22
74
34
17
2
Hydrogen bonding results in an
open lattice structure of ice, and
a maximum density at 3.98 degrees C.
Cold water is denser than warm water…
“Flickering cluster” model explains the
density max at ~ 4 degrees
… so why does ice float?
Liquid water has a large heat capacity (1 cal/g/oC)
Hydrogen bonding and latent heat
At the beach, the water is cool …
… why does the sand burn your feet?
3
Effects of latent heat on global climate
If water has such a high heat capacity,
… why do I feel so cold when I get wet?
Heat is lost at the equator via
evaporation (latent heat). But, net heat
accumulation occurs at the equator and
net loss occurs at the poles. Transport
of water vapor from equator to poles
and transport of water currents
moderates latitudinal variation in
climate.
Evaporation
Depth (km)
Seawater: Effects of temperature and salinity on density
Ocean water can be considered
a two-layer system; a surface
mixed layer over a deep layer.
Depth (km)
T-S diagram indicates major
properties of water masses.
Mixing of water masses along
isopycnals.
Depth (km)
Why is it easier to float in seawater than in freshwater?
4
Why does the fish that got away always look so big?
Scuba diver’s
mask
Fish
Fish appears closer and
bigger than it really is.
Refractive index of water relative to air is ~ 1.33
sin(iair) / sin(iwater) ~ 1.33 = ratio of light velocity (air:water)
Effects of density structure on underwater sound
1. Sound velocity increases with temperature, salinity and pressure
Csound speed = √(axial modulus/density)
2. Low velocity zone at 1000 m (sofar layer)
How do whales keep in touch across thousands of miles of ocean?
3. Reflection and refraction of sound waves due to velocity
changes creates shadow zones, important for submarine
warfare. Subs can “hide below the pycnocline”
Why was it difficult for the Allied navies in WWII keep the German
submarines out of the Mediterranean Sea?
5
Thermally –
stratified
water column
Why is the ocean blue?
Salinity –
stratified
water column
Color in the ocean
Light attenuation in the ocean (Beer’s Law)
IZ=I0e-KDz
Depth
The parameter KD is the light attenuation coefficient.
1/KD is one light attenuation depth.
I0 is the light intensity at the ocean surface
KD can be
IZ is the light intensity at depth z
calculated from
Light intensity (I)
the Secchi depth:
DSecchi=1.5/KD
DSecchi
Why is the ocean blue?
6
Summary
Why are coastal waters green?
Hydrogen bonding makes water a unique molecule with high heat
capacity, high heat of fusion (freezing) and vaporization, anomalous
density maximum at 3.98 deg C, High dipole moment of hydration
Latent heat of vaporization and fusion along with global transport
of water vapor moderates the earth’s climate
Temperature and salinity determine water density
Ocean water is a two-layer system: mixed layer / deep layer
Sound is reflected and refracted in these layers
The ocean is blue due to differences in penetration depths of
light of different wavelengths
7