Chapter 4
Water, Waves, and Tides
Karleskint
Turner
Small
Key Concepts
• The polar nature of water accounts for
many of its physical properties.
• Seawater contains a number of salts, the
most abundant being sodium chloride.
• The density of seawater is mainly
determined by temperature and salinity.
• The gravitational pull of the moon and the
sun on the oceans produces tides.
Nature
of Water
polar molecule!
Marine organisms are ~ 3/4 water by mass,
compared to ~2/3 in terrestrial organisms.
Nature of Water
• Excellent solvent of polar
substances
dissolves salts, but not nonpolar substances, e.g. oil
• High Specific Heat (thermal
capacity)
ocean heats and cools
slowly
Dr. Adam Jones
Nature of Water
•
•
•
•
Ocean’s pH is ~ pH 8 (slightly alkaline)
Pure freshwater is pH 7 (neutral)
Unpolluted rain is ~ 5.6
Acid rain < (below) pH 5.6
Nature of Water
Water and light
• much light reflected into the atmosphere
• different wavelengths (colors) of light
penetrate to different depths
Ultramax
Enterprises
Salt Water
• Salinity
– salinity of surface water varies as a result of
evaporation, precipitation, freezing, thawing,
and freshwater runoff from land
Salt Water
• Salinity
– seawater = 3.5% salt (NaCl a.o.),
96.5% water
– expressed as g per kg water or parts
per thousand (ppt), i.e. 35 ppt
William Waterway
Ocean Heating and Cooling
Energy input
– Sun’s radiant energy heats earth’s surface
– Earth`s spherical shape + presence of atmosphere
energy reaching earth’s surface decreases with latitude
Ocean Heating and Cooling
Energy output
– excess energy absorbed by the earth is transferred
to the atmosphere by evaporation and radiation
– accumulation of greenhouse gases can prevent
heat energy from radiating back to space
Ocean Heating and Cooling
• Sea Surface Temperature (SST)
– varies daily and seasonally
– affected by
• angle of solar radiation
• energy absorption at the surface
• evaporation
• currents
• warming/cooling of atmosphere
• heat loss
Ocean Layers
Density—the mass of a substance in a given
volume, usually measured in g/cm3
density of pure water = 1 g/cm3
density of salt water = 1.0270 g/cm3
• Saltier water is denser (heavier) than fresher water
• Colder water is denser (heavier) than warmer water
• Densest water is found near ocean bottom
Ocean Layers
• ``Two-Layer Ocean``
• Layers separated by
– Thermocline
– Halocline
– Pycnocline
Ocean Layers and Ocean Mixing
• Characteristics of
ocean layers
– seasonal
thermoclines
Currents
Due to solar input, prevailing winds, and the Coriolis Effect from
the Earth`s rotation, major surface currents flow clockwise in the
Northern hemisphere and counter-clockwise in the Southern
hemisphere
Fangz
Currents
S&T
Fall
Air temperature
cools
Surface water
cools, displaces
less dense
water
Summer
Winter
Water column unstable
Warm surface
water
Colder,
denser
water
Thermocline
Water column stable
Wind
Isopycnal
Spring
Air temperature
warms
Surface water
warms
Colder,
denser
water
Storms drive surface
water deeper
Thermocline
Water column stabilizes
Figure 4-20 p84
Ocean Layers and Ocean Mixing
• Upwelling and downwelling
– equatorial upwelling
– coastal upwelling
– coastal downwelling
ANIMATION: Coastal upwelling
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Waves
– wave: a flow of energy or motion, not of water…
– breaking wave:
``feels bottom`` and steepens at water depth = ½ wavelength
breaks when reaching water depth of ~1.3 wave height
Tides
• Tides: periodic changes in water level
occurring along coastlines
Tides
• Spring and neap tides
Tides
• Tidal range
– diurnal tide
– semidiurnal tide
– mixed semidiurnal tide