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Oceanography
Dr. R. B. Schultz
Oceanography and Our Oceans
*71% of Earth's surface is covered with water, so it is important we
know something about the water surrounding us.
Oceanography is the science of our oceans that mixes biology, geology,
chemistry, and physics (among other sciences) to unravel the
mysteries of our seas.
In the Northern Hemisphere, 61% is water and 39% is land, thus it is
called the "Land Hemisphere".
In the Southern Hemisphere, 81% is water and 19% is land, thus it is
called the "Water Hemisphere".
The Hemispheres of the Earth
Northern Hemisphere is
approximately 39% land.
The Southern Hemisphere is
approximately 19% land.
Hydrologic Cycle
The 5 Oceans
• Pacific Ocean
– Largest and deepest ocean
– Mariana Trench: 11 km., 36,000 ft.
• (Mt. Everest 29,000 ft.)
• Atlantic Ocean
– About ½ the size of the Pacific
• Indian Ocean
– Southern hemisphere
• Arctic Ocean
– ¼ as deep, much smaller, sea ice
• Southern Ocean
– South of 50 deg. South latitude
“Just the Facts…”
• Mauna Kea on the Big Island of
Hawaii, measures ~10,600 m from the
ocean floor, making it the tallest
mountain on the planet (surpassing even
Mt. Everest).
• If the Earth’s contours were leveled
to a smooth ball, the ocean would
cover it to a depth of 2686 m.
Earth’s Oceans and Seas
Composition and Chemistry of Seawater:
*Seawater is a complex mixture of water and salts (dissolved
minerals) making up about 3.5% of seawater.
Salinity is the proportion of dissolved salts to pure water. It is
usually expressed in terms of pph, parts per hundred, or
percent. But because salts in seawater are small, we usually
express it as ppt, or parts per thousand.
*Salinity varies in oceans based on:
• the amount of freshwater added to the system or
• the amount of evaporation that takes place.
• If much evaporation occurs, the water is more saline because water
is evaporating faster than freshwater is added. Thus, more salts
are left over.
*Conversely, the more freshwater added to the system, the less the
salinity is.
Where do the salts come from?
1. Weathering of rocks/minerals and salts introduced into streams
that feed into the oceans. The total quantity of this is on the order
of 2.5 billion tons annually.
2. Minerals and salts are also derived from volcanic eruptions, known
as outgassing from Earth's interior. We know this is true because
certain elements (Cl, Br, S, B) are more abundant in oceans than in
Earth's crust. Many speculate that outgassing is responsible for
our oceans' formation.
3. Hard parts of marine organisms. (i.e., shell material)
*Surprisingly, the salinity of the oceans is relatively constant.
1.
Although many billion tons of salts are added annually, salts are
used in:
2.
1.
2.
3.
making hard parts for ocean creatures (shells),
absorbed by marine plants as nutrients, and
much salts are precipitated out as sediment.
Overall, the oceans naturally tend to chemically mass balance
themselves.
Resources from Oceans and Seawater:
*Some resources that humans currently use from seawater are:
1.
sea salt (halite),
2. magnesium (a light metal used in the making of light bulbs),
3. bromine (gasoline additives/fireproofing materials).
*Humans also desalinate seawater to get fresh water. This process is
time-consuming, expensive and is not currently economically
feasible. Many desalinization plants operate, but few are
productive on a commercial scale.
Our Layered Oceans
Surface mixing zone
is warmest; saltiest
near bottom of
zone.
Transitional zone
contains
thermocline and
halocline.
Deep zone is 2 tons
per square inch and
coldest in
temperature.
Ocean Topography:
*Oceanographers studying the oceans and ocean floor have found (3)
major parts:
1. Continental margin
2. Ocean basin floor
3. Mid-oceanic ridges
1. The continental margin includes:
a. Continental shelf -- very gentle slope (submerged land)
b. Continental slope -- steep slope on edge of continental shelf.
c. Continental rise -- gentle slope where trenches do not exist
Surprisingly, we know very little about the mapping of our ocean floor.
We probably have accurately mapped only 5% of the ocean floor. It
is time-consuming, expensive, and our current technology only allows
us to map a few miles at a stretch.
Ocean Topography
Seamount
What else is at the
bottom of the ocean?
Answer: Hydrothermal
vents …a.k.a…
Black smokers!
Echo Sounding Used for Mapping Ocean Floor
Ocean Currents
Surface Currents:
*An important "river" of the ocean is the "Gulf Stream". It flows in
response to atmospheric conditions and has a direct relationship
with climatic conditions.
*Strangely, ocean currents are directed to the right (clockwise) in the
northern hemisphere and to the left (counterclockwise) in the
southern hemisphere. This has a direct relationship with the
Coriolis Effect, which is a deflective force resulting from the
Earth's rotation that causes currents to oftentimes move against
the winds.
*Upwelling is the force that vertically moves cooler water from
approximately 1000 feet below the surface to the near surface.
Oceans, Waves, Currents, and Tides
Ocean circulation:
*Involves surface currents and deep-water masses
*Some are short-lived: seasonal and local
*Others are permanent and extend over large portions of the globe
Shallow Ocean Currents
Deep Ocean Currents:
*In general, deep ocean currents are driven by:
1.
2.
gravity and
density differences.
*Two factors are important in creating a dense mass of moving water:
1. Temperature
2. Salinity
*Colder and salty water is denser than warmer, less salty water.
Thus, deep ocean circulation is referred to as thermohaline circulation.
Deep Ocean Currents