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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.
*The Earth has an area of approximately 197 million square miles of
which 140 million square miles is water.
*The Earth is broken up into hemispheres…Northern and Southern.
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
World population is
expected to
approach 7 billion
by 2020.
The amount of water present in oceans by volume is much greater than
that of the land surface. In fact, the volume of all land is only 1/18
that of the oceans.
The average elevation of continents is over 2700 feet above sea level
whereas the average depth of the oceans is nearly 12,500 feet. In
other words, if the Earth were perfectly spherical, the oceans
would cover the land surface to a depth of more than 10,000 feet
(nearly two miles).
The three major oceans:
Pacific is the largest ocean, nearly as vast as the Indian and Atlantic
Ocean combined, and has an average depth of ~13,000 feet.
Atlantic is the shallowest with an average depth of nearly 11,000 feet.
Why is the Atlantic the shallowest?
Indian is smallest ocean and is present largely in the Southern
Hemisphere.
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.
This may seem small, but if all the water were evaporated, a crust of
the remaining salts remaining would be 200 feet thick over the
entire earth surface.
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.
Main salts/elements present in oceans are in ppt:
1. NaCl (halite) 23.48 (about 2.35%)
2. MgCl 2 4.98 (about 0.50%)
3. Na2SO4 3.92
4. CaCl2 1.10
5. KCl 0.66
6. NaHCO3 (Sodium bicarbonate) 0.192
7. KBr 0.096
8. H3BO3 (Hydrogen borate) 0.026
What is Ocean Water Composed of?
*Cl-, Na+, SO4--, Mg++, Ca++, and K++ are principle ions present in
seawater.
*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).
A great deal of these products in the U.S. come from the Great Salt
Lake in Utah, but other countries not having access to the Great
Salt Lake, still use the oceans for their resources.
*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.
*Gold from our oceans? Yes, gold is present is very low concentrations,
but not economic enough to actually "mine" for profit. Many tons of
water and sediment would have to be processed in order to get a
single ounce of gold.
Our Layered Oceans:
*Temperature and salinity vary with depth in our oceans, thus the
oceans tend to take on a layered effect.
Three general layers are present, except in Polar Regions where only
one or two layers are present because of coldness:
1. Shallow surface mixed zone (2%): warmest from solar energy,
mixed by waves, 1500 feet thick and 70-80 degrees, most saline.
2. Transition zone (18%): includes thermocline, which is point of great
drop-off in temperature to ~39 degrees below 5000 feet and
halocline, which is point of salinity drop-off, which roughly
corresponds to the thermocline.
3. Deep zone (80%): just slightly above or below freezing. Not very
saline.
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 delineated
three (3) major units:
1. Continental margin
2. Ocean basin floor
3. Mid-oceanic ridges
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.
As technology develops, mapping will improve. Currently, we use echosounding devices, which are slow and tedious.
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
Deep sea fans exist where sediment is accumulated and falls off of the
continental slope. Mixture of sediment-laden heavy water forms
submarine turbidity currents.
Ocean Topography
Seamount
What else is at the
bottom of the ocean?
Answer: Hydrothermal
vents …a.k.a…
Black smokers!
Dynamics of Our Ocean Depths
Echo Sounding Used for Mapping Ocean Floor
The Deep Sea includes:
a. Deep ocean trenches (deepest part of ocean) some
as deep as 36,000 feet
b. Abyssal plains are the flat portions of the deep
ocean, likely to be the flattest portions of the earth.
c. Isolated volcanic peaks (mantle hot spots) are
referred to as "seamounts". Likewise volcanic cones
near mid-oceanic ridges are called seamounts as well.
Harry Hess called these “guyots”.
d. Mid-oceanic ridges occur where divergent plate
boundaries occur (Mid-Atlantic) and the narrow
region at the ridge crest is called the rift zone.
e. Coral reefs and atolls develop usually in relatively
shallow water where light is present and organisms
can thrive on nutrients and food sources in a warm
water setting. Atolls develop in response to a sinking
of the oceanic crust.
2.
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
*Generally, circulation patterns of the waters are related to climatic
conditions and the heating of the Earth by the sun.
*Deep ocean currents are not horizontal like surface patterns but
have a vertical component. These are caused primarily by a
response to density differences in the ocean and contrasts in
temperature and salinity.
*Remember, in general, the following are true:
1. Surface salinities increase near the 20-degree latitudes in the
Atlantic and Pacific Oceans.
2. Salinities decrease with depth at the halocline near the equator and
the Tropics, but increase at high latitudes where there is no
halocline.
3. Temperature and density are mostly inversely proportional to each
other.
4. Temperatures in the oceans drop at the thermocline except for at
high latitudes where they remain constant.
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.
Where winds blow towards the equator and parallel to the coastline
(ex: west coast of California), surface water movement is deflected
away from the coast and deeper water is thrust upward to the
surface.
This creates a vertical component that causes temperatures drops in
surface waters to nearly 10-15 degrees.
Thus, extensive nutrients like nitrates and phosphates are "upwelled"
to the surface and plankton and other fish populations flourish.
Cold Water Upwelling
Hurricane causing
algal bloom in
upper portion of
ocean.
Shallow Ocean Currents
El Niño and
La Niña
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.
Here's how thermohaline circulation works:
Cooler water at the surface (due to heat loss to the atmosphere)
becomes saltier (due to much evaporation) and becomes denser,
thus it sinks to the bottom.
As it sinks it replaces lighter less dense water, which moves back to
the zone where the denser water formed.
So, cold dense waters flow away from their sources at the poles and
are replaced by warmer waters from the lower latitudes.
It takes many years, possibly centuries for the dense, saline waters to
migrate to the coastlines where upwelling may occur.
Deep Ocean Currents
Oceanic Conveyor Belt
Key Terminology
Oceanography
Water Hemisphere
Hydrosphere
Atlantic Ocean
Salinity
Layered Oceans
Transitional zone
Continental margin
Continental slope
Abyssal plains
Deep sea fan
Photic zone
Echo sounding
Coral reefs
Gulf Stream
Coriolis Effect
Thermohaline circulation patterns
Land Hemisphere
Hydrologic cycle
Pacific Ocean
Indian Ocean
Desalinization
Surface mixing zone
Deep zone
Continental shelf
Continental rise
Seamounts (Guyots)
Turbidity current
Aphotic zone
Deep ocean trenches
Atolls
El Niño/La Niña
Upwelling