Oceanography by jizhen1947

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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:
     1.   making hard parts for ocean creatures (shells),
     2.   absorbed by marine plants as nutrients, and
     3.   much salts are precipitated out as sediment.
2.   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 echo-
   sounding 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
2. 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.
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.   gravity and
    2.   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                        Land Hemisphere
Water Hemisphere                    Hydrologic cycle
Hydrosphere                         Pacific Ocean
Atlantic Ocean                      Indian Ocean
Salinity                            Desalinization
Layered Oceans                      Surface mixing zone
Transitional zone                   Deep zone
Continental margin                  Continental shelf
Continental slope                   Continental rise
Abyssal plains                      Seamounts (Guyots)
Deep sea fan                        Turbidity current
Photic zone                         Aphotic zone
Echo sounding                       Deep ocean trenches
Coral reefs                         Atolls
Gulf Stream                         El Niño/La Niña
Coriolis Effect                     Upwelling
Thermohaline circulation patterns

								
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