1-10: Ocean Structure and Circulation

Unit Objectives

• To understand the forces that drive the circulation patterns of the global oceans and the relation of global atmospheric circulation to global ocean circulation.
• To understand the time and space scales of flow in the global ocean, including inter-basin transport and its role in transporting heat globally.

Preparation for Online and Class Discussions

1. Read the summary information.

   Class images

2. Print for offline review.

3. Take the summary information quiz. Quizzes are available from your portfolio.

4. Additional Related Reading. Although you are not ultimately responsible for content listed in this section, we encourage you to fully explore the links in order to provide a better scope on the upcoming class discussion.

   	Current Ocean Temperatures
   	The PIRATA Project

Online and Class Discussion

• Social Comments
• Knowledge-building Comments
• Ethical Comments

• Unit Problem to Ponder
• Unit exam questions from previous years
• Unit discussions from previous years

Unit Wrap-up Materials

• Group Discussion Summary:

  Summary prepared by: James Peterson, Todd Pederson, Ross Meade and Justin Manternach

  1-10 Dialogue

  Unit 1-10, Ocean Structure and Circulation, sparked several questions which were compiled in the form of dialogue conversation. A Mr. Steve Van Horn, who asked what would cause water to rise, posted the first response? His question was followed up well with a response that explained that as water sinks it moves away from the surface, it allows room for other water molecules to take its place. It is almost a constant turning action.

  Another interesting response was a brainstorming dialogue provided by Kyle Tackett. His brainstorming regarded farming the oceans in the future. Mr. Tackett did some investigating and found a website explaining the topic. If anyone is interested to further his or her knowledge of ocean farming, check out the dialogue in this section. There is a website address listed.

  The last response was an interesting caper. Apparently, a company told an upset consumer that the reason why "chunk-tuna" wasn't so chunky was because of global warming. This brainstorming dialogue was followed-up four times, all four contained valid information. But specifically the answer to why ocean tuna is mushy is because of a release of OH Mercury is responsible for the deterioration of tuna. If you are interested in this close to home global changing events, check out this section for another website address to do some further analysis.

  Summary Information for Ocean Structure and Circulation:

  Oceans play a critical role in the movement of heat over the planet. The amount of thermal energy (heat) transported is proportional to its density. Since water is about 1,000 times more dense than air, a specified volume of water can transport about 1,000 times as much heat as an equivalent volume of air. Heat flux, or the rate at which heat is transported, is measured in Joules of energy per unit area per unit time. The rate at which heat is transported is also proportional to the speed of the movement of fluid. Wind speed is approximately 1,000 times faster than the ocean current. The values of density and speed for both air and water cancel each other out and both are equally important to transfer heat over the planet.

  The ocean currents can be seen in a close up satellite picture of the Gulf Stream. In the Northern Hemisphere, there is a clockwise circulation and in the Southern Hemisphere, there is a counter-clockwise circulation. The west coasts of continents generally have flow toward the Equator and east coasts have flow away from the Equator. This signifies that the west coasts will have slightly cooler water offshore compared to the east coasts at the same latitude.

  It is stated in the reading that the momentum of an object does not change in the absence of forces due to the law of conservation of momentum. When a parcel of air or water is moving toward the equator, it will speed up (which will violate the consevation of momentum) unless it moves in the direction opposite of the rotation of the earth and curves to the right in the NH. This causes the rotation in the NH to be clockwise. In the SH, the parcel will curve to the left causing a counter-clockwise rotation.

  The vertical motions in the oceans are influenced by the differences in water density. This is caused by two main factors: Salinity and Temperature. Increase in salt content means an increase density of water and generally cold water is more dense than warm water except at 4 degrees C where the density of water decreases with temperature below this point. This explains why water freezes at the top and the water below stays at around 4 degrees C.

  Salinity is not uniformed. Some areas there are a lot of evaporation due to intense solar radiation but little precipitation. The salinity increases because the salt in the oceans does not evaporate with the ocean waters. Areas where there is a lot of precipitation, the fresh-water precipitation will stay at the top of the ocean because it is less dense due to the very low salt content of the rainwater. In the tropical areas, there is not that much mixing because the warm water rides on top of the colder water. In the polar regions, the cold water is at the top and since it is higher in density than the lower layers, it will want to mix. The mixture of the deep ocean is due to these two main factors.

  The Coriolis force pushes water away from the continent near the coasts, lowering the sea level slightly in the area and draws water from deeper levels of the ocean. This process is called upwelling and it provides rich nutrients to the area and helps for the development of higher biological activity.

• Recommended Reading Materials

  	The great ocean conveyor belt
  	Kerr, R. A., 2000: A North Atlantic climate pacemaker for the centuries. Science 288, 1984-1986.
  	Yoder, James A., 2000: Terra's view of the sea. Science 288, 1979-1980.
  	A Primer on Ocean Currents, Woods Hole Oceanographic Institution.
  	British Antarctic Survey Press Release 1/95 27 February 1995: ONE SMALL ICE SHELF DIES, ONE GIANT ICEBERG BORN
  	Gordon, A. L., 1988: The southern ocean and global climate. Oceanus 31, 39-46.
  	Houghton, J. T., L. G. Meira Filho, B. A. Callander N. Harris, A. Kattenberg, and K. Maskell, 1996: Climate Change 1995. The Science of Climate Change. Cambridge University Press, 210-216, 489-504.
  	Kerr, R., 1997: A New Driver for the Atlantic's Moods and Europe's Weather. Science, 7 February 1997.
  	Open University Course Team, 1989: Ocean Circulation. Pergamon Press, Oxford: 238 pp.
  	Perry, A.H., and J. M. Walker, 1977: The Ocean-Atmosphere System. Longman, Inc., New York: 160 pp.
  	Steele, J.H., 1989: The message from the oceans. Oceanus, 32, 5-9.
  	Tolmazin, David, 1985: Elements of Dynamic Oceanography. Allen and Unwin Publishers, Inc., Winchester, MA: 181 pp.

• References

  	Ocenas and Costal Resources: A Briefing Book
  	Excess Heat in the Ocean
  	1998 Conference of the World Ocean Circulation Experiment
  	NOAA Oceanography Resources on the Internet
  	The Scripps Institution of Oceanography International Research Institute
  	Sea Surface Temperature from 1981 to Present
  	C. Hillaire-Marcel, A. de Vernal, G. Bilodeau, and A. J. Weaver, 2001: Absence of deep-water formation in the Labrador Sea during the last interglacial period. Nature 410, 1073-1077.
  	Derr, R. A., 1998: Warming's unpleasant surprise: Shivering in the greenhouse? Science 281, 156-158.
  	Malakoff, David, 1998: Death by suffocation in the Gulf of Mexico. Science 281, 190-192.
  	J. A. McGowan, D. R. Cayan, and L. M. Dorman, 1998: Climate-ocean variability and ecosystem response in the northeast Pacific. Science 281, 210-217.
  	Falkowski, P. G., R. T. Barber, and V. Smetacek, 1998: Biogeochemical controls and feedbacks on ocean primary production. Science 281, 200-206.
  	Jickells, T. D., 1998: Nutrient biogeochemistry of the coastal zone. Science 281, 217-222.
  	Parilla, G., et al., 1994: Rising temperatures in the North Atlantic ocean over the past 35 years. Nature 369, 48-51.
  	Semtner, Albert J. 1995: Modeling ocean circulation. Science 269, 1379-1385.