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Topic(s):

Atmosphere, Biosphere, Climate, Cryosphere, Energy, Geosphere, Hydrosphere, Oceans

 

Scenario:

In 1770, Benjamin Franklin published his Gulf Stream Chart. He had been very interested in surface currents and particularly in the Gulf Stream. During voyages to Europe, Franklin charted the approximate position of the Gulf Stream. He did this by taking surface temperature readings. As time went on, those inquiring about the ocean learned a great deal about surface ocean currents; very few were looking into what was happening beneath the surface.

One notable exception, however, was Henry Ellis, captain of a slave ship. A full 19 years before Franklin published his Gulf Stream Chart, Ellis rigged a makeshift bucket with flaps and lowered it down a mile to find that the water was very cold. He reported his findings and others repeated his experiment. In 1797, Benjamin Thompson suggested that the cold water at depth came from the polar regions. He wrote that the warm water would sink to the bottom of the ocean and begin to flow toward the equator, producing a current in the opposite direction. He was the first to suggest two currents, one surface and one subsurface completing a circuit by flowing in opposite directions.

In 1987 Wallace Broecker's seminal article, the Great Ocean Conveyor, described what came to be known as the thermohaline circulation system (THC). "Thermo" refers to temperature and "haline" refers to salt, both of which are components of water density. Imagining a conveyor belt, picture warm water from the Gulf Stream heading on the surface to the North Atlantic where it grows dense and sinks, then flows into ocean basins, heading south and upwelling in the Southern Ocean. A complete circuit of the system takes a thousand or more years. (Scientists can tell how old water is -- length of time since it has been on the surface -- by analyzing the dissolved oxygen in a water sample.) Broecker emphasized the interconnectedness of all oceans and the role the oceans play in stabilizing world climate by redistributing heat. He also suggested that changes in either the temperature or salinity could impact the great conveyor belt.

Paleoclimatologists have discovered periods when the great ocean conveyor slowed or stopped, with the implication that this caused abrupt climate change. Now scientists are concerned about the impact of climate change on the system. Global Warming raises the potential of unlocking large amounts of fresh water now frozen in the vast Greenland ice sheet and in Arctic Ocean sea ice. Warming air temperatures could also increase evaporation in low latitudes and transport freshwater vapor toward high latitudes, where it falls as rain or snow into the oceans.

More recently, changes to Russian rivers in the form of dams and changes to discharge volume introduces factors that may impact the great ocean conveyor. Close to 85% of the runoff to the Arctic Ocean comes from Russia. Researchers looking at the data are concerned about the increased discharge from these rivers. They suggest that the increase in fresh water may disrupt the Arctic thermohaline circulation. See also IPCC report about Arctic Ocean River Flow.

 

Task:

Basic: Based on observed and potential climate change, your group has been asked to present your Earth system analysis of the slowing or stoppage of the THC. This tasking comes as changes in flow patterns have been noted in Russian River discharge, ocean temperatures and freshwater melt from Greenland's ice sheets.

Comprehensive: In 2003 the Department of Defense received a report entitled An Abrupt Climate Change Scenario and its Implications for United States National Security by Peter Schwartz and Doug Randall. The authors of this report apparently wanted to "cause a stir" and they painted a worst case scenario. The executive summary includes these two paragraphs:

"There is substantial evidence to indicate that significant global warming will occur during the 21st century. Because changes have been gradual so far, and are projected to be similarly gradual in the future, the effects of global warming have the potential to be manageable for most nations. Recent research, however, suggests that there is a possibility that this gradual global warming could lead to a relatively abrupt slowing of the ocean's thermohaline conveyor, which could lead to harsher winter weather conditions, sharply reduced soil moisture, and more intense winds in certain regions that currently provide a significant fraction of the world's food production. With inadequate preparation, the result could be a significant drop in the human carrying capacity of the Earth's environment.

The research suggests that once temperature rises above some threshold, adverse weather conditions could develop relatively abruptly, with persistent changes in the atmospheric circulation causing drops in some regions of 5-10 degrees Fahrenheit in a single decade. Paleoclimatic evidence suggests that altered climatic patterns could last for as much as a century, as they did when the ocean conveyor collapsed 8,200 years ago, or, at the extreme, could last as long as 1,000 years as they did during the Younger Dryas, which began about 12,700 years ago (p. 1)."

Yet there are others who look at the global cooling event of 8,200 years ago as one that could use more scrutiny. They have asked your group to analyze this event from an ESS perspective, detailing both the likelihood of another occurrence of this magnitude and the impact it could have on the United States.

References

Broecker, W.S. (1987) The Great Ocean Conveyor. Oceanography, Vol 4 No. 2-4991.

Murphy, D. (2007). To Follow the Water. New York: Basic Books.

IPCC Report (2006). Sensitivity of Arctic Ocean River Flow, pp 824. Cited June 14, 2010.

Schwartz, P., and Randall, D. (2003, October). An abrupt climate change scenario and its implications for United States national security. Prepared for the Department of Defense.

Monthly Review. (2004, May). The Pentagon and climate change.

 

Date: 1/26/2011

Scenario Images:

Thermohaline Circulation System
Image Courtesy CLIVAR



The Thermohaline Circulation -- The Great Ocean Conveyor Belt
Image Courtesy NOAA. From NOAA visualizations: "The word "thermohaline" is a conjunction of terms referring to "heat" and "salinity." The movement of most mid and deep water in the ocean is driven by changes in heat and salinity--both of which affect density. This animation shows the general circulation pattern of the ocean, where water sinks in the N Pole, becomes cold and travels around the globe, in some places rising to the surface as it warms."



Resources:

 

A Paleo Perspective on Abrupt Climate Change (Cycle A)
A NOAA series of articles on abrupt climate change, ocean circulation and feedback loops.

 

Abrupt Climate Change (Cycle A)
From Robert Stewart's Oceanography in the 21st Century the basics of Abrupt Climate Change and Thermohaline Circulation.

 

Climate Impact Assessment (Comprehensive) (Cycle A)
Arctic Climate Impact Assessment: Impacts of increased precipitation and runoff from major Arctic rivers may reduce ocean salinity with impacts on the thermohaline circulation system. See for example, pages: 990, 994, 999, 1000 and 1018.

 

Global Warming and Atlantic Currents (Cycle A)
Study suggests global warming may alter Atlantic Currents.

 

Modeling Abrupt Change in the Thermohaline Circulation (Cycle A)
Scientists suggest that a high flux of freshwater into the North Atlantic 13,000 years ago caused a reduction in the thermohaline circulation.

 

Researchers Link Ice Age Climate-Change Records To Ocean Salinity (Cycle A)
"Sudden decreases in temperature over Greenland and tropical rainfall patterns during the last Ice Age have been linked for the first time to rapid changes in the salinity of the north Atlantic Ocean, according to research published Oct. 5, 2006, in the journal Nature."

 

Thermohaline Ocean Circulation Journal Article (Cycle A)
S. Rahmstorf, (2006) Thermohaline Ocean Circulation. Encyclopedia of Quarternary Sciences (Ed.) S.A. Elsevier, Amsterdam.

 

Abrupt Climate Change and Thermohaline Circulation (Comprehensive) (Cycle B)
Abrupt climate change and thermohaline circulation:
Mechanisms and predictability by Jochem Marotzke, School of Ocean and Earth Science, University of Southampton, Southampton Oceanography Centre, Southampton, SO14 3ZH, United Kingdom. An older, but advanced level article about changes to the thermohaline circulation system. See also: What if the conveyor were to shut down? Reflections on a possible outcome of the great global experiment by Wallace Broecker.

 

Are We On the Brink of a New Little Ice Age? (Cycle B)
This site from Woods Hole provides background material for possible abrupt climate change. The animations and salinity charts located under
"Related Multimedia" are well worth viewing. See Also: Abrupt Climate Change: Should We Be Worried?

 

Information Sheet on the Giant Ocean Conveyor Belt (Cycle B)
The thermohaline circulation by Tim Osborn and Thomas Kleinen. Contains an animation depicting stages of the circulation. From the Climatic Research Unit, University of East Anglia, Norwich, UK.

 

Shutdown of Thermohaline Circulation (Cycle B)
Links to refereed articles on slowdown or shutdown of the THC.

 

The Once and Future Circulation of the Ocean (Cycle B)
"Did changes in ocean circulation play a role in melting the vast ice sheets that covered North America and Europe during the last ice age? Could global warming cause ocean circulation changes that lead to dramatic climate changes in the future?"

 

The Russian–American Initiative for Land–Shelf Environments in the Arctic (Comprehensive) (Cycle B)
Good overview of research on Russian river discharge. The global representation provides a good view of the river system feeding into the Arctic Ocean.

 

Thermohaline Circulation Climate Effects (Cycle B)
From the Potsdam Institute for Climate Impact Research. Contains additional climatic impacts of thermohaline circulation.

 

Thermohaline Circulation System (Cycle B)
From the Earth System Science Interdisciplinary Center, University of Maryland. (click on the Thermohaline.pdf link at the bottomof the file list).

 

NASA SciFiles Video on the Great Conveyor Belt (Cycle C)
Two young students question Dr. Martin about the thermohaline circulation system.

 

Ocean Literacy (Cycle C)
"An understanding of the oceans influence on you and your influence on the ocean." contains links to the Ocean Literacy Principles.

 

Sample Investigations:

 

Activities from Teaching Physical Concepts in Oceanography (Cycle A)
These activities will help students understand the following concepts:

    Activity 1.4: Effects of Temperature & Salinity on Density & Stratification (Steps 1- 4; p. 8).
    Activity 1.4: Effects of Temperature & Salinity on Density & Stratification (Steps 5-7; p. 9).
    Activity 1.5: Effect of Stratification on Mixing (p. 9-10).
    Activity 1.6: Convection Under Ice (p. 10), and
    Activity 4.3: Convection (p. 36-37).
    Difficulty: beginner

     

    Concept Map Builder (Cycle A)
    Go to the COSEE concept map builder for a tool that will assist your study of science, e.g., global climate change or ocean science. Creating a login and password is well worth your time.
    Difficulty: beginner

     

    Ocean Currents Web Site from John Hopkins University (Cycle A)
    Activities for younger students on the Gulf Stream, Conveyor Belt, and Mediterranean Sea. There is an activity on water density, an important concept in ocean circulation.
    Difficulty: beginner

     

    Ocean Currents: Ship to Shore Education Program (Cycle A)
    An activity based on the 1990 spill of 60,000 Nike shoes into the Pacific.
    Difficulty: beginner

     

    Can Global Warming Cause Global Cooling? (Cycle B)
    If your school uses ArcGIS, this project looks at Greenland and the North Atlantic. This includes analyzing the thermohaline circulation system to determine whether it is slowing down.
    Difficulty: intermediate

     

    Hands On Activites Demonstrating Thermohaline Circulation Concepts. (Cycle B)
    Using the activities at this Web site, plus use of the following three animations will help students understand thermohaline circulation.


    Difficulty: beginner

     

    NOAA Learning Objects (Cycle B)
    See NOAA Learning Objects; especially appropriate are Ocean Currents and the Water Cycle.
    Difficulty: beginner

     

    Temperature and Deep Ocean Circulation (Cycle B)
    This lesson explores the relationship between density and ocean currents. Students hypothesize the cause of ocean currents and then develop a model to help explain the role that temperature plays in deep ocean currents.
    Difficulty: intermediate

     

    National Science Digital Library (NSDL) Resource Guide to Earth's Oceans (Cycle C)
    Very nice site, many activities with links to oceans, climate and more!
    Difficulty: beginner

     

    Video Discussing Water Density (Cycle C)
    From the NASA Science Files: "Third segment of the Ocean Odyssey describes how the salinity and temperature of water increases its density. The Density Current segment describes how the different densities of water in the ocean create currents."
    Difficulty: beginner

     

     

    Standards:

    • Science
      National Science Education Standards - Science Content Standards http://www.nap.edu/readingroom/books/nses/html/overview.html#content The science content standards outline what students should know, understand, and be able to do in the natural sciences over the course of K-12 education.
      • K-12 UNIFYING CONCEPTS AND PROCESSES
        The understandings and abilities associated with the following concepts and processes need to be developed throughout a student's educational experiences:
        • Systems, order, and organization
        • Evidence, models, and explanation
        • Constancy, change, and measurement
      • GRADES K-4 CONTENT STANDARDS
        • Science as Inquiry (Std A)
          • Abilities necessary to do scientific inquiry
          • Understanding about scientific inquiry
        • Physical Science (Std B)
          • Properties of objects and materials
        • Science and Technology (Std E)
          • Understanding about science and technology
        • History and Nature of Science (Std G)
          • Science as a human endeavor
      • GRADES 5-8 CONTENT STANDARDS
        • Science as Inquiry (Std A)
          • Abilities necessary to do scientific inquiry
          • Understanding about scientific inquiry
        • Physical Science (Std B)
          • Transfer of energy
        • Earth and Space Science (Std D)
          • Structure of the earth system
        • History and Nature of Science (Std G)
          • Science as a human endeavor
          • Nature of science
          • History of science
      • GRADES 9-12 CONTENT STANDARDS
        • Science as Inquiry (Std A)
          • Abilities necessary to do scientific inquiry
        • Physical Science (Std B)
          • Motions and forces
          • Conservation of energy and increase in disorder
          • Interactions of energy and matter
        • Earth and Space Science (Std D)
          • Geochemical cycles
        • Science in Personal and Social Perspectives (Std F)
          • Environmental quality
          • Natural and human-induced hazards
        • History and Nature of Science (Std G)
          • Science as a human endeavor
          • Nature of scientific knowledge
          • Historical perspectives
    • Geography
      Geography for Life: National Geography Standards, 1994
      • THE WORLD IN SPATIAL TERMS
        Geography studies the relationships between people, places, and environments by mapping information about them into a spatial context. The geographically informed person knows and understands:
        • How to use maps and other geographic representations, tools and technologies to acquire, process, and report information from a spatial perspective
        • How to use mental maps to organize information about people, places, and environments in a spatial context
        • How to analyze the spatial organization of people, places, and environments on Earth’s surface
      • PHYSICAL SYSTEMS
        Physical processes shape Earth’s surface and interact with plant and animal life to create, sustain, and modify ecosystems. The geographically informed person knows and understands:
        • The physical processes that shape the patterns of Earth’s surface
      • ENVIRONMENT AND SOCIETY
        The physical environment is modified by human activities, largely as a consequence of the ways in which human societies value and use Earth’s natural resources, and human activities are also influenced by Earth’s physical features and processes. The geographically informed person knows and understands:
        • How human actions modify the physical environment
        • How physical systems affect human systems
    • Technology
      The International Society for Technology Education From http://www.iste.org and http://www.edtech.sandi.net/index.php?option=com_docman&task=doc_download&gid=349&Itemid=229
      • BASIC OPERATIONS AND CONCEPTS
        • Students are proficient in the use of technology.
      • TECHNOLOGY RESEARCH TOOLS
        • Students use technology to locate, evaluate, and collect information from a variety of sources.
        • Students use technology tools to process data and report results.
      • TECHNOLOGY PROBLEM- SOLVING AND DECISION-MAKING TOOLS
        • Students use technology resources for solving problems and making informed decisions.
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