Currents and Upwelling

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Oceanic conveyer belt illustration
“The global ocean conveyor belt is a constantly moving system of deep-ocean circulation driven by temperature and salinity. The great ocean conveyor moves water around the globe. ... Cold, salty water is dense and sinks to the bottom of the ocean while warm water is less dense and remains on the surface.” NOAA 

 

Global Ocean Currents

Heat from the sun provides the energy that drives the circulation of ocean water, so it is predicted that ocean warming due to climate change could drastically alter ocean circulation. And ocean circulation helps drive weather patterns and distributes heat, oxygen and nutrients throughout the ocean.

In the Atlantic, both temperature and salinity drive a major ocean current system. Surface ocean currents from the tropics carry warm water to the north Atlantic. This is the Gulf Stream that warms the east coast of the US and carries warm water to Europe. As the water moves north, it gets cooler and evaporation makes it saltier. This makes the water denser so it sinks as it reaches the north Atlantic, becoming a deep cold ocean current moving south. It eventually upwells to the surface again creating a global conveyor belt of moving water called the Atlantic Meridional Overturning Circulation or AMOC. AMOC is important because it keeps the nutrients in the ocean mixed and available.

Scientists worry that the ocean circulation is slowing in the Atlantic because of climate change: evidence already shows it has slowed by about 15 percent since the middle of the last century.

Cold, freshwater from melting Greenland ice is probably the main cause. This disrupts the ocean conveyor belt at a delicate point, where the cooled surface water starts sinking. And there is a danger that if the current slows enough, it may reach a tipping point and totally collapse.

If the AMOC collapses, it could bring extreme cold to Europe and parts of North America, raise sea levels along the U.S. East Coast, provide less nutrients for fish, and disrupt seasonal monsoons that provide water to much of the world. This site has a detailed explanation and lots of great graphics. Here is a discussion on Science Friday about a possible collapse.

Ocean Stratification

Warming oceans alter the patterns of ocean circulation in other ways: the global ocean has become more stratified and stable over the past 50 years with global warming. Warmer surface layers slow the mixing of nutrients from deep water so there are less nutrients for marine algae near the surface.

A 2020 study found that the upper 2000m has become 5% more stratified, but the upper 150m has increased stratification by almost 20%. This will create a negative feedback loop heating the surface even more because the heat absorbed at the surface can’t be distributed to the depths. In addition it prevents carbon storage in the deep ocean. This stratification will impact entire marine ecosystems.

Upwelling

Upwelling occurs along coasts when deep, cold, nutrient-rich water is brought to the surface. It’s the winds that blow along the coast that push the surface water offshore, pulling deep water up. The nutrients from the upwelled water stimulate phytoplankton growth, which in turns feeds the food web creating a rich coastal ecosystem.

There are several upwelling systems in the world’s oceans along the eastern edge of the continents that support important fisheries, so it is important to understand how climate change is going to affect these systems. So far scientists can only say that each system will react differently and it is currently difficult to predict those changes. Some suggest that if high pressure systems in the ocean basins get more intense with climate change, coastal winds may increase and intensify upwelling. In addition, it is predicted that local warming over land will create stronger winds and therefore more local upwelling.  Coastal upwelling systems are very complex and they are not all similar, but they create important global coastal ecosystems that could be disrupted with climate change.

Lesson Plans

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    Lesson Plan
    Carbonated Communities

    Through cutting-edge scientific research, students are introduced to climate change’s effects on the intertidal (ocean acidification and temperature increase) and what is known about how ocean organisms are impacted.

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    Save Our Coral Reefs

    Using this tool, students will practice and deepen their understanding of coral reef basics, what is contributing to their loss, and what is being done to preserve this resource.

    Full Lesson Plan

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    Lesson Plan
    Carbon Cafe

    In this lesson students learn about the effects of different diets and foods on our Climate Crisis and how to make positive changes

    Full Lesson Plan

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    Lesson Plan
    What's the bigger picture

    In this lesson, students combine art and science to interpret and illustrate graphical art. In this way, students will build understanding of the power of data infused art to convey the "bigger picture" of climate change. 

    Full Lesson Plan

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    Lesson Plan
    EXPLORING OCEAN MYSTERIES CURRICULUM

    “There are seven principles of ocean literacy including: the ocean is a major influence on weather and climate; and the ocean and humans are inextricably interconnected.  The Ocean Mysteries Curriculum makes it easy to teach the seven principles while meeting NGSS, Common Core and Climate Literacy Standards.”

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