Lecture 11: Ocean Circulation

• Thermohaline circulation is the circulation of the world's ocean driven by temperature and salt
• Thermohaline circulation

  1. Cold salty water sinks due to its density

  2. Differences in temperature and salinity drive deeper water currents
• Cold salty water sinks


  Important concept for thermohaline circulation
• Thermohaline circulation

  Starts in the North Atlantic by getting really cold and salty, water sinks there
• There is sinking that happens down by Antarctica too
• Most important center of sinking for thermohaline circulation is in the North Atlantic by Greenland and Iceland
• As water freezes, it excludes the salt, creating super salty and super cold water that sinks
• Secondary sinking point for thermohaline circulation is over on the west side of Greenland
• Surface waters move in to replace the sinking water in the North Atlantic
• Thermohaline circulation is sometimes called conveyor belt circulation
• It takes about a thousand years to make a single loop of the ocean
• The Gulf Stream is a surface current driven by wind, transporting warm water across the Atlantic Ocean to Europe
• The Gulf Stream slowly releases its heat as it transports warm water to Europe
• The Gulf Stream transports warm water across the Atlantic Ocean to Europe


  As it does that, it slowly releases its heat
• Factors affecting the climate of Europe

  • Warm water transported by the Gulf Stream
• The Gulf Stream is a hugely important factor in moderating the climate of Europe
• London gets snow but only a few inches despite being at the same latitude as Hudson Bay
• Winter temperatures in Iceland are slightly warmer than Boston due to the Gulf Stream
• Climate change is causing the Greenland ice sheet to melt
• Warm temperatures are melting sea ice along the coast of Greenland and causing the ice on Greenland to melt
• Warm waters and fresher waters don't sink as easily
• If the Gulf Stream shuts down, it changes the climate
• When there is no sinking of warm or fresh water, the Gulf Stream doesn't move in to replace it


  The Gulf Stream doesn't move in to replace it, changing the climate
• The shutdown of the Gulf Stream could make Europe colder
• The major plot point of the movie "The Day After Tomorrow" was the shutdown of the Gulf Stream
• The Gulf Stream is not going to shut down but it's going to slow down
• The Gulf Stream slowing down is due to the rate of sinking slowing down because of the fresh water flowing in off of Greenland
• The cold fresh water that doesn't sink leads to the Gulf Stream not bringing in warm water anymore, resulting in anomalously cold water in the North Atlantic
• The warming hole in the North Atlantic, indicative of global climate change, is caused by the Gulf Stream slowing down
• The Gulf Stream slowing down could have negative impacts on the human population of Europe due to climate change
• Sea level rise is due to warming and has multiple ways it contributes to it
• The last house on Holland Island fell down a few years ago as the island disappeared due to sea level rise
• Ocean acidification is not due to warming but to the amount of carbon dioxide the ocean is absorbing
• Ocean acidification can have a negative impact on many marine species