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The introduction of fresh water from melting ice caps can also affect thermohaline circulation. Since fresh water is less dense than salt water, it floats on the surface in high latitude regions. This cap prevents the sinking of water in regions of downwelling, thus weakening or stopping the overturn of the ocean. Current models predict that a shutdown of downwelling in the North Atlantic could occur soon and lead to a shutdown of the ocean conveyor (Gagosian 2007). Historically, such events have resulted in build-ups of toxins in the ocean that have been linked to mass-extinction events (Bralower 2002). A shutdown of global thermohaline circulation is also likely to cause rapid and severe changes in climate, with similar changes in temperature to what weve seen has been recorded over the past century occuring on the scale of decades (Gagosian 2007).
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