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Our Glaciers: Then and Now activity kit helps you see the changes taking place in glaciers around the world. See all our activity kits and classroom activities.
<a href="/earth/Water/ocean_gyres.html">Ocean gyres</a> are large swirling bodies of water that are often on the scale of a whole <a href="/earth/Water/ocean.html">ocean</a> basin. Ocean gyres dominate the open ocean and represent the long-term average pattern of ocean <a href="/earth/Water/ocean_currents.html">surface currents</a>. This image shows the five major ocean gyres. Gyres rotate in a clockwise direction in the Northern hemisphere and a counter-clockwise direction in the Southern hemisphere because of the <a href="/physical_science/physics/mechanics/Coriolis.html">Coriolis Effect</a>.<p><small><em> Windows Original (Original map is from <a href="">Wikipedia Commons</a>)</em></small></p>The production of sea ice is also important to the layering of water in the Arctic Ocean. As <a href="/earth/polar/sea_ice.html">sea ice</a> is made near the Bering Strait, salt is released into the remaining non-frozen water. This non-frozen water becomes very salty and very dense and so it sinks below the cold, relatively fresh Arctic water, forming a layer known as the <a href="/earth/Water/salinity_depth.html">Halocline</a>. The Halocline layer acts as a buffer between sea ice and the warm, salty waters that have come in from the Atlantic.<p><small><em>   NASA</em></small></p>Satellite observations of lake temperatures at many lakes around the world show that lakes are warming worldwide.  Because lakes play such an important role in society, as a source of food, water, and recreation, these changes can have a significant impact on many aspects of our lives. Watch the NBC Learn video - <a href="/earth/changing_planet/warming_lakes_intro.html">Changing Planet: Warming Lakes</a> to find out more. This is an image of the eastern shore of Lake Tanganyika, Tanzania.<p><small><em> Image Courtesy of Marc Mayes</em></small></p>Coral animals build reefs in warm, tropical seawater. However, <a href="/earth/changing_planet/ocean_temperatures_intro.html">seawater can be too warm</a> for their liking.  If waters get too warm, coral animals lose the algae that live within their little bodies, a process called coral bleaching. Without the algae, corals have less nutrition. Unless cooler temperatures return, allowing algae to
 return, the coral dies.<p><small><em>Credit: UNC</em></small></p>As temperatures rise and soil moisture decreases, plants are stressed, which can lead to <a href="/earth/climate/crops_withering.html">crop withering</a>. <a href="/teacher_resources/online_courses/health/events_health.html">Droughts</a> accompanied by increased temperatures can lead to famine, social and political disruptions. Scientists are  helping with early identification of drought that might trigger food shortages. Watch the NBC Learn video - <a href="/earth/changing_planet/withering_crops_intro.html">Changing Planet: Withering Crops</a> to find out more.<p><small><em>Image taken by Tomas Castelazo, Creative Commons <a href=&quot;;>Attribution 3.0 Unported</a> license.</em></small></p>

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA