<a href="/earth/Water/ocean_gyres.html&edu=elem&dev=">Ocean gyres</a> are large swirling bodies of water that are often on the scale of a whole <a href="/earth/Water/ocean.html&edu=elem&dev=">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&edu=elem&dev=">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&edu=elem&dev=">Coriolis Effect</a>.<p><small><em> Windows Original (Original map is from <a href="http://commons.wikimedia.org/wiki/Main_Page">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&edu=elem&dev=">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&edu=elem&dev=">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&edu=elem&dev=">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&edu=elem&dev=">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&edu=elem&dev=">crop withering</a>. <a href="/teacher_resources/online_courses/health/events_health.html&edu=elem&dev=">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&edu=elem&dev=">Changing Planet: Withering Crops</a> to find out more.<p><small><em>Image taken by Tomas Castelazo, Creative Commons <a href=&quot;http://creativecommons.org/licenses/by/3.0/deed.en&quot;>Attribution 3.0 Unported</a> license.</em></small></p>

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