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<a href="/earth/Water/ocean_gyres.html&edu=elem&dev=1">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=1">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=1">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=1">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=1">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=1">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=1">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=1">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=1">crop withering</a>. <a href="/teacher_resources/online_courses/health/events_health.html&edu=elem&dev=1">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=1">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>Although most of us don't live in the Arctic, it is very important to understand how the <a href="/earth/polar/arctic_currents.html&edu=elem&dev=1">Arctic Ocean works</a> because it has an impact on surrounding areas and on <a href="/earth/climate/climate.html&edu=elem&dev=1">global climate</a>.  This map shows how cold, relatively fresh water comes into the <a href="/earth/polar/arctic_ocean.html&edu=elem&dev=1">Arctic Ocean</a> from the Pacific Ocean through the Bering Strait. This water is swept into the Beaufort <a href="/earth/Water/ocean_gyres.html&edu=elem&dev=1">gyre</a> where <a href="/earth/Atmosphere/wind.html&edu=elem&dev=1">winds</a> force the water into clockwise rotation.<p><small><em> Courtesy of Jack Cook, WHOI (<a href="http://www.whoi.edu">Woods Hole Oceanographic Institute</a>)</em></small></p>

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF