Seen from Space 2005
The largest global tract of sea ice covers the Antarctic Ocean, a huge depository of deep seawater.
This article discusses the sea ice in the Antarctic Ocean. Figure presents an animated movie of the yearly transition of sea ice in the Antarctic Ocean. The movie is composed of pictures captured by the microwave instrument AMSR-E aboard NASA's Aqua satellite. Using the same pattern as we used for the Arctic Ocean, figure presents the observed sea ice in the white area in the center, the land in gray, and the sea surface in blue. The yearly sea-ice extent in the Antarctic Ocean experiences its greatest decrease in March, unlike the Arctic Ocean ice, which decreases in September. In the Arctic, the sea ice remains almost entirely within the Arctic Circle, north of 66.6 degrees north latitude, roughly the north coast of the Iceland except in inland seas at river mouths, like the Sea of Okhotsk and Hudson Bay in winter. The ice is limited because the Arctic Ocean is surrounded by continents, and the warm ocean currents flow in from the North Atlantic Ocean. In contrast, in the Antarctic, the sea ice encompasses most of the Antarctic Circle, south of 66.6 degrees south latitude, roughly the continental coast of Antarctica (on the right side of the figure. In summer, the sea ice almost disappears except in the Weddell Sea and the Ross Sea. In winter, however, it expands into the surrounding Antarctic Ocean and extends beyond the Antarctic Circle for 500 to 600 kilometers, becoming the largest global region of sea ice and exceeding the area of Arctic winter sea ice by about 20 percent. Like the sea ice in the Arctic Ocean, this enormous field of sea ice in the Antarctic Ocean powers the global circulation of seawater that we call the "Thermohaline Circulation" or "Broecker's Conveyor Belt." Sea ice observations by American and Japanese microwave instruments over the past three decades show continued reduction of the extent of sea ice in the Arctic Ocean during the observation period. In contrast, the extent of sea ice in the Antarctic Ocean has expanded gradually, but continuously, except in the sea west of the Antarctic Peninsula (on the left of figure). Until now, no one has investigated the reason for the conflicting observations concerning the estimated Global Warming between the two Polar Regions. JAXA will continue to monitor these climatic trends by using Earth-observation satellites.
Related sites:  "Will a tour of the North Pole by dog sledge be possible?" The reduction in sea ice of the Arctic CircleAntarctica-An isolated continent-Cryosphere, seen from spaceAMSR/AMSR-EAppendix:Thermohaline Circulation (Broecker's Conveyor Belt); sequel chapter In the Arctic region, the seawater grows thick and heavy in salt content with the growth of sea ice off the shore of Greenland and settles to the bottom of the Atlantic Ocean. Due to its weight, this seawater moves along the bottom of the Atlantic Ocean, then streams to the south until it reaches the east end of the Drake Passage, between Antarctica and the South American Continent. The Antarctic Ocean around Antarctica is shallow near the Drake Passage and New Zealand (indicated in figure as "Antarctica-An isolated continent"). The heavily salted seawater cannot pass the shallow sea bottom of the Drake Passage and is forced to flow eastward at that point. Because of the surrounding sea ice, including the permanent ice in the Weddell Sea and the Ross Sea, more heavily salted seawater builds up around Antarctica and settles to the bottom of the Antarctic Ocean. This heavy seawater from the Antarctic region joins with that from the Arctic region at the bottom of the Antarctic Ocean, and they then flow together to the East. The shallow bottom surrounding New Zealand dams this deep seawater current, and the heavy seawater flows slowly to the depths of both the Indian and Pacific Oceans. |
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