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December 19, 2013
(11 May 2012) --- The Sor Kaydak near the northeast Caspian Sea in Kazakhstan are featured in this image photographed by an Expedition 31 crew member on the International Space Station. This striking image shows saline water of different colors in the Sor Kaydak, a salt marsh that leads into the northeast bulb of the Caspian Sea. The central 50 kilometers of this 180 kilometer-long depression is shown in this photograph. The Sor Kaydak depression is inundated on occasion by water from the Caspian Sea since it lies at the same elevation—that is, 29 meters below global sea level—though separated from the Sea by a low bar of land that is 1--2 meters high. The different colors of marsh water (brown to pink to light green, northeast to southwest) result from the interplay of water depth and resident organisms such as algae. Algae color varies depending on water temperature and salinity. The irregular gray areas at bottom right are wet zones between low sand dunes. These interdune flats are whitened with salt derived by evaporation of Caspian Sea water (the sea is just outside the image bottom right). The jagged line following the colored water (crossing the center of the image top to bottom) is the limit of the wetting zone (or perimeter), an irregular zone influenced by wind and the depth of water in the marsh. Small cliffs can be seen marking the east margin of the depression that contains Sor Kaydak. Above the cliffs a plateau surface (approximately 200 meters above the salt marsh, approximately 160 meters above global sea level) extends eastward for hundreds of kilometers. Here the plateau is occupied by a dense pattern of well heads which appear as a geometric pattern of tan dots. By contrast, the west margin (right) rises less than 10 meters above the marsh altitude. The straight line visible at center is a pipeline built across the salt marsh which takes oil to a terminal on the Caspian shore 100 kilometers northwest of the area shown here.

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