> Well, this depends on the "age" of the floe, I have heard. If > frozen very slowly, the crystal > structure of ice tends to exclude salt, so the freshly-formed > floe-ice is much lower in salt than > the proportion of salt in sea water would suggest. (No, it would > not be salt-free; and, no, I > would not expect it to be potable.) In addition, over time, the > floe-ice "loses" salt, apparently > because the portions containing salt are somewhat more fluid-like > (salt depresses the freezing > point), permitting the salt to "diffuse" away from the relatively > pure ice structure. > > Anybody recently melted a floe, to test this hoary information? > > -- > Dave Kruger > Astoria, OR > chemist I think that Dave has it just about right here. Sea water doesn't have absolutely uniform salinity, and areas with lower salinity will freeze first isolating and concentrating the salt in the surrounding water still in the liquid phase. Conversely areas with high salinity thaw first. The result is that the freeze/thaw cycle liberates a stream of high salinity, and therefore dense, water which sinks below the ice, and creates ice and water of lower salinity and density floating on top. Whether old ice is actually 'fresh' or not I don't know, but the process does separate sea water into high and low salinity components and is fundamental to driving many of the major ocean currents. The cold high salinity current which flows deep and north from the pack ice in Antarctica in particular having fairly major global climatic and ecological influence. You can visualise this by making ice cubes out of a coloured salt solution, although I guess tomato or OJ might work, and then floating them in a tank of warm water. When they thaw you see a coloured stream flowing down from the ice. Cheers Colin Calder 57º19'N 2º10'W *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
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