Clearest sea - The Weddell Sea, 71°S, 15°W off Antarctica, has the clearest water of any sea. A Secchi disc was visible to a depth of 262 ft on 13 Oct 1986, as measured by Dutch researchers of the German Alfred-Wegener Institute. Such clarity corresponds to what scientists consider attainable in distilled water. This shot shows broken pack ice in the Weddell Sea. (Photo: Science Photo Library)
