Well now, that makes sense rpage 'ponding' of dirty evaporative water. And this can be seen in one of horton's pics showing the ice 'slab' under the Phoenix a few weeks ago. He wondered what was on the ice face as 2 distinct circular rings, [I said fossils-joking of course] albeit the pic angle made them oval. The ice is evaporating alright. Can't recall the thread at this time.
yt
dx