Ice always builds up and stays in the inlets where it isn’t easily carried out to sea. At low tide it just sits on the bottom, on the mud. There’s always a dynamic edge out there forming, melting, breaking off depending on the wave action, with pieces getting carried out to sea.
The temperature has been bouncing around like a yo-yo – rather like the price of gas, from minus 10 degrees C to plus 10 and back again within a few days.
Unlike fresh water, which is at its most dense around 4 degrees C, salt water is most dense at its freezing point, which is typically around minus 2 C. The more salt is in the water, the lower its freezing point. In oceans that freeze, the water deeper down is saltier, so it stays down, and is less likely to freeze because the high salt concentration lowers its freezing point considerably. The lighter, relatively fresher water stays on top – so it’s more likely to freeze, and when it does freeze it has little salt in it, as I found out by tasting it.