This short clip shows an upside down chimney of ice found underneath the sea ice of the Chukchi Sea near Barrow Alaska in spring 2012. At this time there was a lot of surface melting of the ice layer going on and water was flowing through the ice into the water underneath. The chimney of ice that formed was about 10 cm across. We speculate that the water directly under the ice was relatively fresh and warm (warmer than the ice). The water draining down through the chimney must have been colder (and possibly also saltier) than the underlying water, because it was clearly sinking. As the cold water sinking down hit the underlying water, it cooled it enough to freeze, forming the chimney of ice around the sinking flow.
You may also be interested in the other videos in this album
The Arctic's Secret Garden
for more information about the work of my lab group.