The benthic environment may seem cut off from the rest of the world deep under the ice but under certain conditions the cold from above can reach down and touch the seabed as it does on the surface. The way it does this is in the form of brinicles, these icy stalactite structures form due to extremely cold super saline water being introduced to the water column through brine channels (Cartwright et al., 2013). Starting as just a hollow tube of ice forming and deciding around deciding brine these tubes can become complex structures ranging in size and shape.
In most cases these brinicles won’t reach the sea floor but under the right condition in shallower water the super cold saline water will reach down and thicken with ice as it descends due to the brine being denser than the sea water it displaces. The video linked again from BBC’s life documentary shows one such brinicle event using time lapse of its growth downwards towards the sea floor. Due to the brinicle reaching down to the seabed they are often referred to as anchor ice keeping the sea ice in place. It has been suggested by some authors that due to biological zonation that the limit of these anchors would be 33m but others disagree due to the fact that there is no physical constraints to them going deeper (Mager et al., 2013).
As shown in the video if the brinicle manages to touch the seafloor it continues to spread along the bottom freezing anything it touches killing them instantly. This can be a serious problem for the benthic slower moving organisms that are unable to escape the path of the brinicle with a slower metabolic rate. Luckily for them brinicles that reach the seafloor like this are not too common and so would never effect numbers significantly.