Submitted by Anonymous on Thu, 09/08/2011 - 10:29

Mike - I know from living on the coast that the moon has to do a lot with the level of tides. Do the moon phase effect the sea ice level or movement at all? If so, does that effect your work at all?

Thanks, Alli

Michael League

Hey Alli,Good question. Just like where you live, the Moon's and Sun's gravities
pull on the water here in McMurdo Sound. As a result, the water does
try to rise and fall. What do you think this does to the sea ice?
Well, the ice moves up and down with the water level for the most part.
There is really only one place where this doesn't happen so easily -
that's where the sea ice meets and freezes to the land. Here the ice is
being pushed on when the tide rises, but it is frozen in place to the
land. What do you think happens to the ice with these forces pushing on
it? That's right - it cracks! We call these tidal cracks, because they
were caused by the tide.
Tidal cracks are some of my favorite spots on the ice. First, they are
bumpy and interesting to look at. They also create access to the water
and air, which is the perfect place to find seals. Finally, because
there is open water or only thin ice, tidal cracks let in a lot of light
which lights up the ocean for divers. It is so nice to dive near tidal
cracks!
Great question!
Mike