Note the "water sky" in this image. The darker sky indicate open water, The white sky indicates ice floes.
April 8, 1916 - Orde-Lees' Journal
There has now been more or less of a swell for the last week or so but today the whole pack was heaving in great undulations. So big a swell can indicate nothing but the immediate proximity of much open water, moreover, the very pronounced water sky to the north practically confirms this. It seems that our release is now imminent. The wonder is that our remaining piece of floe had not again bisected, for it is more than twice as big as any of
the floes around us.