a flat mass of ice ( smaller than an ice field) floating at sea

A low, flat mass of floating ice.

A large flat mass of floating ice, or a collection of such masses of ice.

A field of floating ice.

Large cake of floating ice.

A mass of floating polar ice.

A field of ice floating in the ocean.

A mass or collection of floating ice in the ocean.

Towards the end of our day's journey, we landed on the only really level floe we had yet met with. – Three Voyages for the Discovery of a Northwest Passage from the Atlantic to the Pacific, and Narrative of an Attempt to Reach the North Pole, Volume 2 (of 2) by Sir William Edward Parry

So he rose some ninety feet, and finally arrived at the underside of the ice floe. – Seed of the Arctic Ice by H. G. Winter

He's as ugly- tempered as a spearfish, as vicious as a man- eatin' shark, as tricky as a moray, an' about as relentless as a closin' ice- floe. – The Boy With the U. S. Fisheries by Francis Rolt-Wheeler