ice field

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A large expanse of ice covering a mountainous region and consisting of several interconnected glaciers.
• noun An extensive area of ice on the surface of the ocean, consisting of multiple ice floes and covering an area that is greater than 10 kilometers (6 miles) across.

from The Century Dictionary.

• noun A great sheet or floe of ice, at times so extensive in arctic seas that its limits cannot be seen from the masthead.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a network of interconnected glaciers or ice streams having a common source
• noun a large expanse of floating ice (several miles long)

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a large flat mass of ice (larger than an ice floe) floating at sea