ice hole vs polynya

ice hole

noun
  • A hole in the ice of a frozen body of water, often man-made with the scope of fishing. (This entry is a translation hub.) 

polynya

noun
  • A naturally formed transient area of open water surrounded by sea ice, especially in polar or subpolar seas. 

How often have the words ice hole and polynya occurred in a corpus of books? (source: Google Ngram Viewer )