drift ice vs ice field

drift ice

noun
  • One or more floating slabs of ice which have become detached from larger sheets or shoreline glaciers and which are moved by wind or sea currents. 

ice field

noun
  • A large expanse of floating ice (several miles long). 

  • A network of interconnected glaciers or ice streams having a common source. 

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