iceberg vs polar cap

iceberg

noun
  • A huge mass of ocean-floating ice which has broken off a glacier or ice shelf 

  • An aloof person. 

  • An impending disastrous event whose adverse effects are only beginning to show, in reference to one-tenth of the volume of an iceberg being visible above water. 

polar cap

noun
  • A high-latitude region of a celestial body that is covered by ice. 

How often have the words iceberg and polar cap occurred in a corpus of books? (source: Google Ngram Viewer )