Researchers' clues to the Eemian climate come from measurements of the ratios of two slightly different types of oxygen, isotopes oxygen-16 and oxygen-18, preserved in the GRIP core.
Your textbook includes these as types, as a particular type of glacier movement, but you will see that there are as many textbooks that omit it as a type of movement as include it.
In cases where you have two different complex types that are frequently associated with each other for mapping purposes, a Submap is a good way to create a re-useable mapping between the types.
Unlike the song sparrow, which repeats one of its several song types in bouts before switching to another, the warbler continuously composes much longer and more variable songs without repetition.