暖海 is read as だんかい (dankai) and means warm sea.
だんかい
dankai
だんぼう
(indoor) heating
だんりゅう
warm current
だんろ
fireplace
だんとう
mild winter
だんち
warm district
あたたかいめでみまもる
to not be harsh on someone (while awaiting a result)
だんごく
warm country
あたたかいひと
warmhearted person
だんき
warmth
warm up (e.g. engine)
だんとういへん
abnormally warm winter
だんぼうそうち
heater