lit. the blue sea turned into mulberry fields (idiom)
fig. the transformations of the world
Definitions (粵典–words.hk)
語句
大海變為陸地，陸地淪為大海。比喻經歷過好多嘢，改變好大 weathered; hardened; seasoned; describes great change in one after having been through a lot; literally: blue sea mulberry fields (i.e. seas become land and vice versa)
Definitions (Wiktionary)
phrase, idiomatic
time brings drastic changes to the world; the vicissitudes of life (syn.) 滄桑, 桑田滄海, 桑田沧海, 沧桑