Sector 4 (AQA) Underwater Area

Sector 4 (AQA) Underwater Area, as named by the Metroid Prime & Fusion Original Soundtracks, is a music theme from Metroid Fusion. It was composed by Minako Hamano and Akira Fujiwara.

Description
As its name suggests, Sector 4 (AQA) Underwater Area plays in Sector 4 of the Biologic Space Laboratories research station. It plays in the lower area of the sector, which simulates a natural Zebesian marine ecosystem. It continues to play in this area until the endgame, where it is replaced by either Sector 3 Restore the Cooling Installation Timer Mission or Last Instructions depending upon the player's current progress.

Sector 4 (AQA) Underwater Area is a very mysterious-sounding theme. It uses harp and a female choir, and a melody performed slowly and softly on strings. This instrumentation evokes the aquatic environment, while making this song one of the most beautiful and serene themes of the Fusion soundtrack. However, it still carries the foreboding tone present throughout the Fusion soundtrack, showing that even now Samus Aran is not yet free from danger.

Sector 4 (AQA) Underwater Area can be heard here: