In terms of chords and melody, Atlantic has complexity on par with the typical song, having near-average scores in Melodic Complexity and Chord-Bass Melody and below-average scores in Chord Complexity, Chord-Melody Tension and Chord Progression Novelty.
Atlantic is written in the key of E♭ Dorian. According to the Theorytab database, it is the 8th most popular key among Dorian keys and the 40th most popular among all keys. The E♭ Dorian scale is similar to the E♭ Minor scale except that its 6th note is a half step higher (C). Chord progressions in Dorian have a characteristic sound due to the major quality of the chord built on the 4th scale degree. See the E♭ Dorian Cheat Sheet for popular chords, chord progressions, downloadable midi files and more!