Karlsen´s early works are characterised by an ecclesiastical liturgical-musical traditional rooting, while later works display an evolving tonal spectrum and a gradual introduction of dissonance, bringing the composer closer to contemporary styles while retaining traditional musical elements.
Following a pivotal year of studies in 1983-84 with Finnish composer Joonas Kokkonen, Mørk Karlsen emerges as a symphonic composer, having penned a number of symphonies and oratories. Mørk Karlsen´s sonatas and string quartets are also cornerstones of his compositional output, displaying the composers predilection for classical chamber music formats.
Mørk Karlsen´s list of works also includes a considerable output of church music compositions for choirs, soloists, instruments and organ, including the collection Laudate Dominum which encompasses 100 choir motets written for each Sunday of the church year. Mørk Karlsen has also focused on renewing the larger format church music with such works as the symphonic oratory Lilja (1987), Johannespasjonen (1991), Sinfonia da Requiem (1995) and St.Hallvards litani (2000).