Figure 5. Photon budget for biological and atmospheric light sources in Kongsfjord.

The two components of the underwater light field in Kongsfjord are plotted as a function of depth in equivalent units (μmol photons m⁻³ s⁻¹). Atmospheric light is scalar irradiance (solid line; 400–700 nm, E_o,PAR) modeled from diffuse atmospheric irradiance measured at approximately solar noon on 25 January 2015. Bioluminescence is mean bioluminescence potential (±SE, black dots) measured at midday and midnight in January 2014. The colors represent photic zones dominated by atmospheric light (red shading) and bioluminescent light (blue shading).