Modeled underwater light during Polar Night.

• Main Authors: Jonathan H. Cohen (7958483), Kim S. Last (11581392), Corie L. Charpentier (3200505), Finlo Cottier (749186), Malin Daase (471602), Laura Hobbs (9152223), Geir Johnsen (257802), Jørgen Berge (235355)
• Format: Still Image
• Language: unknown
• Published: 2021
• Subjects: Physiology; Ecology; Inorganic Chemistry; Environmental Sciences not elsewhere classified; Astronomical and Space Sciences not elsewhere classified; Biological Sciences not elsewhere classified; thysanoessa inermis </; therefore question whether; main migratory species; acoustic field observations; 81 ° n; 5 ° n; arctic ocean extends; light measurements demonstrate; characterize light across; weak midday twilight; div >< p; arctic krill (<; arctic polar night; arctic krill; light plays; polar night; zooplankton community; using electroretinogram; traditional definitions; sun ’; subjective night; photophysiological cycles; north pole; midnight sun; maximum extent; lower latitudes; latitudinal gradient; high latitudes; fundamental role; darkest parts; constant darkness; circadian clock; auroral components; although differences; Arctic; Antarctic; Arctic Ocean; Svalbard; North Pole; Rijpfjorden; Antarc*; Arctic krill; Rijpfjord*; Zooplankton; Thysanoessa inermis
• Online Access: https://doi.org/10.1371/journal.pbio.3001413.g004

Underwater light intensity plotted as scalar irradiance (E o irradiance on a point from all directions weighted equally). Light values were derived from radiative transfer model results of diffuse skylight irradiance measured at Rijpfjorden, Svalbard (80° 37.79N 22° 4.14E) at solar noon on January 15, 2016, then propagated through the water column (bold black line showing irradiance as a function of depth). The dotted vertical line denotes the visual sensitivity threshold for T . inermis (1% of V max for subjective midnight V- log I ). Dashed vertical lines show thresholds for light-mediated processes in a range of other taxa: entrainment of circadian rhythms in fruit flies [ 53 ] and mice [ 55 ]; 1% of V max from V- log I for Antarctic fish Pagothenia [ 56 ]. Depth-stratified abundance of T . inermis at Rijpforden (06:30 on January 14, 2016) is plotted as bubbles of proportional size. For data, see S2 Data .