| Summary: | (a) Northern Hemisphere of Earth, centered on the North Pole. Concentric circles represent the increasing extent of Polar Night as latitude increases; bands are based on the sun’s elevation relative to the horizon at solar noon on the winter solstice: civil twilight (0 to 6°), nautical twilight (6 to 12°), and astronomical twilight (12 to 18°) (modified from [ 78 ]). (b) Svalbard archipelago, with locations of light measurements shown as stars, and locations of krill collection for physiological experiments ( Fig 3 , S2 Fig ) shown as open circles. Basemap for panel (a) is from Natural Earth Data using the combined datasets for Physical Vectors with Land ( https://naturalearth.s3.amazonaws.com/10m_physical/ne_10m_land.zip ) and Minor Islands ( https://naturalearth.s3.amazonaws.com/10m_physical/ne_10m_minor_islands.zip ). Basemap for panel (b) is from Geonorge using S100 Map data ( https://kartkatalog.geonorge.no/metadata/s100-map-data/bd6050e8-7182-459b-9989-66c4ecbae874 ). (c) Hyperspectral irradiance measured at sunset for a midlatitude location (38.7 o N at 21:54 GMT, upper panel) and 3 high-latitude locations around Svalbard in January (lower panel). For high-latitude spectra, diagnostic spectral bands from aurora borealis (391, 557, and 630 nm) and the research vessel’s SVLs are annotated. All-sky images taken at the time of spectrum acquisition are shown at right. Inset is irradiance integrated as photosynthetically active radiation (400 to 700nm, E PAR ). Black, red, and green colors represent 3 stations of increasing latitude (measured at times: 11:35, 11:11, and 11:50 GMT, respectively), which correspond to stars (panel b). For data, see S1 Data . SVL, sodium vapor lamp.
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