Pan-Arctic diel vertical migration during the polar night

Diel vertical migration (DVM) has generally been assumed to cease during the polar night in the high Arctic, although recent studies have shown the occurrence of lunar vertical migrations (LVMs) and shallow DVMs. Here, we quantified when and where full-depth (>20 m), solar-mediated DVM exists on a pan-Arctic scale. We observed the scattering population, most likely to be comprised of zooplankton, using 300 kHz acoustic Doppler current profilers (ADCPs). We quantified the presence/absence of DVM, and found that DVM continues throughout the year to at least 20 m at all locations south of 74° N. North of 77° N, DVM ceases for a period of time dur- ing the polar night. The dates of this cessation accurately align with the date of the winter solstice (± 2 d). Between 74 and 77° N, DVM presence/absence is variable. Acoustic data sampled at 89° N, however, showed no evidence of DVM at any time during the year — a new observation. Using indicators of presence/absence of sea ice from ADCPs and satellite-derived sea ice concentration data, we revealed that local variations in sea ice cover directly determine the continuation or ces- sation of DVM during the polar night. Earlier-forming and higher-concentration sea ice causes a cessation in DVM, whereas low-concentration or late-forming sea ice results in continuous DVM compared to similar latitudes.