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 show the occurrence of Lunar Vertical Migrations (LVMs) and shallow DVMs.

Here we quantify when and where full-depth (>20m), solar mediated DVM exists on a pan-Arctic scale. We observe the scattering population, most likely to be comprised of zooplankton, using 300 kHz Acoustic Doppler Current Profilers (ADCPs). We quantify the presence/absence of DVM, and find 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 during the polar night. The dates of this cessation accurately align with the date of the winter solstice (± 2 days). Between 74 and 77° N, DVM presence/absence is variable. Acoustic data sampled at 89° N, however, show 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 reveal that local variations in sea ice cover directly determine the continuation or cessation 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 when compared to similar latitudes. 

Authors:

Hobbs LJ, Cottier FR, Last FS, Berge J

Marine Ecology Progress Series
10, 24, 2018
Pages:
DOI: 10.3354/meps12753