Premium
Wintertime water dynamics and moonlight disruption of the acoustic backscatter diurnal signal in an ice‐covered Northeast Greenland fjord
Author(s) -
Petrusevich Vladislav,
Dmitrenko Igor A.,
Kirillov Sergey A.,
Rysgaard Søren,
FalkPetersen Stig,
Barber David G.,
Boone Wieter,
Ehn Jens K.
Publication year - 2016
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2016jc011703
Subject(s) - polar night , fjord , zooplankton , oceanography , geology , sea ice , diel vertical migration , meltwater , moonlight , arctic ice pack , environmental science , snow , fast ice , atmospheric sciences , arctic , climatology , antarctic sea ice , geomorphology , physics , optics
Six and a half month records from three ice‐tethered Acoustic Doppler Current Profilers deployed in October 2013 in Young Sound fjord in Northeast Greenland are used to analyze the acoustic backscatter signal. The acoustic data suggest a systematic diel vertical migration (DVM) of scatters below the land‐fast ice during polar night. The scatters were likely composed of zooplankton. The acoustic signal pattern typical to DVM persisted in Young Sound throughout the entire winter including the period of civil polar night. However, polynya‐enhanced estuarine‐like cell circulation that occurred during winter disrupted the DVM signal favoring zooplankton to occupy the near‐surface water layer. This suggests that zooplankton avoided spending additional energy crossing the interface with a relatively strong velocity gradient comprised by fjord inflow in the intermediate layer and outflow in the subsurface layer. Instead, the zooplankton tended to remain in the upper 40 m layer where relatively warmer water temperatures associated with upward heat flux during enhanced estuarine‐like circulation could be energetically favorable. Furthermore, our data show moonlight disruption of DVM in the subsurface layer and weaker intensity of vertical migration beneath snow covered land‐fast ice during polar night. Finally, by using existing models for lunar illuminance and light transmission through sea ice and snow cover, we estimated under ice illuminance and compared it with known light sensitivity of Arctic zooplankton species.