Abstract
An Autonomous Underwater Vehicle (AUV) carrying 600 kHz RDI Acoustic
Doppler Current Profilers (ADCPs) was deployed at four locations over the
West Spitsbergen outer shelf in July 2010. The backscatter signal recorded by
the ADCPs was extracted and analysed to document the vertical distribution
and patchiness of the pelagic scattering layer during midnight sun. At the
northernmost locations (Norskebanken and Woodfjorden), fresher and colder
water than at the southernmost locations (Kongsfjordbanken and
Isfjordbanken) prevailed in the surface layer (0-20 m) and scatterers
(interpreted as zooplankton) were distributed over the entire sampling depth
(0-150 m). In contrast, more saline and warmer Atlantic Water dominated the
surface layer at Kongsfjordbanken and Isfjordbanken and scatterers were
concentrated in the top 20 m, above the pycnocline. Scatterers formed patchy
aggregations at all locations, but patchiness generally increased with the
density of organisms and decreased at depths >80 m. This study contributes
to our understanding of the vertical distribution of pelagic organisms in the
Arctic and the spatial coverage of the AUV has extended early acoustic
studies from 1-dimensional observations limited to Arctic fjords to a broader,
more general offshore coverage. No synchronised or unsynchronized vertical
migrations were detected, but the short time scale associated with AUV
deployments resulted in high variance and autonomous vehicles are therefore
not as effective as long-term mooring deployments to study vertical
migrations. AUV-based acoustic surveys of the pelagic communities are
nonetheless highly complementary to Eulerian studies, for instance by
providing spatial measurements of patchiness.
Original language | English |
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Publication status | Published - 9 May 2016 |