| Summary: | Data on zooplankton abundance and biovolume were collected in concert with data on the biophysical environment at 12 stations along a transect crossing the Atlantic Water inflow into the Arctic Ocean, in May 2014. The data were sampled along vertical profiles by a Laser Optical Plankton Counter (LOPC; ODIM-Brooke Ocean Rolls Royce Canada Ltd., Herman et al. 2004) and a Conductivity-Temperature-Depth Sensor (CTD, Seabird 19plusV2, Seabird Electronics Inc., USA), both mounted on a sturdy rosette frame. Sampling depth was from surface to ca. 10 m above the bottom, but restricted to 1000 m at maximum, only down profiles are used. Based on the LOPC data, abundance (individuals/m**3) and biovolume (mm**3/m**3) were calculated as described in the LOPC Software Operation Manual [(Anonymous, 2006), http://www.brooke-ocean.com/index.html]. LOPC data were regrouped into 49 size groups of equal log10(body volume) increments, see Edvardsen et al. (2002, doi:10.3354/meps227205). LOPC data quality was checked as described in Basedow et al. (2013, doi:10.1016/j.pocean.2012.10.005). CTD data were screened for erroneous (out of range) values and then averaged to the same frequency as the LOPC data (2 Hz). All data were processed using especially developed scripts in the python programming language. The LOPC is an optical instrument designed to count and measure particles (0.1 to 30 mm equivalent spherical diameter) in the water column, see Herman et al., (2004, doi:10.1093/plankt/fbh095). In addition to zooplankton also particles are registered by the LOPC and might contribute to the small size classes in this data set, see discussion in Espinasse et al. (in press). The size of particles as equivalent spherical diameter (ESD) was computed as described in the manual (Anonymous, 2006), and in more detail in Checkley et al. (2008, doi:10.4319/lo.2008.53.5_part_2.2123) and Gaardsted et al. (2010, doi:10.1111/j.1365-2419.2010.00558.x).
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