DOI: 10.5285/69eb8320-9d2b-4cc1-818a-83d14c15c491
title: Epi- and mesopelagic mesozooplankton depth-discrete distribution and abundance between Greenland and Svalbard (2018 and 2019)

description: Mesozooplankton were collected with a MOCNESS net system during the oceanographic cruise JR17005 (May and June 2018) and JR18007 (August 2019). The MOCNESS comprised 9 separate nets which opened in sequence such that the closing of one net opened the next; net 1 was open during the descent of the net to its maximum depth (about 1000 m) while the remaining 8 depths opened at regular intervals during the reascent to the surface. Catches were immediately preserved in 4 percent buffered formaldehyde after division by a Folsom splitter into either 0.5 or 0.25 fractions. Identification of taxa was performed by Continuous Plankton Recorder survey analysts at the Marine Biological Association UK, led by Marianne Wootton. Specimens were categorised to the lowest possible taxonomic level, which, in some cases, encompassed developmental stages but, in other cases, was limited to higher order taxa. Each taxa was enumerated to determine abundance with the preserved fraction of the catch. These were scaled up to the whole catch and divided by the volume filtered of the respective net to determine abundance in units of individuals m-3. These values were also multiplied by the sampled depth interval to derive the alternative unit of individuals m-2. The samples from three net deployments were analysed from both JR17005 and JR18005 in approximately matching locations between Greenland and Svalbard, encompassing the Fram Strait. The dataset allows examination of the distribution and abundance of these species across the region in two separate years, with the first year covering early summer and the second year, late summer.

Financial support for was provided by Changing Arctic Ocean (CAO) Programme DIAPOD, funded by UKRI Natural Environment Research Council (NERC; NE/P006213/1, NE/P006353/1, NE/P006302/1, NE/P006183/1,and NE/P005985/1, amongst others), and by CAO Project
CHASE, jointly funded by NERC (NE/R012733/1) and the German Federal Ministry of Education and Research (BMBF; 03F0803A).
description: Data were gathered during two oceanographic cruises (JR17005, JR18007) aboard the RRS James Clark Ross to the region between Greenland and Svalbard, encompassing the Fram Strait. The cruises took place between 8/5/2018 to 8/6/2018 (JR17005) and 4/8/2019 to 29/8/2019 (JR18007). Depth discrete mesozooplankton samples to a maximum depth of about 1000 m were collected by a MOCNESS net system (1m2 opening area, 330 µm meshes) at a number of locations in the region, of which three were analysed for the present dataset. The MOCNESS comprised 9 separate nets which opened in sequence such that the closing of one net opened the next; net 1 was open during the descent of the net to its maximum depth (about 1000 m) while the remaining 8 depths opened at regular intervals (about every 125 m) during the reascent to the surface (minimum depth 5m). The exception was Event 18 on JR17005 where the maximum depth was 1200 m and depth interval, 150 m. Samples were split by a Folsom splitter and the subsequent fractions preserved. Either 0.5 or 0.25 of the sample was preserved in buffered 4 % formalin while another fraction was preserved in 96 % ethanol. Taxa were identified in the formalin preserved samples through examination by light microscopy by analysts at the Marine Biological Association UK, led by Marianne Wootton. Note that net 1 (0-1000 m) was not considered for taxonomic analysis. The abundance of each taxa within a sample was determined through examining a known fraction of the sample and then making an inverse multiplication of that fraction. Volumetric abundances (individuals m-3) were determined through dividing sample abundance by the volume of water sampled by the respective net. Net volume was mainly derived through a calibrated flow meter or, if that failed, through multiplying the net opening diameter by average speed of the vessel during hauling. This calculation assumes 100% net sampling efficiency and no avoidance. Values in units of individuals m-2 were also calculated through multiplying volumetric abundances by the respective depth interval (in m).

Contributions: Bj∅rg Apeland, Gareth Flint and Carwyn Davies serviced and helped to operate the MOCNESS net. Geraint Tarling, Dan Mayor, Florence Atherden, Holly Jenkins, Claudia Castellani, Anna Belcher, Jennifer Freer, Jordan Grigor, Gabi Stowasser, Aidan Hunter, David Conway and David Pond helped in deploying the net and preserving the samples. Taxonomic analyses were performed by Continuous Plankton Survey analysts at the Marine Biological Association, UK led by Marianne Wootton. Geraint Tarling, Katy Buckland, Amena Boyd and Petra ten Hoopen prepared the data for publication. Geraint Tarling wrote the metadata.
description: 1. A MOCNESS net system (1m2 mouth diameter, 330um meshes) 
2. Sample splitting apparatus (Folsom splitter)
3. Binocular light microscope
description: All species were identified according to the taxonomic guides available at time of analysis and the user must be aware that some species names may have since been updated.

The value 0 represents an instance where the taxon was actively looked for but no specimens were present in the sample.