-Nutrient data

°Water samples were collected with Niskin bottles. Subsamples (10 mL) for nutrients were filtered through 0.45 µm filters (Q-Max GPF syringe filters) and directly frozen at -20 °C until analysis. Nutrients were measured using standard colorimetric methods on a Seal QuAAtro autoanalyzer (Skalar, type SA 400).

°NH4 [µmol/L], NO2 [µmol/L], NO3 [µmol/L], NOX [µmol/L], PO4 [µmol/L] and DSi [µmol/L]

-Chlorophyll a data

°Water samples were collected with Niskin bottles. Water samples (0.5 L) were filtered through 25 mm GF/F filters (Whatman, nominal pore size 0.7 µm) for chlorophyll-a analysis. Filters were placed in 10 mL in a mixture of 90% acetone and 10% dimethylsulfoxide (Shoaf and Lium 1976). Extracts were measured on a scanning spectrophotometer (Varian Cary BIO-100, Palo Alto) and chlorophyll a was calculated from absorbance following Ritchie (2006).

°Chlorophyll a [µg/L] concentration

-Fatty acid profiles

 °Samples from a 50 µm MultiNet of the entire water column were stored for 5 - 6 h in a refrigerator for the plankton to release their gut content, allowing identification of the FA profile of the zooplankton and not their gut content. The microzooplankton fraction (50 - 200 µm) was separated from the mesozooplankton fraction (>200 µm) by sieving, and at certain stations an extra MultiNet was taken to pick out 50 specimens of the dominant species. Samples were stored in a -80 °C freezer until further analysis. FA methyl esters (FAMEs) were prepared from freeze-dried samples using a direct transesterification procedure with 2.5 % (v : v) sulfuric acid in methanol as described by De Troch et al. (2012). The FAMEs were subsequently extracted with hexane. FA composition analysis was carried out with a gas chromatograph (GC; HP 7890B, Agilent Technologies, Diegem, Belgium) equipped with a flame ionization detector (FID) and connected to an Agilent 5977A Mass Selective Detector (MSD; Agilent Technologies, Diegem, Belgium). The GC was further equipped with a PTV injector (CIS-4, Gerstel, Mülheim an der Ruhr, Germany). An HP88 fused-silica capillary column (60 m × 0.25 mm × 0.20 µm film thickness, Agilent Technologies) was used at a constant helium flow rate (2 ml min−1). The injected sample (2 µl, split ratio 1:10) was split equally between the MS and FID at the end of the GC column using an Agilent Capillary Flow Technology Splitter. The oven temperature programme was as follows: at the time of sample injection the column temperature was 50 °C for 2 min, then gradually increased at 30 °C/min to 150 °C, followed by a second increase at 2 °C/min to 230 °C. The injection volume was 2 μL. The injector temperature was held at 250 °C. The transfer line for the column was maintained at 250 °C. The quadrupole and ion source temperatures were 150 and 230 °C, respectively. Mass spectra were recorded at 70 eV ionization voltage over the mass range of 50 - 550 m/z units.

°Fatty acid relative abundance [%]

-Phytoplankton identifications and counts

°Phytoplankton samples were collected by hauling 50 L of surface water with a bucket from the rear deck of the vessel and pouring it through a 20 µm Apstein net. The samples were fixed with Lugol (5 % final concentration) and stored in cold (4 °C) and dark conditions. In transit, four samples leaked to become unusable (EF1, EF12, EF18 and EF35) and all samples reached room temperature which reduced the quality of the phytoplankton sample. In the lab, samples were processed with a FlowCAM VS-4 (Fluid Imaging Technologies, Yarmouth, Maine, U.S.A.). Each sample was processed twice: once with the 300 µm deep flow cell, the 4X objective and the 5 mL syringe pump, and once with the 100 µm deep flow cell, the 10X objective and the 1 mL syringe pump.

°Count [ind]

° It should be noted that some samples leaked during transport and it therefore is advised to calculate and work with relative abundances instead of absolute abundances. 

- Zooplankton identifications (microscopy) of MultiNet samples

°Zooplankton samples were collected with a MultiNet mini (Hydrobios), which was deployed vertically at a speed of 0.4 m/s and was equipped with a flowmeter. During the cruise one net broke resulting in only four nets and thus only four intervals in the remainder of the cruise. Samples were fixated in a 4 % borax-buffered formaldehyde solution. The samples were sent to the Polar Agency in Poland for microscopic identification, counting and measuring at species or genera, stage and sex level.  The length of maximum 10 individuals per species were measured, represented in L1 until L10.

°Total [ind] in net, abundance [ind/m3], L1 - L10 [µm] length measurements of individuals. 

- Zooplankton identifications of the Video Plankton Recorder data

°Zooplankton was sampled by means of a Real Time Video Plankton Recorder (VPR, Seascan, Inc.). The VPR was deployed for approximately 1.5 hours at each station, while it was vertically lowered and raised through the water column at a speed of 0.2 m/s. During deployment the VPR stayed 3 m from the surface and sea bottom to avoid hitting the vessel or seafloor. Maximum depth of the VPR was around 250 m, limited by the length of the winch cable. On station EF01 - EF12, the VPR undulated between surface and as deep as possible whereas on station EF15 - EF47 the VPR made two undulations as deep as possible followed by undulations in the top 50 m layer as most of the zooplankton was observed there. The imaged volume of every VPR frame was 335.622 mL which was computed as the field of view (magnification setting S3: 46.5 x 34.5 mm) multiplied by focal depth. This latter was determined by the parameters used with the VPR AutoDeck software: a segmentation threshold – low of 0, a segmentation threshold – high of 132, a focus – sobel of 45 and a focus – std dev of 0. The lowest magnification, S3, was chosen due to the large size of the plankton. Simultaneously, fluorescence, turbidity, salinity, temperature and depth data was collected with the ECO Puck FLNTU fluorometer and turbidity sensor (WETLabs) and SBE 49 CTD sensor (Sea-Bird Electronics, Inc.) that was mounted on the VPR, allowing to link plankton images with in situ environmental and position data at the moment of collection.

°Species, Temperature [°C], Chlorophyll concentration [µg/L], Depth [m], Salinity [PSU] and Turbidity [NTU]