Fig 1.
Map showing the location of a) main currents: the Norwegian Coastal Current (blue arrow) and the Norwegian Atlantic Current (red arrow) and Runde Island in the western coast of Norway (red square). b) Map showing the location of the mooring buoy and the survey area. c) Detailed map showing the area where the AUV missions were conducted (box A and B), and stations where shipboard deployments of in-situ sensors and discrete seawater and net samples were collected. d) Scheme showing several sampling approaches: 1) AUV surveys, 2) in-situ profile of the Silcam for particle imaging and fluorometer for photo-physiological measurements, 3) CTD casts and discrete seawater sampling, 4) zooplankton net tows and 5) time-series of temperature, salinity and wind speed retrieved from the mooring buoy (figure was modified from Fossum et al. (2019)).
Table 1.
Different observational platforms used in this study, their sampling location and time of collection: 1) AUV missions, 2) shipboard measurements, including vertical in-situ profiles of imaging (Silcam) and optical sensors (FRRf), in addition to traditional seawater and net sampling and 3) mooring buoy with sensors equipped for wind speed and conductivity (salinity) and temperature at 1, 20, 40, and 80 m depth.
Fig 2.
Collages of particle images collected from the upper 20 m of a) stations 1 & 2 using the high magnification lens and b) stations 4&5 with a low magnification lens. Note the presence of several species of Tripos in a) and copepods and fecal pellets in b).
Table 2.
List of measured variables, their symbology and unit measurement.
Fig 3.
Time-series of a) salinity, b) temperature (°C) from 2, 20, 40 and 80 m and c) wind speed (m s-1) collected every 10 minutes from the 1st March until 1st August 2017 and d) zoomed from 15th June– 25th June. Note the period of intense mixing in mid-June (arrows and boxes), which coincides with the time of field sampling: 19th and 20th June (blue arrows in a, b and red and green boxes in c,d).
Fig 4.
(a,b) Tri-dimensional in-situ profiling of AUV-derived chlorophyll a fluorescence (FChlaAUV, mg m-3). c,d) Vertical distributions of FChlaAUV (mg m-3, red line), temperature (°C, black line) and salinity (blue line) derived from AUV from the two survey areas (A-left and B-right, see survey areas in Fig 1C). Shipboard vertical profile of e) temperature (°C) and f) salinity from stations 1–5 with distinct mixed layer depth (30 m at stations 3, 4 and 5 and 50 m at stations 1 and 2). Note the dashed box in c,d showing the highest values of FChlaAUV and the black lines in e,f showing the depth of the mixing layer from each station.
Fig 5.
Mean vertical concentrations of a) ammonia, b) nitrate, c) phosphate and d) silicate (μM) from stations where the mixed layer depth was deep (50 m, grey) and shallow (30 m, pink).
Fig 6.
Ciliates, phytoplankton and meso-zooplankton abundances.
Average abundance (from traditional microscopy) of a) ciliates, b) the diatom Proboscia spp. c) the dinoflagellate Tripos spp., d) other flagellates and e) meso-zooplankton groups. Colors represent pooled stations from offshore (1 and 2, grey) and inshore (3–5, pink). Other flagellates here refer to cryptophytes, dinoflagellates (other than Tripos spp.) and unidentified flagellates (see Materials and Methods).
Fig 7.
a) Abundance of particles identified mostly as a) Tripos spp. (×103 cell L-1), b) fecal pellets and c) copepods (ind m-3) derived from the Silcam algorithms and human inspection. The scatterplots with the size spectra of particles imaged per depth interval (1–20 m, 20–40 m and 40–60 m) from the high (red) and low (blue) magnification lenses that most likely represents Tripos spp. (100–160 μm), fecal pellets (400–600μm) and copepods (800–1200μm) are shown in S1 and S2 Figs. Asterisks in b) and c) represent lack of data due to technical problems.
Fig 8.
Vertical measurements of a) in-situ FRRf-derived (FChlaFRRf, thin dots and in-vitro chlorophyll (Chlain-vitro, thick dots), b) diffuse light attenuation coefficient (kd), c) Photosystem II efficiency under ambient light (φPII’, dimensionless), d) absorption cross-section of PII photochemistry under ambient light (σPII’, nm2 PSII-1), e) photochemical flux through each open reaction center (JPII, electrons PSII-1 s-1) and f) scatterplot of relative electron transport rate (rETR) versus irradiance (EPAR) derived from the FRRf measurements from pooled stations from areas with deeper mixed layer depth (MLD) (50 m, grey) and shallower MLD (30 m, pink).