Figure 1.
Ellet Line stations include shelf stations 1G–10G and open Atlantic Ocean stations M and F. Lines represent bathymetry and arrows represent circulation patterns of the Scottish coastal current and the North Atlantic surface water, redrawn after Ellett [51] and McKay et al. [50]. OH is the Outer Hebrides, the island chain lying to the west of the Minch.
Figure 2.
Temperature, salinity and density depth profiles and contour plots.
Depth profiles of: (a) Temperature, (b) salinity and (c) density profiles within the top 250 m of at Open Atlantic stations M and F. Contour plots of (d) water temperature [°C], (e) salinity and (f) density, for shelf stations 1G to 10G.
Figure 3.
Temperature-salinity diagram of all sampled stations.
Figure 4.
Depth profiles and contour plots of nutrients at stations M and F.
Depth profiles of: (a) dissolved inorganic phosphate (DIN), (b) silicate (DSi) and (c) nitrate (DIN) concentrations in µM within the top 250 m at stations M and F. Contour plots of (d) dissolved inorganic phosphate, (e) dissolved inorganic silicate, (f) dissolved inorganic nitrate, for shelf stations 1G to 10G.
Figure 5.
(a) N∶Si in the water column as a function of depth at all stations, (b) Chl a depth profile in mg m−3 at the two open ocean and three of the shelf stations.
Table 1.
Enumerated phytoplankton species.
Figure 6.
Depth profiles of cell densities off shelf.
Abundances of the most abundant diatoms and dinoflagellates at station M and F within the top 250 m.
Figure 7.
Contour plots of Chaetoceros and Pseudo-nitzschia on shelf.
Vertical and horizontal distribution [cells L−1] of (a) large Chaetoceros spp. (b) small Chaetoceros spp. (c) P. delicatissima group (d) P. seriata group abundance, at the shelf stations (10G to 1G).
Figure 8.
Contour plot of Lauderia annulata and Asterionellopsis glacialis on shelf.
Vertical and horizontal distribution [cells L−1] of (a) dinoflagellates < 20 µm. (b) dinoflagellates > 20 µm, (c) Lauderia annulata and (d) Asterionellopsis glacialis, at the shelf stations (10G to 1G).
Figure 9.
MDS ordinations of environmental variables.
MDS ordination of stations along the Ellett Line transect, sampled during D257. Samples above 100 m depth were included, data were fourth root transformed. (a) all stations, (b) expanded view of stations 1G, 2G, 4G, 6G, 7G, 10G.
Figure 10.
PCA ordination of environmental variables.
Principal component analysis normalized environmental data from stations along the Ellett Line transect. Parameters included are temperature, salinity, density, phosphate, silicate and nitrate from the upper 100 m of the water column. The majority (60.4%) of the variance in the data was explained by the principal component 1 (PC1), while component 2 (PC2) accounted for 36.9%, giving a total explained of variation 97.3% from these two axes alone (Table 2).
Table 2.
PCA eigenvalues.
Figure 11.
RDA correlation triplots of the relationship between phytoplankton and environmental variables.
RDA of samples taken in the upper 100 m of the water column along the Ellett Line transect. a) whole phytoplankton assemblage data b) diatom species only. Analysis was based on the relative phytoplankton abundance (standardized by norm). Sampled stations are indicated by circles, phytoplankton species and environmental variables are represented by arrows with bold typeface being used for those environmental variables that were statistically significant. Environmental abbreviations: S: salinity, T: temperature, D: density, DIN, DIP, DSi: concentrations of inorganic nitrogen, phosphorous and silicon respectively, N∶Si: the inorganic DIN∶DSi ratio. Species abbreviations: Asg, Asterionellopsis glacialis, Cb, Chaetoceros spp. > 10 µm; Cfc, Ceratium furca; Cfs, Ceratium fusus; Cho, Ceratium horridum; Co, Corethron sp.; Cs, Chaetoceros spp. < 10 µm; Cyl, Cylindrotheca closterium; Dac, Dinophysis acuta; Daf, Dactyliosolen sp.; Dam, Dinophysis acuminata; Db, Dinoflagellates > 20 µm; Dib, Ditylum brightwellii; Dis, Dictyocha speculum, Ds, Dinoflagellates < 20 µm; Ezo, Eucampia zodiacus; Gui, Guinardia striata; Lau, Lauderia borealis; Led, Leptocylindrus danicus; Mem, Meuniera membranacea; Pd, P. delicatissima group; Prm, Prorocentrum micans; Ps, P. seriata group; Tha, Thalassiosira sp.; Thn, Thalassionema nitzschoides.