Fig. 4: Mixed-layer-integrated concentrations of selected biomarker lipids.

Concentrations of individual lipids representative of different microbial groups integrated over the surface mixed layer in samples collected in and around a cyclonic eddy off Mauritania. a chlorophyll a (Chl a) as biomarker for oxygenic photosynthetic organisms, b–d polyunsaturated fatty acid-containing intact polar and energy storage lipids indicative of eukaryotic algae, e, f a monounsaturated glycolipid (MGDG) and the carotenoid pigment zeaxanthin indicative of cyanobacteria, g divinyl (DV) Chl a diagnostic for Prochlorococcus, h a monounsaturated phospholipid (PG) indicative of heterotrophic bacteria, i a menaquinone (MK) indicative of gram-positive bacteria, j an intact Crenarchaeol diagnostic for Nitrososphaerota, k a carotenoid pigment (Hex-kfuco) indicative of haptophytes, and l a ubiquinone (UQ) as generic biomarker for aerobic respiration. The black circle indicates the eddy core and dashed line indicates potential edge of the eddy-influenced area (eddy periphery). For interpolation between data points, weighted-average gridding was used, which is integrated in Ocean Data View¹⁰³. MGDG monogalactosyldiacylglycerol, PC phosphatidylcholine, PE phosphatidylethanolamine, TAG triacylglycerol, 1G monohexose, Hex-kfuco 19’Hexanoyloxy-4-ketofucoxanthin. Nomenclature of lipids: For intact polar diacylglycerol lipids and triacylglycerols the sum composition of acyl double bonds and acyl carbon atoms in each compound is provided as C a:b, where C indicates the lipid group, a the number of acyl carbons and b the number of acyl double bonds. For respiratory quinones, the nomenclature after Elling et al.¹⁰⁴ is used (Q_m:n) where Q indicates head group type, m the number of isoprenoid units in the side chain and n the number of double bonds.