Fig. 4: Trophic position of the seston sampled at surface along the Amazon River plume based on Glu and Ala relative to Phe.
From: Mixotrophy emerges as an optimal strategy in mature waters of the Amazon River plume
A δ15NPhe (phenylalanine) vs δ15NGlu (glutamic acid + glutamine) of the seston samples. B δ15NPhe (phenylalanine) vs δ15NAla (alanine) of the seston samples. All values expressed in delta notation (δ15N ‰, relative to atmospheric N2). In 2018, total particles (combined square and triangle) were collected, while in 2021, seston was separated into two size fractions (triangles for >3 µm, squares for 0.2 − 3 µm). A total of n = 46 individual samples were collected at surface in 29 stations along the Amazon River plume. Triple analytical measurements were done for each sample, with a reproducibility for individual amino acids typically better than 1‰. The gray dashed and dotted lines represent the trophoclines like in Fig. 1A, B. Colors represent the different habitats defined by Pham et al.31 ordered by apparent age: Riverine Input (RI, gray), Young Plume Core (YPC, red), Outer Plume Margin (OPM, purple), Western Plume Margin (WPM, yellow), modified Oceanic Water (MOW, cyan) and Oceanic Water (OSW, blue).
