Lipid stoichiometry and biomarkers reflect microbial acclimation and nutrient stress across the Atlantic Ocean

The stoichiometry of particulate organic matter (POM) in the ocean influences global elemental cycles, but elemental distributions within macromolecule classes that comprise POM (e.g. lipids) are poorly constrained. Using publicly available datasets of lipids, nutrients, and POM stoichiometry, we conduct a basin-scale survey of lipid stoichiometry spanning the western Atlantic Ocean from ~40°S to ~55°N, and demonstrate that surface ocean lipid stoichiometry variability is primarily linked to phosphate availability and is strongly correlated with POM stoichiometry. We evaluate lipid biomarkers of nutrient scarcity, finding they are not uniformly in agreement. We then describe a lipid class, diacylglycerylcarboxyhydroxysulfocholine, only known in the coccolithophore genus Gephyrocapsa, potentially indicative of nitrogen and phosphorus stress. We advance three biomarkers of nutrient scarcity, specific to oligotrophic heterotrophic bacteria and to the coccolithophore, G. (ex Emiliania) huxleyi, and elucidate a transition from nitrogen to phosphorus stress in the Atlantic Ocean. In the surface Atlantic Ocean, microbial lipid stoichiometry is highly variable and is linked to phosphate availability. Lipid biomarkers can be used to determine where different microbial clades are experiencing resource scarcity.