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 the global carbon, nitrogen, and phosphorus cycles, but elemental distributions within macromolecule classes are not well constrained. Using publicly available datasets of lipid abundances, nutrient concentrations, and POM stoichiometry, we conduct the first basin-scale survey of lipid stoichiometry along a north-south transect spanning the western Atlantic Ocean from ~ 40°S to ~ 55°N, and demonstrate that surface ocean lipid stoichiometry is highly variable, is primarily linked to phosphate (P) availability, and is strongly correlated with POM stoichiometry. We evaluate lipid biomarkers of microbial nutrient stress and find they are not uniformly in agreement (i.e. some indicate P-stress in regions where others do not). To that end, we describe a novel polar lipid class, diacylglycerylcarboxyhydroxysulfocholine, thus far detected only in the coccolithophore genus Gephyrocapsa , potentially indicative of nitrogen (N) and phosphorus stress. We also advance three new biomarkers of nutrient stress, specific to oligotrophic heterotrophic bacteria and to the globally significant coccolithophore, G. (ex Emiliania) huxleyi . We find they effectively elucidate a transition from proximal N- to P-stress in the Atlantic Ocean.