Diverse arsenic‐containing lipids in the surface ocean

Arsenic is present at nanomolar levels throughout the ocean, and microbes assimilate this potentially toxic element due to its similarity to inorganic phosphorus. Although dissolved arsenic has been a focus of several oceanographic studies, the size and chemical character of the particulate arsenic pool is poorly understood. We measured particulate arsenic in five samples from the open ocean and determined the contribution of arsenic‐containing lipids to this pool. Here we show that the accumulation of arsenic into lipids is a widespread phenomenon in the surface ocean. Particulate arsenic concentrations were 15–42 pmol L −1 with 7–20% of the particulate arsenic pool within arsenolipids. We found that arsenosugar phospholipids dominated the arsenolipid pools in our samples with a minor component of arsenohydrocarbons and other unidentified lipids. A significant portion of the arsenosugar phospholipids (up to 35%) was present as previously undescribed mixed acyl ether lipids, suggesting a bacterial source.