The autonomous clean environmental (ACE) sampler: a trace-metal-clean seawater sampler suitable for open-oceantime-series applications

The fundamental role of the micronutrient Fe in controlling phytoplankton growth in large parts of Earth's oceans and a lack of information on seasonal transitions in remote regions motivated us to create an autonomous water sampler capable of collecting uncontaminated open‐ocean seawater samples with monthly resolution over a full annual cycle. Phytoplankton are at the base of the food chain, which take up carbon dioxide through photosynthesis. Assessing Fe availability is essential to understanding both ocean productivity and our climate. This need is particularly important in the Southern Ocean, where Fe limitation is wide spread and access is difficult especially in winter. To address this need, we have developed an autonomous system capable of observing iron concentrations over a full seasonal cycle, at the subnanomolar concentrations that are important in the open ocean. The automated clean environmental sampler has been developed initially for 1‐yr deployments on oceanographic moorings. Twelve samples per unit can be programmed to collect 65 mL of seawater through a noncontaminating, primarily Teflon sample path. The system is vaned to maintain its intake tubes in upstream water and has been tested to 100 m depth. The system was deployed during a GEOTRACES section (SR3 line, GS01) in 2018 alongside an industry standard, trace metal clean rosette, and no significant difference was found in Fe concentrations in the 50 pmol L^–1 range, proving its capability at collecting uncontaminated seawater samples in the open ocean at temperatures above 0°C.