This dataset contains real-time total dissolved iron concentrations ((Fe(II) + Fe(III); µmol/l) acquired from the EMSO-Azores seafloor observatory TEMPO from July 2011 to March 2012 (n=1780). Data are purchased by the CHEMINI Fe (CF0), a CHEmical MINIaturized analyser dedicated to in situ determination of iron concentrations (every 12 hours, without in situ calibration, Vuillemin et al., 2009). The instrument is deployed on TEMPO part of Seamon East environmental monitoring node. The sample inlet is located on a mussel bed at the base of the Eiffel Edifice at 1695m depth.