This dataset contains measurements of dissolved nitrate, phosphate and silica during two deployments, each lasting several weeks each at the OBSEA observatory during 2022 and 2023.

Three prototype lab on chip in situ chemical analysers developed at the National Oceanography Centre, UK, were deployed at the site during summer 2022 and summer 2023.

The nitrate sensor uses the Griess colorimetric assay and a copperised cadmium column to measure dissolved nitrate (and nitrite). Each sample measurement was calibrated by measuring onboard calibration standards prepared in artificial seawater with a salinity of 35. A blank solution and a standard solution containing 10 µmol / L of potassium nitrate were measured immediately prior to each sample measurement. Nitrate data is available between 2022-06-16 and 2022-07-06. Sample measurements were made every 2 hours initially, but this was decreased to once every 4 hours from 2022-06-30.

The phosphate sensor uses a colorimetric assay based on the Molybdenum Blue method. Each sample measurement was calibrated by measuring onboard calibration standards prepared in artificial seawater with a salinity of 35. A blank solution and two standard solutions containing 0.5 µmol / L and 2 µmol / L of potassium dihydrogen phosphate were measured immediately prior to each sample measurement. Phosphate data is available between 2022-06-16 and 2022-07-05, with a sampling frequency of every 2 hours (decreasing to every 4 hours from 2022-06-30), and between 2023-07-21 and 2023-09-12, with a sampling frequency of every 12 hours.

The dissolved silica sensor uses a colorimetric assay also based on the Molybdenum Blue method. Each sample measurement was calibrated by measuring onboard calibration standards prepared in artificial seawater with a salinity of 35. A blank solution and two standard solutions containing 5 µmol / L and 15 µmol / L of sodium hexafluorosilicate were measured immediately prior to each sample measurement. Dissolved silica data is available between 2023-07-21 and 2023-08-12, with a sampling frequency of every 6 hours.

Timestamps in the datafiles are in UTC and concentration units are µmol / L.

This work was made possible by a TNA from the JERICO-S3  project funded by the European Commission – H2020 Framework Programme (grant agreement No.871153).