Understanding the stability of the ECOPuck optical sensor: evaluation of long-term ocean glider data streams across decades

Over 16 years, Australia’s Integrated Marine Observing System (IMOS) Ocean Glider program has collected high-resolution optical sensor data (scatter, chlorophyll-a (Chl)) and colored dissolved organic matter (CDOM) fluorescence) across 400+ missions. While these data are consistent within a mission, end users require assurance of dataset comparability over numerous missions and years. To understand sensor data stability, we compared ECOPuck scale factors (SFs) following calibrations and between instruments of the same model. We also examined variability in the fluorescent response of different phytoplankton species and the effect on Chl estimates. Finally, we compared matchups between ECOPuck fluorescence and Chl bottle samples. We found that SFs for Chl were stable and highly comparable over different missions and sensors, changing < 9% following calibration and <15% between instruments of the same model. SFs for scatter and CDOM following calibration for most sensors were also stable (changing <8%) but showed variability between sensors of the same model (generally <18%, but reaching 35%). We found large variations in the fluorescent response of different phytoplankton species compared to the factory-provided Chl SF (from a centric diatom species), indicating that in situ phytoplankton community composition may affect Chl estimates from fluorescence. Finally, we found that ECOPuck data overestimates in situ Chl by 1.1–2.9 times. Overall, our results indicate that Chl estimates between instruments of the same model are comparable. This significant finding provides researchers with confidence to unlock the treasure trove of IMOS glider data via ‘big data’ analyses and build vital regional oceanographic climatologies.