Primary productivity estimates derived from ocean gliders in situ sensors and photosynthetically available radiation (PAR) estimates from in situ and satellite data in the North Sea, November 2017-May 2019 (version 2).

As part of the Alternative Framework to Assess Marine Ecosystem Functioning in Shelf Seas (AlterECO) project (NERC grant reference NE/P013902/1), Seagliders and Slocum gliders were deployed in a physically dynamic region of the North Sea, known to undergo seasonal oxygen depletion, between November 2017 and May 2019. These deployments are part of an 18 month observational programme using marine autonomous vehicles. During each deployment the gliders tracked repeat North-South or East-West transects close to Dogger Bank. Each glider carried a standard CTD package measuring temperature and water conductivity (salinity) and an oxygen optode sensor with additional sensors such as downwelling PAR and optical sensors for chlorophyll fluorescence and backscatter deployed for some missions. For glider deployments carrying an in situ downwelling PAR sensor, primary productivity is calculated. Primary productivity is also calculated for all glider deployments using Earth observation-based PAR derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) daily product. Estimates of primary productivity are calculated from glider deployments carrying optical sensors for chlorophyll fluorescence, using the method described in Loveday et al. (2022), a modification of that presented in Hemsley et al. (2015). The Morel (1991) model calculates net primary production (NPP) at regularly spaced depth intervals from the surface to the euphotic depth. In the previous version of the dataset, the depth integrated NPP was calculated from this regularly spaced data. The regularly spaced NPP data was then linearly interpolated onto the glider depths on a dive-by-dive basis. This approach gave rise to two issues. Firstly, due to the effects of the interpolation, it was not previously possible to recreate the depth integrated NPP estimates from the NPP values at glider depth intervals. Secondly, in occasional cases where the euphotic depth was greater than the glider dive depth, the integrated value was artificially high. These issues are corrected in the new version. The integration depth is now truncated at the maximum glider depth, and not the euphotic depth. The interpolated NPP values are now scaled such that they match the depth integrated value, more accurately reflecting the results of the Morel (1991) model. The variables in each file consist of; corrected in situ PAR, quenching corrected chlorophyll, mixed layer depth, euphotic depth, depth resolved estimates of primary productivity and depth integrated primary productivity. The chlorophyll fluorescence and PAR data are recorded at a lower sampling frequency when compared to the CTD sensor. Therefore, chlorophyll and PAR data values have been linearly interpolated onto the depth record time base. During the 3-year programme, and by developing and implementing a novel monitoring framework, AlterEco aims to deliver an improved spatio-temporal understanding of shelf sea function and provide measurements of critical indicators of marine ecosystem health over seasonal timescales.