Fig. 5: Upper ocean biogeochemistry at HG-IV from upper instrument depth (~30 m).

a Logarithm of photosynthetically available radiation [μmol m⁻² s⁻¹] from hourly sensor measurements at depth (blue) and their 5-day average (black); from reanalysis at the surface reduced to 30 m depth using a constant extinction coefficient in order to make it comparable to the sensor measurements (dark yellow); and from the reanalysis value distributed over the mixed layer depth (red). b Chlorophyll a concentration [~μg l⁻¹] from chlorophyll fluorescence sensor measurements (blue); and from average of Sentinel 3 A OLCI satellite grid points within 30-km radius of mooring location (dark yellow); times when individual 1-second measurements of scattering exceeded 0.002 m⁻¹ sr⁻¹ (red diamonds) indicative of aggregation. c Apparent oxygen utilization [μmol l⁻¹] at the three measurement depths as colored in Fig. 4c. d pCO₂ [μatm] (black) and pH [] (blue); note the reversed y-axis for pH. e Inorganic nutrients [μmol l⁻¹] from water samples in 2016–2017 and from nitrate sensor in 2017–2018; nitrate (blue), silicate (magenta), phosphate (cyan), nitrite (black); negative of (N*=nitrate-phosphate*16) (red); negative of (Si*=silicate-nitrate) (green); note the different y-scale for phosphate and nitrite.