QC SSS, O₂ and chlorophyll surface series

Sensors in buoys are intended to run unattended for long periods of time in a harsh environment. In the upper ocean equipments are affected by the growing of marine organisms (biofouling). The sensors designed formeasurement of some variables are more robust than the sensors designed for others. All in all it is common than the reading of some sensors become unreliable after some time and it is needed to get to buoy to cleanremove the sensor for recalibration. A major plus of the AGL buoy is the monthly visit by a research vesselthe nearby hydrographical station, which allows to follow the behaviour of all sensors in detail.

Conductivity sensors (to infer salinity) had become more and more reliable in recent times. The cross-check between SSS from the buoy and the CTD are performed monthly but after years of operation it can be concluded that under normal functioning no correction of salinity is required.

Chlorophyll-fluorescence sensor is very sensitive to biofouling and uses to start drifting before the 4-monthly scheduled maintenance of the buoy and subsequent cleaning. Normally, such cleaning restores the normal functioning of the sensor. The problem enhances in spring, a period with strong biological activity. Oncesensor has started to drift the record becomes invalid and must be discarded so the chlorophyll-fluorescence record has several gaps. A new sensor provided by a bio-wiper is going to be installed together with the currently running sensor. We provide the series of raw chlorophyll-fluorescence (if available) calibrated against laboratory determined chlorophyll.

Dissolved Oxygen sensor is also problematic. This is also a optic sensors affected by biofouling andobserve frequent periods of amok behaviour that are discarded. Periods with realistic smooth variations present strong offsets that are corrected based on the winkler analysis of water samples. the