Norwegian Sea net community production estimated from O2 and prototype CO2 optode measurements on a Seaglider.

We report on a pilot study using a CO[sub 2] optode deployed on a Seaglider in the Norwegian Sea for 8 months (March to October 2014). The optode measurements required drift- and lag-correction, and in situ calibration using discrete water samples collected in the vicinity. We found the optode signal correlated better with the concentration of CO[sub 2], 푐(CO[sub 2]), than with its partial pressure, 푝(CO[sub 2]). Using the calibrated 푐(CO[sub 2]) and a regional parameterisation of total alkalinity (퐴[sub T]) as a function of temperature and salinity, we calculated total dissolved inorganic carbon concentrations, 퐶[sub T], which had a standard deviation of 10 µmol kg[sup -1] compared with direct 퐶[sub T] measurements. The glider was also equipped with an oxygen (O[sub 2]) optode. The O[sub 2] optode was drift-corrected and calibrated using a 푐(O[sub 2]) climatology for deep samples (푅[sup 2] = 0.89; RMSE = 0.009 µmol kg[sup -1]). The calibrated data enabled the calculation of C[sub T] - and oxygen-based net community production, 푁(퐶[sub T]) and 푁(O[sub 2]). To derive 푁, C[sub T] and O[sub 2] inventory changes over time were combined with estimates of air-sea gas exchange and entrainment of deeper waters. Glider-based observations captured two periods of increased Chl a inventory in late spring (May) and a second one in summer (June). For the May period, we found 푁(C[sub T]) = (24±5) mmol m[sup -2] d[sup -1], 푁(O[sub 2]) = (61±14) mmol m[sup -2] d[sup -1] and an (uncalibrated) Chl 푎 peak concentration of craw(Chl 푎) = 3 mg m[sup -3]. During the June period, craw(Chl 푎) increased to a summer maximum of 4 mg m[sup -3], which drove 푁(퐶[sub T) to (64±67) mmol [sup -2] d[sup -1] and 푁(O[sub 2]) to (166±75) mmol m[sup -2] d[sup -1]. The high-resolution dataset allowed for quantification of the changes in 푁 before, during and after the periods of increased Chl 푎 inventory. After the May period, the remineralisation of the material produced during the period of increased Chl 푎 inventory decreased 푁(퐶[sub T) to (- 80±107) mmol [sup -2] d[sup -1] and 푁(O[sub 2]) to (–15±27) mmol [sup -2] d[sup -1]. The survey area was a source of O[sub 2] and a sink of CO[sub 2] for most of the summer. The deployment captured two different surface waters: the Norwegian Atlantic Current (NwAC) and the Norwegian Coastal Current (NCC). The NCC was characterised by lower 푐(O[sub 2]) and 퐶[sub T] than the NwAC, as well as lower 푁(O[sub 2]), 푁(퐶[sub T]) and craw(Chl 푎). Our results show the potential of glider data to simultaneously capture time and depth-resolved variability in 퐶[sub T] and O[sub 2]. [ABSTRACT FROM AUTHOR]