Norwegian Sea Net Community Production Calculated Using O2 And CO2 Optodes on a Seaglider

Luca Possenti1, Jan Kaiser2, Matthew Humphreys2, Ingunn Skjelvan3, Socratis Loucaides4, Matthew C Mowlem5 and Liam Fernand6, (1)University of East Anglia, Environmental Science, Norwich, NR4, United Kingdom, (2)University of East Anglia, Norwich, United Kingdom, (3)Norce, Bergen, Norway, (4)National Oceanography Centre, Southampton, United Kingdom, (5)National Oceanography Centre, Southampton, Ocean Technology and Engineering Group, Southampton, United Kingdom, (6)Centre-for-Environment-Fisheries-and-Aquaculture-Science, Lowestoft, United Kingdom
The ocean carbon cycle is influenced by processes such as respiration, photosynthesis, air-sea gas exchange, vertical and horizontal mixing and CaCO3 dissolution. To resolve these processes on all relevant temporal and spatial scales, higher resolution-sampling than daily CTD casts on research cruises is needed. In this study, for the first time a CO2 optode was deployed on a Seaglider for eight months in the Norwegian Sea, together with an O2 optode and a chlorophyll fluorometer, repeating the same transect eight times. The raw CO2 optode measurements were not accurate and needed correction for drift, thermal lag and recalibration using discrete samples of total alkalinity (AT) and dissolved inorganic carbon (CT). Carbon (NCPC) and oxygen (NCPO)-based net community production were derived from the dataset.

In particular, using a salinity of 35 the data were divided between the fresh Norwegian Coastal Current and the saline Norwegian Atlantic Current. Then, the data were binned into 0.1° latitude bins to calculate the NCP through the repeat glider transects. The inventory changes were corrected for air-sea flux and entrainment to calculate NCP. NCPO and NCPC were found to agree with each other and in line with corresponding changes in the chlorophyll concentration. It was possible to identify two phytoplankton blooms at the beginning of May and June. During the first bloom, NCPO increased to 74 mmol m-2 d-1 and NCPC to 17 mmol m-2 d-1. During the second bloom, NCPO increased to 178 mmol m-2 d-1 and NCPC to 90 mmol m-2 d-1. Moreover, during all of summer the surface water was oversaturated with O2 creating a continuous mean flux to the atmosphere of 19 mmol m-2 d-1 and making it the main driver for NCPO changes. In contrast, in the case of carbon the Norwegian Sea took up 3 mmol m-2 d-1 of CO2 during all of summer and the NCPC changes were mainly driven by the inventory.