Simultaneous assessment of oxygen-and nitrate-based net community production in a temperate shelf sea from a single ocean glider

Abstract

The continental shelf seas are important at a global scale for ecosystem services. These highly dynamic regions are under a wide range of stresses, and as such future management requires appropriate monitoring measures. A key metric to understanding and predicting future change are the rates of biological production. We present here the use of an autonomous underwater glider with an oxygen (O2) and a wet-chemical microfluidic total oxidised nitrogen (NOx-NO3-+NO2-) sensor during a spring bloom as part of a 2019 pilot autonomous shelf sea monitoring study. We find exceptionally high rates of net community production using both O2 and NOx-water column inventory changes, corrected for air-sea gas exchange in case of O2. We compare these rates with 2007 and 2008 mooring observations finding similar rates of NOx-consumption. With these complementary methods we determine the O2:N amount ratio of the newly produced organic matter (7.8g±0.4) and the overall O2:N ratio for the total water column (5.7g±0.4). The former is close to the canonical Redfield O2:N ratio of 8.6g±1.0, whereas the latter may be explained by a combination of new organic matter production and preferential remineralisation of more reduced organic matter at a higher O2:N ratio below the euphotic zone.