Abstract
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 (7.8 ± 0.4) and the overall O2:N ratio for the total water column (5.7 ± 0.4). The former is close to the canonical Redfield O2:N ratio of 8.6 ± 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.
Highlights
The coastal shelf seas are a vitally important human resource for numerous ecosystem services, including food, carbon storage, biodiversity, energy, and livelihoods (Halpern et al, 2015)
The Seaglider reached the transect on March 2019 at 04:00 UTC (Fig. 1), at which point the water column was weakly stratified, with the base of the surface mixed layer at m and a 0.03 ◦C temperature difference across the thermocline (Fig. 2b)
While the bottom mixed layer (BML) oxygen concentrations on the eastern side of the transect were 3 to 5 mmol m−3 higher than elsewhere, the saturation is similar throughout, which indicates that the increased oxygen concentration was mostly due to higher solubility at lower temperatures
Summary
The coastal shelf seas are a vitally important human resource for numerous ecosystem services, including food, carbon storage, biodiversity, energy, and livelihoods (Halpern et al, 2015) They have a disproportionately large impact, relative to their surface area, on global carbon cycling (Thomas, 2004) as shelf seas provide 10 %–30 % of all marine primary production while comprising less than 10 % of the ocean surface (Harris et al, 2014; Sharples et al, 2019). The northern boundary is facing the North Atlantic It can be divided into two energetically distinct regimes: a seasonally stratifying northern part and a fully mixed southern and coastal part (Emeis et al, 2015). A more recent synthesis of Kitidis et al (2019) indicates that the seasonally stratified regions were a source of CO2 during December and January in 2015
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