High-resolution net and gross biological production during a Celtic Sea spring bloom

摘要

Shelf seas represent only 10% of the ocean area, but support up to 30% of all oceanic primary production. There are few measurements of shelf-sea biological production at high spatial and temporal resolution in such heterogeneous and physically dynamic systems. Here, we use dissolved oxygen-to-argon (O-2/Ar) ratios and oxygen triple isotopes (O-16, O-17, O-18) to estimate net and gross biological production in the Celtic Sea during spring 2015. O-2/Ar ratios were measured continuously using a shipboard membrane inlet mass spectrometer (MIMS). Additional discrete water samples from CTD hydrocasts were used to measure O-2/Ar depth profiles and the delta(O-17) and delta(O-18) values of dissolved O-2. These high-resolution data were combined with wind-speed based gas exchange parameterisations to calculate biologically driven air-sea oxygen fluxes. After correction for disequilibrium terms and diapycnal diffusion, these fluxes yielded estimates of net community (N(O-2/Ar)) and gross O-2 production (G(O-17)). N(O-2/Ar) was spatially heterogeneous and showed predominantly autotrophic conditions, with an average of (33 +/- 41) mmol m(-2) d(-1). G(17O) showed high variability between 0 and 424 mmol m(-2) d(-1). The ratio of N(O-2/Ar) to G(O-17),f(O-2), was (0.18 +/- 0.03) corresponding to 0.34 +/- 0.06 in carbon equivalents. We also observed rapid temporal changes in N(O-2/Ar), e.g. an increase of 80 mmol m(-2) d(-1) in <6 h during the spring bloom, highlighting the importance of high-resolution biological production measurements. Such measurements will help reconcile the differences between satellite and in situ productivity observations, and improve our understanding of the biological carbon pump.