Quantifying pelagic primary production and respiration via an automated in-situ incubation system

Abstract

Pelagic photosynthesis and respiration serve critical roles in controlling the dissolved oxygen concentration (DO) in seawater. The consumption and production via pelagic primary production are of particular importance in surface ocean and in shallow aquatic ecosystems where photosynthetically active radiation (PAR) is abundant. However, the dynamic nature and large degree of heterogeneity in these ecosystems pose substantial challenges for providing accurate estimates of marine primary production and metabolic state. The resulting lack of data in these systems hinders efforts in scaling and including primary production in predictive models. To bridge the gap, we developed and validated a novel automated water incubator that measures in-situ rates of photosynthesis and respiration. The automated water incubation system uses commercially available optodes and microcontrollers to record continuous measurements of DO within a closed chamber at desired intervals. With fast response optodes, the incubation system produced measurements of photosynthesis and respiration with hourly resolution, resolving diel signals in the water column. The high temporal resolution of the timeseries also enabled the development of Monte-Carlo simulation as a new data analysis technique to calculate DO fluxes, with improved performance in noisy timeseries. Deployment of the incubator was conducted near Ucantena Island, Massachusetts, USA. The data captured diel fluctuations in metabolic fluxes with hourly resolution, allowed for a more accurate correlation between oxygen cycling and environmental conditions, and provided improved characterization of the pelagic metabolic state.