Abstract
Abstract. The sensitivity of the biological parameters in a nutrient-phytoplankton-zooplankton-detritus (NPZD) model in the calculation of the air-sea CO2 flux, primary production and detrital export is analysed. We explore the effect on these outputs of variation in the values of the twenty parameters that control ocean ecosystem growth in a 1-D formulation of the UK Met Office HadOCC NPZD model used in GCMs. We use and compare the results from one-at-a-time and all-at-a-time perturbations performed at three sites in the EuroSITES European Ocean Observatory Network: the Central Irminger Sea (60° N 40° W), the Porcupine Abyssal Plain (49° N 16° W) and the European Station for Time series in the Ocean Canary Islands (29° N 15° W). Reasonable changes to the values of key parameters are shown to have a large effect on the calculation of the air-sea CO2 flux, primary production, and export of biological detritus to the deep ocean. Changes in the values of key parameters have a greater effect in more productive regions than in less productive areas. The most sensitive parameters are generally found to be those controlling well-established ocean ecosystem parameterisations widely used in many NPZD-type models. The air-sea CO2 flux is most influenced by variation in the parameters that control phytoplankton growth, detrital sinking and carbonate production by phytoplankton (the rain ratio). Primary production is most sensitive to the parameters that define the shape of the photosynthesis-irradiance curve. Export production is most sensitive to the parameters that control the rate of detrital sinking and the remineralisation of detritus.
Highlights
The ocean absorbs approximately 2 Pg per year of carbon from the atmosphere (Takahashi et al, 2002; Gruber et al, 2009) – around a third of current anthropogenic emissions
Phytoplankton and zooplankton mortality, undigested waste resulting from incomplete injestion of phytoplankton prey by grazing zooplankton, and excretion generate organic waste that sinks through the water column
We have shown that reasonable variation in the values of the biological parameters used in the Hadley Centre Ocean Carbon Cycle (HadOCC) NPZD ocean biogeochemistry model have a large effect on the calculation of three fundamental outputs for biogeochemical modelling and climate prediction
Summary
The ocean absorbs approximately 2 Pg per year of carbon from the atmosphere (Takahashi et al, 2002; Gruber et al, 2009) – around a third of current anthropogenic emissions. A relatively simple way of modelling this process is to use a fourcompartment Nutrient-Phytoplankton-Zooplankton-Detritus (NPZD) model Such models are widely used in GCMs due to their computational efficiency and typically contain around twenty biological parameters. Many of these parameters represent bulk properties across the whole ocean, and are poorly constrained in value (Frenette et al, 1993; Fennel et al, 2001) leading to large uncertainties in model predictions. Understanding which of these parameters have the greatest influence on model output is important to understanding model results and developing improved models
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