Abstract
Abstract. Treatment of the underwater light field in ocean biogeochemical models has been attracting increasing interest, with some models moving towards more complex parameterisations. We conduct a simple sensitivity study of a typical, highly simplified parameterisation. In our study, we vary the phytoplankton light attenuation parameter over a range constrained by data during both pre-industrial equilibrated and future climate scenario RCP8.5. In equilibrium, lower light attenuation parameters (weaker self-shading) shift net primary production (NPP) towards the high latitudes, while higher values of light attenuation (stronger shelf-shading) shift NPP towards the low latitudes. Climate forcing magnifies this relationship through changes in the distribution of nutrients both within and between ocean regions. Where and how NPP responds to climate forcing can determine the magnitude and sign of global NPP trends in this high CO2 future scenario. Ocean oxygen is particularly sensitive to parameter choice. Under higher CO2 concentrations, two simulations establish a strong biogeochemical feedback between the Southern Ocean and low-latitude Pacific that highlights the potential for regional teleconnection. Our simulations serve as a reminder that shifts in fundamental properties (e.g. light attenuation by phytoplankton) over deep time have the potential to alter global biogeochemistry.
Highlights
Treatment of marine light availability for photosynthesis in biogeochemical compartments of ocean general circulation models (OGCMs) has largely avoided careful scrutiny until recently (e.g. Dutkiewicz et al, 2015; Kim et al, 2015; Gregg and Rousseaux, 2016)
Patterns of equilibrated net primary production (NPP) in the UVic ESCM are sensitive to kc within the tested range
Our study demonstrates the importance of considering transient model behaviour in both parameter estimation and estimates of uncertainties for biogeochemistry in OGCMs and earth system models (ESMs)
Summary
Treatment of marine light availability for photosynthesis in biogeochemical compartments of ocean general circulation models (OGCMs) has largely avoided careful scrutiny until recently (e.g. Dutkiewicz et al, 2015; Kim et al, 2015; Gregg and Rousseaux, 2016). Dutkiewicz et al, 2015; Kim et al, 2015; Gregg and Rousseaux, 2016) These models typically use simplified, empirically based parameterisations of phytoplankton growth rates related to photosynthetically available radiation (PAR) based on the state of the science in the 1970s and 1980s. (Schmittner et al, 2005; Kirk, 1983), where PAR stands for photosynthetically available radiation, kw, kc, and ki are light attenuation coefficients for water, phytoplankton (diazotrophs and general phytoplankton), and ice, z is the effective vertical coordinate, ai is the fractional sea ice cover, and hi and hs are calculated sea ice and snow cover thicknesses. Light attenuation coefficients kw and ki have the unit of m−1, but light attenuation by phytoplankton is dependent on phytoplankton concentration (Kirk, 1975) and kc is expressed in units of (m mmol N m−3)−1. Light attenuation coefficients are classified as apparent optical properties (AOP) because they rep-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
