iMarNet: an ocean biogeochemistry model intercomparison project within a common physical ocean modelling framework

[摘要] Ocean biogeochemistry (OBGC) models span a wide variety of complexities, includinghighly simplified nutrient-restoring schemes, nutrient–phytoplankton–zooplankton–detritus (NPZD) models that crudelyrepresent the marine biota, models that represent a broadertrophic structure by grouping organisms as plankton functional types (PFTs)based on their biogeochemical role (dynamic green ocean models) andecosystem models that group organisms by ecological function and trait.OBGC models are now integral components of Earth system models (ESMs), butthey compete for computing resources with higher resolution dynamical setupsand with other components such as atmospheric chemistry and terrestrialvegetation schemes. As such, the choice of OBGC in ESMs needs to balancemodel complexity and realism alongside relative computing cost. Here wepresent an intercomparison of six OBGC models that were candidates forimplementation within the next UK Earth system model (UKESM1). The modelscover a large range of biological complexity (from 7 to 57 tracers) but allinclude representations of at least the nitrogen, carbon, alkalinity andoxygen cycles. Each OBGC model was coupled to the ocean general circulation model Nucleus for EuropeanModelling of the Ocean (NEMO) andresults from physically identical hindcast simulations were compared. Modelskill was evaluated for biogeochemical metrics of global-scale bulkproperties using conventional statistical techniques. The computing cost ofeach model was also measured in standardised tests run at two resourcelevels. No model is shown to consistently outperform all other models acrossall metrics. Nonetheless, the simpler models are broadly closer toobservations across a number of fields and thus offer a high-efficiencyoption for ESMs that prioritise high-resolution climate dynamics. However,simpler models provide limited insight into more complex marinebiogeochemical processes and ecosystem pathways, and a parallel approach oflow-resolution climate dynamics and high-complexity biogeochemistry isdesirable in order to provide additional insights into biogeochemistry–climate interactions.

[学科分类] 地球化学与岩石