MEDUSA-1.0: A new intermediate complexity plankton ecosystem model for the global domain

Abstract

The ongoing, anthropogenically-driven changes to the global ocean areexpected to have significant consequences for plankton ecosystems inthe future. Because of the role that plankton play in the ocean's"biological pump", changes in abundance, distribution andproductivity will likely have additional consequences for the widercarbon cycle. Just as in the terrestrial biosphere, marine ecosystemsexhibit marked diversity in species and functional types oforganisms. Predicting potential change in plankton ecosystemstherefore requires the use of models that are suited to thisdiversity, but whose parameterisation also permits robust andrealistic functional behaviour. In the past decade, advances in modelsophistication have attempted to address diversity, but have beencriticised for doing so inaccurately or ahead of a requisiteunderstanding of underlying processes. Here we introduceMEDUSA-1. 0(Model of Ecosystem Dynamics, nutrient Utilisation, Sequestration and Acidification), a new "intermediate complexity" plankton ecosystem model that expandson traditional nutrient-phytoplankton-zooplankton-detritus (NPZD)models, and remains amenable to global-scale evaluation. MEDUSA-1.0 includes the biogeochemical cycles of nitrogen, silicon and iron,broadly structured into "small" and "large" plankton size classes,of which the "large" phytoplankton class is representative of a keyphytoplankton group, the diatoms. A full description of MEDUSA-1.0's state variables, differential equations, functional forms andparameter values is included, with particular attention focused on thesubmodel describing the export of organic carbon from the surface tothe deep ocean. MEDUSA-1.0 is used here in a multi-decadal hindcastsimulation, and its biogeochemical performance evaluated at the globalscale. © Author(s) 2011.