Current representations of marine ecosystems in Earth System Models (ESMs) are greatly simplified, neglecting key interactions between dynamic food webs, biogeochemistry, and climate change. We use the Marine Biogeochemistry Library (MARBL) code base within the Community Earth System Model 2.2.0 to create an expanded marine ecosystem model that includes eight phytoplankton groups and four zooplankton size classes (MARBL-8P4Z). The incorporation of more specific plankton types and size classes enhances the capacity to represent important ecological and biogeochemical processes, and allows for additional observational constraints, including observations of plankton group-specific biomass distributions.

MARBL-8P4Z simulations reproduce observed, global-scale patterns in biomass and community composition for both the phytoplankton and zooplankton. Picophytoplankton carbon biomass (Prochlorococcus, Synechococcus, picoeukaryotes) shows similar spatial patterns and magnitudes to the observed distributions. The model simulates large-scale geographical shifts in community composition with picophytoplankton groups and microzooplankton dominating in oligotrophic, subtropical regions (>50% of biomass), and nano-size phytoplankton, diatoms and larger zooplankton groups dominating at higher latitudes and within upwelling zones. The MARBL-8P4Z model improves seasonal simulation of the spring bloom compared with more simplified MARBL configurations, benefiting from dampened diatom blooms at higher latitudes due to a combination of bottom-up and top-down drivers. Given that plankton community composition strongly impacts the magnitude and efficiency of carbon export by the ocean biological pump, properly accounting for these processes is key for projecting the impacts of climate change on marine ecosystems, biogeochemistry and associated climate feedbacks, as well as, potential fishery yields, under uncertain future climate scenarios.

ocean biogeochemisry,earth system modeling,marine ecosystem