BGC-val: a model- and grid-independent Python toolkit to evaluate marine biogeochemical models

Lee de Mora1, Andrew Yool2, Julien Palmieri2, Alistair Sellar3, Till Kuhlbrodt4,Ekaterina Popova2, Colin Jones5, and J. Icarus Allen1

  • 1Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH, UK
  • 2National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton SO14 3ZH, UK
  • 3Met Office Hadley Centre, Exeter, EX1 3PB, UK
  • 4NCAS, Department of Meteorology, University of Reading, Reading, RG6 6AH, UK
  • 5NCAS, School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK

Abstract: The biogeochemical evaluation toolkit, BGC-val, is a model- and grid-independent Python toolkit that has been built to evaluate marine biogeochemical models using a simple interface. Here, we present the ideas that motivated the development of the BGC-val software framework, introduce the code structure, and show some applications of the toolkit using model results from the Fifth Climate Model Intercomparison Project (CMIP5). A brief outline of how to access and install the repository is presented in Appendix A, but the specific details on how to use the toolkit are kept in the code repository.

The key ideas that directed the toolkit design were model and grid independence, front-loading analysis functions and regional masking, interruptibility, and ease of use. We present each of these goals, why they were important, and what we did to address them. We also present an outline of the code structure of the toolkit illustrated with example plots produced by the toolkit.

After describing BGC-val, we use the toolkit to investigate the performance of the marine physical and biogeochemical quantities of the CMIP5 models and highlight some predictions about the future state of the marine ecosystem under a business-as-usual CO2concentration scenario (RCP8.5).

Big in the benthos: Future change of seafloor community biomass in a global, body size‐resolved model

Andrew Yool, Adrian P. Martin, Thomas R. Anderson, Brian J. Bett, Daniel O. B. Jones, Henry A. Ruhl

National Oceanography Centre, University of Southampton Waterfront Campus, Southampton, UK

Abstract: Deep‐water benthic communities in the ocean are almost wholly dependent on near‐surface pelagic ecosystems for their supply of energy and material resources. Primary production in sunlit surface waters is channelled through complex food webs that extensively recycle organic material, but lose a fraction as particulate organic carbon (POC) that sinks into the ocean interior. This exported production is further rarefied by microbial breakdown in the abyssal ocean, but a residual ultimately drives diverse assemblages of seafloor heterotrophs. Advances have led to an understanding of the importance of size (body mass) in structuring these communities. Here we force a size‐resolved benthic biomass model, BORIS, using seafloor POC flux from a coupled ocean‐biogeochemistry model, NEMO‐MEDUSA, to investigate global patterns in benthic biomass. BORIS resolves 16 size classes of metazoans, successively doubling in mass from approximately 1 μg to 28 mg. Simulations find a wide range of seasonal responses to differing patterns of POC forcing, with both a decline in seasonal variability, and an increase in peak lag times with increasing body size. However, the dominant factor for modelled benthic communities is the integrated magnitude of POC reaching the seafloor rather than its seasonal pattern. Scenarios of POC forcing under climate change and ocean acidification are then applied to investigate how benthic communities may change under different future conditions. Against a backdrop of falling surface primary production (−6.1%), and driven by changes in pelagic remineralization with depth, results show that while benthic communities in shallow seas generally show higher biomass in a warmed world (+3.2%), deep‐sea communities experience a substantial decline (−32%) under a high greenhouse gas emissions scenario. Our results underscore the importance for benthic ecology of reducing uncertainty in the magnitude and seasonality of seafloor POC fluxes, as well as the importance of studying a broader range of seafloor environments for future model development.