Articles | Volume 10, issue 6
Geosci. Model Dev., 10, 2169–2199, 2017

Special issue: Coupled Model Intercomparison Project Phase 6 (CMIP6) Experimental...

Geosci. Model Dev., 10, 2169–2199, 2017

Methods for assessment of models 09 Jun 2017

Methods for assessment of models | 09 Jun 2017

Biogeochemical protocols and diagnostics for the CMIP6 Ocean Model Intercomparison Project (OMIP)

James C. Orr1, Raymond G. Najjar2, Olivier Aumont3, Laurent Bopp1, John L. Bullister4, Gokhan Danabasoglu5, Scott C. Doney6, John P. Dunne7, Jean-Claude Dutay1, Heather Graven8, Stephen M. Griffies7, Jasmin G. John7, Fortunat Joos9, Ingeborg Levin10, Keith Lindsay5, Richard J. Matear11, Galen A. McKinley12, Anne Mouchet13,14, Andreas Oschlies15, Anastasia Romanou16, Reiner Schlitzer17, Alessandro Tagliabue18, Toste Tanhua15, and Andrew Yool19 James C. Orr et al.
  • 1LSCE/IPSL, Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, Gif-sur-Yvette, France
  • 2Dept. of Meteorology and Atmospheric Science, Pennsylvania State University, University Park, Pennsylvania, USA
  • 3Laboratoire d'Océanographie et de Climatologie: Expérimentation et Approches Numériques, IPSL, Paris, France
  • 4Pacific Marine Environmental Laboratory, NOAA, Seattle, Washington, USA
  • 5National Center for Atmospheric Research, Boulder, Colorado, USA
  • 6Marine Chemistry & Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
  • 7NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA
  • 8Dept. of Physics, Imperial College, London, UK
  • 9Climate and Environmental Physics, Physics Inst. & Oeschger Center for Climate Change Res., Univ. of Bern, Bern, Switzerland
  • 10Institut fuer Umweltphysik, Universitaet Heidelberg, Heidelberg, Germany
  • 11CSIRO Oceans and Atmosphere, Hobart, Tasmania 7000, Australia
  • 12Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, Madison, Wisconsin, USA
  • 13Max Planck Institute for Meteorology, Hamburg, Germany
  • 14Astrophysics, Geophysics and Oceanography Department, University of Liege, Liege, Belgium
  • 15GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
  • 16Columbia University and NASA-Goddard Institute for Space Studies, New York, NY, USA
  • 17Alfred Wegener Institute, Bremerhaven, Germany
  • 18Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool, UK
  • 19National Oceanographic Centre, Southampton, UK

Abstract. The Ocean Model Intercomparison Project (OMIP) focuses on the physics and biogeochemistry of the ocean component of Earth system models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). OMIP aims to provide standard protocols and diagnostics for ocean models, while offering a forum to promote their common assessment and improvement. It also offers to compare solutions of the same ocean models when forced with reanalysis data (OMIP simulations) vs. when integrated within fully coupled Earth system models (CMIP6). Here we detail simulation protocols and diagnostics for OMIP's biogeochemical and inert chemical tracers. These passive-tracer simulations will be coupled to ocean circulation models, initialized with observational data or output from a model spin-up, and forced by repeating the 1948–2009 surface fluxes of heat, fresh water, and momentum. These so-called OMIP-BGC simulations include three inert chemical tracers (CFC-11, CFC-12, SF6) and biogeochemical tracers (e.g., dissolved inorganic carbon, carbon isotopes, alkalinity, nutrients, and oxygen). Modelers will use their preferred prognostic BGC model but should follow common guidelines for gas exchange and carbonate chemistry. Simulations include both natural and total carbon tracers. The required forced simulation (omip1) will be initialized with gridded observational climatologies. An optional forced simulation (omip1-spunup) will be initialized instead with BGC fields from a long model spin-up, preferably for 2000 years or more, and forced by repeating the same 62-year meteorological forcing. That optional run will also include abiotic tracers of total dissolved inorganic carbon and radiocarbon, CTabio and 14CTabio, to assess deep-ocean ventilation and distinguish the role of physics vs. biology. These simulations will be forced by observed atmospheric histories of the three inert gases and CO2 as well as carbon isotope ratios of CO2. OMIP-BGC simulation protocols are founded on those from previous phases of the Ocean Carbon-Cycle Model Intercomparison Project. They have been merged and updated to reflect improvements concerning gas exchange, carbonate chemistry, and new data for initial conditions and atmospheric gas histories. Code is provided to facilitate their implementation.

Short summary
The Ocean Model Intercomparison Project (OMIP) is a model comparison effort under Phase 6 of the Coupled Model Intercomparison Project (CMIP6). Its physical component is described elsewhere in this special issue. Here we describe its ocean biogeochemical component (OMIP-BGC), detailing simulation protocols and analysis diagnostics. Simulations focus on ocean carbon, other biogeochemical tracers, air-sea exchange of CO2 and related gases, and chemical tracers used to evaluate modeled circulation.