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

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

Evaluation of OCMIP-2 ocean models' deep circulation with mantle helium-3

We compare simulations of the injection of mantle helium-3 into the deep ocean from six global coarse resolution models which participated in the Ocean Carbon Model Intercomparison Project (OCMIP). We also discuss the results of a study carried out with one of the models, which examines the effect of the subgrid-scale mixing parameterization. These sensitivity tests provide useful information to interpret the differences among the OCMIP models and between model simulations and the data.We find that the OCMIP models, which parameterize subgrid-scale mixing using an eddy-induced velocity, tend to underestimate the ventilation of the deep ocean, based on diagnostics with 3He. In these models, this parameterization is implemented with a constant thickness diffusivity coefficient. In future simulations, we recommend using such a parameterization with spatially and temporally varying coefficients in order to moderate its effect on stratification.The performance of the models with regard to the formation of AABW confirms the conclusion from a previous evaluation with CFC-11. Models coupled with a sea-ice model produce a substantial bottom water formation in the Southern Ocean that tends to overestimate AABW ventilation, while models that are not coupled with a sea-ice model systematically underestimate the formation of AABW.We also analyze specific features of the deep 3He distribution (3He plumes) that are particularly well depicted in the data and which put severe constraints on the deep circulation. We show that all the models fail to reproduce a correct propagation of these plumes in the deep ocean. The resolution of the models may be too coarse to reproduce the strong and narrow currents in the deep ocean, and the models do not incorporate the geothermal heating that may also contribute to the generation of these currents. We also use the context of OCMIP-2 to explore the potential of mantle helium-3 as a tool to compare and evaluate modeled deep-ocean circulations. Although the source function of mantle helium is known with a rather large uncertainty, we find that the parameterization used for the injection of mantle helium-3 is sufficient to generate realistic results, even in the Atlantic Ocean where a previous pioneering study [J. Geophys. Res. 100 (1995) 3829] claimed this parameterization generates inadequate results. These results are supported by a multi-tracer evaluation performed by considering the simulated distributions of both helium-3 and natural 14C, and comparing the simulated tracer fields with available data

Evaluation of ocean model ventilation with CFC-11: comparison of 13 global ocean models

We compared the 13 models participating in the Ocean Carbon Model Intercomparison Project (OCMIP) with regards to their skill in matching observed distributions of CFC-11. This analysis characterizes the abilities of these models to ventilate the ocean on timescales relevant for anthropogenic CO2 uptake. We found a large range in the modeled global inventory (±30%), mainly due to differences in ventilation from the high latitudes. In the Southern Ocean, models differ particularly in the longitudinal distribution of the CFC uptake in the intermediate water, whereas the latitudinal distribution is mainly controlled by the subgrid-scale parameterization. Models with isopycnal diffusion and eddy-induced velocity parameterization produce more realistic intermediate water ventilation. Deep and bottom water ventilation also varies substantially between the models. Models coupled to a sea-ice model systematically provide more realistic AABW formation source region; however these same models also largely overestimate AABW ventilation if no specific parameterization of brine rejection during sea-ice formation is included. In the North Pacific Ocean, all models exhibit a systematic large underestimation of the CFC uptake in the thermocline of the subtropical gyre, while no systematic difference toward the observations is found in the subpolar gyre. In the North Atlantic Ocean, the CFC uptake is globally underestimated in subsurface. In the deep ocean, all but the adjoint model, failed to produce the two recently ventilated branches observed in the North Atlantic Deep Water (NADW). Furthermore, simulated transport in the Deep Western Boundary Current (DWBC) is too sluggish in all but the isopycnal model, where it is too rapid.<br/

Marine ecosystems'responses to climatic and anthropogenic forcings in the Mediterranean

International audienceNot Availabl

Marine ecosystems' responses to climatic and athropogenic forcings in the Mediterranean

The semi-enclosed nature of the Mediterranean Sea, together with its smaller inertia due to the relative short residence time of its water masses, make it highly reactive to external forcings, in particular variations of water, energy and matter fluxes at the interfaces. This region, which has been identified as a 'hotspot' for climate change, is therefore expected to experience environmental impacts that are considerably greater than those in many other places around the world. These natural pressures interact with the increasing demographic and economic developments occurring heterogeneously in the coastal zone, making the Mediterranean even more sensitive. This review paper aims to provide a review of the state of current functioning and responses of Mediterranean marine biogeochemical cycles and ecosystems with respect to key natural and anthropogenic drivers and to consider the ecosystems¿ responses to likely changes in physical, chemical and socio-economical forcings induced by global change and by growing anthropogenic pressure at the regional scale. The current knowledge on and expected changes due to single forcing (hydrodynamics, solar radiation, temperature and acidification, chemical contaminants) and combined forcing (nutrient sources and stoichiometry, extreme events) affecting the biogeochemical fluxes and ecosystem functioning are explored. Expected changes in biodiversity resulting from the combined action of the different forcings are proposed. Finally, modeling capabilities and necessity for modeling are presented. Modeling acts as an integrative tool to investigate the question of how climate change and anthropogenic activities impact the cycle of biogenic elements and marine ecosystems. A synthesis of our current knowledge of expected changes is proposed, highlighting relevant questions for the future of the Mediterranean ecosystems that are current research priorities for the scientific community. Finally, we discuss how these priorities can be approached by national and international multi-disciplinary research, which should be implemented on several levels, including observational studies and modeling at different temporal and spatial scales.JRC.H.5-Land Resources Managemen

Marine ecosystems’ responses to climatic and anthropogenic forcings in the Mediterranean

Corrigendum : https://doi.org/10.1016/j.pocean.2011.08.003International audienceThe semi-enclosed nature of the Mediterranean Sea, together with its smaller inertia due to the relative short residence time of its water masses, make it highly reactive to external forcings, in particular variations of water, energy and matter fluxes at the interfaces. This region, which has been identified as a “hotspot” for climate change, is therefore expected to experience environmental impacts that are considerably greater than those in many other places around the world. These natural pressures interact with the increasing demographic and economic developments occurring heterogeneously in the coastal zone, making the Mediterranean even more sensitive. This review paper aims to provide a review of the state of current functioning and responses of Mediterranean marine biogeochemical cycles and ecosystems with respect to key natural and anthropogenic drivers and to consider the ecosystems’ responses to likely changes in physical, chemical and socio-economical forcings induced by global change and by growing anthropogenic pressure at the regional scale. The current knowledge on and expected changes due to single forcing (hydrodynamics, solar radiation, temperature and acidification, chemical contaminants) and combined forcing (nutrient sources and stoichiometry, extreme events) affecting the biogeochemical fluxes and ecosystem functioning are explored. Expected changes in biodiversity resulting from the combined action of the different forcings are proposed. Finally, modeling capabilities and necessity for modeling are presented. A synthesis of our current knowledge of expected changes is proposed, highlighting relevant questions for the future of the Mediterranean ecosystems that are current research priorities for the scientific community. Finally, we discuss how these priorities can be approached by national and international multi-disciplinary research, which should be implemented on several levels, including observational studies and modeling at different temporal and spatial scales

Marine ecosystems’ responses to climatic and anthropogenic forcings in the Mediterranean

Corrigendum : https://doi.org/10.1016/j.pocean.2011.08.003International audienceThe semi-enclosed nature of the Mediterranean Sea, together with its smaller inertia due to the relative short residence time of its water masses, make it highly reactive to external forcings, in particular variations of water, energy and matter fluxes at the interfaces. This region, which has been identified as a “hotspot” for climate change, is therefore expected to experience environmental impacts that are considerably greater than those in many other places around the world. These natural pressures interact with the increasing demographic and economic developments occurring heterogeneously in the coastal zone, making the Mediterranean even more sensitive. This review paper aims to provide a review of the state of current functioning and responses of Mediterranean marine biogeochemical cycles and ecosystems with respect to key natural and anthropogenic drivers and to consider the ecosystems’ responses to likely changes in physical, chemical and socio-economical forcings induced by global change and by growing anthropogenic pressure at the regional scale. The current knowledge on and expected changes due to single forcing (hydrodynamics, solar radiation, temperature and acidification, chemical contaminants) and combined forcing (nutrient sources and stoichiometry, extreme events) affecting the biogeochemical fluxes and ecosystem functioning are explored. Expected changes in biodiversity resulting from the combined action of the different forcings are proposed. Finally, modeling capabilities and necessity for modeling are presented. A synthesis of our current knowledge of expected changes is proposed, highlighting relevant questions for the future of the Mediterranean ecosystems that are current research priorities for the scientific community. Finally, we discuss how these priorities can be approached by national and international multi-disciplinary research, which should be implemented on several levels, including observational studies and modeling at different temporal and spatial scales