Marie-France Weirig

Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms

Todays surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms—such as corals and some plankton—will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean–carbon cycle to assess calcium carbonate saturation under the IS92a ‘business-as-usual’ scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously.

Evaluation of ocean carbon cycle models with data-based metrics

New radiocarbon and chlorofluorocarbon-11 data from the World Ocean Circulation Experiment are used to assess a suite of 19 ocean carbon cycle models. We use the distributions and inventories of these tracers as quantitative metrics of model skill and find that only about a quarter of the suite is consistent with the new data-based metrics. This should serve as a warning bell to the larger community that not all is well with current generation of ocean carbon cycle models. At the same time, this highlights the danger in simply using the available models to represent the state-of-the-art modeling without considering the credibility of each model.

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.

Evaluating global ocean carbon models: The importance of realistic physics

A suite of standard ocean hydrographic and circulation metrics are applied to the equilibrium physical solutions from 13 global carbon models participating in phase 2 of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2). Model-data comparisons are presented for sea surface temperature and salinity, seasonal mixed layer depth, meridional heat and freshwater transport, 3-D hydrographic fields, and meridional overturning. Considerable variation exists among the OCMIP-2 simulations, with some of the solutions falling noticeably outside available observational constraints. For some cases, model-model and model-data differences can be related to variations in surface forcing, subgrid-scale parameterizations, and model architecture. These errors in the physical metrics point to significant problems in the underlying model representations of ocean transport and dynamics, problems that directly affect the OCMIP predicted ocean tracer and carbon cycle variables (e.g., air-sea CO2 flux, chlorofluorocarbon and anthropogenic CO2 uptake, and export production). A substantial fraction of the large model-model ranges in OCMIP-2 biogeochemical fields (±25–40%) represents the propagation of known errors in model physics. Therefore the model-model spread likely overstates the uncertainty in our current understanding of the ocean carbon system, particularly for transport-dominated fields such as the historical uptake of anthropogenic CO2. A full error assessment, however, would need to account for additional sources of uncertainty such as more complex biological-chemical-physical interactions, biases arising from poorly resolved or neglected physical processes, and climate change.

Modelling and Adaptive Control of Aerobic Continuous Stirred Tank Reactors

A biotechnological aerobic process is modelled as an ordinary differential equation which, under mild assumptions, ensures invariance of the positive orthant and boundedness of the concentrations. An adaptive controller is designed for this general class of processes so that the external substrate can be regulated by the dilution rate into a prespecified arbitrarily small neighbourhood of a constant setpoint reference. The adaptive controller is robust, simple in its design without invoking any identification mechanisms, and is based on output data only. It is shown that the prominent example of a bakers yeast fermentation belongs to this setup, and adaptive tracking is illustrated by simulations.

The Gosac Project to Predict the Efficiency of Ocean CO2 Sequestration Using 3-D Ocean Models

Publisher Summary This chapter presents a set of standard injection simulations that were made by eight ocean modeling groups to evaluate the efficiency of the ocean in retaining purposefully sequestered CO 2 . Injection was made simultaneously at seven separate sites; separate 7-site simulations were made for injection at 800 m, 1500 m, and 3000 m. For injection at 3000 m, all models showed 85% or greater global efficiency in year 2200—that is, 100 years after the end of the specified 100-year injection period; at the same time, the 1500-m injection is 60-80% efficient and 800-m injection is only 42-61% efficient. Most of the CO 2 injected at 3000 m was lost from the Southern Ocean (the principal region by which the deep ocean is ventilated); at shallower depths, relatively more was lost sooner, from the northern hemisphere and the tropics. The simulated global injection efficiency at 3000 m is correlated with both the simulated global mean CFC-11 inventory and deep-ocean natural inc. Based on these correlations, the global observational constraints for these two tracers, and model diversity, it appears likely that the range of model-predicted efficiencies would bracket real ocean behavior under the same 3000-m injection scenario.

Narrowing the uncertainty for deep-ocean injection efficiency

Publisher Summary The chapter proposes a basic ground rule for future studies of ocean injection efficiency: to be credible they must also demonstrate the associated models skill in simulating the global inventory of GFG-11 and the global mean for radiocarbon in the deep ocean. A model that performs well in regards to both those constraints will be more likely to simulate reasonable global injection efficiencies. Nonetheless, efficiencies for a given injection site in coarse resolution models could be biased. For instance, the majority of injection sites will be located on eastern or western boundaries, which have known problems in coarse resolution models. Furthermore, coarse-resolution grids are unable to resolve important subgrid-scale processes (e.g., eddies, boundary currents, convection). Properly accounting for these processes may affect large-scale transport and could alter model predictions of CO2 sequestration efficiency. Although, global-scale ocean general circulation models are now becoming available which do resolve these processes, their high resolution means that they can only be integrated for relatively short periods, a few decades at most.

Modelling and Adaptive Control of Biochemical Processes

Abstract For a general dynamic biochemical process described by an ordinary differential equation, we introduce the concept of non-cyclic processes. This replaces the conservation of mass assumption and is sufficient to guarantee invariance of the positive orthant and boundedness of the trajectories. Non-cyclic processes are characterized in terms of the stoichiometric matrix and an algorithm is presented which decides in finitely many steps whether a process is non-cyclic or not. The concept of λ-tracking is applied to an example to regulate some external substrate concentration by the feedrate in the presence of noise corrupting the output and in the presence of input constraints.