Bibliography - J. C. Orr

1. Orr, J. C., V. J. Fabry, O. Aumont, L. Bopp, S. C. Doney, R. A. Feely, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos, R. M. Key, and K. Lindsay, et al., 2005: Anthropogenic ocean acidification over the 21st century and its impact on marine calcifying organisms. Nature, 437, doi:10.1038/nature04095 681-686
   [ Abstract ]

   Today’s 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.

2. Dutay, J. C., P. Jean-Baptiste, J.-M. Campin, A. Ishida, E. Maier-Reimer, R. J. Matear, A. Mouchet, I. J. Totterdell, Y. Yamanaka, K. B. Rodgers, G. Madec, and J. C. Orr, 2004: Evaluation of OCMIP-2 Ocean Models’ Deep Circulation with Mantle Helium-3. Journal of Marine Systems, 48(1-4), doi:10.1016/j.jmarsys.2003.05.010 15-36
   [ Abstract ]

   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 δ³He. 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.

3. Watson, A. J., and J. C. Orr, 2003: Carbon dioxide fluxes in the global ocean. Ocean Biogeochemistry: A JGOFS Synthesis, Springer-Verlag Publishers, http://lgmacweb.env.uea.ac.uk/ajw/Watson_and_Orr_2002.pdf,
   [ Abstract ]

   Atmospheric carbon dioxide concentration is one of the key variables of the “Earth system” -- the web of interactions between the atmosphere, oceans, soils and living things that determines conditions at the Earth surface. Atmospheric CO₂ plays several roles in this system. For example, it is the carbon source for nearly all terrestrial green plants, and the source of carbonic acid to weather rocks. It is also an important greenhouse gas, with a central role to play in modulating the climate of the planet. During the five thousand years prior to the industrial revolution, we know (from measurements of air trapped in firn ice and ice cores) that atmospheric CO₂ varied globally by less than 10ppm from a concentration of 280ppm (Indermuhle et al. 1999). During the late Quaternary glaciations, the regular advance and retreat of the ice was accompanied by, and to some extent at least driven by (Li et al. 1998; Shackleton 2000), an oscillation in atmospheric CO₂ of about 80ppm. Evidence from the geologically recent past indicates therefore, that quite small changes in atmospheric carbon dioxide have big effects on planetary climate. Conversely, a stable concentration of CO₂ is necessary for a stable climate. By this reasoning, we can be fairly certain that human activities will have a major effect on the climate of the planet in the near future, given that we have raised CO₂ by 90ppm in the last 150 years and it is projected to double from the pre-industrial concentration during the coming century. This gives our investigations into sources and sinks of carbon dioxide a special urgency. For reasons that are made clear below, the oceans occupy a central role in the global carbon cycle and the processes influencing the concentration of CO₂ in the atmosphere. The JGOFS program represented the first sustained global effort to document the present state of the oceanic carbon cycle, and to test our understanding by comparing that state with the predictions of increasingly sophisticated numerical models. In the subsequent sections, we first discuss the role of the oceans in setting global atmospheric CO₂. JGOFS has made a major contribution to our estimate of the size of the present net flux of CO₂ from atmosphere to ocean, and we next review our estimates of this “sink” and how it may change in the future. This leads us to a discussion of the advances made in understanding the processes involved in setting that flux. Finally we summarize what we have learned during JGOFS and what the major topics of research are likely to be in the next 10 years.

4. Dutay, J. C., J. L. Bullister, S. C. Doney, J. C. Orr, R. G. Najjar, K. Caldeira, J.-M. Campin, H. Drange, M. Follows, Y. Gao, and N. Gruber, et al., 2002: Evaluation of ocean model ventilation with CFC-11: comparison of 13 global ocean models. Ocean Modelling, 4(2), doi:10.1016/S1463-5003(01)00013-0 89-120
   [ Abstract ]

   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

5. Orr, J. C., E. Maier-Reimer, U. Mikolajewicz, P. Monfray, Jorge Sarmiento, J. R. Toggweiler, N. K. Taylor, J. Palmer, N. Gruber, C. L. Sabine, C. Le Quere, R. M. Key, and J. Boutin, 2001: Estimates of anthropogenic carbon uptake from four three-dimensional global ocean models. Global Biogeochemical Cycles, http://www.agu.org/pubs/crossref/2001/2000GB001273.shtml, 15(1), 43-60
   [ Abstract ]

   We have compared simulations of anthropogenic CO₂ in the four three dimensional ocean models that participated in the first phase of the Ocean Carbon-Cycle Model Intercomparison Project (OCMIP), as a means to identify their major differences. Simulated global uptake agrees to within ±19%, giving a range of 1.85 ± 0.35 Pg Cy r^-1 for the 1980-1989 average. Regionally, t he Southern Ocean dominates the present-day air-sea flux of anthropogenic CO₂ in all models, with one third to one half of the global uptake occurring south of 30°S. The highest simulated total uptake in the Southern Ocean was 70% larger than the lowest. Comparison with recent data-based estimates of anthropogenic CO₂ suggest that most of the models substantially overestimate storage in the Southern Ocean; elsewhere they generally underestimate storage by less than 20%. Globally, the OCMIP models appear to bracket the real ocean's present uptake, based on comparison of regional data-based estimates of anthropogenic CO₂ and bomb ¹⁴C. Column inventories of bomb ¹⁴C have become more similar to those for anthropogenic CO₂ with the time that has elapsed between the Geochemical Ocean Sections Study (1970s) and Word Ocean Circulation Experiment ( 1990s) global sampling campaigns. Our ability to evaluate simulated anthropogenic CO₂ would improve if systematic errors associated with the data-based estimates could be provided regionally.

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