Yamanaka Yasuhiro

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Correction to “Using altimetry to help explain patchy changes in hydrographic carbon measurements”

2009-12-09 , Rodgers, Keith B. , Key, Robert M. , Gnanadesikan, Anand , Sarmiento, Jorge L. , Aumont, Olivier , Bopp, Laurent , Doney, Scott C. , Dunne, John P. , Glover, David M. , Ishida, Akio , Ishii, Masao , Jacobson, Andrew R. , Monaco, Claire Lo , Maier-Reimer, Ernst , Mercier, Herlé , Metzl, Nicolas , Perez, Fiz F. , Rios, Aida F. , Wanninkhof, Rik , Wetzel, Patrick , Winn, Christopher D. , Yamanaka, Yasuhiro

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Preprint

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

2005-07-29 , Orr, James C. , Fabry, Victoria J. , Aumont, Olivier , Bopp, Laurent , Doney, Scott C. , Feely, Richard A. , Gnanadesikan, Anand , Gruber, Nicolas , Ishida, Akio , Joos, Fortunat , Key, Robert M. , Lindsay, Keith , Maier-Reimer, Ernst , Matear, Richard J. , Monfray, Patrick , Mouchet, Anne , Najjar, Raymond G. , Plattner, Gian-Kasper , Rodgers, Keith B. , Sabine, Christopher L. , Sarmiento, Jorge L. , Schlitzer, Reiner , Slater, Richard D. , Totterdell, Ian J. , Weirig, Marie-France , Yamanaka, Yasuhiro , Yool, Andrew

The surface ocean is everywhere saturated with respect to calcium carbonate (CaCO3). Yet increasing atmospheric CO2 reduces ocean pH and carbonate ion concentrations [CO32−] and thus the level of saturation. Reduced saturation states are expected to affect marine calcifiers even though it has been estimated that all surface waters will remain saturated for centuries. Here we show, however, that some surface waters will become undersaturated within decades. When atmospheric CO2 reaches 550 ppmv, in year 2050 under the IS92a business-as-usual scenario, Southern Ocean surface waters begin to become undersaturated with respect to aragonite, a metastable form of CaCO3. By 2100 as atmospheric CO2 reaches 788 ppmv, undersaturation extends throughout the entire Southern Ocean (< 60°S) and into the subarctic Pacific. These changes will threaten high-latitude aragonite secreting organisms including cold-water corals, which provide essential fish habitat, and shelled pteropods, an abundant food source for marine predators.

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Article

Using altimetry to help explain patchy changes in hydrographic carbon measurements

2009-09-18 , Rodgers, Keith B. , Key, Robert M. , Gnanadesikan, Anand , Sarmiento, Jorge L. , Aumont, Olivier , Bopp, Laurent , Doney, Scott C. , Dunne, John P. , Glover, David M. , Ishida, Akio , Ishii, Masao , Jacobson, Andrew R. , Monaco, Claire Lo , Maier-Reimer, Ernst , Mercier, Herlé , Metzl, Nicolas , Perez, Fiz F. , Rios, Aida F. , Wanninkhof, Rik , Wetzel, Patrick , Winn, Christopher D. , Yamanaka, Yasuhiro

Here we use observations and ocean models to identify mechanisms driving large seasonal to interannual variations in dissolved inorganic carbon (DIC) and dissolved oxygen (O2) in the upper ocean. We begin with observations linking variations in upper ocean DIC and O2 inventories with changes in the physical state of the ocean. Models are subsequently used to address the extent to which the relationships derived from short-timescale (6 months to 2 years) repeat measurements are representative of variations over larger spatial and temporal scales. The main new result is that convergence and divergence (column stretching) attributed to baroclinic Rossby waves can make a first-order contribution to DIC and O2 variability in the upper ocean. This results in a close correspondence between natural variations in DIC and O2 column inventory variations and sea surface height (SSH) variations over much of the ocean. Oceanic Rossby wave activity is an intrinsic part of the natural variability in the climate system and is elevated even in the absence of significant interannual variability in climate mode indices. The close correspondence between SSH and both DIC and O2 column inventories for many regions suggests that SSH changes (inferred from satellite altimetry) may prove useful in reducing uncertainty in separating natural and anthropogenic DIC signals (using measurements from Climate Variability and Predictability's CO2/Repeat Hydrography program).

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Article

Comparing food web structures and dynamics across a suite of global marine ecosystem models

2013-05-16 , Sailley, Sevrine F. , Vogt, Meike , Doney, Scott C. , Aita, M. N. , Bopp, Laurent , Buitenhuis, Erik T. , Hashioka, Taketo , Lima, Ivan D. , Le Quere, Corinne , Yamanaka, Yasuhiro

Dynamic Green Ocean Models (DGOMs) include different sets of Plankton Functional Types (PFTs) and equations, thus different interactions and food webs. Using four DGOMs (CCSM-BEC, PISCES, NEMURO and PlankTOM5) we explore how predator–prey interactions influence food web dynamics. Using each model's equations and biomass output, interaction strengths (direct and specific) were calculated and the role of zooplankton in modeled food webs examined. In CCSM-BEC the single size-class adaptive zooplankton preys on different phytoplankton groups according to prey availability and food preferences, resulting in a strong top-down control. In PISCES the micro- and meso-zooplankton groups compete for food resources, grazing phytoplankton depending on their availability in a mixture of bottom-up and top-down control. In NEMURO macrozooplankton controls the biomass of other zooplankton PFTs and defines the structure of the food web with a strong top-down control within the zooplankton. In PlankTOM5, competition and predation between micro- and meso-zooplankton along with strong preferences for nanophytoplankton and diatoms, respectively, leads to their mutual exclusion with a mixture of bottom-up and top-down control of the plankton community composition. In each model, the grazing pressure of the zooplankton PFTs and the way it is exerted on their preys may result in the food web dynamics and structure of the model to diverge from the one that was intended when designing the model. Our approach shows that the food web dynamics, in particular the strength of the predator–prey interactions, are driven by the choice of parameters and more specifically the food preferences. Consequently, our findings stress the importance of equation and parameter choice as they define interactions between PFTs and overall food web dynamics (competition, bottom-up or top-down effects). Also, the differences in the simulated food-webs between different models highlight the gap of knowledge for zooplankton rates and predator–prey interactions. In particular, concerted effort is needed to identify the key growth and loss parameters and interactions and quantify them with targeted laboratory experiments in order to bring our understanding of zooplankton at a similar level to phytoplankton.

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Article

Evaluation of ocean carbon cycle models with data-based metrics

2004-04-02 , Matsumoto, K. , Sarmiento, Jorge L. , Key, Robert M. , Aumont, Olivier , Bullister, John L. , Caldeira, Ken , Campin, J.-M. , Doney, Scott C. , Drange, Helge , Dutay, J.-C. , Follows, Michael J. , Gao, Y. , Gnanadesikan, Anand , Gruber, Nicolas , Ishida, Akio , Joos, Fortunat , Lindsay, Keith , Maier-Reimer, Ernst , Marshall, John C. , Matear, Richard J. , Monfray, Patrick , Mouchet, Anne , Najjar, Raymond G. , Plattner, Gian-Kasper , Schlitzer, Reiner , Slater, Richard D. , Swathi, P. S. , Totterdell, Ian J. , Weirig, Marie-France , Yamanaka, Yasuhiro , Yool, Andrew , Orr, James C.

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.

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Article

Impact of circulation on export production, dissolved organic matter, and dissolved oxygen in the ocean : results from Phase II of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2)

2007-08-08 , Najjar, Raymond G. , Jin, X. , Louanchi, F. , Aumont, Olivier , Caldeira, Ken , Doney, Scott C. , Dutay, J.-C. , Follows, Michael J. , Gruber, Nicolas , Joos, Fortunat , Lindsay, Keith , Maier-Reimer, Ernst , Matear, Richard J. , Matsumoto, K. , Monfray, Patrick , Mouchet, Anne , Orr, James C. , Plattner, Gian-Kasper , Sarmiento, Jorge L. , Schlitzer, Reiner , Slater, Richard D. , Weirig, Marie-France , Yamanaka, Yasuhiro , Yool, Andrew

Results are presented of export production, dissolved organic matter (DOM) and dissolved oxygen simulated by 12 global ocean models participating in the second phase of the Ocean Carbon-cycle Model Intercomparison Project. A common, simple biogeochemical model is utilized in different coarse-resolution ocean circulation models. The model mean (±1σ) downward flux of organic matter across 75 m depth is 17 ± 6 Pg C yr−1. Model means of globally averaged particle export, the fraction of total export in dissolved form, surface semilabile dissolved organic carbon (DOC), and seasonal net outgassing (SNO) of oxygen are in good agreement with observation-based estimates, but particle export and surface DOC are too high in the tropics. There is a high sensitivity of the results to circulation, as evidenced by (1) the correlation of surface DOC and export with circulation metrics, including chlorofluorocarbon inventory and deep-ocean radiocarbon, (2) very large intermodel differences in Southern Ocean export, and (3) greater export production, fraction of export as DOM, and SNO in models with explicit mixed layer physics. However, deep-ocean oxygen, which varies widely among the models, is poorly correlated with other model indices. Cross-model means of several biogeochemical metrics show better agreement with observation-based estimates when restricted to those models that best simulate deep-ocean radiocarbon. Overall, the results emphasize the importance of physical processes in marine biogeochemical modeling and suggest that the development of circulation models can be accelerated by evaluating them with marine biogeochemical metrics.

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Article

Phytoplankton competition during the spring bloom in four plankton functional type models

2013-11-02 , Hashioka, Taketo , Vogt, Meike , Yamanaka, Yasuhiro , Le Quere, Corinne , Buitenhuis, Erik T. , Aita, M. N. , Alvain, S. , Bopp, Laurent , Hirata, T. , Lima, Ivan D. , Sailley, Sevrine F. , Doney, Scott C.

We investigated the mechanisms of phytoplankton competition during the spring bloom, one of the most dramatic seasonal events in lower-trophic-level ecosystems, in four state-of-the-art plankton functional type (PFT) models: PISCES, NEMURO, PlankTOM5 and CCSM-BEC. In particular, we investigated the relative importance of different ecophysiological processes on the determination of the community structure, focusing both on the bottom-up and the top-down controls. The models reasonably reproduced the observed global distribution and seasonal variation of phytoplankton biomass. The fraction of diatoms with respect to the total phytoplankton biomass increases with the magnitude of the spring bloom in all models. However, the governing mechanisms differ between models, despite the fact that current PFT models represent ecophysiological processes using the same types of parameterizations. The increasing trend in the percentage of diatoms with increasing bloom magnitude is mainly caused by a stronger nutrient dependence of diatom growth compared to nanophytoplankton (bottom-up control). The difference in the maximum growth rate plays an important role in NEMURO and PlankTOM5 and determines the absolute values of the percentage of diatoms during the bloom. In CCSM-BEC, the light dependency of growth plays an important role in the North Atlantic and the Southern Ocean. The grazing pressure by zooplankton (top-down control), however, strongly contributes to the dominance of diatoms in PISCES and CCSM-BEC. The regional differences in the percentage of diatoms in PlankTOM5 are mainly determined by top-down control. These differences in the mechanisms suggest that the response of marine ecosystems to climate change could significantly differ among models, even if the present-day ecosystem is reproduced to a similar degree of confidence. For further understanding of plankton competition and for the prediction of future change in marine ecosystems, it is important to understand the relative differences in each physiological rate and life history rate in the bottom-up and the top-down controls between PFTs.

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Evaluating global ocean carbon models : the importance of realistic physics

2004-09-15 , Doney, Scott C. , Lindsay, Keith , Caldeira, Ken , Campin, J.-M. , Drange, Helge , Dutay, J.-C. , Follows, Michael J. , Gao, Y. , Gnanadesikan, Anand , Gruber, Nicolas , Ishida, Akio , Joos, Fortunat , Madec, G. , Maier-Reimer, Ernst , Marshall, John C. , Matear, Richard J. , Monfray, Patrick , Mouchet, Anne , Najjar, Raymond G. , Orr, James C. , Plattner, Gian-Kasper , Sarmiento, Jorge L. , Schlitzer, Reiner , Slater, Richard D. , Totterdell, Ian J. , Weirig, Marie-France , Yamanaka, Yasuhiro , Yool, Andrew

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.

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