scholarly journals Generic analysis of the response of calcifying microalgae to an elevation of pCO2 : qualitative vs quantitative analysis

2008 ◽  
Vol Volume 9, 2007 Conference in... ◽  
Author(s):  
Olivier Bernard ◽  
Antoine Sciandre
Keyword(s):  
Large Scale ◽  
Co2 Concentration ◽  
Emiliania Huxleyi ◽  
Atmospheric Co2 ◽  
Quantitative Prediction ◽  
General Level ◽  
Sont Encore ◽  
Chemostat Cultures ◽  
International Audience ◽  
Parameter Values

International audience Calcifying microalgae can play a key role in atmospheric CO2 trapping through large scale precipitation of calcium carbonate in the oceans. However, recent experiments revealed that the associated fluxes may be slow down by an increase in atmospheric CO2 concentration. In this paper we design models to account for the decrease in calcification and photosynthesis rates observed after an increase of pCO2 in Emiliania huxleyi chemostat cultures. Since the involved mechanisms are still not completely understood, we consider various models, each of them being based on a different hypothesis. These models are kept at a very general level, by maintaining the growth and calcification functions in a generic form, i.e. independent on the exact shape of these functions and on parameter values. The analysis is thus performed using these generic functions where the only hypothesis is an increase of these rates with respect to the regulating carbon species. As a result, each model responds differently to a pCO2 elevation. Surprisingly, the only models whose behaviour are in agreement with the experimental results correspond to carbonate as the regulating species for photosynthesis. Finally we show that the models whose qualitative behaviour are wrong could be considered as acceptable on the basis of a quantitative prediction error criterion. Les microalgues calcifiantes jouent un rôle clé dans le piégeage du CO2 atmosphérique d’origine anthropique en précipitant du carbonate de calcium qui sédimente au fond des océans. Toutefois, des expériences en laboratoire ont suggéré que cette activité biologique pourrait être diminuée par l’augmentation de la pression partielle de CO2 (pCO2) dans les océans qui a tendance à s’ équilibrer avec celle de l’atmosphère. Dans ce papier, nous concevons des modèles dynamiques pour essayer de simuler la diminution des taux de calcification et de photosynthèse observés chez Emiliania huxleyi après une hausse de la pCO2 reproduite en chémostat. Comme les mécanismes physiologiques impliqués sont encore loin d’ être complètement élucidés, nous considérons différents modèles, chacun d’eux étant basé sur une hypothèse biologique différente. Ces modèles, construits en utilisant des fonctions génériques pour caractériser les processus de croissance et de calcification, peuvent être analysés indépendamment de la forme exacte de ces fonctions et de la valeur des paramètres. L’ étude s’appuie donc sur ces fonctions génériques où la seule hypothèse est une régulation de ces taux par une des trois formes qui composent la totalité du carbone inorganique dissous : le CO2, les carbonates et les bicarbonates. Il s’en suit que chaque modèle réagit différemment à une élévation de la pCO2. Contrairement aux hypothèses classiquement admises, notre étude montre que les seuls modèles dont le comportement est en accord avec les résultats expérimentaux sont ceux pour lesquels une régulation de la photosynthèse par les carbonates a été supposée, ce qui corrobore les conclusions de travaux récents. Enfin, nous montrons que les modèles dont le comportement qualitatif est mauvais ne seraient pas rejetés sur la base d’un critère quantitatif d’erreur de prédiction.

scholarly journals Present state of global wetland extent and wetland methane modelling: conclusions from a model inter-comparison project (WETCHIMP)

2013 ◽  
Vol 10 (2) ◽  
pp. 753-788 ◽  
Author(s):  
J. R. Melton ◽  
R. Wania ◽  
E. L. Hodson ◽  
B. Poulter ◽  
B. Ringeval ◽  
...  
Keyword(s):  
Large Scale ◽  
Positive Response ◽  
Co2 Concentration ◽  
Remotely Sensed ◽  
Atmospheric Co2 ◽  
Emission Rates ◽  
Ch4 Emission ◽  
Wetland Area ◽  
Large Variability ◽  
Ch4 Emissions

Abstract. Global wetlands are believed to be climate sensitive, and are the largest natural emitters of methane (CH4). Increased wetland CH4 emissions could act as a positive feedback to future warming. The Wetland and Wetland CH4 Inter-comparison of Models Project (WETCHIMP) investigated our present ability to simulate large-scale wetland characteristics and corresponding CH4 emissions. To ensure inter-comparability, we used a common experimental protocol driving all models with the same climate and carbon dioxide (CO2) forcing datasets. The WETCHIMP experiments were conducted for model equilibrium states as well as transient simulations covering the last century. Sensitivity experiments investigated model response to changes in selected forcing inputs (precipitation, temperature, and atmospheric CO2 concentration). Ten models participated, covering the spectrum from simple to relatively complex, including models tailored either for regional or global simulations. The models also varied in methods to calculate wetland size and location, with some models simulating wetland area prognostically, while other models relied on remotely sensed inundation datasets, or an approach intermediate between the two. Four major conclusions emerged from the project. First, the suite of models demonstrate extensive disagreement in their simulations of wetland areal extent and CH4 emissions, in both space and time. Simple metrics of wetland area, such as the latitudinal gradient, show large variability, principally between models that use inundation dataset information and those that independently determine wetland area. Agreement between the models improves for zonally summed CH4 emissions, but large variation between the models remains. For annual global CH4 emissions, the models vary by ±40% of the all-model mean (190 Tg CH4 yr−1). Second, all models show a strong positive response to increased atmospheric CO2 concentrations (857 ppm) in both CH4 emissions and wetland area. In response to increasing global temperatures (+3.4 °C globally spatially uniform), on average, the models decreased wetland area and CH4 fluxes, primarily in the tropics, but the magnitude and sign of the response varied greatly. Models were least sensitive to increased global precipitation (+3.9 % globally spatially uniform) with a consistent small positive response in CH4 fluxes and wetland area. Results from the 20th century transient simulation show that interactions between climate forcings could have strong non-linear effects. Third, we presently do not have sufficient wetland methane observation datasets adequate to evaluate model fluxes at a spatial scale comparable to model grid cells (commonly 0.5°). This limitation severely restricts our ability to model global wetland CH4 emissions with confidence. Our simulated wetland extents are also difficult to evaluate due to extensive disagreements between wetland mapping and remotely sensed inundation datasets. Fourth, the large range in predicted CH4 emission rates leads to the conclusion that there is both substantial parameter and structural uncertainty in large-scale CH4 emission models, even after uncertainties in wetland areas are accounted for.

scholarly journals Carbon fixation prediction during a bloom of <i>Emiliania huxleyi</i> is highly sensitive to the assumed regulation mechanism

2009 ◽  
Vol 6 (3) ◽  
pp. 5339-5372 ◽  
Author(s):  
O. Bernard ◽  
A. Sciandra ◽  
S. Rabouille
Keyword(s):  
Large Scale ◽  
Carbon Fixation ◽  
Co2 Concentration ◽  
Carbon Fluxes ◽  
Emiliania Huxleyi ◽  
Regulation Mechanism ◽  
Fixation Rate ◽  
Saturation State ◽  
Calcite Saturation ◽  
Order Of Magnitude

Abstract. Large scale precipitation of calcium carbonate in the oceans by coccolithophorids plays an important role in carbon sequestration. However, there is a controversy on the effect of an increase in atmospheric CO2 concentration on both calcification and photosynthesis of coccolithophorids. Indeed recent experiments, performed under nitrogen limitation, revealed that the associated fluxes may be slowed down, while other authors claim the reverse. We designed models to account for various scenarii of calcification and photosynthesis regulation in chemostat cultures of Emiliania huxleyi, based on different hypotheses on the regulation mechanism. These models consider that either carbon dioxide, bicarbonate, carbonate or calcite saturation state (Ω) is the regulating factor. All were calibrated to predict the same carbon fixation rate in nowadays pCO2, but they turn out to respond differently to an increase in CO2 concentration. Thus, using the four possible models, we simulated a large bloom of Emiliania huxleyi. It results that models assuming a regulation by CO32− or Ω predicted much higher carbon fluxes. The response when considering a doubled pCO2 was different and models controlled by CO2 or HCO3 − led to increased carbon fluxes. In addition, the variability between the various scenarii proved to be in the same order of magnitude than the response to pCO2 increase. These sharp discrepancies reveal the consequences of model assumptions on the simulation outcome.

scholarly journals Influence of Global Warming on Baroclinic Rossby Radius in the Ocean: A Model Intercomparison

2006 ◽  
Vol 19 (7) ◽  
pp. 1354-1360 ◽  
Author(s):  
Oleg A. Saenko
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Rossby Waves ◽  
Co2 Concentration ◽  
General Circulation Models ◽  
Atmospheric Co2 ◽  
Western Boundary ◽  
Boundary Currents ◽  
Atmospheric Co2 Concentration ◽  
Rossby Radius Of Deformation

Abstract Results from eight ocean–atmosphere general circulation models are used to evaluate the influence of the projected changes in the oceanic stratification on the first baroclinic Rossby radius of deformation in the ocean, associated with atmospheric CO2 increase. For each of the models, an oceanic state corresponding to the A1B stabilization experiment (with atmospheric CO2 concentration of 720 ppm) is compared to a state corresponding to the preindustrial control experiment (with atmospheric CO2 concentration of 280 ppm). In all of the models, the first baroclinic Rossby radius increases with increasing oceanic stratification in the warmer climate. There is, however, a considerable range among the models in the magnitude of the increase. At the latitudes of intense eddy activity associated with instability of western boundary currents (around 35°–40°), the increase reaches 4 km on average, or about 15% of the local baroclinic Rossby radius. Some of the models predict an increase of the baroclinic Rossby radius by more than 20% at these latitudes under the applied forcing. It is therefore suggested that in a plausible future warmer climate, the characteristic length scale of mesoscale eddies, as well as boundary currents and fronts, may increase. In addition, since the speed of long baroclinic Rossby waves is proportional to the squared baroclinic Rossby radius of deformation, the results suggest that the time scale for large-scale dynamical oceanic adjustment may decrease in the warmer climate, thereby increasing the frequency of long-term climate variability where the oceanic Rossby wave dynamics set the dominant period. Finally, the speed of equatorial Kelvin waves and Rossby waves, carrying signals along the equator, including those related to ENSO, is projected to increase.

scholarly journals Present state of global wetland extent and wetland methane modelling: conclusions from a model intercomparison project (WETCHIMP)

2012 ◽  
Vol 9 (8) ◽  
pp. 11577-11654 ◽  
Author(s):  
J. R. Melton ◽  
R. Wania ◽  
E. L. Hodson ◽  
B. Poulter ◽  
B. Ringeval ◽  
...  
Keyword(s):  
Large Scale ◽  
Positive Response ◽  
Co2 Concentration ◽  
Remotely Sensed ◽  
Atmospheric Co2 ◽  
Emission Rates ◽  
Ch4 Emission ◽  
Wetland Area ◽  
Large Variability ◽  
Ch4 Emissions

Abstract. Global wetlands are believed to be climate sensitive, and are the largest natural emitters of methane (CH4). Increased wetland CH4 emissions could act as a positive feedback to future warming. The Wetland and Wetland CH4 Inter-comparison of Models Project (WETCHIMP) investigated our present ability to simulate large scale wetland characteristics and corresponding CH4 emissions. To ensure inter-comparability, we used a common experimental protocol driving all models with the same climate and carbon dioxide (CO2) forcing datasets. The WETCHIMP experiments were conducted for model equilibrium states as well as transient simulations covering the last century. Sensitivity experiments investigated model response to changes in selected forcing inputs (precipitation, temperature, and atmospheric CO2 concentration). Ten models participated, covering the spectrum from simple to relatively complex, including models tailored either for regional or global simulations. The models also varied in methods to calculate wetland size and location with some models simulating wetland area prognostically, while other models relied on remotely-sensed inundation datasets, or an approach intermediate between the two. Four major conclusions emerged from the project. First, the suite of models demonstrate extensive disagreement in their simulations of wetland areal extent and CH4 emissions, in both space and time. Simple metrics of wetland area, such as the latitudinal gradient, show large variability, principally between models that use inundation dataset information and those that independently determine wetland area. Agreement between the models improves for zonally summed CH4 emissions, but large variation between the models remains. For annual global CH4 emissions, the models vary by ±40 % of the all model mean (190 Tg CH4 yr−1). Second, all models show a strong positive response to increased atmospheric CO2 concentrations (857 ppm) in both CH4 emissions and wetland area. In response to increasing global temperatures (+3.4 % globally spatially uniform), on average, the models decreased wetland area and CH4 fluxes, primarily in the tropics, but the magnitude and sign of the response varied greatly. Models were least sensitive to increased global precipitation (+3.9 % globally spatially uniform) with a consistent small positive response in CH4 fluxes and wetland area. Results from the 20th century transient simulation show that interactions between climate forcings could have strong non-linear effects. Third, we presently do not have sufficient wetland methane observation datasets adequate to evaluate model fluxes at a spatial scale comparable to model grid cells (commonly 0.5°). This limitation severely restricts our ability to model global wetland CH4 emissions with confidence. Our simulated wetland extents are also difficult to evaluate due to extensive disagreements between wetland mapping and remotely-sensed inundation datasets. And fourth, the large range in predicted CH4 emission rates leads to the conclusion that there is both substantial parameter and structural uncertainty in large-scale CH4 emission models, even after uncertainties in wetland areas are accounted for.

scholarly journals A comparative study of large scale atmospheric circulation in the context of future scenario (RCP4.5) and past warmth (Mid Pliocene)

2013 ◽  
Vol 9 (2) ◽  
pp. 1449-1483
Author(s):  
Y. Sun ◽  
G. Ramstein ◽  
C. Contoux ◽  
T. Zhou
Keyword(s):  
Large Scale ◽  
Co2 Concentration ◽  
Future Climate ◽  
Hadley Cell ◽  
Atmospheric Co2 ◽  
Future Scenario ◽  
Atmospheric Co2 Concentration ◽  
Walker Cell ◽  
Tropical Areas ◽  
Modern Level

Abstract. The Pliocene climate (3.3 ~ 3.0 Ma) is often considered as the last sustained warm period with close enough geographic configurations compared to the present one and associated with atmospheric CO2 concentration (405 ± 50 ppm) higher than the modern level. It is therefore suggested that the warm Pliocene climate may provide a plausible scenario for the future climate warming with the important advantage, that for mid-Pliocene, many marine and continental data are available. To investigate this issue, we selected RCP4.5 scenario, one of the current available future projections, to compare the pattern of tropical atmospheric response with past warm mid-Pliocene climate. We performed three OAGCM simulations (RCP4.5 scenario, mid-Pliocene and present day simulation) with the IPSL-CM5A model and investigated atmospheric tropical dynamics through Hadley and Walker cell responses to warmer conditions. Our results show that there is a damping of the Hadley cell intensity in the northern tropics and an increase in both subtropics. Moreover, northern and southern Hadley cells expand poleward. The response of Hadley cell is stronger for RCP4.5 scenario than for mid-Pliocene, but in very good agreement with the fact the atmospheric CO2 concentration is higher in future scenario than mid-Pliocene (543 versus 405 ppm). Concerning the response of the Walker cell, we showed that, despite very large similarities, there are also some differences. i.e. the common features are for both scenarios: weakening of the ascending branch, leading to a suppression of the precipitation over the western tropical Pacific. The response of Walker cell is stronger in RCP4.5 scenario than mid-Pliocene but also depicts some major difference as an eastward shift of the rising branch of Walker cell in future scenario compared to the mid-Pliocene. In this paper, we explain the dynamics of the Hadley and Walker cell, and show that despite minor discrepancy, mid-Pliocene is certainly an interesting analogue for future climate changes in the tropical areas.

scholarly journals Response of simulated burned area to historical changes in environmental and anthropogenic factors: a comparison of seven fire models

2019 ◽  
Vol 16 (19) ◽  
pp. 3883-3910 ◽  
Author(s):  
Lina Teckentrup ◽  
Sandy P. Harrison ◽  
Stijn Hantson ◽  
Angelika Heil ◽  
Joe R. Melton ◽  
...  
Keyword(s):  
Land Use ◽  
Co2 Concentration ◽  
Fire Regimes ◽  
Atmospheric Co2 ◽  
Anthropogenic Factors ◽  
Burned Area ◽  
Earth System ◽  
Atmospheric Co2 Concentration ◽  
Fire Models ◽  
The Impact

Abstract. Understanding how fire regimes change over time is of major importance for understanding their future impact on the Earth system, including society. Large differences in simulated burned area between fire models show that there is substantial uncertainty associated with modelling global change impacts on fire regimes. We draw here on sensitivity simulations made by seven global dynamic vegetation models participating in the Fire Model Intercomparison Project (FireMIP) to understand how differences in models translate into differences in fire regime projections. The sensitivity experiments isolate the impact of the individual drivers on simulated burned area, which are prescribed in the simulations. Specifically these drivers are atmospheric CO2 concentration, population density, land-use change, lightning and climate. The seven models capture spatial patterns in burned area. However, they show considerable differences in the burned area trends since 1921. We analyse the trajectories of differences between the sensitivity and reference simulation to improve our understanding of what drives the global trends in burned area. Where it is possible, we link the inter-model differences to model assumptions. Overall, these analyses reveal that the largest uncertainties in simulating global historical burned area are related to the representation of anthropogenic ignitions and suppression and effects of land use on vegetation and fire. In line with previous studies this highlights the need to improve our understanding and model representation of the relationship between human activities and fire to improve our abilities to model fire within Earth system model applications. Only two models show a strong response to atmospheric CO2 concentration. The effects of changes in atmospheric CO2 concentration on fire are complex and quantitative information of how fuel loads and how flammability changes due to this factor is missing. The response to lightning on global scale is low. The response of burned area to climate is spatially heterogeneous and has a strong inter-annual variation. Climate is therefore likely more important than the other factors for short-term variations and extremes in burned area. This study provides a basis to understand the uncertainties in global fire modelling. Both improvements in process understanding and observational constraints reduce uncertainties in modelling burned area trends.

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