Christian
James R.
Christian
James R.
No Thumbnail Available
Search Results
Now showing
1 - 4 of 4
-
ArticleAssessment of skill and portability in regional marine biogeochemical models : role of multiple planktonic groups(American Geophysical Union, 2007-08-02) Friedrichs, Marjorie A. M. ; Dusenberry, Jeffrey A. ; Anderson, Laurence A. ; Armstrong, Robert A. ; Chai, Fei ; Christian, James R. ; Doney, Scott C. ; Dunne, John P. ; Fujii, Masahiko ; Hood, Raleigh R. ; McGillicuddy, Dennis J. ; Moore, J. Keith ; Schartau, Markus ; Spitz, Yvette H. ; Wiggert, Jerry D.Application of biogeochemical models to the study of marine ecosystems is pervasive, yet objective quantification of these models' performance is rare. Here, 12 lower trophic level models of varying complexity are objectively assessed in two distinct regions (equatorial Pacific and Arabian Sea). Each model was run within an identical one-dimensional physical framework. A consistent variational adjoint implementation assimilating chlorophyll-a, nitrate, export, and primary productivity was applied and the same metrics were used to assess model skill. Experiments were performed in which data were assimilated from each site individually and from both sites simultaneously. A cross-validation experiment was also conducted whereby data were assimilated from one site and the resulting optimal parameters were used to generate a simulation for the second site. When a single pelagic regime is considered, the simplest models fit the data as well as those with multiple phytoplankton functional groups. However, those with multiple phytoplankton functional groups produced lower misfits when the models are required to simulate both regimes using identical parameter values. The cross-validation experiments revealed that as long as only a few key biogeochemical parameters were optimized, the models with greater phytoplankton complexity were generally more portable. Furthermore, models with multiple zooplankton compartments did not necessarily outperform models with single zooplankton compartments, even when zooplankton biomass data are assimilated. Finally, even when different models produced similar least squares model-data misfits, they often did so via very different element flow pathways, highlighting the need for more comprehensive data sets that uniquely constrain these pathways.
-
ArticleNorth Pacific carbon cycle response to climate variability on seasonal to decadal timescales(American Geophysical Union, 2006-07-04) McKinley, Galen A. ; Takahashi, Taro ; Buitenhuis, Erik T. ; Chai, Fei ; Christian, James R. ; Doney, Scott C. ; Jiang, Mingshun ; Lindsay, Keith ; Moore, J. Keith ; Le Quere, Corinne ; Lima, Ivan D. ; Murtugudde, Raghu ; Shi, L. ; Wetzel, PatrickClimate variability drives significant changes in the physical state of the North Pacific, and thus there may be important impacts of climate variability on the upper ocean carbon balance across the basin. We address this issue by considering the response of seven biogeochemical ocean models to climate variability in the North Pacific. The models’ upper ocean pCO2 and air-sea CO2 flux respond similarly to climate variability on seasonal to decadal timescales. Modeled seasonal cycles of pCO2 and its temperature and non-temperature driven components at three contrasting oceanographic sites capture the basic features found in observations [Takahashi et al., 2002, 2006; Keeling et al., 2004; Brix et al., 2004]. However, particularly in the Western Subarctic Gyre, the models have difficulty representing the temporal structure of the total pCO2 cycle because it results from the difference of these two large and opposing components. In all but one model, the airsea CO2 flux interannual variability (1σ) in the North Pacific is smaller (ranges across models from 0.03 to 0.11 PgC/yr) than in the Tropical Pacific (ranges across models from 0.08 to 0.19 PgC/yr), and the timeseries of the first or second EOF of the air-sea CO2 flux has a significant correlation with the Pacific Decadal Oscillation (PDO). Though air-sea CO2 flux anomalies are correlated with the PDO, their magnitudes are small (up to ±0.025 PgC/yr (1σ)). Flux anomalies are damped because anomalies in the key drivers of pCO2 (temperature, dissolved inorganic carbon (DIC) and alkalinity) are all of similar magnitude and have strongly opposing effects that damp total pCO2 anomalies.
-
PreprintAssessing the uncertainties of model estimates of primary productivity in the tropical Pacific Ocean( 2008-03) Friedrichs, Marjorie A. M. ; Carr, Mary-Elena ; Barber, Richard T. ; Scardi, Michele ; Antoine, David ; Armstrong, Robert A. ; Asanuma, Ichio ; Behrenfeld, Michael J. ; Buitenhuis, Erik T. ; Chai, Fei ; Christian, James R. ; Ciotti, Aurea M. ; Doney, Scott C. ; Dowell, Mark ; Dunne, John P. ; Gentili, Bernard ; Gregg, Watson ; Hoepffner, Nicolas ; Ishizaka, Joji ; Kameda, Takahiko ; Lima, Ivan D. ; Marra, John F. ; Melin, Frederic ; Moore, J. Keith ; Morel, Andre ; O'Malley, Robert T. ; O'Reilly, Jay ; Saba, Vincent S. ; Schmeltz, Marjorie ; Smyth, Tim J. ; Tjiputra, Jerry ; Waters, Kirk ; Westberry, Toby K. ; Winguth, ArneDepth-integrated primary productivity (PP) estimates obtained from satellite ocean color based models (SatPPMs) and those generated from biogeochemical ocean general circulation models (BOGCMs) represent a key resource for biogeochemical and ecological studies at global as well as regional scales. Calibration and validation of these PP models are not straightforward, however, and comparative studies show large differences between model estimates. The goal of this paper is to compare PP estimates obtained from 30 different models (21 SatPPMs and 9 BOGCMs) to a tropical Pacific PP database consisting of ~1000 14C measurements spanning more than a decade (1983- 1996). Primary findings include: skill varied significantly between models, but performance was not a function of model complexity or type (i.e. SatPPM vs. BOGCM); nearly all models underestimated the observed variance of PP, specifically yielding too few low PP (< 0.2 gC m-2d-2) values; more than half of the total root-mean-squared model-data differences associated with the satellite-based PP models might be accounted for by uncertainties in the input variables and/or the PP data; and the tropical Pacific database captures a broad scale shift from low biomass-normalized productivity in the 1980s to higher biomass-normalized productivity in the 1990s, which was not successfully captured by any of the models. This latter result suggests that interdecadal and global changes will be a significant challenge for both SatPPMs and BOGCMs. Finally, average root-mean-squared differences between in situ PP data on the equator at 140°W and PP estimates from the satellite-based productivity models were 58% lower than analogous values computed in a previous PP model comparison six years ago. The success of these types of comparison exercises is illustrated by the continual modification and improvement of the participating models and the resulting increase in model skill.
-
ArticleInconsistent strategies to spin up models in CMIP5 : implications for ocean biogeochemical model performance assessment(Copernicus Publications on behalf of the European Geosciences Union, 2016-05-12) Seferian, Roland ; Gehlen, Marion ; Bopp, Laurent ; Resplandy, Laure ; Orr, James ; Marti, Olivier ; Dunne, John P. ; Christian, James R. ; Doney, Scott C. ; Ilyina, Tatiana ; Lindsay, Keith ; Halloran, Paul R. ; Heinze, Christoph ; Segschneider, Joachim ; Tjiputra, Jerry ; Aumont, Olivier ; Romanou, AnastasiaDuring the fifth phase of the Coupled Model Intercomparison Project (CMIP5) substantial efforts were made to systematically assess the skill of Earth system models. One goal was to check how realistically representative marine biogeochemical tracer distributions could be reproduced by models. In routine assessments model historical hindcasts were compared with available modern biogeochemical observations. However, these assessments considered neither how close modeled biogeochemical reservoirs were to equilibrium nor the sensitivity of model performance to initial conditions or to the spin-up protocols. Here, we explore how the large diversity in spin-up protocols used for marine biogeochemistry in CMIP5 Earth system models (ESMs) contributes to model-to-model differences in the simulated fields. We take advantage of a 500-year spin-up simulation of IPSL-CM5A-LR to quantify the influence of the spin-up protocol on model ability to reproduce relevant data fields. Amplification of biases in selected biogeochemical fields (O2, NO3, Alk-DIC) is assessed as a function of spin-up duration. We demonstrate that a relationship between spin-up duration and assessment metrics emerges from our model results and holds when confronted with a larger ensemble of CMIP5 models. This shows that drift has implications for performance assessment in addition to possibly aliasing estimates of climate change impact. Our study suggests that differences in spin-up protocols could explain a substantial part of model disparities, constituting a source of model-to-model uncertainty. This requires more attention in future model intercomparison exercises in order to provide quantitatively more correct ESM results on marine biogeochemistry and carbon cycle feedbacks.