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ArticleProjected 21st century decrease in marine productivity : a multi-model analysis(Copernicus Publications on behalf of the European Geosciences Union, 2010-03-11) Steinacher, M. ; Joos, Fortunat ; Frolicher, T. L. ; Bopp, Laurent ; Cadule, P. ; Cocco, V. ; Doney, Scott C. ; Gehlen, M. ; Lindsay, Keith ; Moore, J. Keith ; Schneider, B. ; Segschneider, J.Changes in marine net primary productivity (PP) and export of particulate organic carbon (EP) are projected over the 21st century with four global coupled carbon cycle-climate models. These include representations of marine ecosystems and the carbon cycle of different structure and complexity. All four models show a decrease in global mean PP and EP between 2 and 20% by 2100 relative to preindustrial conditions, for the SRES A2 emission scenario. Two different regimes for productivity changes are consistently identified in all models. The first chain of mechanisms is dominant in the low- and mid-latitude ocean and in the North Atlantic: reduced input of macro-nutrients into the euphotic zone related to enhanced stratification, reduced mixed layer depth, and slowed circulation causes a decrease in macro-nutrient concentrations and in PP and EP. The second regime is projected for parts of the Southern Ocean: an alleviation of light and/or temperature limitation leads to an increase in PP and EP as productivity is fueled by a sustained nutrient input. A region of disagreement among the models is the Arctic, where three models project an increase in PP while one model projects a decrease. Projected changes in seasonal and interannual variability are modest in most regions. Regional model skill metrics are proposed to generate multi-model mean fields that show an improved skill in representing observation-based estimates compared to a simple multi-model average. Model results are compared to recent productivity projections with three different algorithms, usually applied to infer net primary production from satellite observations.
ArticleClimate-induced interannual variability of marine primary and export production in three global coupled climate carbon cycle models(Copernicus Publications on behalf of the European Geosciences Union, 2008-04-23) Schneider, B. ; Bopp, Laurent ; Gehlen, M. ; Segschneider, J. ; Frolicher, T. L. ; Cadule, P. ; Friedlingstein, Pierre ; Doney, Scott C. ; Behrenfeld, Michael J. ; Joos, FortunatFully coupled climate carbon cycle models are sophisticated tools that are used to predict future climate change and its impact on the land and ocean carbon cycles. These models should be able to adequately represent natural variability, requiring model validation by observations. The present study focuses on the ocean carbon cycle component, in particular the spatial and temporal variability in net primary productivity (PP) and export production (EP) of particulate organic carbon (POC). Results from three coupled climate carbon cycle models (IPSL, MPIM, NCAR) are compared with observation-based estimates derived from satellite measurements of ocean colour and results from inverse modelling (data assimilation). Satellite observations of ocean colour have shown that temporal variability of PP on the global scale is largely dominated by the permanently stratified, low-latitude ocean (Behrenfeld et al., 2006) with stronger stratification (higher sea surface temperature; SST) being associated with negative PP anomalies. Results from all three coupled models confirm the role of the low-latitude, permanently stratified ocean for anomalies in globally integrated PP, but only one model (IPSL) also reproduces the inverse relationship between stratification (SST) and PP. An adequate representation of iron and macronutrient co-limitation of phytoplankton growth in the tropical ocean has shown to be the crucial mechanism determining the capability of the models to reproduce observed interactions between climate and PP.
ArticleClimate-carbon cycle feedback analysis : results from the C4MIP model intercomparison(American Meteorological Society, 2006-07-15) Friedlingstein, Pierre ; Cox, P. ; Betts, Richard A. ; Bopp, Laurent ; von Bloh, W. ; Brovkin, V. ; Cadule, P. ; Doney, Scott C. ; Eby, Michael ; Fung, Inez Y. ; Bala, G. ; John, Jasmin G. ; Jones, C. D. ; Joos, Fortunat ; Kato, T. ; Kawamiya, M. ; Knorr, W. ; Lindsay, Keith ; Matthews, H. D. ; Raddatz, T. ; Rayner, Peter ; Reick, C. ; Roeckner, E. ; Schnitzler, K.-G. ; Schnur, R. ; Strassmann, K. ; Weaver, Andrew J. ; Yoshikawa, C. ; Zeng, NingEleven coupled climate–carbon cycle models used a common protocol to study the coupling between climate change and the carbon cycle. The models were forced by historical emissions and the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A2 anthropogenic emissions of CO2 for the 1850–2100 time period. For each model, two simulations were performed in order to isolate the impact of climate change on the land and ocean carbon cycle, and therefore the climate feedback on the atmospheric CO2 concentration growth rate. There was unanimous agreement among the models that future climate change will reduce the efficiency of the earth system to absorb the anthropogenic carbon perturbation. A larger fraction of anthropogenic CO2 will stay airborne if climate change is accounted for. By the end of the twenty-first century, this additional CO2 varied between 20 and 200 ppm for the two extreme models, the majority of the models lying between 50 and 100 ppm. The higher CO2 levels led to an additional climate warming ranging between 0.1° and 1.5°C. All models simulated a negative sensitivity for both the land and the ocean carbon cycle to future climate. However, there was still a large uncertainty on the magnitude of these sensitivities. Eight models attributed most of the changes to the land, while three attributed it to the ocean. Also, a majority of the models located the reduction of land carbon uptake in the Tropics. However, the attribution of the land sensitivity to changes in net primary productivity versus changes in respiration is still subject to debate; no consensus emerged among the models.