Drivers and uncertainties of future global marine primary production in marine ecosystem models

• Published in: Biogeosciences
• Main Authors: Laufkötter, C, Vogt, M, Gruber, N, Aita-Noguchi, M, Aumont, O, Bopp, L, Buitenhuis, E, Doney, S C, Dunne, J, Hashioka, T, Hauck, J, Hirata, T, John, J, Le Quéré, C, Lima, D I, Nakano, H, Seferian, R, Totterdell, I, Vichi, M, Völker, C
• Format: Article in Journal/Newspaper
• Language: English
• Published: Faculty of Science 2015
• Subjects: Ecology; Biology (General); Q; QH501-531; Geology; Life; QH540-549.5; QE1-996.5; QH301-705.5; Science; Southern Ocean
• Online Access: http://hdl.handle.net/11427/34235; https://open.uct.ac.za/bitstream/11427/34235/1/LaufktterC_Driversuncertai_2015.pdf

Past model studies have projected a global decrease in marine net primary production (NPP) over the 21st century, but these studies focused on the multi-model mean and mostly ignored the large inter-model differences. Here, we analyze model simulated changes of NPP for the 21st century under IPCC's high emission scenario RCP8.5 using a suite of nine coupled carbon–climate Earth System Models with embedded marine ecosystem models with a focus on the spread between the different models and the underlying reasons. Globally, five out of the nine models show a decrease in NPP over the course of the 21st century, while three show no significant trend and one even simulates an increase. The largest model spread occurs in the low latitudes (between 30° S and 30° N), with individual models simulating relative changes between −25 and +40%. In this region, the inter-quartile range of the differences between the 2012–2031 average and the 2081–2100 average is up to 3 mol C m -2 yr -1 . These large differences in future change mirror large differences in present day NPP. Of the seven models diagnosing a net decrease in NPP in the low latitudes, only three simulate this to be a consequence of the classical interpretation, i.e., a stronger nutrient limitation due to increased stratification and reduced upwelling. In the other four, warming-induced increases in phytoplankton growth outbalance the stronger nutrient limitation. However, temperature-driven increases in grazing and other loss processes cause a net decrease in phytoplankton biomass and reduces NPP despite higher growth rates. One model projects a strong increase in NPP in the low latitudes, caused by an intensification of the microbial loop, while the remaining model simulates changes of less than 0.5%. While there is more consistency in the modeled increase in NPP in the Southern Ocean, the regional inter-model range is also very substantial. In most models, this increase in NPP is driven by temperature, but is also modulated by changes in light, macronutrients and ...