Articles | Volume 12, issue 23
Biogeosciences, 12, 6955–6984, 2015
Biogeosciences, 12, 6955–6984, 2015

Research article 07 Dec 2015

Research article | 07 Dec 2015

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

C. Laufkötter1,16, M. Vogt1, N. Gruber1, M. Aita-Noguchi7, O. Aumont2, L. Bopp3, E. Buitenhuis4, S. C. Doney5, J. Dunne6, T. Hashioka7, J. Hauck8, T. Hirata9, J. John6, C. Le Quéré14, I. D. Lima5, H. Nakano13, R. Seferian15, I. Totterdell10, M. Vichi11,12, and C. Völker8 C. Laufkötter et al.
  • 1Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Zürich, Switzerland
  • 2Laboratoire de Physique des Oceans, Centre IRD de Bretagne, Plouzane, France
  • 3Laboratoire des sciences du climat et de l'Environnement (LSCE), IPSL, CEA-UVSQ-CNRS,UMR8212, Gif-sur-Yvette, France
  • 4Tyndall Centre for Climate Change Research, School of Environmental Sciences, University of East Anglia, Norwich, UK
  • 5Woods Hole Oceanographic Institution, Department of Marine Chemistry & Geochemistry, Woods Hole MA, USA
  • 6NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA
  • 7Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Tokyo, Japan
  • 8Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • 9Faculty of Environmental Earth Science, Hokkaido University, Japan
  • 10Met Office, Exeter, UK
  • 11Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC), Bologna, Italy
  • 12Department of Oceanography, University of Cape Town (UCT), South Africa
  • 13Meteorological Research Institute, Tsukuba, Ibaraki, Japan
  • 14Tyndall Centre for Climate Change Research, University of East Anglia, Norwich Research Park, Norwich, NR47TJ, UK
  • 15CNRM-GAME, Centre National de Recherche Météorologique, Groupe d'Étude de l'Atmosphère Météorologique, Météo-France/CNRS, 42 Avenue Gaspard Coriolis, 31100 Toulouse, France
  • 16NOAA/Geophysical Fluid Dynamics Laboratory, Princeton University, Princeton, New Jersey, USA

Abstract. 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 rather than on the large inter-model differences. Here, we analyze model-simulated changes in NPP for the 21st century under IPCC's high-emission scenario RCP8.5. We use a suite of nine coupled carbon–climate Earth system models with embedded marine ecosystem models and focus on the spread between the different models and the underlying reasons. Globally, NPP decreases in five out of the nine models 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 %. 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 leading to reduced phytoplankton growth. 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 reduce 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 NPP in the remaining model changes by less than 0.5 %. While models consistently project increases 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 it is also modulated by changes in light, macronutrients and iron as well as grazing. Overall, current projections of future changes in global marine NPP are subject to large uncertainties and necessitate a dedicated and sustained effort to improve the models and the concepts and data that guide their development.

Short summary
We analyze changes in marine net primary production (NPP) and its drivers for the 21st century in 9 marine ecosystem models under the RCP8.5 scenario. NPP decreases in 5 models and increases in 1 model; 3 models show no significant trend. The main drivers include stronger nutrient limitation, but in many models warming-induced increases in phytoplankton growth outbalance the nutrient effect. Temperature-driven increases in grazing and other loss processes cause a net decrease in biomass and NPP.
Final-revised paper