GREENCYCLESII

T2.5 Charlotte Laufkotter

Marine phytoplankton fix atmospheric CO2 and contribute 50 percent to global primary production [2], [6]. Their growth and photosynthetic activity influences the cycling of many major chemical elements on Earth, such as N, P, C and S, among others. In their last assessment, the IPCC identify the overall reaction of marine biological cycling to warmer and CO2-rich water as one of the key uncertainties of the carbon cycle [1]. The phytoplankton community in the ocean shows great diversity, and the different phytoplankton types have different functions in the biogeochemical cycling of elements and in particular in their contribution to production and export. Hence, their response to global environmental change is challenging to model. To reduce the biological complexity but still maintain the main features of the plankton distribution, modelers developed the concept of plankton functional types (PFTs). A PFT is a set of different plankton taxal groups which have a similar an distinct biogeochemical function [5]. Important PFTs are for instance silicifiers, calcifiers, nitrogen _fixers or picophytoplankton. With the help of PFTs, a larger set of ecosystem processes can be included in a model and thus interactions between climate, ocean biogeochemistry and marine ecosystems can be investigated. So far, little is known about the distribution of PFTs and their relative contribution to net primary production and export, as well as the influence of climate change on their distribution and therewith on export. Using PFTs allow for better estimates of global production and export in a changing world. Moreover the response of marine ecosystems to climate change and the consequential impact on biogeochemical cycling and fisheries can be analyzed. PFTs may play an important role in the global carbon cycle, and including them in model analysis may provide explanations to variations in atmospheric CO2 content and may help to predict how the ocean uptake of anthropogenic CO2 is likely to evolve over time. The main goal of this research project is to develop further understanding of these processes.

References

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[2] Christopher B. Field, Michael J. Behrenfeld, James T. Randerson, and Paul Falkowski. Primary production of the biosphere: Integrating terrestrial and oceanic components. Science, 281:237{240, 1998.

[3] X. Jin, N. Gruber, D.P. Dunne, J.L. Sarmiento, and R.A. Armstrong. Diagnosing the contribution of phytoplankton functional groups to the production and export of particulate organic carbon, caco3, and opal from global nutrient and alkalinity distributions. Global Biogeochemical Science, 20:GB2015, 2006.

[4] J. Keith Moore, Scott C. Doney, Joanie A. Kleypas, David M. Glover, and Inez Y. Fung. An intermediate complexity marine ecosystem model for the global domain. Deep-Sea Research II, 49:403{462, 2002.

[5] C. Le Qu_er_e, Sandy P. Harrison, I. Colin Prentice, Erik T. Bruitenhuis, O. Aumont, Laurent Bopp, H. Claustre, L.c. Da Cunha, R.J. Geider, Xavier Giraud, Christine Klaas, Karen E. Kohfeld, L. Legendre, Manfredi Manizza, T. Platt, R.B. Rivkin, S. Sathyendranath, J. Uitz, A.J. Watson, and D. Wolf-Gladrow. Ecosystem dynamics based on plankton functional types for global ocean biogeochemistry models. Global Change Biology, 11:2016{2040, 2005.

[6] Christopher L. Sabine et al. The oceanic sink for anthropogenic co2. Science, 305:267{371, 2004.