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Subproject 3, the biogeochemical component
Project leader: Dr. G. J. Reichart, Dr. E. N. Speelman
Researcher(s):
Starting date: 15-jul-06

Abstract
The Arctic Basin was during the Eocene characterized by huge Azolla blooms with potentially major impacts on biogeochemical cycling and, consequently, climate. This sub-project aims at reconstructing nutrient cycling and the paleo-environmental conditions responsible for the occurrence of these blooms. Novel organic geochemical and stable isotope methods will be applied to reconstruct past ocean surface salinities, temperatures and river influx, which, together with subproject 2, will allow evaluating Eocene biogeochemical cycling in the Arctic. We will investigate the role of Azolla in creating local bottom water disoxia by enhancing organic matter fluxes through the water column, possibly resulting in enhanced phosphorus regeneration and denitrification. Results will be compared with measurements on Azolla material cultivated in subproject 1 under different temperature, pCO2, light regimes and salinity. The role of sulfurisation in enhancing organic matter preservation will be investigated by laboratory sulfurisation of fresh Azolla biomass. The potential of massive Azolla blooms as a global carbon sink will be assessed using box models. We will examine whether the large nitrogen fixation potential of the Azolla-Anabaena complex resulted in significant export of fixed nitrogen from the Arctic Ocean in spite of possible water column denitrification using nitrogen isotopes.

Publications
Speelman, E.N., van Kempen, M.M.L., Barke, J., Brinkhuis, H., Reichart, G.J., Smolders, A.J.P., Roelofs, J.G.M., Sangiorgi, F., de Leeuw, J.W., Lotter, A.F., Sinninghe Damsté, J.S. (2009). The Eocene Arctic Azolla bloom: environmental conditions, productivity and carbon drawdown . Geobiology7 (2): 155-170.
Darwin Center authors: Barke J., Brinkhuis H., van Kempen M. M. L., Lotter A. F., Reichart G. J., Roelofs J. G. M., Sinninghe Damsté J. S., Speelman E. N.

Speelman, E.N., Reichart, G.-J., de Leeuw, J.W., Rijpstra, W.I.C., Sinninghe Damsté, J.S. (2009). Biomarker lipids of the freshwater fern Azolla and its fossil counterpart from the Eocene Arctic Ocean . Organic Geochemistry40 (5): 628-637.
Darwin Center authors: Reichart G. J., Sinninghe Damsté J. S., Speelman E. N.

Bauersachs, T., Speelman, E.N., Hopmans, E.C., Reichart, G.J., Schouten, S., Sinninghe Damsté, J.S. (2010). Fossilized glycolipids reveal past oceanic N2 fixation by heterocystous cyanobacteria. Proceedings of the National Academy of Sciences USA (PNAS)107: 19190-19194.
Darwin Center authors: Bauersachs T., Hopmans E. C., Reichart G. J., Schouten S., Sinninghe Damsté J. S., Speelman E. N.

Eveline N. Speelman, Jacob O. Sewall, David Noone, Matthew Huber, Anna von der Heydt, Jaap Sinninghe Damsté, Gert-Jan Reichart (2010). Modeling the influence of a reduced equator-to-pole sea surface temperature gradient on the distribution of water isotopes in the Early/Middle Eocene. Earth and Planetary Science Letters298: 57-65-
Darwin Center authors: Reichart G. J., Sinninghe Damsté J. S., Speelman E. N.

Eveline Speelman (2010). Reconstruction of the Arctic Ocean environment during the Eocene Azolla interval using geochemical proxies and climate modeling.
Darwin Center authors: Speelman E. N.

Judith Barke, Johan van der Burgh, Johanna H.A. van Konijnenburg-van Cittert, Margaret E. Collinson, Martin A. Pearce, Jonathan Bujak, Claus Heilmann-Clausen, Eveline N. Speelman, Monique M.L. van Kempen, Gert-Jan Reichart, André F. Lotter, Henk Brinkhuis (2012). Coeval Eocene blooms of the freshwater fern Azolla in and around Arctic and Nordic seas. Palaeogeography, Palaeoclimatology, Palaeoecology337-338: 108-119.
Darwin Center authors: Barke J., Brinkhuis H., van Kempen M. M. L., Lotter A. F., Reichart G. J., Speelman E. N.