| Azolla is a small fresh water fern that nowadays occurs worldwide in temperate and subtropical aquatic environments. A generally accepted classification of extant Azolla species comprises three subgenera: Azolla to which A. filiculoides, A. rubra, A. caroliniana, A. microphylla and A. mexicana belong, Rhizosperma to which A. pinnata belongs and Tetrasporocarpia to which A. nilotica belongs (Saunders & Fowler, 1993). Azolla species live in symbiosis with a blue green alga Anabaena azollae which is able to fixate sufficient nitrogen for both itself and its host plant. In exchange Azolla provides the Anabaena with a protected environment and a fixed source of carbon (Wagner, 1997). Analysis of central Arctic drilling cores recently showed that ancestral Azolla spp. grew and reproduced in situ in the Arctic Ocean some 48.5 million years ago during the mid Eocene (Brinkhuis et al., 2006). Interestingly, around this same period a climatic transition occurred from greenhouse to icehouse. Using extant Azolla species we want to assess the possible environmental conditions during the mid Eocene Azolla interval. In combination with the geological and oceanographical evolution of the Arctic Ocean we want to evaluate if Azolla may have acted as a moderator of global nutrient cycles through subsequent burial of organic carbon thereby influencing the climatic transition. |
