Coccolithophores are the dominant marine phytoplankton group in the oceanic domain. Coccolithus pelagicus, a common North Atlantic species for long has been considered typical of its subpolar water masses (McIntyre & Be, 1967). Later work showed this species could also be found in distinct ecological context on the Iberian and other upwelling influenced coastal areas (Cachao & Moita, 2000) while its placoliths are more widely present throughout Atlantic surface sediments (Ziveri et al., 2004). In fact, this species showed to be a complex entity including at least two distinct entities, C. pelagicus and C. pelagicus braarudii, based on morphometry, life cycle (Geisen et al., 2002) and genetics (Saez et al. 2003). Further morphometric studies recognized the existence of these two subspecies on the Upper Pleistocene off Iberia, restricting their placolith size ranges to 6-10 mm and 10-13 mm, respectively, while added new evidences for a larger subspecies, C. pelagicus azorinus, and denomination based on its preferential occurrence in surface sediments around the Azores islands (Parente et al., 2004). Since then efforts has been made to add water column evidences of C. pelagicus azorinus as living cells, but so far with no success (Ramos, J., 2003). Reasons for this may be related to the still poor knowledge of the phytoplankton communities around the Azores archipelago. Following recent research (Narciso et al., 2006) a model for the development of placolith size-distinct morphotypes will be discussed relating changes in size to conditions favoring more r- or K-ecological behavior. This model further predicts C. pelagicus azorinus may be related to the Azores frontal system and thus may be used as a proxy of its variations and influence on Central and Eastern North Atlantic.

From: Centre of Geology, University of Lisbon, Edif. C6 Campo Grande, 1749-016 Lisboa, Portugal