Late pleistocene pteropod-rich sediment layer in the northeast atlantic and protoconch variation of Clio pyramidata Linné 1767
Abstract Sediment samples from the northeastern Atlantic are compared with recent plankton samples from the same area. Special attention is given to the protoconch variation in the pteropod Clio pyramidata. The dominance/diversity ratio of pteropods and the variation in volume of protoconchae of Clio pyramidata prove that the upwelling off NW Africa in the Late Wurm is present in the same region as today, and that temperatures were 4–6°C lower in this period than during recent times. Possible reasons for the formation of the thin sediment layer rich in pteropods, synchronous from Portugal to Senegal, are discussed. As an hypothesis, red tides are proposed to be responsible for mass mortality of pteropods (and benthonic molluscs), thus forming the pteropod-rich sediment layer.