Planktic and Benthic Foraminifera as Indicators of Past Ocean Changes in Surface and Deep Waters of the Nordic Seas

Sediment cores from the Nordic seas covering the past five climatic cycles have been investigated to elucidate the climate-induced relation between the pelagic and benthic realm from studies of foraminifera. A comparison of the total number of benthic and planktic foraminiferal tests (specimens per gram sediment) reveals corresponding fluctuations over the entire time range investigated. Highest abundances are normally observed during peak interglacial periods, whereas glacial periods are marked by generally reduced numbers offoraminiferal tests. Despite an overall similarity, on a spatial basis, the relative proportion of planktic and benthic foraminiferal abundance seems to have varied between each interglaciation. Moreover, distinct differences in species composition characterize some interglacial periods and short time intervals. Because these compositions have had no modem analogue at any time during the present interglacial (Holocene), it is suggested that they result from oceanographic conditions other than those that prevail in the Nordic seas today.A high-resolution study of the past 25 ka reveals that benthic and planktic foraminifer increased in number after the end of the last glaciation, implying that changes in postglacial water masses had a direct impact on sea-surface and -bottom bioproductivity. This direct linkage between pelagic and benthic faunal productivity persists, although with some notable variations, throughout the Holocene. Furthermore, based on a high correlation coefficient between thermophile surfacewater species and the most dominant benthic suspension feeder, a strong pelagic-benthic coupling gives evidence of a continuous vertical connection of surface and bottom habitats in the Nordic seas during this time.