North-east Atlantic Neogene benthic foraminiferal faunas: tracers of deep-water palaeoceanogra phy

(1659 m) in the north-eastern North Atlantic have undergone strong changes during the past 27 Ma, very probably reflecting changes in the deep oceanic environment. Throughout this time interval the faunas of the deepest site (400) were distinctly different from the faunas of the shallower sites, indicating a persistent depth stratification of the deep water masses. The strongest qualitative faunal change occurred during the middle Miocene, about 15-13 Ma ago, when at all depths everal species that had persisted since the Oligocene became extinct, several new species appeared for the first time, and the quantitative faunal composition of all sites changed rastically. This change is thought to be indicative of the (re-)initiation of North Atlantic Deep Water formation, and occurred at the same time as the rapid growth of the Antarctic ice sheet and a strong change in the carbon and oxygen isotopic omposition ofdeep sea foraminifers worldwide. At the shallower and intermediate sites, the composition of benthic faunas changed again about 6.5-7 Ma ago, a change that also affected several key species at the abyssal site as well. This change was probably caused by the closure of the Mediterranean, the Messinian Crisis. The introduction of a new 'shallow water ' species into the bathyal and upper abyssal sites, as well as a change in dominance in the deep abyss at 2.