Deep-Sea Benthic Foraminifers: Food and Bottom Water Masses

Abstract

Benthic foraminifers are an abundant, nearly cosmopolitan and easily preserved component of the deep-sea meiofauna. The benthic foraminiferal faunas are very strongly structured on regional scales. In the western North and South Atlantic the distribution of benthic assemblages follows the distribution of named “water masses,” leading to the expectation that fossil benthic foraminifers from sediment cores allow a reconstruction of past deep-water circulation patterns. However, in many other areas the faunal composition is strongly correlated with the productivity of the overlying surface waters. Such results demonstrate that the benthic meiofauna responds to the integral of the deep environment and it is the limiting or overwhelming influence that determines the success or failure of individual species and thus the composition of the fauna. Analysis of available data clearly indicates that benthic foraminifers are unequivocal indicators of productivity in areas where productivity is high. In areas of low or very uniform productivity the composition of the benthic fauna clearly carries the imprint of deep water mass structure as the dominant feature. Faunal sequences from late Quaternary cores from the Atlantic and Pacific oceans show very strong differentiations. Not only is the glacial/postglacial transition shown, but also much superimposed fine structure. Faunal composition is as sensitive to deep-water environmental change as are geochemical indicators. The faunal composition allows at least some appreciation of the cause for the major changes, but a quantitative differentiation between productivity or water mass changes is not yet possible. If, however, an independent assessment of productivity change is available, then the benthic foraminiferal faunas are exquisite indicators of changes in deep water circulation.