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Department of Geology, University of Southampton, Highfield, Southampton SO17 1BJ, UK
Circulation within oceans is closely linked to climate through feedback mechanisms and both are controlled by insolation and the rotation of the Earth. Because the distribution of organisms is related to the water masses in modern oceans their distribution in the fossil record can be used as a proxy of past water masses. For surface waters the main proxies are calcareous nannofossils, diatoms, radiolaria and planktonic foraminifera. Transfer functions have been derived to determine sea surface temperatures from planktonic microfossils from the Pleistocene and Pliocene. Upwelling regions have distinctive characteristics, notably a great abundance of diatoms and a high dominance of Globigerina bulloides d’Orbigny. For bottom waters the principal proxies are benthic foraminifera and, to a minor extent, ostracods. Some assemblages of epifaunal benthic foraminifera seem to be correlated with specific bottom-water masses, but this is not so for infaunal assemblages. The development of thermohaline circulation caused benthic taxa to adjust their depth distribution patterns; some species became extinct and were replaced by others. Changes in distribution patterns in the Neogene have been interpreted as indicating changes in bottom-water mass structure and distribution. For instance, Nuttallides umboniferus (Cushman) has been used by several authors to map the past distribution of Antarctic Bottom Water. Sometimes processes operating at the ocean surface produce effects on the ocean floor which override benthic processes. Examples of this include seasonal input of phytodetritus which leads to blooms of Epistominella exigua (Brady), and deposition of laminated diatom mats which inhibit bioturbators.
