K D Mackinnon

Biostratigraphy and late Cenozoic paleoceanography of the Arctic Ocean: Foraminiferal, lithostratigraphic, and isotopic evidence

Detailed studies of benthonic foraminifera, stable isotopes, and lithofacies in cores from the southeastern Alpha Ridge, central Arctic Ocean, reveal some new aspects of Arctic Ocean paleoceanography. High ratios of benthonic to planktonic foraminifera are found in most of the Quaternary sediment units, and ratios of 1:1 appear to characterize the Arctic deep-water sediments. Benthonic foraminifera in the carbonate mud unit M show a succession of calcareous species reflecting increased influx of Norwegian Sea bottom water to the Arctic Ocean during the past 0.4 m.y. Foraminiferal and lithological data indicate less-uniform sedimentation during a warmer interval from 0.4 to 0.6 Ma, when most of the silty lutite unit L was deposited at the CESAR site. Lower Pleistocene units J to I contain less limestone and more dolomite, and they contain a uniform faunal assemblage with low numbers of calcareous foraminifera. Upper Pliocene units H to AB contain rare limestone and relatively large amounts of do-lomite and quartz sand. Middle to upper Pliocene units AB to A3 are marked by abundant sand-sized ferromanganese-coated particles, which in many cases have a silt nucleus; hence, much of the coarse sand in these units does not indicate increased ice rafting. The Pliocene sediments mostly contain a low-diversity assemblage of agglutinated foraminifera, but a mixed calcareous/arenaceous fauna occurs in a short interval above the Matuyama-Gauss boundary (2.4 Ma). Stable-isotopic curves occur within sequences which broadly correspond to stages 1-9 of the global record; below stage 9, the record is discontinuous. Strong vertical mixing apparently prevailed during most of the Pliocene and early Pleistocene, then decreased during the past 0.4 m.y. owing to damping by a perennial ice cover. Isotopic and foraminiferal data, however, suggest that an interval of perennial sea ice also occurred during the late Pliocene at the time of the earliest glacial event recorded in the North Atlantic.