The presence or absence of certain planktonic Foraminifera in marine sedimentary layers is indicative of oceanic conditions prevailing during the time of deposition. The oceanic conditions are in turn related to broad climatic conditions prevailing during the same time interval. Planktonic assemblages in sediments from the Scotian shelf and slope, South Atlantic, Caribbean Sea, and Mid-Atlantic Ridge are related to oceanic fluctuations during both Tertiary and Pleistocene times. Subtropical faunas in sediments from northern areas indicate the existence of warm oceanic conditions at least 15° farther north than previously believed; also, cool-temperate to boreal faunas in southern latitudes are indicative of general ocean cooling.

Analyses of several core and dredge samples show the simultaneous occurrence in northern latitudes of cold-brackish benthonics and warm West Indian planktonics during and after Wisconsin glaciation. Moreover, faunal extinctions and evolutionary changes are indicative of both abrupt and gradual climatic changes during the past 15 million yr. Faunal evidence clearly shows the nonpermanence of, and recurrence of, oceanic currents. Consequently, evidence of drastic and relatively abrupt planktonic faunal changes in marine cores must be related to changes in ocean circulation, climatic changes, continental glaciation, and other catastrophic events such as volcanism and extreme variations in salinity.

Data gathered from the Recent distribution of planktonic Foraminifera are utilized in interpreting the environments of deposition of ancient sediments. Most previous studies have suggested a relatively abrupt climatic change at the onset of the glacial period (represented by extinctions and additions in relatively short core intervals) and restriction during the Tertiary of warm subtropical waters to latitudes south of 34°00^primeN. The similarity of both planktonic and benthonic assemblages in northern latitudes with those in the Caribbean area during both the Pleistocene and Tertiary strongly suggests the presence (for lengthy periods) of a warm climatic belt or proto-Gulf Stream extending from the Caribbean to at least latitude 46°00^primeN.

Alternate warm and cold sequences in sediments from both the Scotian slope and Mid-Atlantic Ridge support the hypothesis of a fluctuating subarctic convergence in close proximity to a mid-Atlantic gyral during the Pleistocene and late Tertiary. It is the writer's contention that oscillating cooling conditions

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in northern latitudes were developing in late Miocene time approximately 15 million yr ago, that the Pliocene-Pleistocene boundary is approximately 1.8 million yr old, and that the warm latitudinal belt postulated for the Tertiary must be extended to at least 46°00^primeN. If these conclusions are valid, they demand a re-evaluation of paleoclimatology, paleogeography, and paleoceanography.

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