Pleistocene Temperatures

Oxygen isotopic analyses of pelagic Foraminifera from Atlantic, Caribbean, and Pacific deep-sea cores indicate that the temperature of superficial waters in the equatorial Atlantic and Caribbean underwent periodic oscillations during the Pleistocene with an amplitude of about 6° C. The temperature record of the Pacific cores was much affected by local oceanographic conditions. Seven complete temperature cycles are shown by a Caribbean core. By extrapolating rates of sedimentation based on radiocarbon data, an age of about 280,000 years is obtained for the earliest temperature minimum. Correlation with continental events suggests that the earliest temperature minimum corresponds to the first major glaciation. The chronology of Pacific cores proposed by Arrhenius (1952) must be modified if correspondence with the chronology of Atlantic and Caribbean cores is desired. In one Pacific core which extends to the Pliocene, the 610-cm. level below top is believed to represent the Plio-Pleistocene boundary. About fifteen complete temperature cycles occur above this level, and the length of Pleistocene time is estimated at about 600,000 years. The so-called pre-Günzian stages appear to span a time interval about as long as the Giinz and post-Giinzian stages. A glacial lowering of sea-level of about 100 m. is indicated. Closely spaced samples from short pilot cores furnish a detailed temperature record for postglacial times. A continuous temperature increase from about 16,500 to about 6,000 years ago is indicated, followed by a small temperature decrease. The temperature maximum at about 6,000 years ago is correlated with the "Climatic Optimum." Isotopic analyses of calcareous benthonic Foraminifera show that the temperature of bottom water in the equatorial Pacific during glacial ages was similar to the present, but in the eastern equatorial Atlantic it was about 2.1° C. lower. This difference resulted from the large amount of marine ice present in the North Atlantic. Interglacial bottom temperature in the equatorial Pacific was not more than about 0.8° C. higher than glacial temperatures; interglacial data for the equatorial Atlantic are inconclusive with respect to temperature but indicate an influx of ice meltwater along the bottom larger than at present. Correspondence in time between temperature variations in the low latitudes, as shown by the cores, and glacial events in the high northern latitudes indicates close correspondence between glacial or interglacial phases and wet or dry phases, respectively. Good correlation exists between times of temperature minima as indicated by extrapolated rates of sedimentation and times of insolation minima in high northern latitudes. Control of world climate during the Pleistocene by insolation in the high northern latitudes is indicated. A retardation of about 5,000 years occurred between temperature and insolation cycles. Complete revision of current correlations between the insolation curve and continental events is necessary. The glacial epoch and its ages may be explained by a theory combining topographical and insolation effects. Conditions may be suitable for the beginning of a new ice age in about 10,000 years.