Plio-Pleistocene sediment core

Figure 11. (a) Late Pleistocene 5 Ca record based on measiwe-ments of G. sacculifer (from Nagler et al. 2000). The inferred variations of temperature are similar to diose inferred from variations of Mg/Ca in die same sediment core, (b) Plio-Pleistocene record of seawater b Ca based on bulk coccolith ooze from DSDP Site 590B in the soudiwestem Pacific (Tasman Sea). The 2.5 m.y. record shows only small variations of 5 Ca. The seawater curve is constructed assuming that the fractionation between seawater and bulk sediment remained constant. The decrease of S Ca at ca. 0.7 Ma could reflect cooling rather than a change in the seawater 5 Ca. 

A tremendous amount of data on past climate has been collected from deep-sea sediment cores, ice cores, and terrestrial archives such as lake sediments. However, several of the most fundamental questions posed by this data remain unanswered. In particular, the Plio-Pleistocene glacial cycles which dominated climate during the past 2.8My have puzzled scientists. More often than not during this period large parts of North America and northern Europe were covered by massive ice sheets up to 3 km thick, which at regular intervals rapidly retreated, giving a sea level rise of as much as 120 m. 

Uranium transport throu the undisturbed, unsaturated Plio-Pleistocene core resulted in similar retardation (R = 3.1) (Figure 6c) to that observed in the repacked sediments (Figure 6b). This is surprising considering the longer residence time in die intact core (280 h) versus the shorter residence time (2 h) and observed geochemical nonequilibrium in the repacked sediments. The... 

Figure 6. Coupled hydrology and geochemistry of the adsorption and displacement of U(VI) through the Plio-Pleistocene Unit, (a) Equilibrium adsorption isotherm showing both Freundlich and linear fits, (b) Observed (points) and modeled (lines) of the displacement of nonreactive tracer Br and U through repacked sediments, (c) Observed (points) and modeled (lines) of the displacement of multiple nonreactive tracers through the intact core, under saturated and unsaturated conditions. The displacement of U occurred under...

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