G

1000

1100

1200-1

FIGURE 6.1 I A composite oxygen isotope record for the Brunhes chron, derived by correlating the common features in I I planktonic and 2 benthic formanifera records from different oceanic regions. Each record was normalized before they were combined, so the composite record is scaled in terms of standard deviation units. Isotope stage boundaries are shown (Prell et a/., 1986).

31.1

FIGURE 6.1 I A composite oxygen isotope record for the Brunhes chron, derived by correlating the common features in I I planktonic and 2 benthic formanifera records from different oceanic regions. Each record was normalized before they were combined, so the composite record is scaled in terms of standard deviation units. Isotope stage boundaries are shown (Prell et a/., 1986).

Climatic State

Estimated Summer Sea-Surface Temperature

Deglacial termination I

Main glacial transition

Glacial inception

Deglacial termination II

Isotope Age Stratigraphie Stage (years B P.) Control

Climatic State

Estimated Summer Sea-Surface Temperature

Deglacial termination I

Main glacial transition

Glacial inception

Deglacial termination II

Present Interglacial

_____S '

Main Wisconsin, Glaciation

4 -

Early Wisconsin, Glaciation

-V

Peak Interglaciation "

FIGURE 6.12 Summer sea-surface temperature reconstructions for the North Atlantic Ocean based on foramlniferal assemblage paleotemperature estimates, using coreV23-82 from 53° N 22° W (Sancetta et a/., 1973a,b). Chronological controls used in other cores are shown on the right (tephra layers and Barbados sea-level stands). Isotopic stages are after Shackleton and Opdyke (1973). Generalized climatic conditions and major changes are shown at left (Ruddiman, 1977b).

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

120'000 Barbados3 130,000 (~125,000 B.P.)

FIGURE 6.12 Summer sea-surface temperature reconstructions for the North Atlantic Ocean based on foramlniferal assemblage paleotemperature estimates, using coreV23-82 from 53° N 22° W (Sancetta et a/., 1973a,b). Chronological controls used in other cores are shown on the right (tephra layers and Barbados sea-level stands). Isotopic stages are after Shackleton and Opdyke (1973). Generalized climatic conditions and major changes are shown at left (Ruddiman, 1977b).

higher temperatures, with substage 5e being the peak of the last interglacial (Shackleton, 1969). Stages 5b and 5d were periods of cooler temperature and/or terrestrial ice growth, but on a smaller scale than occurred in stage 4. Interestingly, the change in benthic 8180 commonly recorded between stages 5e and 5d is so large and so rapid that it is almost impossible to account for it only in terms of ice-sheet growth. Ice sheets take thousands of years to grow to such a size that they affect oceanic isotopic composition (Barry et ai, 1975). It seems likely that at least part of this change reflects a rapid temperature decline (of >1.5 °C) in abyssal water temperature (Shackleton, 1969, 1987). Subsequent changes in 8lsO (in stages 5c to 1) were then primarily the result of changing ice volumes on the continents, according to this argument. However, paleo-sea-level data from New Guinea also points to a very rapid change in eustatic sea level (-60 m) between -115,000 and -105,000 yr B.P., which bears out the simple ice-growth interpretation of the 8lsO record (Fig. 6.13). If this change did indeed occur, it represents an extraordinary episode in late Quaternary history, with the water equivalent of one Greenland ice sheet being transferred from the oceans to the continents every 1000 yr during this interval (see also Section 6.34).

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