Clues to Ocean History: a Brief Overview of Proxies
17
bration from the South Atlantic is ± 1°C, the one
derived from the global compilation I.SoC.
MUller et al. (1997) achieved promising results
in the application of this method over longer time
intervals (Fig. 9). The calibration of Prahl et al.
(1988) based on cultures of E.huxleyi (SST (0C)
= (U k ' l7 - 0.039) / 0. 034) has been applied to times
when E.huxleyi was either not extant (older than
280 ka) or only appeared as a minor component
of the total coccolith flora (280-80 ka). The results suggest that other species ofGephyrocapsa
forms similar C l7 alkenone ratios.
GeoB 1028-5
:;;
;.
:J
0
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350
400
28
26
24
E
22
fen 20
en
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16
(c)
14
0
50
100
150
200
250
300
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400
AGE (ka)
Fig. 9. Temperature determination using unsaturated alkenones ofthe sediments for the past 400,000 years. (a)
8"0 values ofGlobigerinoides ruber (white); (b) alkenone U k ' ] 7 unsaturation index; (c) comparison of the isotopic
temperature SST estimates (shaded area) with SST values derived from the U k ']7 record using relationships for E.
huxleyi (thick solid curve) and G. oceanica (thin solid curve). Dashed curve is linearily weighted average. Realistic
temperature estimates are obtained using relationships for E.huxleyi even before the first appearance or abundant
appearance of E.huxleyi. From MUller et al. (1997).