Climate in Earth History Studies in Geophysics (1982) / Chapter Skim
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18 Stable Isotopes in Climatic Reconstructions
18 Stable Isotopes in Climatic Reconstructions
Pages 164-171
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From page 164... ...
In addition, paleoclimatic informabon from nollisotopic sources becomes more difficult to obtain as we proceed backward through the geologic record and knowledge of climatic history becomes correspondingly poorer Hence, while the kinds of paleoclimatic information obtainable using isotopic techniques becomes increasingly imprecise as we proceed back through ume, the important queshons about the climate of those earlier Ames can be meaningfully answered with less precisely interpretable data. For these earlier Ames, other isotope paleoclimatic techniques, in addition to the calcium carbonate water paleothermometer, become uxefu .
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From page 165... ...
Uncertainty in the magnitude and isotopic compnsihon of the Antarctic icecap in middle Miocene and later times does create ambiguihes when interpreting the midd e and late Miocene and Pliocene isotopic record in terms of temperature changes. (As discussed below, most, but not all, investigators involved with the isotopic record would argue that, prior to middle Miocene time, late Mesozoic and Cenozoic conbnental ice was never so extensive as to introduce ambiguities into the interpretation of the isotopic data.)
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From page 166... ...
This introduces a degree of uncertainty about the extent to which late Miocene and Pliocene benthic foraminifera isotopic variations should be taken to reflect bottom-water temperature variabons as opposed to variations in continental ice volume and isotopic composition. Through most of Cretaceous and Tertiary time, benthio and planktonic oxygen isotopic compositions fluctuated in roughly parallel manner.
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From page 167... ...
- - ' ~ ~ ~ ''my Ha. Or 6 8 1 1 1 1 1 1 1 1 i , 1,, 10 IZ 14 16 la 20 The earliest application of oxygen isotope measurements to paleoclimates was the study of Cretaceous climates by Urey et al.
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From page 168... ...
Kolodny and Epstein (1976) have presented a comparison be tween Tertiary and Cretan ous benthic foraminiferal isotopic temperatures and chart isotopic temperatures based on the study of DSDP materials, and the comparison is consistent with the behavior out ined above.
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From page 169... ...
The scarcity of suitable old material for analysis and uncertainties about preservation of original iso tope ratios over long periods of time indicate that for the fore xceahle future most applications of this method will he to Quaternary samples. Clay minerals formed during weathering acquire D/H and 180:l60 ratios that reflect the temperature and isotopic eom position of bbe weathering environment.
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From page 170... ...
analyzed DJH and 180'l60 rahos of kaolinite-rich soils of Tertiary age from the western Unated States and found a distribution pattern of D/H generally similar to those of today. However, he found a smaller dihferenoe between Ternary D/H ratios of coastal regions and those of inland regions, suggesting less extreme climatic differences between the two areas than at present, Studies of roil isotopic composib on cannot be expected to provide climatic information of the same precision as can a number of other isotopic paleoclimate tools.
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From page 171... ...
. Temperature limits on the early Archaean oo an from oxygen isotope variations in the Isua supracrustal sequenoe, West Green and, Nature 259, 192 194.
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