Paleotemperatures

Marcel Dekker, Inc. 270 Madison Avenue, New York, New York 10016 

The application of noble gas based paleotemperature determination is demonstrated in the following sections by case studies, and thereafter some aspects of paleoclimatic feedback are discussed as a requirement of a better understanding of the reconstructed paleotemperatures. Finally, the relevance of paleotemperatures to the topic of global temperature changes is addressed. 

Other examples of noble gas paleotemperatures have been reported by Rudolph et al. (1983). They calculated temperatures as low as 1-2 °C 22,000 years ago (dated by 14C) in Germany, accompanied by relatively negative 5D and 5lsO values and a measurable excess of radiogenic helium. 

3 Paleotemperatures During the Last Glacial Maximum Real or Apparent Differences Between Terrestrial and Oceanic Evidence 

In contrast, noble gas paleotemperatures defined in groundwaters from the Carizzo aquifer (Texas) revealed that during the last glacial 

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The power of this technique is due to the fact that the temperature-depth profile is a direct remnant of paleotemperatures at the ice-sheet surface. It provides a quantitatively accurate measure of long-term average temperatures. This allows the stable isotope records to be calibrated for major climate events (Cuffey et ah, 1995). 

Over the past 220 000 years methane concentrations ranged between 350 and 750ppbv, compared to modem values in excess of 1700-1800 (Fig. 18-15). Over tens of millennia, methane variations appear to correspond to northern hemisphere insolation changes, correlate with Vostok paleotemperatures (Chappel-... 

Stute, M., Schlosser, P., Clark, J. F., and Broecker, W. S. (1992). Paleotemperatures in the southwestern United States derived from noble gases in ground-water. Science 256,1000-1003. 

McCrea, J.M. 1950 On the isotopic chemistry of carbonates and a paleotemperature scale. Journal ofChemical Physics 18(6) 849-857. 

These data show that both models identify important variables that affect 5 Obody w.ier and 8 Ophospha in mammals. Both serve to identify the dikdik as an outlier which may be explained by their sedentary daytime pattern. On the other hand, the body-size model (Bryant and Froelich 1995), which may reliably predict animal 5 0 in temperate, well-watered regions, does not predict 8 Opho,phaw in these desert-adapted species. The second model (Kohn 1996), by emphasizing animal physiology independent of body size, serves to identify species with different sensitivities to climatic parameters. This, in conjunction with considerations of behavior, indicate that certain species are probably not useful for monitoring paleotemperature because their 5 Obodyw er is not tied, in a consistent way, to The oryx, for example, can... 

Tudge, A.P. 1960 A method of analysis of oxygen isotopes in orthophosphate-its use in the measurement of paleotemperatures. Geochimica et Cosmochimica Acta 18 81-93. 

Fig. 4.1. Isotopic paleotemperature analyses of planktonic and benthic foraminifera from the sub-Antarctic Pacific indicating considerably warmer conditions in the Early Cenozoic (Shackleton and Kennett, 1975a).

Fig. 4.2. Paleotemperature change in Tertiary age estimated from pollen assemblages (modified after Yamanoi, 1993).

Fig. 4.3. (A) Composite multispecies benthic foraminiferal Mg/Ca records from three deep-sea sites DSDP Site 573, ODP Site 926, and ODP Site 689. (B) Species-adjusted Mg/Ca data. Error bars represent standard deviations of the means where more than one species was present in a sample. The smoothed curve through the data represents a 15% weighted average. (C) Mg temperature record obtained by applying a Mg calibration to the record in (B). Broken line indicates temperatures calculated from the record assuming an ice-free world. Blue areas indicate periods of substantial ice-sheet growth determined from the S 0 record in conjunction with the Mg temperature. (D) Cenozoic composite benthic foraminiferal S 0 record based on Atlantic cores and normalized to Cibicidoides spp. Vertical dashed line indicates probable existence of ice sheets as estimated by (2). 3w, seawater S 0. (E) Estimated variation in 8 0 composition of seawater, a measure of global ice volume, calculated by substituting Mg temperatures and benthic 8 0 data into the 8 0 paleotemperature equation (Lear et al., 2000).

Shackleton, N.J. and Kennett, J.P. (1975a) Paleotemperature history of the Cenozoic and the initiation of Antarctic glaciation oxygen and carbon isotope analyses in DSDP Sites 277, 279, and 281. Initial Reports of the DSDP, 29, Washington, D.C. U.S. Gov. Printing Office, pp. 743-755. 

Zheng, Y.F. (1996) Oxygen isotope fractionations involving apatites Application to paleotemperature determination. Chem. Geol, 127, 177-187. 

Lauritzen S-E (1993) Natural errvirorrmental change in karst The qrratemary record. Catena Supp 25 21-40 Lauritzen S-E (1995) High-resolution paleotemperature proxy record for the last interglaciation based on Norwegian speleothems. Quat Res 43 133-146... 

Paleotemperatures derived from noble gas analyses are potentially more meaningful than those from oxygen-deuterium analyses because the noble gas content is a direct measure of the temperature of the water at the time of infiltration rather than a complex function of geographic and meteorological factors as is the case with 2H and 180. Despite this potential superiority, few noble gas studies of water paleotemperatures have been published. Specifically, questions need to be answered relative... 

Bender, M. L., Reliability of Amino Acid Racemization Dating and Paleotemperature Analysis on Bones, Nature, 1974, 252, 378-379. 

The haptophyte microalga Emiliania huxleyi produces biomarkers in the form of long-chain (C37, C38, and C39) alkenones (Brassell, 1993). Alkenones are well preserved in marine sediments and their molecular distributions and isotopic composition have been used to infer paleo-temperatures (Brassell, 1993) and pC022 values (Jasper et ak, 1994), respectively. Unsaturation patterns in the alkenone series are related to the growth temperature of the haptophyte algae that produce these compounds (Brassell et ak, 1986 Prahl and Wakeham, 1987), and hold great promise as indicators of absolute ocean paleotemperature. 

Prahl, F.G., and S.G. Wakeham. 1987. Calibration of unsaturation patterns in long-chain ketone compositions for paleotemperature assessment. Nature 320 367-369. 

Emiliani, C. and Shackleton, N. J. The Brunhies epoch Isotopic paleotemperatures and geochronology. Science 183, 511-514 (1974). 

Figure 17. Plot of Li isotopic composition vs. temperature of growth for synthetic calcite crystallized from a solution containing Li from L-SVEC (Marriott et al. 2004). The results are most consistent with temperature not being a significant control on mass fractionation of Li during crystallization from aqueous solution, thus essentially eliminating Li isotopes as a paleotemperature proxy in marine carbonates.

He postulated that the determination of temperatures of the ancient oceans should be possible, in principle, by measuring the 0 content of fossil shell calcite. The first paleotemperature scale was introduced by McCrea (1950). Subsequently, this scale has been refined several times. Through experiments which compare the actual growth temperatures of foraminifera with calculated isotope temperatures Erez and Luz (1983) determined the following temperature equation ... 

Shell-secreting organisms to be used for paleotemperature studies must have been precipitated in isotope equilibrium with ocean water. As was shown by studies of Weber and Raup (1966a, b), some organisms precipitate their skeletal carbonate in equilibrium with the water in which they live, but others do not. Wefer and... 

Of special geological interest is the isotopic analyses of coeval carbonate-phosphate pairs (Wenzel et al. 2000), which helps to distinguish primary marine signals from secondary alteration effects and sheds light on the causes for 5 0 variations of fossil ocean water. Wenzel et al. (2000) compared Silurian cal-citic brachiopods with phosphatic brachiopods and conodonts from identical stratigraphic horizons. They showed that primary marine oxygen isotope compositions are better preserved in conodonts than in brachiopod shell apatite and suggested that conodonts record paleotemperature and ratios of Silurian sea water. 

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