Paleo temperature

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. 

One of the more important applications of the carbonate paleo-temperature scale was to aid our understanding of the climate changes Earth has experienced during the last 3 million years, a period of intermittent glaciation. 8lsO data from a Caribbean sedimentary core corresponding to the most recent 700,000 years are shown in Fig. 9.2. The repeated variations in 8lsO of amplitude 1.6%o and... 

Geochemists have, since the 1950s, already come up with a remarkable array of paleo-temperature proxies in marine carbonates. These proxies work in diverse oceanic settings, in different organisms, in different parts of the water column, and on varied timescales. Each proxy has different strengths and weaknesses, and some of the proxies, such as Mg/Ca and oxygen isotopes in... 

Figure 9 Summary of available data used to calibrate the influence of calcification temperature on the Mg/Ca of benthic foraminifera, after Lear et al. (2002). Data are from multiple sources. Data included both core-top samples and analyses of cultured foraminifera. Panel (a) displays the full data set used to obtain the exponential calibration given in the text (( ) Rosenthal et al., 1997 (corrected)). Panel (b) displays a subset of the core-top data that suggest a steeper slope than the full data set. This complicating aspect of the calibration is particularly important to paleo-temperature reconstructions in the Late Cenozoic when deep-water temperatures fall in this low-temperature range ((o) Martin et al., 2002 ( ) Lear et al, 2002). See text for further discussion.

Craig, H. 1965. Measurement of oxygen isotope paleo-temperatures. In TONGIORGI, E. (ed.) Stable Isotopes in Oceanographic Studies and Paleotemperatures. Laboratory of Nuclear Geology, National Research Council, Pisa, 161-182. 

Muller, RJ., Kirst, G., Ruhland, G, von Storch, I. and Rosell-Mele, A. 1998. Calibration of the alkenone paleo-temperature index U based on core-tops from the eastern South Atlantic and the global ocean (60°N-60°S). Geochim. Cosmochim. Acta, 62 1757-1772. 

Fig. 10.2 Comparison of the results of different paleo-temperature equations (see Bemis et al. 1998 for review).

Zeebe, R.E., 2001. Seawater pH and isotopic paleo-temperatures of Cretaceous oceans. Palaeogeogra-phy, Palaeoclimatology, Palaeoecology, 170 49-57. 

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