Temperature proxies

Besides readings of Earth s surface temperatures taken with standard glass thermometers, direct readings of atmospheric temperatures have been taken with satellites and weather balloons. In addition to direct measurements of Earth s recent temperatures, proxy measurements of temperatures from farther in the past can be derived from borehole temperature measurements, from historical and physical evidence regarding the e xtent and mass of land and sea ice, and from the bleaching of coral reefs. 

Fig. 18-12 Record of atmospheric CO2 over the past 220 000 years from the Vostok ice core (Jouzel et al., 1993 Bamola et al., 1987), and the corresponding deuterium isotope record temperature proxy (Jouzel et al., 1993) (see Section 18.3.2).

Fig. 18-13 High-resolution measurements of CO2 over the last glacial-interglacial transition from the Byrd ice core in west Antarctica (Neftel et ai, 1982). Also plotted is the oxygen isotope record temperature proxy from the Byrd core (Johnsen et ai, 1972). The time scale for the records plotted here is from Sowers and Bender (1995).

Mahasenan, N., R. G. Watts, and H. Dowlatabadi, Low-Frequency Oscillations in Temperature-Proxy Records and Implications for Recent Climate Change, Geophys. Res. Lett, 24, 563-566 (1997). 

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... 

Temperature dependence of foraminiferal Mg/ Ca ratios was first reported back in the 1950s (Chave 1954 Blackmon Todd 1959). In recent years there have been various attempts to calibrate this, including culture, sediment trap and core-top approaches that have given consistent results for both planktonic and benthic foraminifera (Fig. 6) thanks to careful studies such as these, foraminiferal Mg/Ca is now emerging as an important temperature proxy. 

Fig. 1-2 Chemical data from the Vostok ice core. The graph of 5D can be taken as a proxy for temperature changes, as described in Chapter 18. CO2 and CH4 are greenhouse gases and vary in the same direction as temperature. Non-seasalt sulfate and methane sulfonic acid are both sulfur species existing in the particle phase, and are positively correlated with each other, but negatively with T. Major variations for all of these variables seem to correlate either positively or negatively with each other, indicating a coupled system. <5D, non-seasalt sulfate, and methane sulfonic acid data kindly provided by Dr Eric Saltzman. CO2 data are from Bamola et al. (1987) and Jouzel et al. (1993). CH4 data are from Chappellaz et al. (1990) and Jouzel et al. (1993). (ppmv = parts per million by volume ppbv = parts per billion by volime)...

The approach taken here is to use the lattice strain model to derive the partition coefficient of a U-series element (such as Ra) from the partition coefficient of its proxy (such as Ba) under the appropriate conditions. Clearly the proxy needs to be an element that forms ions of the same charge and similar ionic radius to the U-series element of interest, so that the pair are not significantly fractionated from each other by changes in phase composition, pressure or temperature. Also the partitioning behavior of the proxy must be reasonably well constrained under the conditions of interest. Having established a suitable partition coefficient for the proxy, the partition coefficient for the U-series element can then be obtained via rearrangement of Equation (2) (Blundy and Wood 1994) ... 

An additional advantage of the proxy approach is that the relationship between a U-series element and its proxy is unlikely to be significantly modified by the presence of water. Wood and Blundy (2002) have shown that water can have the effect of either increasing or decreasing partition coefficients due to the combined effect of water on melting temperatures and component activities in melts. For the same reason water can fractionate one valence group from another. It will not, however, produce fractionation between different-sized ions of the same valence entering a specific lattice site. The principal effect of water on the proxy relationship lies in the lower temperature at which hydrous processes tend to occur, relative to anhydrous processes. This is readily accounted for by the presence of temperature in the denominator of Equation (8). 

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.

Modern sea surface temperatures in the Western Equatorial Pacific (0.3°N, 159.4°E) as compared with paleoclimate proxy data for the past 1.35 million years. Modern data are the 5-y running mean, while the paleoclimate data have a resolution on the order of 1000 y. Source-. From Elansen, J., M., et al. (2006). Proceedings of the National Academy of Science of the United States of America 103, 14288-14293. 

Oxygen isotope compositions of phosphates have also been used as a paleotemper-ature indicator. Since the body temperature of mammals is constant at around 37°C, 8 0-values in either bones or teeth depend only on the 5 0-value of the body water, which in turn depends on drinking water (Kohn 1996). Thus, phosphates from continental environments are an indirect proxy of ancient meteoric waters. 

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