Abstract
Abstract. Thermoluminescence (TL) of feldspar is investigated for its potential to extract temperature histories experienced by rocks exposed at Earth's surface. TL signals from feldspar observed in the laboratory arise from the release of trapped electrons from a continuous distribution of trapping energies that have a range of thermal stabilities. The distribution of trapping energies, or thermal stabilities, is such that the lifetime of trapped electrons at room temperature ranges from less than a year to several billion years. Shorter lifetimes are associated with low-temperature TL signals, or peaks, and longer lifetimes are associated with high temperature TL signals. Here we show that trapping energies associated with shorter lifetimes, or lower-temperature TL signals (i.e. between 200 and 250 ∘C), are sensitive to temperature fluctuations occurring at Earth's surface over geological timescales. Furthermore, we show that it is possible to reconstruct past surface temperature histories in terrestrial settings by exploiting the continuous distribution of trapping energies. The potential of this method is first tested through theoretical experiments, in which a periodic temperature history is applied to a kinetic model that encapsulates the kinetic characteristics of TL thermometry. We then use a Bayesian approach to invert TL measurements into temperature histories of rocks, assuming that past temperature variations follow climate variations observed in the δ18O records. Finally, we test the approach on two samples collected at the Mer de Glace (Mont Blanc massif, European Alps) and find similar temperature histories for both samples. Our results show that the TL of feldspar may be used as a paleothermometer.
Highlights
Earth’s climate fluctuates in a cyclic way, on timescales of years to millions of years, driven by Earth’s orbital processes and rare aberrant shift and extreme climate transients during the last 103 to 105 years (e.g. Zachos et al, 2001)
Examples of such proxies include ice cores, tree rings, subfossil pollen, boreholes, corals, lake sediments and carbonate speleothems (e.g. Jones and Mann, 2004 for a review). They have provided invaluable insights into past climates and their physical characteristics, very few of these proxies provide a direct measure of temperature variations in continental settings, and many of these methods often suffer from methodological limitations that limit reliable construction of terrestrial temperatures
We investigate how n changes for 10 different TL thermometers, in the temperature range of 200– 300 ◦C with 10 ◦C intervals, each having an independent set of kinetic parameters
Summary
Earth’s climate fluctuates in a cyclic way, on timescales of years to millions of years, driven by Earth’s orbital processes and rare aberrant shift and extreme climate transients during the last 103 to 105 years (e.g. Zachos et al, 2001). Reconstructions of past terrestrial climates often rely on the use of climate proxies that preserve the physical and/or chemical characteristics related to Earth’s past climate. Examples of such proxies include ice cores, tree rings, subfossil pollen, boreholes, corals, lake sediments and carbonate speleothems Jones and Mann, 2004 for a review) They have provided invaluable insights into past climates and their physical characteristics, very few of these proxies provide a direct measure of temperature variations in continental settings (e.g. glycerol dialkyl glycerol tetraether, GDGT; Tierney et al, 2012), and many of these methods often suffer from methodological limitations that limit reliable construction of terrestrial temperatures.
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