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Determination of paleotemperatures from fluid inclusion liquid-vapour homogenization in speleothems

Applicant Frenz Martin
Number 119966
Funding scheme Project funding (Div. I-III)
Research institution Institut für angewandte Physik Universität Bern
Institution of higher education University of Berne - BE
Main discipline Other disciplines of Physics
Start/End 01.04.2008 - 31.03.2011
Approved amount 406'069.00
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All Disciplines (4)

Discipline
Other disciplines of Physics
Other disciplines of Earth Sciences
Geochronology
Climatology. Atmospherical Chemistry, Aeronomy

Keywords (8)

speleothems; fluid inclusions; femtosecond laser; phase nucleation; microthermometry; paleoclimate; paleotemperature; bubble collapse

Lay Summary (English)

Lead
Lay summary
Speleothems, such as stalagmites and flowstones, grow continuously for thousands to hundreds of thousands of years and thus provide long-term records of continental climate variability. They can be dated precisely using absolute 230Th-ages. As a result, speleothems have become increasingly attractive to paleoclimate research. We propose a new approach to reconstruct paleotemperatures by measuring liquid-vapour homogenization temperatures (Th) of fluid inclusions in stalagmites. Fluid inclusions in stalagmites are all one-phase liquid at room temperature, except for those in which air was trapped or those which were strongly stretched; therefore, we apply a novel technique that uses single, amplified femtosecond laser pulses to induce bubble nucleation in metastable one-phase (all-liquid) inclusions. Metastability of the fluid is readily achieved by cooling the inclusions below the homogenization temperature, for example to 4.0 °C (the density maximum of pure water). After bubble nucleation Th can subsequently be measured by microthermometry in the same experimental setup. In the particular case of speleothems, which are deposited at ambient atmospheric pressure, Th is expected to be equal to the formation temperatures of the fluid inclusions, which is closely related to cave air temperatures. As cave air temperature in almost all caves is close to the mean annual surface temperature, this new analytical approach will allow us to reconstruct variations in mean annual surface temperatures back to 400,000 years before the present. This technique will provide a calibration-free method for determining paleotemperatures at high temporal resolution. This is a crucial aspect of this project, mainly because current estimates of continental paleotemperatures are primarily based on biological proxies (pollen, midget assemblages) in lake sediments, trees (tree ring width) and physical proxies in ice cores (stable isotopes). As stalagmites can be collected from caves in many of the different climatic zones outside of the polar regions, the data obtained from them perfectly complement the climate data derived from ice cores and other climate archives. Importantly, the results of this project would also aid in filling spatial and temporal gaps, in particular in the tropics and subtropics where almost no information on continental paleotemperatures are currently available.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
134861 Determination of paleo-temperatures using fluid inclusion liquid-vapour homogenization in speleothems: Correction of the measured temperature data 01.04.2011 Project funding (Div. I-III)
130450 Holocene to Late-Pleistocene Paleoclimatic Changes in Turkey and the Eastern Mediterranean Recorded in Speleothems 01.10.2010 SNSF Professorships
140777 Exploration of the phase diagram of liquid water in the metastable region by means of synthetic fluid inclusions 01.03.2013 Project funding (Div. I-III)
132646 STALCLIM - Multi-proxy climatic and environmental reconstructions from stalagmites from Switzerland, Turkey, Arabia and India 01.01.2011 Sinergia
133817 Environmental Analysis and Dating with Radiocarbon using MICADAS 01.12.2010 R'EQUIP

Abstract

Speleothems, such as stalagmites and flowstones, grow continuously for thousands to hundreds of thousands of years (Burns et al., 2003) and thus provide long-term records of continental climate variability. They can be dated precisely using absolute 230-Th-ages. As a result, they have become increasingly attractive to paleoclimate research (Henderson, 2006). To date, paleoclimatic information from stalagmites has mainly been obtained from oxygen (delta18O) and carbon (delta13C) and from hydrogen (deltaD) isotope compositions of speleothem calcite and fluid inclusions, respectively (e.g., Wang et al., 2001; Bar-Matthews et al., 1999; Fleitmann et al., 2003a,b). However, because stable isotope ratios in speleothem calcite and fluid inclusions are influenced by several climatic and environmental factors (e.g., seasonality and amount of precipitation, evaporation in the epikarst or cave, cave air temperature), it is not possible to employ isotopic data for temperature reconstruction. The study of noble gases in fluid inclusions may potentially be used to estimate paleotemperatures, but this approach is in an early stage of development and it is still uncertain if sufficiently precise temperature estimates can be obtained (Yvonne Scheidegger, ETH-Zürich, pers. comm., Aug. 2007).Here we propose a new approach to reconstructing paleotemperatures by measuring liquid-vapour homogenization temperatures (Th) of fluid inclusions in stalagmites. Fluid inclusions in stalagmites are all one-phase liquid at room temperature, except for those in which air was trapped or those which were strongly stretched; therefore, we apply a novel technique that uses single, amplified femtosecond laser pulses to induce bubble nucleation in metastable one-phase (all-liquid) inclusions. Metastability of the fluid is readily achieved by cooling the inclusions below the homogenization temperature, for example to 4.0 °C (the density maximum of pure water). After bubble nucleation Th can subsequently be measured by microthermometry in the same experimental setup. This technique was very recently developed at the Institute of Applied Physics at the University of Bern (Krüger et al., in press). In the particular case of speleothems, which are deposited at ambient atmospheric pressure, Th is expected to be equal to the formation temperatures of the fluid inclusions, which is closely related to cave air temperatures. As cave air temperature in almost all caves is close to the mean annual surface temperature (Wigley and Brown, 1976), this new analytical approach will allow us to reconstruct variations in mean annual surface temperatures back to 400,000 years before the present. A pilot study conducted by Dr. Y. Krüger and Prof. D. Fleitmann on an actively growing stalagmite from Northern Turkey shows that the measured Th values display a clear mode that is in good agreement with measured present day cave air temperature. Although, Th values display a large overall scatter from 6 to > 30 °C, Th-values of individual fluid inclusions are, with few exceptions, reproducible within ± 0.1 °C. In this pilot study we identified several mechanisms responsible for the scatter of the Th-values and can thus suggest appropriate measures to rule out, minimize or quantify these effects to obtain more accurate temperature estimates. The promising preliminary results strongly encourage further investigations, since this method would provide a calibration-free method for determining paleotemperatures at high temporal resolution. This is a crucial aspect of this project, since current estimates of continental paleotemperatures are primarily based on biological proxies (pollen, midget assemblages) in lake sediments, trees (tree ring width) and physical proxies in ice cores (stable isotopes). The estimates are based on transfer functions obtained by calibrating measured parameters against recent instrumental measurements of temperatures. However, it remains uncertain whether such transfer functions remain valid for thousands of years. Thus, a primary goal of future paleoclimate research is to explore new temperature proxies in order to provide more accurate temperature estimates with smaller uncertainties. Such data are crucial to improving and to providing a robust test of climate prediction models. Furthermore, quantification of paleotemperatures will facilitate the interpretation of stable isotope data in speleothems and thereby lead to more accurate reconstruction of climatic and environmental conditions in the past. As stalagmites can be collected from caves in many different climatic zones outside of the polar regions, the data obtained from them perfectly complement the climate data derived from ice cores and other climate archives. Importantly, the results of this project would also aid in filling spatial and temporal gaps, in particular in the tropics and subtropics where almost no information on continental paleotemperatures are currently available. To achieve the objectives outlined above, we intend to systematically investigate the different factors that affect fluid inclusion volumes, fluid densities and liquid-vapour homogenization temperatures (e.g. sample handling and preparation, capillary forces during inclusion formation, effects of the pressure wave emitted during laser-induced bubble nucleation, and surface tension mediated bubble collapse). We will test different approaches to minimizing or quantifying such effects. A key aim of this project is to establish the best sampling strategies and analytical methodologies to obtain paleotemperatures with a precision of ±1°C or even better. Since the development of adequate methodologies is highly demanding and crucial to the success of the project, we plan to employ an experienced scientist in this research area in order to support and train two PhD candidates during this first stage of the project. The results and know-how gained will also be of fundamental importance to investigation of fluid inclusions in other host minerals that formed under supergene or diagenetic conditions (e.g., in oxidation zones of sulfide ore deposits).We will apply the new paleothermometer technique to stalagmites from Switzerland, Turkey and Yemen. Determination of paleotemperatures from liquid-vapour homogenization of the fluid inclusions will complement the stable isotope and trace element data, and offers new possibilities for interpretation of these data with respect to the reconstruction of climatic fluctuations for the last 400,000 years.
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