FluidMICS
Geological archives preserve crucial information about past climate changes and help us to extend our “climate memory” and to understand how the climate system reacts to different boundary conditions. Drip stones from caves (so-called speleothems) are a particularly useful climate archive because they grow, protected under ground, over long time periods, contain a multitude of climate proxies, and can be reliably dated by U-Th chronology. In the FluidMICS project and the fluid inclusion laboratory, we use the density of former drip water enclosed in microscopic fluid inclusions as a quantitative proxy to determine past cave air temperatures by means of nucleation-assisted microthermometry.
About the research project
The FluidMICS project is funded by the European Research Council (Consolidator Grant, 2021-2027). Our goal is to further improve and apply fluid inclusion microthermometry in speleothems. The microthermometry approach takes advantage of the temperature dependence of the density of the water that is enclosed in speleothem fluid inclusions. This purely physical basis distinguishes the method from other paleo-thermometers that often rely on empirical calibrations. While our initial focus has been on generating a new land temperature record for the tropical West Pacific with speleothems from Borneo covering half a million years, we have also together with collaborators been applying the method to an increasing number of samples from different locations and climates,. The information we obtain about the magnitude and timing of past land temperature changes contributes to a better understanding of our climate system under different atmospheric CO2 concentrations, and in times of rapid change, to test climate models used for future projections.
In parallel, we work on further improvements of the method both on the analytical and the theoretical side. The main objectives are to explore and extend the applicability of the method to stalagmites with various calcite fabrics and to small inclusions of less than 500 µm3. Furthermore, we investigate potential non-thermal influences on the fluid inclusion - calcite system that may affect the measured temperatures and contribute to the scatter of the data. To this end, we conduct a series of experiments and apply various imaging techniques to better understand the structural relations between inclusions and surrounding calcite.
Study sites
Fluid inclusion microthermometry is applicable in tropical and sub-tropical settings, or past warm periods in mid latitudes, due to its physical limitation to cave temperatures above 8-10 °C (depending on fluid inclusion size).
Together with our international collaborators, we have been investigating speleothems from the following locations:
- Northern Borneo
- South Africa
- Mexico
- New Zealand
- Cook Island
- Sulawesi
- Brazil
- Spain
Overview
Fluid inclusions in stalagmites contain relics of drip water from which the surrounding calcite formed. The density of the enclosed water is directly related to the temperature at the time the inclusions sealed off from the cave environment. Assuming that the inclusions have not undergone any chemical and physical changes, and based on the well-known thermodynamic properties of water, the density of the enclosed water can be used to accurately and precisely determine stalagmite formation temperatures.
The density of fluid inclusion water can be determined by means of the liquid-vapor homogenization temperature using classical microthermometry. The measurements are performed on a microscope equipped with a heating-cooling stage. In addition, the microscope is coupled to a femtosecond laser that allows us to stimulate vapour bubble nucleation in monophase liquid fluid inclusions that are characteristic for stalagmites. This powerful method, also referred to as nucleation-assisted microthermometry, however, requires the presence of well-sealed fluid inclusions of appropriate size (>20-30 μm in the largest dimension), which is not the case for all stalagmites.