Paleoclimate records provide essential constraints for models to predict complex climate variability. However, paleotemperature proxies are scarce in warm, arid regions of the Earth. Surface water equilibrated with the atmosphere at ambient temperatures may be trapped as fluid inclusions in minerals forming evaporite minerals under such conditions. As noble gas solubility in water is temperature-dependent, this project will examine the potential of evaporites for noble gas-based paleothermometry.
Active salt farms and modern halite provide relatively well-controlled open-air environments in which halite precipitation occurs. These modern environments allow us to examine how short-term temperature fluctuations are reflected in the noble gas temperatures of fluid inclusions in halite, and thus to calibrate the proxy record. In this project, the assembled research time will analyze noble gas concentrations of fluid inclusions in halite that formed at known locations and during known periods of time (i.e. known average temperature) in order to investigate how the noble gas temperature relates to the local temperature record. A positive result will lead to further studies for establishing this new paleotemperature proxy and may have broad implications on climate modeling by providing temperature records for dry regions over extended time periods.
Broader Significance and Importance.
Being able to predict climate change on our planet is arguably of critical for humans on this planet, as climate can directly affect important activities such as agriculture. In order to understand climate in our modern world, it is very helpful to know about Earth?s climate throughout the ancient past. Usually we learn about past climates via geological records. However, geological materials that preserve records of ancient temperature are scarce in warm, dry regions of the Earth, which makes it difficult for us to determine the climate record for such areas.
This award provides support to explore a potentially very useful method for examining climates of these regions by examining natural salt samples. When these salt crystals form, tiny bubbles of liquid and gas are trapped inside. These trapped bubbles are known as inclusions. It has been established that concentrations of chemically inert (noble) gases in water and brine depend upon temperature. Therefore, it is possible that the gas content of the inclusions could be measured to determine ancient Earth temperatures.
To establish whether this method could really be useful, the investigators plan to measure the gas concentrations in inclusions of salt crystals formed under known conditions (mainly salt farms). They will see if the temperatures derived from gas concentrations in these modern salt crystal inclusions actually match or correspond to the local temperature records. If the method proves to be successful way to measure temperature, it will lead to further study on whether the method can be applied to obtain paleotemperature estimates from ancient samples. Consequently such work could enable better climate prediction for the modern world.
Ancient climate records help us understand the climate variability and enhance the capability of future climate predictions. However, geological materials that preserve records of ancient temperature are scarce in warm, dry regions of the Earth. Concentrations of chemically inert (noble) gases in water and brine at the surface are temperature-dependent, and salt crystals may form as the brine evaporates. These salt crystals contain tiny fluid inclusions. We explored the concept that dissolved noble gases in fluid inclusions of evaporite salt crystals may preserve a record of Earth surface temperatures. For this purpose, we measured the gas concentrations in fluid inclusions of salt crystals formed under known conditions (mostly at salt farms) along with detailed microscopic observations. In order to compare the temperature indicated by gas concentrations of the fluid inclusions with those predicted by available noble gas solubility data and actual local temperature records during salt formation, it is necessary to determine both the amount of trapped noble gases and brine water. We discovered that the water released from the evaporites is absorbed by the salt matrix, which prevents an accurate temperature estimation. We plan to continue investigating the viability of this thermometer using improved analytical methods. Two undergraduate students participated in this project. They were trained through petrographic observations, technical developments and gas analyses.
