Paleotemperatures preserved in fluid inclusions in halite

Abstract

A variety of paleoclimate proxy records allow determination of relative warming or cooling. However, if we are to understand climate change, quantification of past temperature fluctuations is essential. Our research indicates that fluid inclusions in halite can yield homogenization temperatures that record surface brine temperatures at the time of halite precipitation. To avoid problems with stretching, leaking, and initial trapping of air, samples with primary, single-phase (liquid) fluid inclusions are chilled in a freezer to nucleate vapor bubbles. We tested the reliability of this method of obtaining fluid-inclusion homogenization temperatures using modern salts precipitated at Badwater Basin, Death Valley, California. Homogenization temperatures correlate well with measured brine temperatures. The same method is applied to fluid inclusions in Pleistocene halite from a core taken at the same location in Death Valley. Results are at several scales, recording diurnal temperature variations, seasonal temperature fluctuations, and longer-term warming and cooling events that correlate with major changes in the sedimentary environment related to climate. This technique is uniquely instrumental for paleoclimate studies because it offers actual, not just proxy, paleotemperature data.