165 KA PALEOTEMPERATURE RECORD FROM FLUID INCLUSIONS, SALAR DE UYUNI, BOLIVIA

Salar de Uyuni (20º S, 68º W), a 10,000 km2 salt flat located on the Altiplano of Bolivia, is underlain by hundreds of meters of interbedded salt and mud. Salar de Uyuni was continuously cored and logged to a depth of 220 m in 1999. Twelve 14C and fourteen uranium series dates from the top 100m (~165 ka) of the core provide the chronological framework for a preliminary paleotemperature record, obtained from fluid inclusions in halite. Salt layers in the Uyuni core commonly contain halite that crystallized at the bottom of a perennial saline lake. These halite “chevrons” contain numerous single-phase brine inclusions that were trapped at the time of crystallization. Cooling of halite chevron crystals in a laboratory freezer causes shrinkage of the enclosed brine inclusions and nucleation of vapor bubbles. Homogenization of these fluid inclusions by microthermometry gives the temperatures of the brines from which the halites precipitated. Fluid inclusion homogenization temperatures from modern halites at Salar de Uyuni compare closely with austral summer air temperatures from a nearby weather station, which verifies that fluid inclusions provide proxy air temperature “snapshots”. Each stratigraphic interval in the Uyuni core was analyzed for a minimum of 80 fluid inclusions, the number needed for 95% confidence of ±1° C. Fluid inclusion homogenization temperatures from 25 stratigraphic intervals so far analyzed have maximum temperatures of 14° to 32° C and average temperatures of 8° to 13° C, with all measurements near or below the range of modern austral summer air temperatures. Average fluid inclusion homogenization temperatures from Holocene and modern halites are 10° to 13° C. Lower temperatures of halite precipitation at ~28 to 34 ka suggest 2° to 5° C cooler conditions on the Bolivian Altiplano during the last glacial.