Geocheminar spring-2012

The phase stability and high pressure and temperature equation of state of cobalt oxide was measured up to 65 GPa and 2600 K using the laser heated diamond anvil cell. We find that the B1 structure is stable relative to the low density rhombodedral phase at high temperature throughout this pressure range. We fit a Mie-Grüneisen-Debye model to the B1 data and use it in conjunction with existing thermoelastic parameters of cobalt metal to extend the CoO/Co oxygen fugacity buffer to high pressures and temperatures and to predict relative redox behavior in the deep Earth. ++++++++++++++++++++ Lake Tanganyika, Africa is one of the world’s largest rift lakes and is a hotspot of endemism. Our ability to predict the lake’s ecological response to climate change is of the utmost importance for fishery economy in eastern Africa. Here, we use ostracode trace metal geochemistry as a paleoenvironmental indicator. The trace element composition of ostracode valves reflects ambient environmental conditions and has previously shown promise for quantitative paleotemperature determination. In this study, HR-ICP-MS geochemical data are compared to an existing TEX-86 temperature record from Lake Tanganyika. Two ostracode species were chosen for analyses from core LT-98-58 (1759 +/- 133 AD to modern). Molar Mg/Ca ratios for M. opaca range from .04 to .16, and a trend towards increased Mg/Ca begins ~1880 AD. Molar Mg/Ca ratios for R. ampla range from .05 to .2 but lack a clear anthropogenic warming signal. Sr/Ca ratios in both species range from .003-.006 and remain relatively stable, indicating that changes in Mg/Ca are likely the result of temperature rather than salinity. The M. opaca Mg/Ca record closely resembles the existing TEX-86 paleotemperature record of the past ~240 years. Finally, preliminary data from an initial calibration set for the use of carbonate clumped isotope thermometry in lakes are shown.