Scientific Objectives and Lab Approach
My research group at Johns Hopkins University uses stable isotope geochemistry to study different aspects of the Earth system, focusing mainly on the junction of geology, biology, and climate. Our basic objectives are 1) to learn more about the Earth system; 2) to develop methods for studying the Earth system; and 3) to provide students with solid scientific training by carrying out objectives 1 and 2.
Topics we have worked on include the history of the East Asian monsoons, the global expansion of C4 vegetation during the late Neogene, paleoenvironments of human evolution, and seawater paleotemperature and isotopic reconstruction during the late Paleozoic and Mesozoic.
Most of our research centers on the development and interpretation of new isotopic datasets. We take a 'hands on' approach, often designing new methods, building custom equipment, and developing models, theory, and mathematics to carry out our research objectives.
Triple oxygen isotope compositions of CO2 and carbonates We have recently optimized methods enabling high-precision triple oxygen isotope analysis of CO2 and carbonates. Using the new methods, grad student Huanting Hu is studying the triple oxygen isotope compositions of dinosaurian eggshells as a basis for reconstructing Mesozoic carbon cycle dynamics and CO2 levels. Grad student Haoyuan Ji has initiated a study of recent soil and lacustrine carbonates, seeking to find out whether evidence of evaporation and aridity can be retrieved with this measurement.
Solid-state clumped isotope reordering We are working on developing a geothermometer / geospeedometer based on solid-state diffusion of C and O in carbonate minerals. We recently published on the 'retrograde' (geospeedometry) aspect of this thermometer, describing how clumped isotope compositions of carbonate minerals evolve during the cooling of rocks, and how the final 'locked-in' clumped isotope compositions relate to the rate of cooling (Passey and Henkes, 2012, EPSL). Graduate student Greg Henkes is now working the prograde and circuit part of the story: How do clumped isotope compositions evolve given specific temperature histories during burial and exhumation, and how 'hot can a sample get' before it loses it's primary, paleoclimate-relevant clumped isotope signature?
Benjamin H. Passey ** Johns Hopkins University ** Department of Earth and Planetary Sciences
120 Olin Hall ** 3400 N Charles St, Baltimore MD 21218