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 motivations are simple: We seek to learn more about the Earth system, to develop methods for studying the Earth system, and to provide students with solid scientific training by carrying out these objectives.
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 methods and 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 solved the analytical problem of making high-precision triple oxygen isotope measurements on CO2 and carbonates (Passey et al., 2014, GCA). This opens the door to a wealth of new applications, ranging from animal (paleo)ecology, paleoaridity, and reconstruction of deep-time pCO2 / carbon cycling. 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 well into the development of a geothermometer / geospeedometer based on solid-state diffusion of C and O in carbonate minerals. The 'retrograde' (geospeedometry) aspect of this thermometer centers on 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 has been working on the prograde and burial circuit part of the story (Henkes et al., 2014, GCA): 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