Greg Balco

Greg Balco
Berkeley Geochronology Center
2455 Ridge Road
Fields of interest
Geochronology, paleoclimate, ice sheet and glacier change, Antarctic ice sheets
Description of scientific projects
Antarctic ice sheet change. A group of projects focuses on applying cosmogenic-nuclide geochronology to reconstruct past ice sheet change in Antarctica. Mainly this involves locating and visiting parts of Antarctica that are not now covered by ice, looking for geologic evidence for past ice cover, and dating it. This work involves many collaborators and its result is a large data set of surface exposure ages on Antarctic glacial deposits that can be used to reconstruct past changes in ice sheet thickness and extent and also for purposes of ice sheet model evaluation and validation.

One weakness of this work is that, by definition, glacial deposits preserved above the present ice sheet can only provide information about past times when the ice sheet was larger than present, which is important in a a general Earth-history sense, but is not very useful for understanding ice sheet response to warmer-than-present climate conditions that are likely to occur in future. The real challenge is to learn about times when ice sheets were smaller than present, which is much more difficult, because by definition any direct geological evidence that an ice sheet was smaller than present is now buried beneath the ice sheet. Thus, new and future projects in this area aim to take advantage of recently developed drill systems capable of recovering bedrock samples from beneath the Antarctic and Greenland ice sheets, and use cosmogenic-nuclide exposure- and burial-dating methods to find out whether and when subglacial bedrock was exposed by ice sheet shrinkage during past warm periods.

Geochronology data management and discovery. Focuses on building a computational and data management infrastructure for cosmogenic-nuclide geochemistry to make synoptic analysis of global exposure-age and erosion rate data sets feasible, routine, and transparent.

Cosmogenic-nuclide burial dating. Another group of projects (currently with collaborators Charles Rovey, Kim Blisniuk, and Alan Hidy) focuses on applications of the "burial dating" method, which relies on decay of cosmic-ray-produced radionuclides in rocks or sediments that have been exposed to the cosmic-ray flux at the surface for a time and subsequently buried in sedimentary deposits. These methods are very useful for dating late Cenozoic clastic sediments that are difficult to date by other means, and these projects are exploring applications in Quaternary terrestrial stratigraphy and paleoclimate, paleoseismology, and human origins research.

Cosmogenic-nuclide systematics. Work in this area focuses on better methods of measuring cosmic-ray-produced radionuclides and stable noble gases in a variety of minerals; estimating production rates for various nuclide-mineral systems; and building online systems for computing exposure ages and erosion rates from cosmogenic-nuclide concentrations.

Cosmogenic noble gas thermochronometry. This project, with collaborators Marissa Tremblay and David Shuster, aims to understand thermally activated diffusion of cosmic-ray produced noble gases in minerals at the Earth's surface. This is useful because the sensitivity of diffusivity to temperature implies that this approach can potentially be used to reconstruct past surface temperatures.

Other. Precariously balanced rocks. Exposure-dating applications to paleoseismology, tectonics, and glacier change chronology beyond Antarctica.