2006 Annual Science Report

Pennsylvania State University Reporting  |  JUL 2005 – JUN 2006

Modeling Early Atmospheric Composition and Climate (Kasting)

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

My students and I, along with my collaborator Dave Pollard, have made progress on several fronts: 1) Dave Pollard and I have published our “thin-ice” model of Neoproterozoic Snowball Earth (see publications listed below). This is a follow-up to the original paper by Chris McKay (GRL, 2000) in which this idea was first proposed. Dave and I showed that the equatorward flow of sea glaciers, discussed by Goodman and Pierrehumbert (JGR, 2003) does not necessarily preclude the existence of thin (~1-m) ice in the tropics. The thin ice model can explain the existence of cap carbonates, like the hard Snowball model, but it also explains how photosynthetic algae survived these global glaciations. Comments by Steve Warren and Jason Goodman, along with our response, are in press. 2) We have made new progress in understanding climate during the Archean Era. In Kasting and Ono (2006), we discuss the possible significance of the low Δ33S values seen in sulfides deposited between about 2.8 Ga and 3.2 Ga. The interpretation offered there is that this corresponds to a period in which photochemically produced O2 increased, perhaps as a consequence of the origin of bacterial sulfate reduction. The increase in O2 should have triggered a decrease in CH4, which in turn may have triggered the 2.9-Ga, mid-Archean glaciation. 3) A paper has been submitted to EPSL proposing a new explanation for the decrease in the δ18O values of sedimentary cherts and carbonates in the distant past. We propose that seawater δ18O increased with time as a consequence of changing tectonic styles and their effect on water-rock interactions within the midocean ridge hydrothermal vents. If correct, this implies that low δ18O values of ancient sedimentary rocks cannot be taken as evidence for a hot Archean