2010 Annual Science Report
VPL at University of Washington Reporting | SEP 2009 – AUG 2010
Postdoctoral Fellow Report: Mark Claire
I am interested in how biological gases affect the atmosphere of Earth (and possibly other planets.) Specifically, I use computer models to investigate how biogenic sulfur gases might build up in a planetary atmosphere, and if this would lead to observable traces in Earth’s rock record or in the atmospheres of planets around other stars. I’ve also worked on how perchlorate formed in Earth’s Atacama desert as an attempt to explain how perchlorate formed on Mars
This document reports on activities during year 0.5 through 1.5 of my NAI/NPP postdoctoral fellowship. Significant model development was undertaken, and a first publication on the astronomical detection of biogenic sulfur gases is in review (Domagal-Goldman et al. , submitted). For the biogenic sulfur project (described in Project Report “Detectability of Biosignatures”), I enhanced the VPL photochemical model to enable simple user changes for chemical species, reaction rates, and boundary conditions. I also helped compile the chemical reaction tables for biogenic sulfur gases. This initial biogenic sulfur project was designed to address the “biosignatures” part of my NPP proposal, and work is underway looking at the “biospheres” component, as we build a case that biogenic sulfur metabolism played a vital role during the great oxidation event. We are actively exploring how biogenic sulfur gases may have affected the climate and chemistry of the late Archean and early Proterozoic (Zahnle et al. 2009 ; Zahnle et al. 2010)
Another primary science goal during this period of performance was to enhance the photochemical model to include sulfur isotopes so as to increase predictability for the early Earth. The model was updated to perform high resolution radiative transfer from 180-220 nm, where the SO2 cross sections undergo isotopologue specific changes in their magnitudes, giving rise to non-mass dependent fractionation (NMDF) of sulfur isotopes (Danielache, 2008). All reactions and species involving sulfur were carefully triplicated to allow for the inclusion and interaction of 33S and 34S in the reaction network. This allows us to provide critical tests of recent hypothesis regarding the magnitude of NMDF in the Archean rock record. We are investigating claims of self-shielding by SO2 (Lyons, 2009), shielding by (potentially biogenic) OCS (Ueno et al. 2009), and CO2 (Halevy et al. 2010). At ABSciCon and Goldschmidt, I argued that these other works use oversimplified versions of atmospheric chemistry that are not sufficient to resolve the complexities of the Archean rock record (Claire and Kasting, 2010a,b)
In addition, I worked to complete a number of additional VPL related projects during this time period. These include:
- I enhanced my numerical model for the early Solar flux, which I will submit for publication during the next performance period. Working with VPL co-investigator Martin Cohen, I extended the results of Ribas et al. 2005 into the near UV, and have been investigating uncertainties in the model with the assistance of UW undergrad.
- I went on a field excursion to Chile’s Atacama desert, digging soil pits for analysis of their atmospherically deposited salts, including perchlorate. This data set will help us constrain our models of perchlorate formation on both Earth and Mars. The field excursion had equal contingents of geochemists and biologists, and I became involved in some fascinating geobiology projects looking at the interplay of life in these extreme soils.
PROJECT INVESTIGATORS:Mark Claire
PROJECT MEMBERS:David Catling
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Indirect and direct astronomical observations of extrasolar habitable planets.
Earth's early biosphere.
Biosignatures to be sought in nearby planetary systems