2007 Annual Science Report
Pennsylvania State University Reporting | JUL 2006 – JUN 2007
Investigations of Modern Analogues of Precambrian Microbial Ecosystems
1) Permian-Triassic Events:We published two manuscripts on the Permian/Triassic boundary event with graduate student Tony Riccardi The first (Palaeogeography, Palaeoclimatology, Palaeoecology) discusses patterns in Δ13C (δ13Ccarbonate-δ13Corganic) across the Permian-Triassic boundary, and the second (Geochimica et Cosmochimica Acta) interprets changes in oceanic sulfur isotopes of sulfate and sulfide in terms of CUEs (chemocline upward excursions) in a followup to the hypothesis put forth by Kump, Pavlov and Arthur (2005). A. Riccardi also analyzed samples from two other Permian-Triassic sections in Turkey documented in a draft manuscript, and successfully defended his PhD dissertation.
2) Nitrogen and Sulfur Cycling at Chemoclines: We have investigated sulfur and nitrogen isotope systematics in modern anaerobic environments and at oxic/anoxic interfaces using the modern Black Sea and Fayetteville-Green Lake. These environments allow us to determine the relative importance of water-column processes (nitrogen fixation, ammonia and nitrate assimilation, denitrification) as determinants of particulate N fluxes to sediments and their N isotopic values. We (graduate student Jamie Fulton), in collaboration with Kate Freeman, have developed a new method for analyzing nanomolar quantities of organic material for carbon and nitrogen isotopes and has analyzed individual pigment fractions to document in situ processes and the effects of diagenesis. In addition we (graduate student Chris Junium) have analyzed black shales deposited in ancient anoxic marine basins (Neoproterozoic, Cretaceous, Devonian) for comparison. Thus far it appears that nitrogen fixation is an important process in black-shale forming environments; most black shales have nitrogen isotope values near 0 permil. We published a paper (Junium and Arthur, 2007) on the Cenomanian-Turonian anoxic event (Geosystems, Gechemistry, Geophysics).
3) Large Igneous Provinces and Extinction: We have explored biotic extinction records and proposed mechanisms, including extraterrestrial impacts and eruption of large igneous provinces (LIPs). Our analysis suggests that not all large impacts or volcanic events cause substantial extinctions and that terrain is an important factor. The Cretaceous/Tertiary impactor and the Siberian Traps, in the case of the Permo-Triassic event, had more profound effects on global environment because they impacted or erupted through carbonate and sulfur rich rocks, thereby increasing the volatile output. Work continues on the possible global effects of an early Cretaceous (121 Ma) LIP, the Ontong-Java/Hikurangi/Manahiki LIP, as the largest known Phanerozoic volcanic province. Concepts and techniques from this work can be applied to understand effects of large Paleoproterozoic volcanic provinces.
PROJECT INVESTIGATORS:Michael Arthur
PROJECT MEMBERS:Galen Halverson
RELATED OBJECTIVES:Objective 4.1
Earth's early biosphere
Effects of extraterrestrial events upon the biosphere
Environmental changes and the cycling of elements by the biota, communities, and ecosystems