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National Science Foundation (USA) 2013

Tracing Aridity : Sedimentary Preservation of Scytonemin from Microbiotic Desert Soil Crusts

Desert Soil Crusts


Titre : Tracing Aridity : Sedimentary Preservation of Scytonemin from Microbiotic Desert Soil Crusts

Organismes NSF : Division of Earth Sciences (EAR)

Durée : August 15, 2013 - July 31, 2017

Deserts are a critical end-member in biome reconstructions used to help constrain our understanding of paleoclimatology. Yet given the lower fossilization potential for desert plants and animals, direct paleontological evidence of climate change is much less abundant from arid environments than from other terrestrial ecosystems. However, following the model of wind-blown pollen, potentially continuous sedimentary records can be derived from small eolian particles carrying molecular biomarkers. We posit that one such molecule is scytonemin, a pigment that is produced by cyanobacteria in desert microbiotic soil crusts to protect against UV exposure. We have recently published a mid-Holocene record of sedimentary scytonemin from the Black Sea, and stable isotope analysis supports a desert microbiotic soil source for these molecules. Furthermore, the Black Sea record coincided with 7-methylheptadecane, which is also enriched in desert microbiotic soil cyanobacteria. In a pilot study, we showed that scytonemin is preserved in Great Salt Lake sediments as old as 11,000 years, and its highest concentrations appear to be associated with other sedimentary signs of arid conditions, suggesting that scytonemin may be a representative tracer of cyanobacteria in desert microbiotic soil crusts. Thus, we hypothesize that scytonemin is a biomarker of aridity, with increased accumulation when deserts expanded and cyanobacteria-dominated microbiotic soil crusts became more prevalent.

We propose developing scytonemin and 7-methylheptadecane as molecular biomarkers to reconstruct records of past aridity in the late Quaternary and deeper into the Phanerozoic by addressing four overarching questions : (1) Does scytonemin degradation yield molecular fragments that are chemically recognizable and analytically tractable in ancient geological samples ? (2) What is the physiological relationship between scytonemin and 7-methylheptadecane production in desert microbiotic soil cyanobacteria ? (3) Do scytonemin and 7-methylheptadecane distributions in the Great Salt Lake and the Gulf of California reflect changes in aridity since the Last Glacial Maximum ? (4) Were the Late Permian and Early Triassic characterized by increased aridity ?

Partenaires : James Fulton James_Fulton (Principal Investigator)

Sponsor  : Baylor University One Bear Place #97360 Waco, TX 76798-7360 (254)710-3817

Financement : $251,000.00

Présentation (National Science Foundation )

Page publiée le 11 février 2017, mise à jour le 22 novembre 2017