Webinar Series on Geo-Science For Sustainable Development Episode: 7

Understanding of sediment provenance and diagenesis using stable isotopes in phosphate

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About Presenter

Dr. Deb P Jaisi is an associate professor in the Department of Plant and Soil Sciences at the University of Delaware, Newark, DE, USA. His environmental chemistry research focuses on biogeochemical processes revolving around phosphorus (P) under three axes: P as an essential nutrient for all living beings, P as a contaminant to open waters, and P as a biocidal agent. His research is carried over a trillion-fold scale from chemical bonds to micro-processes in soil and water and to ecosystems. The ecosystem-scale research addresses questions on the source, sink, transformation, and internal phosphorus cycling in terrestrial and coastal environments.

Dr. Jaisi received a BS/MS degree from Tribhuvan University, Nepal, a second MS degree Asian Institute of Technology, Thailand, and a Ph.D. from Miami University, OH. He was a Bateman Scholar at Yale University before joining the University of Delaware. He currently holds a visiting professorship at California Institute of Technology (CalTech), CA, and Huazhong A. University, China, and is a senior visiting fellow at Xiamen University, China. He is an associate editor in Clays and Clay Minerals, PLOS One, Soil System, and Pedosphere and an editorial board member in ACS Earth and Space Chemistry and Soil Methods.

Dr. Jaisi has published more than 73 peer-reviewed papers and book chapters with a Google h-index of 30. His research outputs are included in state and federal advisory board reports on water quality including the annual science report draft to the White House and in 20+ local and regional media news. In the past 9 years, his research garnered $9 million in federal grants and awards. He is a co-founder and co-director of the Environmental Isotope System (EIS), a central facility at UD. He serves in various regional, national, and international professional organizations and advisory councils. He received National Science Foundation’s CAREER and EPSCoR Fellowship, ACS Early Investigator Award, and ORAU Innovation Award.

Abstract:

Understanding of sediment provenance and diagenesis using stable isotopes in phosphate

Many (bio)geochemical processes that bring about changes in sediment chemistry normally begin at the sediment-water interface continue at depth within the sediment column and may persist throughout the lifetime of sediments. Because of the differential reactivity of sedimentary phosphate phases in response to diagenesis, dissolution/precipitation, and biological cycling, the oxygen isotope ratios of phosphate (d18OP) can carry a distinct signature of these processes and inform the origin. Analysis of sediment P pools with d18OP of phosphate phases in Peru Margin sediments allowed the identification of both the sources and processes. Authigenic phosphates were found to be either precipitated at/near the sediment-water interface or derived from the hydrolysis of organic matter. Detrital phosphates were found with two possible terrigenous sources: phosphate from igneous/metamorphic rocks and phosphate precipitated in source regions in equilibrium with meteoric water. Original isotopic compositions of some authigenic phosphates and all detrital phosphates are not altered by post-diagenetic changes within the sediment column and thus prove a strong proxy in interpreting sedimentary geology. These approaches are expected to be useful in the source, provenance, and paleoenvironmental research in Siwalik and Himalayas.