Expanded Calibrations and Standardization of the Phosphate Oxygen Isotope System

Yale University, New Haven CT

Investigators

Abstract

To better facilitate analyses and interpretations of phosphate oxygen isotope ratio values obtained from the wide and growing range of natural systems currently under study and more extreme environments planned for future study, here we propose a series of comprehensive controlled laboratory calibrations and standardizations of the phosphate?water O-isotope system covering the range of temperature, pH and ionic strength relevant to natural systems and the microorganisms that inhabit these systems (e.g., thermophiles, acidophiles). The primary objectives of the proposed research are to: (1) Refine and extend calibrations of PO4-water O isotope fractionations to encompass environmental conditions (e.g., temperature, pH) relevant to the wide range of natural systems and microorganisms (e.g., extremophiles, archaea) currently under investigation; (2) Make direct comparisons among different published methods for analysis of the oxygen isotope composition of dissolved inorganic PO4 (DIP); and 3) Prepare a suite of silver phosphate standards for PO4 oxygen isotope analysis to replenish waning stocks prepared in 2002 that will be distributed to various laboratories and members of the scientific community for inter-laboratory comparisons and standardization of various methods of isotopic analysis. Furthermore, we propose investigations of phosphate-water O-isotope systematics across major domains of life (bacteria, archaea) and associated with common metabolisms (e.g., BSR, methanogenesis) and geobiologically important groups (microbial mat-forming anoxygenic phototrophs--purple and green sulfur bacteria; iron-oxidizing and iron-reducing bacteria). The general approach to proposed research will be to conduct controlled laboratory experiments to calibrate oxygen isotope fractionations between PO4 and water as a function of temperature, pH, and ionic strength, and to synthesize new silver phosphate standards for O isotope analysis following previously published and well -established experimental protocols. Intellectual Merit: The proposed research will primarily address deficiencies in calibrations of the phosphate oxygen isotope system, and a growing community-wide need for phosphate oxygen isotopic standards and standardization/comparison of recently developed analytical methods. These studies are crucial to many ongoing and future applications of oxygen isotope methods in low-temperature geochemistry as well as to studies of the geobiology of P. Research applications that will benefit from results of the proposed research include research on PO4 d18OP biosignatures and the biogeochemical cycling of P in environments and samples ranging from the marine water column, soils, sediments, hydrothermal systems and contaminated aquifers to the sub-seafloor deep biosphere; as well as general research on the metabolism of PO4 by bacteria and especially archaea whose P metabolism has not been studied in detail. Broader impacts: The silver phosphate standards for O isotope analysis of PO4 that will synthesize as part of the proposed research will be made available to the wider scientific community through the Yale Center for Stable Isotope Analysis. Also the comparison of methods of analysis of dissolved inorganic PO4 in natural waters will benefit current and future researchers employing d18OP in studies of P cycling. The proposed research will train 2 female postdoctoral associates: Dr. Lisa Stout and Dr. Saejung Chang as well as undergraduate summer interns and pre-college students involved in K-12 educational programs sponsored by the Yale Peabody Museum to which Co-PI Ruth Blake is a regular contributor. Results from the proposed studies will be incorporated into graduate and undergraduate courses in Geomicrobiology taught by PI Blake and postdoctoral associate Lisa Stout at Yale University; as well as into public presentations given at both national and international meetings. This research will also be used in K-12 teacher training internships sponsored through the EVOLUTIONS program at the Yale Peabody Museum.