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.
The oxygen (O2) we breathe as well as that found in carbon dioxide (CO2) and water, (H2O), occurs in three different masses 16, 17 and 18 (oxygen-16, oxygen-17, oxygen-18). The relative amounts of oxygen mass 18 and 16 in many substances, varies with temperature such that the temperature at which the substance forms is ‘recorded’ in the ratio of oxygen 18:16 in the substance. This property forms the basis for several thermometers for minerals that contain oxygen. The temperature at which the mineral is formed (e.g., phosphate (PO4) mineral in bones, teeth, scales and shells) is recorded in the ratio of oxygen 18:16. However, in order for such mineral thermometers to be useful, for example, in studies of earth's climate history, they must be precisely calibrated, preferably through careful and controlled laboratory experiments. A primary goal of this project was to replenish the standard materials required to analyze the oxygen 18:16 ratio of phosphates from calibration experiments and natural samples. These new standards would then be made available to the rapidly growing community of international researchers employing oxygen-based phosphate thermometers to address a range of environmental and geological questions. The other major goal of this project was to refine calibrations for the phosphate thermometer system, which have heretofore been based solely on empirical measurements of phosphatic hardpart remains of organisms (e.g., invertebrate shells, fish bones), by using controlled and defined laboratory systems and also to expand calibrations to as high a temperature as possible. This will allow for future application of the phosphate thermometer to high temperature environments such as volcanic hot springs and earth’s deep subsurface, recently discovered to be teeming with life. The primary product of research is a suite of 4 phosphate standards, 8-20 grams each, covering a broad compositional range to facilitate analyses of both natural samples as well as artificially-labeled tracer and isotope probing studies. These standards will be made available to the wider scientific community. In addition to the 3 published studies related to this grant, the results of refined calibration experiments and expansion to temperatures above 80 degrees celcius form the basis of two additional manuscripts (in-preparation). Additionally, a supplement to this grant was used to support the participation of nine New Haven, CT public school teachers--K-12 and special education, in a summer seminar led by P.I. Blake as part of her participation in the 2010 Yale New Haven Teacher’s Institute (YNHTI). Curriculum units based on fundamental components of this research were developed by each teacher participant and taught during the following school year in K-12 classes, as well as made available to instructors worldwide through the YNHTI website.
