EAR-PF: First evidence for low temperature oxygen isotope exchange and fractionation between crystalline iron oxides and water: Role of biogeochemical iron cycling

安德鲁·J·弗里德奇博士被授予NSF地球科学博士后奖学金，在爱荷华州大学和威斯康星大学麦迪逊分校开展研究和教育计划。他将研究铁氧化物和水之间的氧同位素交换和分馏。氧化铁是一种普遍存在的矿物，其与当地大气降水的密切关系使其氧同位素组成成为古气候的潜在代用指标。然而，铁氧化物中氧同位素特征的使用受到无法准确确定矿物质-水氧同位素平衡分馏因子和对改变其同位素组成的时间过程的有限理解的阻碍。Friedich博士将通过研究氧化铁矿物和水之间的氧同位素交换和分馏来解决这些挑战，该交换和分馏是由Fe（II）水溶液引发的，Fe（III）是微生物Fe（III）还原的产物，最近已被证明在低温下催化此类反应。实验的主要前提是利用一种新的“双三同位素方法”（57 Fe-56 Fe-54 Fe和18 O-17 O-16 O），通过测量富集的57 Fe和17 O示踪剂来评估矿物质-水的同位素交换，并通过监测56 Fe/54 Fe和18 O/16 O比值来确定铁和氧的天然质量依赖同位素分馏。这些测量将有助于从根本上了解铁和氧的键合、反应性和氧化铁中的同位素分馏，氧化铁是环境科学和地质学中的一种重要矿物。这项提议将通过为地质学和工程学的本科生研究人员提供指导机会，提供广泛的参与活动，以增加地球科学的多样性，并创造影响众多学科的科学知识。跨学科和多机构的工作计划提供了一个独特的机会进行合作研究。该奖学金还将使Friedich博士能够发展他的指导技能和社区外展经验。以调查为基础的扩大参与活动将指导本科研究人员，吸引爱荷华州市当地学校的小学生和家长，并教育当地女童子军了解地球科学对社会问题的重要性。拟议的研究还将通过确定控制氧化铁反应性的基本过程来提供社会效益，氧化铁反应性影响水质，营养物质的可用性和污染物的命运。

Dr. Andrew J. Frierdich has been awarded an NSF Earth Sciences Postdoctoral Fellowship to carry out a research and education plan at the University of Iowa and the University of Wisconsin-Madison. He will investigate oxygen isotope exchange and fractionation between iron oxides and water. Iron oxides are ubiquitous minerals whose intimacy with local meteoric precipitation makes their oxygen isotope composition a potential proxy for paleoclimate. However, the use of oxygen isotope signatures in iron oxides is stymied by the inability to accurately determine mineral-water oxygen isotope equilibrium fractionation factors and a limited understanding of the temporal processes that alter their isotopic composition. Dr. Frierdich will address these challenges by investigating oxygen isotope exchange and fractionation between iron oxide minerals and water that is initiated by aqueous Fe(II), a product of microbial Fe(III) reduction, which has recently been shown to catalyze such reactions at low temperature. The main premise of the experiments is to utilize a novel "double three-isotope approach" (57Fe-56Fe-54Fe and 18O-17O-16O) whereby mineral-water isotopic exchange is assessed by measuring enriched 57Fe and 17O tracers, and natural mass-dependent isotope fractionation for iron and oxygen is determined by monitoring the 56Fe/54Fe and 18O/16O ratios, respectively. These measurements will contribute to the fundamental understanding of iron and oxygen bonding, reactivity, and isotopic fractionations in iron oxides, an important mineral group in environmental science and geology.This proposal will generate an innovative research and education outreach experience by establishing mentoring opportunities for undergraduate student researchers in geology and engineering, provide broadening participation activities to increase diversity in the geosciences, and create scientific knowledge that impacts numerous disciplines. The interdisciplinary and multi-institutional work plan provides a unique opportunity to perform collaborative research. This fellowship will also allow Dr. Frierdich to develop his mentoring skills and community outreach experiences. The inquiry-based broadening participation activities will guide undergraduate researchers, engage grade school students and parents at Iowa City local schools, and educate local Girl Scout troops about the importance of geosciences to societal problems. The proposed research will also offer societal benefits by identifying the fundamental processes controlling iron oxide reactivity which affects water quality, nutrient availability, and contaminant fate.