Collaborative Research: Biosignatures of coupled iron and carbon cycling in ferruginous lakes

地球生物学的重大挑战之一是推断在地球演化的早期阶段塑造生物圈的微生物类别，并了解它们的活动对早期海洋和大气的影响。解决这一挑战的最直接方法是使用可以被视为早期地球环境的现代环境。这种类似的环境是罕见的和有价值的。该项目将利用美国中西部的两个湖泊--明尼苏达州布朗尼湖和密歇根州峡谷湖--其沃茨最近被发现含有丰富的溶解亚铁，这使其成为持续了20多亿年地球历史（太古代和元古代）的缺氧“含铁”海洋的良好类似物。通过实地和分析工作，这些研究人员将研究一种早期形式的光合作用，这种光合作用依赖于铁的氧化还原循环（光铁营养）和相应的甲烷循环，这将是古代碳循环的重要组成部分。该项目将限制相关微生物的活性和生物特征。这是了解地球上氧气上升的必要步骤，代表现代铁矿床的大部分的广泛富铁沉积物的沉积，以及主要的气候扰动，以及早期地球上神秘的碳同位素漂移。一个新出现的主要问题是，在含铁海洋中产生和流失到大气中的温室气体甲烷有多大程度，以及这对全球碳循环和气候有何影响。由于先前对含铁湖泊作为早期地球类似物的调查利用了国际地点，该项目将通过建立这两个国家研究地点为美国科学家服务。该项目将支持两名早期职业研究人员，教育两名研究生，并涉及几名本科生的研究。项目结果和已建立的研究地点将用于湖沼学的研究生实践培训。该项目将与两个湖泊的土地管理者合作，提供详细的理化基线，为未来湖泊流域的水质监测工作提供信息，并将为明尼阿波利斯市的环境教育推广计划做出贡献。 光铁营养是前寒武纪含铁海洋初级生产力的主要途径。然而，目前的类似物- meromictic ferruginous湖泊-要么遭受光铁营养的光限制，固定碳主要通过基于硫的光合作用途径，或位于不适合季节性监测的地区。布朗尼湖有充足的光照和丰富的缺氧光养生物（包括光养铁生物）群落，而更深的峡谷湖有一个扩展的缺氧-缺氧过渡区，营养物质比布朗尼湖低得多。总之，这些湖泊包括一系列的条件，调查控制，不同的营养水平，自然地理，季节性对光铁营养初级生产力和甲烷循环。该小组将监测布朗尼湖和峡谷湖水柱中微粒的水和碳同位素地球化学、微生物群落组成和元素组成/矿物学，以确定：（1）调节光养铁菌的存在和活性的物理化学条件，（2）常驻微生物在铁和碳循环中的作用，（3）类似微生物群落可能在前寒武纪富铁沉积物（如条带状铁建造（BIF））中留下的无机和矿物生物特征;（4）光铁营养和甲烷生成/甲烷营养对碳和铁循环的同位素印记。

One of the grand challenges of Geobiology is to infer the classes of microbes that shaped the biosphere at the early stages of Earth evolution, and to understand the effects of their activities on the early oceans and atmosphere. The most direct way of addressing this challenge is to use modern environments that can be considered as analogues for those of early Earth. Such analogue environments are rare and valuable. This project will use two lakes in the Midwestern U.S. - Brownie Lake, MN and Canyon Lake, MI - whose waters were recently discovered to harbor abundant dissolved ferrous iron, which makes them good analogues for the anoxic "ferruginous" oceans that persisted for more than 2 billion years of Earth's history (during Archean and Proterozoic eons). Using field and analytical work, these researchers will investigate an early form of photosynthesis that relies on the redox cycling of iron (photoferrotrophy) and the corresponding cycle of methane, which would have been an important part of the ancient carbon cycle. This project will constrain the activity and biosignatures of the involved microorganisms. This is a necessary step to understand the rise of oxygen on Earth, the deposition of extensive iron-rich sediments that represent the majority of modern-day iron ore deposits, as well as major climate perturbations, and enigmatic carbon isotope excursions on the early Earth. A major emerging question is to what extent the greenhouse gas methane was generated and lost to the atmosphere in ferruginous oceans, and how this contributed to the global carbon cycle and climate. As prior investigations of ferruginous lakes as early Earth analogues utilized international sites, this project will serve U.S. scientists by establishing these two national research sites. The project will support two early career researchers, educate two graduate students, and involve several undergraduates in research. Project results and the established study sites will be used in hands-on graduate training in limnology. In collaboration with land managers of the two lakes, the project will provide a detailed physicochemical baseline to inform future water quality monitoring efforts in the lake watersheds, as well as will contribute to the City of Minneapolis environmental education outreach programs.   Photoferrotrophy is thought to have been the major pathway for primary productivity in ferruginous Precambrian oceans. However, current analogues - meromictic ferruginous lakes - either suffer from light limitation for photoferrotrophy, fix carbon through predominantly sulfurbased photosynthetic pathways, or are located in regions unsuitable for seasonal monitoring. Brownie Lake has sufficient light and an abundant community of anoxygenic phototrophs (including photoferrotrophs), and deeper Canyon Lake has an extended oxic-anoxic transition zone and much lower nutrients than Brownie Lake. Together, these lakes comprise a range of conditions to investigate the controls that varying nutrient levels, physiography, and seasonality have on photoferrotrophic primary productivity and methane cycling. The team will monitor aqueous and carbon isotope geochemistry, microbial community composition, and elemental makeup/mineralogy of particulates from the Brownie and Canyon Lake water columns in order to determine: (1) the physicochemical conditions that regulate the presence and activity of photoferrotrophs, (2) the role of resident microbes in iron and carbon cycling, (3) the inorganic and mineral biosignatures that similar microbial communities might have left in Precambrian iron-rich sediments such as Banded Iron Formations (BIF), and (4) the isotopic imprint of photoferrotrophy and methanogenesis/methanotrophy to carbon and iron cycling.