Collaborative Research: Iron- and Manganese-Depositing Cold-Seeps: Mineral Formation Along a Freshwater to Marine Ecosystem

这个合作项目研究了阿拉斯加州苏打湾富铁(Fe)和富锰(Mn)的低温碳酸盐生态系统的地球化学和地质微生物学。这些地点包括许多冷泉和泉水，其中含有二氧化碳(CO2)的冒泡水已被证明是非常不寻常的，因为它们还活跃地沉积铁和锰矿物，而这些矿物反过来又蕴藏着广泛的微生物垫群落。在这个独特的分水岭内发现的泉水和渗漏形成了一个盐度梯度，上游的淡水更多，而下游则受到潮汐驱动的海洋影响。这些栖息地是形成大片微生物-矿物丘(即凝灰岩矿床)的地点。高达三米的凝灰岩位于苏打湾小溪两岸，苏打湾小溪流入苏打湾河口。高流量系统主要是铁氧化物沉积环境，而低流量系统则是锰氧化物沉积环境。该项目将研究这一独特的分水岭，努力描述从上游小溪到苏打湾的物理化学梯度上铁和锰矿物形成的生物地球化学和地质微生物学。研究人员推测，这些土丘是自养生态系统，寄生着微生物，能够从金属氧化反应捕获的能量中生长并固定二氧化碳。他们建议在考虑两个主要问题的情况下研究这些生态系统的微生物生态。首先，这些微生物利用哪些代谢过程来获取能量，从而养活自己？其次，这些微生物群落(由矿物质和富含二氧化碳的流体提供燃料)可能会随着物理化学梯度的变化而发生变化？对这些问题的回答将使他们能够解决未来的重要问题，即这些环境是否保留了微生物化石的痕迹或可以显示历史存在的生物签名，从而提供了对过去的一瞥。这是一项新的潜在的变革性调查，因为几乎没有关于低温富铁和富锰地下水对淡水或海洋生态系统的影响的信息，无论这些系统是否有助于固碳和碳循环，或者支持这些生态系统的微生物的能量或代谢基础。该项目将与海达堡学区合作。自2008年以来，其中一名研究人员与海达堡学区和海达堡合作协会(部落政府)建立了一个长期的地球科学教育和研究计划。该计划包括5-12年级的科学课程和教师培训，强调地球科学的跨学科性质。感兴趣的学生有机会参与实地采样，并将在苏打湾之旅中与科学家互动。这个项目与当地部落团体紧密结合在一起，这些部落团体与这个网站有很长的历史。反过来，研究人员将定期与部落组织分享他们的科学发现。该项目非常适合获得热切的支持，因为它具有探索性和潜在的高影响力。它将汇集多方面的技术(例如，航空现场调查、分子生物学、显微镜和地球化学)，以努力实现对这一可能由金属作为能源驱动的新生态系统的多尺度了解，并将在其中保留独特的生物地球化学特征。对地质记录中这些特征的解释可能会为重要的地质学问题提供新的见解，例如古代的生命，微生物在金属矿床形成中的作用，甚至是地球上生命从缺氧进化到有氧世界的演化。最终，研究人员希望更好地预测这些类型的多维强梯度驱动的环境强迫作用之间的相互作用，从而更好地预测生命如何适应和矿化发生。

This collaborative project examines the geochemistry and geomicrobiology of low-temperature iron-(Fe) and manganese-(Mn) rich carbonate ecosystems in Soda Bay, Alaska. These sites comprise numerous cold seeps and springs with bubbling waters containing carbon dioxide (CO2) that have proven to be very unusual in that they are also actively depositing Fe and Mn minerals, which in turn are harboring extensive microbial mat communities. The springs and seeps found within this unique watershed form along a salinity gradient with upstream being more freshwater while downstream has a tidally-driven marine influence. These habitats are sites where extensive microbial-mineral mounds (i.e., tufa deposits) form. Tufas as high as three meters are located along the length of both sides of Soda Bay Creek which drains into Soda Bay Estuary. The high flow systems are predominantly iron oxide deposition environments while the systems exhibiting low flow deposit manganese oxides. This project will investigate this unique watershed in an effort to describe thebiogeochemistry and geomicrobiology of Fe- and Mn-mineral formation along the physicochemical gradients from the upper creek to Soda Bay. Researchers hypothesize that the mounds are autotrophic ecosystems hosting microorganisms able to grow and fix CO2 from the energy captured from metal oxidation reactions. They propose to examine the microbial ecology of these ecosystems with two primary questions in mind. First, what are the metabolic processes these microbes use to capture energy and thereby feed themselves? Second, how might these microbial communities (fueled by mineral and CO2-rich fluids) change in response to the physicochemical gradients? Answers to these questions will allow them to address future important questions relating to whether these environments preserve traces of microbial fossils or biosignatures that can show a historical presence and thereby provide a glimpse into the past. This is a new and potentially transformative investigation as there is virtually no information regarding the impact of low-temperature Fe- and Mn-rich groundwater on freshwater or marine ecosystems, whether such systems contribute to carbon fixation and the carbon cycle, or the energetic or metabolic basis of the microbes supporting these ecosystems.This project will partner with the Hydaburg School District. One of the researchers has built a longterm geoscience education and research program with the Hydaburg School District and Hydaburg Cooperative Association (tribal government) since 2008. The program involves 5th-12th grade science classes and teacher training with an emphasis on the interdisciplinary nature of the geosciences. Interested students have the opportunity to participate in field sampling and will interact with scientists during trips to Soda Bay. This project is closely coupled with local tribal groups that have a long history with this site. Researchers will, in turn, routinely share their scientific discoveries with the tribal organization.The project is well suited for EAGER support as it is exploratory in nature and potentially high impact. It will bring together multifaceted-technologies (e.g., aerial site survey, molecular biology, microscopy and geochemistry) in an effort to achieve a multi-scale understanding of this novel ecosystem potentially driven by metals as energy sources and where unique biogeochemical signatures will be preserved. Interpretation of such signatures in the geological record may provide new insights into important geological questions such as life in the ancient past, the role of microbes in the formation of metal ore deposits and even the evolution of life on Earth as the planet evolved from an anoxic to an oxic world. Ultimately, investigators hope to better predict how life now adapts to and mineralization occurs from interactions among these types of multi-dimensional strong gradient-driven environmental forcing functions.