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

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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.