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Open access publications by faculty, postdocs, and graduate students in the Department of Earth Sciences.
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- ItemThe role of iron in the formation of Ediacaran ‘death masks’(Geobiology, 2023-02-26) Gibson, Brandt M.; Schiffbauer, James D.; Wallace, Adam F.; Darroch, Simon A. F.The Ediacara biota are an enigmatic group of Neoproterozoic soft-bodied fossils that mark the first major radiation of complex eukaryotic and macroscopic life. These fossils are thought to have been preserved via pyritic “death masks” mediated by seafloor microbial mats, though little about the chemical constraints of this preservational pathway is known, in particular surrounding the role of bioavailable iron in death mask formation and preservational fidelity. In this study, we perform decay experiments on both diploblastic and triploblastic animals under a range of simulated sedimentary iron concentrations, in order to characterize the role of iron in the preservation of Ediacaran organisms. After 28 days of decay, we demonstrate the first convincing “death masks” produced under experimental laboratory conditions composed of iron sulfide and probable oxide veneers. Moreover, our results demonstrate that the abundance of iron in experiments is not the sole control on death mask formation, but also tissue histology and the availability of nucleation sites. This illustrates that Ediacaran preservation via microbial death masks need not be a “perfect storm” of paleoenvironmental porewater and sediment chemistry, but instead can occur under a range of conditions.
- ItemAqueous Geochemical Controls on the Sestonic Microbial Community in Lakes Michigan and Superior(Microorganisms, 2023-02-17) Rani, Asha; Ranjan, Ravi; Bonina, Solidea M. C.; Izadmehr, Mahsa; Giesy, John P.; Li, An; Sturchio, Neil C.; Rockne, Karl J.Despite being the largest freshwater lake system in the world, relatively little is known about the sestonic microbial community structure in the Laurentian Great Lakes. The goal of this research was to better understand this ecosystem using high-throughput sequencing of microbial communities as a function of water depth at six locations in the westernmost Great Lakes of Superior and Michigan. The water column was characterized by gradients in temperature, dissolved oxygen (DO), pH, and other physicochemical parameters with depth. Mean nitrate concentrations were 32 μmol/L, with only slight variation within and between the lakes, and with depth. Mean available phosphorus was 0.07 μmol/L, resulting in relatively large N:P ratios (97:1) indicative of P limitation. Abundances of the phyla Actinobacteria, Bacteroidetes, Cyanobacteria, Thaumarchaeota, and Verrucomicrobia differed significantly among the Lakes. Candidatus Nitrosopumilus was present in greater abundance in Lake Superior compared to Lake Michigan, suggesting the importance of ammonia-oxidating archaea in water column N cycling in Lake Superior. The Shannon diversity index was negatively correlated with pH, temperature, and salinity, and positively correlated with DO, latitude, and N2 saturation. Results of this study suggest that DO, pH, temperature, and salinity were major drivers shaping the community composition in the Great Lakes.
- ItemMixotrophy broadens the ecological niche range of the iron oxidizer Sideroxydans sp. CL21 isolated from an iron-rich peatland(FEMS Microbiology Ecology, 2023-02-14) Cooper, Rebecca E.; Finck, Jessica; Chan, Clara; Küsel, KirstenSideroxydans sp. CL21 is a microaerobic, acid-tolerant Fe(II)-oxidizer, isolated from the Schlöppnerbrunnen fen. Since the genome size of Sideroxydans sp. CL21 is 21% larger than that of the neutrophilic Sideroxydans lithotrophicus ES-1, we hypothesized that strain CL21 contains additional metabolic traits to thrive in the fen. The common genomic content of both strains contains homologs of the putative Fe(II) oxidation genes, mtoAB and cyc2. A large part of the accessory genome in strain CL21 contains genes linked to utilization of alternative electron donors, including NiFe uptake hydrogenases, and genes encoding lactate uptake and utilization proteins, motility and biofilm formation, transposable elements, and pH homeostasis mechanisms. Next, we incubated the strain in different combinations of electron donors and characterized the fen microbial communities. Sideroxydans spp. comprised 3.33% and 3.94% of the total relative abundance in the peatland soil and peatland water, respectively. Incubation results indicate Sideroxydans sp. CL21 uses H2 and thiosulfate, while lactate only enhances growth when combined with Fe, H2, or thiosulfate. Rates of H2 utilization were highest in combination with other substrates. Thus, Sideroxydans sp. CL21 is a mixotroph, growing best by simultaneously using substrate combinations, which helps to thrive in dynamic and complex habitats.
- ItemFrequent Storm Surges Affect the Groundwater of Coastal Ecosystems(Geophysical Research Letters, 2023-01-09) Nordio, Giovanna; Frederiks, Ryan; Hingst, Mary; Carr, Joel; Kirwan, Matt; Gedan, Keryn; Michael, Holly; Fagherazzi, SergioRecent studies have focused on the effect of large tropical cyclones (hurricanes) on the shore, neglecting the role of less intense but more frequent events. Here we analyze the effect of the offshore tropical storm Melissa on groundwater data collected along the North America Atlantic coast. Our meta-analysis indicates that both groundwater level and specific conductivity significantly increased during Melissa, respectively reaching maximum values of 1.09 m and 25.2 mS/cm above pre-storm levels. Time to recover to pre-storm levels was 10 times greater for groundwater specific conductivity, with a median value of 20 days, while groundwater level had a median recovery time of 2 days. A frequency-magnitude analysis indicates that the percent of time with salinization is higher for Melissa than for energetic hurricanes. Given the high frequency of these events (return period of 1–2 years), and the long time needed for groundwater conditions to return to normal levels, we conclude that increasingly frequent moderate storms will have a significant impact on the ecology of vegetated shorelines. Key Points: - Salinization - Coastal areas - Groundwater Plain Language Summary: Salinization and flooding events due to sea level rise and storm surges threaten coastal ecosystems, changing groundwater characteristics. Moderate and more frequent storm surges can have a significant impact on coastal ecology, similar to larger tropical cyclones. Salinity and water table elevation need time to recover to normal conditions. The recovery time is compared to the frequency of these moderate storm surge events to determine the effect on the coastal groundwater.
- ItemCoastal topography and hydrogeology control critical groundwater gradients and potential beach surface instability during storm surges(Hydrology and Earth System Sciences, 2022-12-02) Paldor, Anner; Stark, Nina; Florence, Matthew; Raubenheimer, Britt; Elgar, Steve; Housego, Rachel; Frederiks, Ryan S.; Michael, Holly A.Ocean surges pose a global threat for coastal stability. These hazardous events alter flow conditions and pore pressures in flooded beach areas during both inundation and subsequent retreat stages, which can mobilize beach material, potentially enhancing erosion significantly. In this study, the evolution of surge-induced pore-pressure gradients is studied through numerical hydrologic simulations of storm surges. The spatiotemporal variability of critically high gradients is analyzed in three dimensions. The analysis is based on a threshold value obtained for quicksand formation of beach materials under groundwater seepage. Simulations of surge events show that, during the run-up stage, head gradients can rise to the calculated critical level landward of the advancing inundation line. During the receding stage, critical gradients were simulated seaward of the retreating inundation line. These gradients reach maximum magnitudes just as sea level returns to pre-surge levels and are most accentuated beneath the still-water shoreline, where the model surface changes slope. The gradients vary along the shore owing to variable beach morphology, with the largest gradients seaward of intermediate-scale (1–3 m elevation) topographic elements (dunes) in the flood zone. These findings suggest that the common practices in monitoring and mitigating surge-induced failures and erosion, which typically focus on the flattest areas of beaches, might need to be revised to include other topographic features.