Oral Presentations
Session 1:
Clocks, proxies and analogues: diverse methods for understanding environments in deep time
9:00 - 9:15
Recent origin of iron oxidation in extant microbial groups and low clade fidelity of iron metabolisms
Erik Tamre, Greg Fournier
Reduced iron was abundant in Earth’s surface environments before their oxygenation, so iron oxidation could have been a common metabolism on the early Earth. Consequently, modern microbial iron oxidation is sometimes seen as a holdover from an earlier biosphere, but the continuity of involved lineages or the metabolic process itself has not been verified. Modern neutrophilic iron oxidizers use cytochrome-porin Cyc2 as the initial electron acceptor in iron oxidation. With the protein as a proxy for the metabolism, we performed a phylogenetic analysis of Cyc2 to understand the evolutionary history of this iron oxidation pathway.
In addition to known iron oxidizers, we identified Cyc2 orthologs in gammaproteobacterial endosymbionts of lucinid bivalves. These bivalves have a robust fossil record and rely on sea-grass meadows that only appear in the Cretaceous, providing a valuable time calibration in the evolutionary history of Cyc2. Our molecular clock analysis shows that extant sampled Cyc2 diversity has surprisingly recent common ancestry, and iron oxidation metabolisms in Gallionellaceae, Zetaproteobacteria, and photoferrotrophic Chlorobi likely originated in the Neoproterozoic or the Phanerozoic via multiple transfer events.
The groups responsible for microbial iron oxidation have thus changed over Earth history, possibly reflecting the instability of niches with sufficient reduced iron. We note that frequent transfer and changing taxonomic distribution may be a general pattern for traits which are selected for sporadically across space and time. Based on iron metabolism and other processes, we further explore this concept of a trait’s “clade fidelity” (or lack thereof) and establish its evolutionary importance.
9:15 - 9:30
Investigating biomarkers associated with Ordovician period stromatolites from the Ottawa River
Kyla Malo, Allyson Brady
Stromatolites are laminated rock formations produced by mat-forming microorganisms that offer important insight into ancient microbial ecosystems [1,2]. Cell membrane derived organic compounds, e.g. lipids, that become trapped and preserved during stromatolite formation may be used as biomarkers of extant or extinct life [1,3]. However, questions remain with respect to distinguishing between modern contributions and biomarkers hypothesized to be captured during stromatolite formation. Here, Ordovician period stromatolites collected from the Ottawa River [4] in Fall 2023 and Fall 2024 were used to investigate the organic contributions of modern ecosystems and the preservation potential of biomarkers. Stromatolite biomarkers, in addition to water, sediment, and modern microbial samples, were analyzed using organic solvent extraction and gas chromatography-mass spectroscopy. Preliminary results identified compound classes such as fatty acids, alkanes, phenols, and fatty acid amides. Heterogeneity in the biomarker abundance between stromatolite samples underscore the potential variability in potential modern contributions to these organics. Targeted comparisons of exterior versus pristine interior stromatolite material showed a marked decrease in biomarker abundance and a loss of some compounds, suggesting that these may represent modern contribution rather than organic deposited during formation. Overall, this research adds to existing knowledge on elucidating modern contributions from the stromatolite forming microbial ecosystem biomarkers. Additionally, it aids in understanding the preservation potential of biomarkers over geologic time scales helping to identify more robust biosignatures.
9:30 - 9:45
Bioturbation intensity as a control on organic carbon preservation in middle Paleozoic sediments
Kate Pippenger, Andrea Chow, Dana Polomski, Lidya Tarhan
Bioturbation plays an important role in regulating organic carbon preservation in marine sediments. In modern marine settings, bioturbation generally increases rates of decomposition, which decreases the size of the preserved reactive organic carbon pool. However, how organic carbon preservation is shaped by differences in bioturbation intensity (i.e., degree of disruption of sedimentary fabric) and style (i.e., biodiffusive sediment churning versus the flushing of burrow structures by bioirrigation) remains poorly constrained, and largely unquantified for previous intervals of Earth’s history. Here we explore the nature of the relationship between bioturbation intensity and organic carbon burial using sedimentary drill cores from Devonian- and Carboniferous-aged strata in the Appalachian, Antler, Paradox, and Denver Basins recording oxygenated marine settings. Paired, high-resolution sediment geochemistry measurements (total organic carbon (TOC), total sulfur, and redox state proxies) and data on bioturbation intensity and style show that highly bioturbated intervals are consistently characterized by low TOC values. However, lightly to moderately bioturbated strata display a range of TOC values also observed in unbioturbated sediments, suggesting that low to moderate intensities of sediment disruption may not have strongly impacted organic carbon burial in these basins. A more quantitative and mechanistic understanding of bioturbation-TOC relationships provides much-needed context for reconstruction of the long-term evolution of the global carbon and oxygen cycles, especially crucial in intervals when bioturbation is considered to have been less intense on a global scale.
9:45 - 10:00
Unveiling the biogeochemistry of Lake Untersee: an analogue of early Proterozoic oceans
Daniel Fillion, Denis Lacelle, Ludovic Pascal, Dale T. Andersen, Stephanie Kusch and Andre Pellerin
Lake Untersee (East Antarctica) is a perennially ice-covered lake with a 100-meter-deep anoxic basin and a chemocline at ~70 m depth, where steep chemical gradients separate the oxygenated surface from sulfidic depths. The permanent ice cover isolates the lake from the atmosphere, creating a nutrient-poor environment where biogeochemical cycles are driven by microbial metabolisms. During two field campaigns (2023-2024), we measured high-resolution geochemical profiles of key chemical species and performed in-situ incubations with labelled ammonium to investigate nitrogen redox transformations. The water column profiles reveal steep gradients at the oxic-anoxic interface, with substantial ammonium and methane consumption occurring approximately 10 meters below the depth where oxygen is depleted. The production of 30N2 during the incubations suggest that oxidation by micro concentrations of oxygen or anammox, anaerobic ammonium oxidation, are not the only metabolic pathways driving nitrogen cycling. We hypothesize that in the chemocline of Lake Untersee, sulfate may play a crucial role in the oxidation of reduced species since it is the only electron acceptor available, even for ammonium. Sulfate-driven ammonium oxidation is a rarely reported but thermodynamically viable metabolic pathway already observed in marine sediments and in anaerobic bioreactors. Given that periods of the Proterozoic were characterized by high organic carbon fluxes to stratified continental margins, sulfate-driven ammonium oxidation could have played a more significant role in past ocean biogeochemical cycles.
Session 2:
Analysis of ancient ecosystems, from biomechanics to macroevolution: Part 1
11:45 - 12:00
Resolving species’ stratigraphic distributions in the Late Cretaceous outcrops of Dinosaur Provincial Park (Alberta, Canada) using high-resolution aerial imagery and 3D digital outcrop reconstruction
Alexandre V. Demers-Potvin, Louis-Philippe Bateman, André S. Mueller, Sofia Staley & Hans C.E. Larsson
The fossil record has long been accepted to provide a broad overview of climate and biodiversity patterns on global spatial and deep-time temporal scales. Now, there is a growing interest in specific localities with sufficiently well understood fossil assemblages and robust absolute age constraints to investigate the persistence of ecosystems in response to perturbations over relatively short geological time. Therefore, we are contributing to this fundamental palaeoecological question by assessing the stability of the Dinosaur Provincial Park palaeobiota, a well-studied non-marine Cretaceous North American ecosystem. However, uncertainties remain on species’ stratigraphic distributions across the Park since no ground-based stratigraphic correlation of individual fossil sites has ever been completed due to the apparent lack of lateral continuity of several sedimentary horizons in those fluvial deposits. Therefore, we have begun a 3D digital outcrop reconstruction of the Park through structure-from-motion photogrammetry, using high-resolution images acquired with drones. We expect this dataset to facilitate the tracing of marker beds with a ‘bird’s eye view’ over sufficiently long distances to enable meaningful quarry correlations. Initial results confirm that the erosional contact between the Oldman and Dinosaur Park Formations is not a suitable datum to measure relative stratigraphic heights as a proxy for species’ stratigraphic distributions because its elevation is too variable locally. This leads us to investigate the potential of the Lethbridge Coal Zone as a more robust relative height datum due to its more consistent absolute elevation. This project demonstrates the great potential of the application of high-resolution digital outcrop models in geology and palaeontology.
12:00 - 12:15
Biomechanical analyses of enigmatic archaeocyathid ornamentation
Zaid Qureshi, Brandt M. Gibson, Simon A.F. Darroch, and Marc Laflamme
Since their first appearance, reef ecosystems have concentrated biodiversity by fostering complex ecological interactions at these sites. In contrast to modern reefs that have coral-built frameworks, Cambrian-aged reefs were built by Archaeocyatha – extinct filter-feeding putative sponges adapted to specific environmental conditions. These organisms typically constructed elaborate cylindroconical or mound-shaped calcium carbonate skeletons with a cone-in-cone morphology and occasional ornamentation. One such unique example is the taxon Yukonensis yukonensis, which was composed of stacked porous subspherical units ornamented by a protruding thorny corolla structure at the intersection between each unit. The spines of the thorny corolla are characterized by a radial pattern of longitudinal ‘T’-shaped ridges along a given spine. We undertook fluid and structural mechanics modelling to study the feeding ecology of Y. yukonensis and assess the biomechanical impacts of its ornamentation. Our results demonstrate that the presence of thorny corolla drastically reduces the fluid velocity entering the organism, thus limiting communication between internal anatomy and the ambient environment. This is suggestive that a purely passive filter-feeding strategy was unlikely. Furthermore, individual T-shaped spines that composed the thorny corolla experienced heightened stress when compared to hypothetical cylindrical spines, implying that the architecture of the spines did not increase structural rigidity as previously proposed.
12:15 - 12:30
Tempos and modes of ecosystem evolution: exploring stable states and transitions in Cenozoic mammal communities
Louis-Philippe Bateman & Hans C.E. Larsson
Ecosystems are inherently complex systems, shaped by dynamic interactions between species, environmental factors, and evolutionary processes. Ecosystem change often proceeds abruptly. They may display stable behaviour until critical "tipping points" are exceeded, leading to potentially irreversible changes. Thus, developing methods to fully capture ecosystem complexity and evolution through these transitions is essential. To this extent, quantitative ecosystem networks are an emerging approach thanks to their potential to combine biodiversity, species interactions, and ecosystem function. Yet, application of these methods to Deep Time are limited, fraught with several biases. Compared to modern ecosystems, ancient Phanerozoic ecosystems were more diverse, environmentally broader, and evolved across multiple sweeping transformations. These latter factors bring the study of ancient ecosystems to the forefront of exploring how these complex systems evolve and respond to environmental and biotic perturbations. In this study, we reconstruct 264 fossil mammalian trophic networks in North America that are concentrated in the western interior and span relatively evenly throughout the entire Cenozoic Era. Our model uses extant mammal community observations to predict interactions using matching species traits like body size, broad dietary category, and life habit, and refines these predictions using phylogenetic comparisons. Each trophic network is used to track changes in network properties over the Cenozoic. Although some network properties change monotonically, others have nonlinear trajectories, and some remain constant. This suggests that some network properties are constrained or insensitive, while others are labile to fluctuating biotic and abiotic conditions. We also cluster networks based on their properties, revealing the existence of at least three “states”: a post-K-Pg extinction recovery state, a warm Paleogene state, and a post-Paleogene cool state. We discuss the biotic and abiotic factors that possibly mediated these state shifts. Finally, we discuss the best approaches and heuristics to study ecosystem evolution, with a focus on ecological networks. We draw parallels to evolutionary biology, including the use of evolutionary landscapes to track how ecosystems might optimize certain properties such as stability through time. We also discuss how studying time-series of past ecological networks might help predict and even detect impending state shifts in extant ecosystems.
Session 3:
Analysis of ancient ecosystems, from biomechanics to macroevolution: Part 2
14:00 - 14:15
A comparison of insect disarticulation during simulated transport
Johnathan A. Sorrentino; Peter R. Liberty; Brandt M. Gibson; Alika Maharaj; Corentin Jouault; Marc Laflamme
Insects are ubiquitous and serve as indicators of local climate in modern ecosystems, therefore allowing their extensive fossil record to elucidate and characterize ancient ecosystems . Fossilized insects are often found in a range of lacustrine and coastal marine settings in varying states of articulation. Given that most insects are terrestrial, it remains unclear to what extent transport would affect insect articulation and therefore bias our interpretation of fossil collections. Through a series of simulated transport experiments, we compare the disarticulation of live insects tumbled in rotary jewelry polishers in a water and silica silt medium for 48 hours. We studied six insect groups with diverse morphology: Bombus spp. (bumble bees), Teleogryllus oceanicus (oceanic house crickets), Polyommatus sp. (butterflies), Coccinellidae (ladybird beetles), Camponotus spp. (carpenter ants), and Enallagma spp. (blue damselflies). Disarticulation varied greatly among taxa, ranging from virtually untouched (bumble bees) to heavily damaged and unrecognizable (damselflies). Crickets and bumble bees exhibited high preservation potential due to rapid sinking (within 24 hours) and low disarticulation. In contrast, butterflies showed the lowest preservation potential given their delayed and lack of sinking (~48 hours) and extensive disarticulation. Ladybird beetles showed high levels of disarticulation despite their supposed robustness; however, their decay-resistant elytra remained intact. Our findings underscore the impact of turbulent transport on insect fossilization, disproportionately removing taxa with elongated, delicate, or easily isolated body parts—structures often critical for taxonomic identification. These results provide valuable insights into biases in the insect fossil record and the differential preservation of insect lineages.
14:15 - 14:30
High ecological disparity in Cretaceous ichthyosaurs
Dirley Cortés; Hans C.E. Larsson; Mary Luz Parra-Ruge
With an evolutionary history spanning nearly 160 million years, ichthyosaurs represent one of the best examples of secondarily aquatic marine adaptation. Despite their early ecological diversity, Cretaceous ichthyosaurs experienced a decline in morphological disparity, with reduced niche differentiation compared to their Jurassic predecessors. However, this perspective is largely shaped by an incomplete fossil record. The Lower Cretaceous Paja Formation Biota of Colombia, home to one of the richest marine assemblages of the Neotropics, provides a critical window into this understudied evolutionary phase of ichthyosaurs. We described a newly discovered ichthyosaur that challenges traditional views of Cretaceous ichthyosaur ecology. This taxon exhibits an unprecedented combination of cranial and postcranial traits, including a rostrum wider than high, highly labiolingually compressed dentition, a uniquely configuration of the dorsal skull, and unique bone patterning in the hindfin, occupying a novel ecomorph within ophthalmosaurians. Our comparative, ecomorphological and phylogenetic analyses reveal unexpectedly high craniodental ecological disparity among Paja ichthyosaurs, comparable to the best-documented and highly diverse Early Jurassic Posidonia Shale lagerstätten. These comparisons indicate the Paja ichthyosaur assemblage evolved toward a prevalence of macropredatory adaptations. Across seventeen examined taxa, we document a spectrum of feeding strategies, suggesting complex niche partitioning and trophic interactions in the Paja ichthyosaurs. These findings not only expand the known ecological range of Cretaceous ichthyosaurs but also indicate a broad shift while maintaining an equally diverse ecomorphospace in these taxa. The new taxon is one of many examples of Cretaceous ichthyosaurs evolving a broader ecology in their environments.
Session 4:
Microbes in a modern world: the biogeochemistry of dynamic environments
14:45 - 15:00
Trunk River Lagoon, Falmouth: Biogeochemical Signals of Contemporary Human Occupation
Diana Dumit, Benjamin T. Uveges, Gareth Izon, Molly A. Moynihan, Catherine A. Crowley, S. Emil Ruff, Mark L. Roberts, Roger E. Summons
Aiming to understand how algal/bacterial blooms are preserved in modern sediments we discovered geochemical evidence of fossil fuel hydrocarbon contamination in the system. In search of an earlier pristine biogeochemical signal, we then took a long core of the system and captured ~3000 years of environmental history. Here we investigate the modern history of Trunk River Lagoon by examining a sediment core using radiocarbon, stable isotope geochemistry, and lipid biomarker analyses. Radiocarbon data of the long core reveal a system at least three thousand years old at its base with an abrupt change at around 600 BC where a likely human disturbance in the sediment deposition resulted in missing time. The upper layers of the core appear to capture the contemporary setting. We find a system that has changed over this time interval of 3000 years which likely began as a freshwater environment with mostly terrestrial organic inputs and no evidence of anthropogenic contamination. The top of the core represents the current setting of a brackish lagoon with marine organic matter inputs together with evidence of fossil hydrocarbon and domestic sewage contamination. A search for pristine lipid biomarker signals through characterization of unsaturated components and sulfur-bound lipids revealed a dichotomy in the lipid profiles and distribution with implications on lipid preservation and how the biomarkers are used to interpret past environment and depositional conditions.
15:00 - 15:15
Carbon dynamics and microbiology are influenced by permafrost history at a retrogressive thaw slump in the Canadian Arctic
Lexi Mollica, Laura Lapham, Roger MacLeod, Marcus Phillips, Adam Gillespie, Peter Morse, Scott Dallimore, Jackie Goordial
The Arctic is warming up to four times faster than the rest of the planet [1]. Permafrost (perennially frozen ground) stores ~50% of the soil organic carbon on Earth [2] and is thawing as the climate warms. Permafrost carbon is becoming increasingly vulnerable to degradation by microbiota, as they can utilize newly thawed nutrients and produce greenhouse gases (GHGs) such as methane (CH4) and carbon dioxide (CO2) as part of their regular metabolism [3]. Permafrost thaw features such as retrogressive thaw slumps (RTSs) are increasing across the Arctic, and may release up to 80±19 PgC by 2300 [4]. Geologic history of permafrost can influence the distribution of carbon cycling microbiota in cryostratigraphic units exposed by thaw features [5], however the influence of this relationship on GHG flux at RTSs has not been investigated [6,7]. We examined microbial community composition and soil properties from cryostratigraphic layers representing different stages of permafrost history at an RTS on Niglintgak Island, NT. Permafrost cores were extracted and in-situ CH4 and CO2 fluxes were measured. Bacterial and archaeal community composition was assessed using 16S rRNA gene amplicon sequencing, and soil properties such as age, total organic carbon (TOC) and total nitrogen (TN) were measured. The highest CH4 and CO2 fluxes were observed in Late Holocene soils that were preserved by an aggrading permafrost table. High GHG fluxes correlated with high microbial diversity, TOC, and TN. Our findings highlight the importance of considering geologic context in permafrost carbon dynamics research, as it can significantly influence GHG flux, microbial communities, and soil properties.
15:15 - 15:30
Metagenomic analyses reveal the potential for organosulfur metabolism across sulfur-impacted freshwater systems
Amanda Patsis, Cara Santelli, Cody Sheik
Excess accumulation of sulfur is a pressing concern in Minnesota surface water, as mining and industrial deposition have led to high levels of sulfate that threatens culturally and ecologically important wild rice populations. Understanding the scope and scale of microbially-mediated organosulfur (OrgS) transformations in these systems is paramount to constraining overall fate and transport of sulfur, as up to 95% of total sulfur in wetland, lake and stream sediments occurs within organic matter. Here, we use shotgun metagenome sequence data from sulfur-impacted freshwater systems across Minnesota’s Mesabi Iron Range to investigate the relationship between the taxonomic and functional diversity of microbial communities at sites with varying levels of excess sulfur. Our preliminary results indicate that microbial communities are highly heterogeneous across small spatial scales but are nevertheless primed for OrgS transformation and utilization across all environments investigated. Metagenomes encode pathways such as taurine and sulfoquinovose catabolism alongside those for dissimilarity oxidation and reduction of inorganic sulfur compounds, suggesting that microbial OrgS transformations could be a key control on the flux of sulfur in these systems.
15:30 - 15:45
Effects of Pleistocene and Holocene Environmental Change on Coastal Bioturbation at Willapa Bay, Washington
Maya T. LaGrange Rao, Murray K. Gingras, Kate H. Pippenger, Brette S. Harris, and Lidya G. Tarhan
Biological reworking and mixing of sediments (i.e., bioturbation) plays a key role in the decomposition of organic matter and the exchange of nutrients between seawater and marine sediments. Still, the effects of climate change on the behaviours and physiologies of bioturbating animals remain poorly understood. Experimental studies have focused on the short-term impacts of marine heat waves, but little is known about the effects of long-term warming or shifts in climate on animal-sediment interactions. To address these longstanding questions, we investigated Willapa Bay in western Washington (USA) as a “natural laboratory” for study of both modern-day animal-sediment interactions and bioturbation in warmer- and cooler-than-present climates in Earth’s recent past. We compare the style, intensity, and scale of bioturbation in modern tidal sediments to bioturbation recorded in sedimentary strata that formed in this same region of coastline (and in a similar bay setting) during three previous interglacials. Preliminary findings suggest that intertidal flat deposits from the warmer-than-present Last Interglacial are commonly characterized by larger animal burrows relative to similar modern or past, cooler-interglacial deposits. Moreover, a greater abundance of decapod crustacean burrows in modern and Last Interglacial sediments, in contrast to a higher proportion of bivalve traces in units from previous, cooler interglacials highlight striking shifts through time and across climate states in dominant bioturbators. This work enhances our understanding of how changing global temperatures influenced coastal bioturbation in the Earth’s recent past and how rising temperatures may continue to shape bioturbation in the future.
Poster Presentations
Session 1: 10:15 - 11:45
N. L. Marshall, G.D. Love, R.D. Pancost, A. Pohl, A. Ridgwell
By producing and consuming methane, microbial ecosystems play a critical role in the Earth’s carbon cycle and climate. In modern aquatic systems, the oxidation of methane is all most entirely facilitated through the process of anaerobic oxidation of methane. AOM in modern marine environments is responsible for the consumption of >90% of the annually produced methane before it can reach the open water column or atmosphere [1]. This raises the question of how the global methane cycle operated during the Ordovician and Silurian Periods, particularly under conditions of lower oxygen concentrations in the atmosphere and lower dissolved sulphate in the ocean [2]. We extracted and analyzed lipid biomarker assemblages in a large suite of over 550 well-preserved sedimentary rocks from over 20 localities deposited in offshore environments. Anomalously high relative and absolute abundances of lipid biomarkers derived from certain groups of bacteria and archaea suggests that strong and pervasive marine methane cycling was sustained in Ordovician and Silurian oceans, spanning at least 80 million years of geologic time. We consistently find abundant 3-methylhopane index values (3-20%, an order of magnitude above Phanerozoic baselines [3,4]) for Ordovician, Silurian and Early to Middle Devonian successions from marine shelf environments for a variety of locations. Additionally, compound-specific δ13C ratios reveal significant 13C-depletion of hopanes and acyclic isoprenoids in samples. Furthermore, simulations with an Earth system model (cGENIE); configured under appropriate Paleozoic climatic, environmental and paleogeographical conditions, predict very high global average methane oxidation rates in the surface ocean compared with other intervals of Earth history.
Maria Bayder, Prof. Nicolas Cowan, Prof. Nagissa Mahmoudi, Prof. Stephanie Loeb
Changes in the Sun’s irradiance spectrum and Earth’s atmospheric composition likely played a significant role in driving the evolution of life on Earth. We examine whether changes in ultraviolet (UV) flux over geological time acted as a selective pressure for microbes to evolve exoenzymes. In the presence of high UV flux, photodegradation can rapidly break down complex molecules, but whether this occurred in the early oceans remains unknown. To address this, we simulated UV flux available for photodegradation in the ocean’s surface layer throughout geological time. We developed Python code combining existing models of the Sun’s irradiance spectrum across geological time with estimates of Archean Earth’s atmospheric composition to generate the irradiance spectrum at Earth’s surface throughout different epochs. We programmed a simple ocean mixed layer model to calculate the average irradiance spectrum and average UV flux in the ocean’s mixed layer at different times. Our findings demonstrate that in the ocean’s mixed layer, flux of the least energetic UV light was almost unaffected by changes in Earth’s atmosphere, monotonically increasing similarly to UV flux at the top of Earth’s atmosphere. However, flux of the most energetic UV light in the ocean’s mixed layer decreased by about 20% during the Great Oxygenation Event (2.4 gigayears ago) and by a factor of 5 during the Neoproterozoic Oxygenation Event (0.8 gigayears ago). If only the most energetic UV photons break down organic molecules, the significant decrease in this photodegrading UV flux may have triggered microbes to evolve exoenzymes to degrade organic molecules.
Meghan Craughwell, Tim Goudge, Rebecca Shapiro, Peter Morse, Élise Devoie, Jackie Goordial
Rising global temperatures are causing rapid change in the Arctic, threatening the diversity of permafrost microorganisms [1]. The heterogeneity of permafrost complicates the task of studying these systems as microbial communities can be influenced by site characteristics such as carbon content, pH, and latitude [2,3]. This study investigates microbial diversity, quantity, and activity associated with various surface geology settings in the Inuvialuit Settlement Region (ISR), NT. Bacterial, archaeal, and fungal communities were characterized using 16S rRNA gene and internal transcribed spacer (ITS) region amplicon sequencing, respectively. Shallow permafrost was collected from eight sites across the ISR. Sites were classified by geologic history (glaciofluvial vs morainal) and present-day landscape (top or bottom of a slope). High bacterial, archaeal, and fungal diversity was found across all sites, while geological history of samples was only correlated with fungi and not other microbial diversity. This research contributes to our broader understanding of microbial life in permafrost and assists in establishing baseline data in a rapidly changing environment, particularly fungi which are often excluded from microbial analyses. Additionally, the results of this study can give insight into the habitability of ancient Mars as Arctic deltas are excellent analogs to the cold and wet conditions pervasive on the planet ~3.5 Ga.
Christopher J. Schuler, Darcy L. McRose
Phosphorous is abundant in soils but often has low bioavailability, as it readily sorbs to the surfaces of ubiquitous iron (oxyhydr)oxide minerals. Because of this, the biogeochemical cycling of iron and phosphorous are closely linked. In recent years, many studies have focused on the use of small, redox-active molecules by plants and microbes to access mineral iron; however, the impact of this activity on phosphorous bioavailability remains poorly characterized. Coumarins are a class of these molecules and produced in plant roots during Fe-limited growth. We tested the reactivity of fraxetin, a coumarin linked to iron mobilization, with several phosphate-treated minerals. Over 24-hours, fraxetin effectively promoted iron dissolution and phosphate desorption. Over a longer time frame, though, soluble iron and phosphorous concentrations began to decrease, suggesting that fraxetin is driving mineral transformations as well as dissolution. To determine whether coumarins truly impacted the bioavailability of P, we grew Pseudomonas aeruginosa, a soil-dwelling bacterium, with phosphate-doped ferrihydrite as their only P source. The addition of fraxetin to these cultures led to a small increase in microbial abundance but no clear increase in per-cell P content. This work provides mechanistic insight into biogenic weathering and suggests that coumarins effectively increase immediate P bioavailability; however, this impact may not continue over longer timescales. Moreover, the acceleration of soil weathering processes may lead to lower availability of Fe and P after repeated redox cycling. Future investigations will focus on imaging- and spectroscopy-based studies of the rhizosphere to better understand how coumarins alter the soil environment.
Amanda N. Calhoun, William D. Leavitt, Carolynn M. Harris, Dan R. Colman, Eric S. Boyd, Ann Pearson
The carbon isotope (δ13C) composition of organic matter in the geologic record is used as evidence for or against the presence of life in Earth’s early history. While the modern biosphere is dominated by Calvin cycle-based oxygenic photosynthesis that fractionates biomass carbon by ~25‰, anaerobic autotrophs that predominated during the Archean (>2.5 Ga) may have utilized carbon fixation pathways that fractionate carbon differently. Phylogenetic, genomic, and thermodynamic/bioenergetic data suggest that the earliest forms of life were anaerobic thermophilic chemolithoautotrophs, which are well-represented among archaeal and bacterial organisms in contemporary hot springs. To better constrain biological carbon isotope fractionation (ɛ) in hot springs and the potential environmental influences on fractionation, we measured the δ13C values of microbial biomass in diverse modern terrestrial hot springs from Yellowstone National Park (Wyoming), California, Nevada, and El Tatio (Chile). We focus on archaeal carbon assimilation, providing the first δ13C measurements of intact isoprenoid glycerol dibiphytanyl glycerol tetraethers (iGDGTs) in terrestrial hot springs using spooling-wire micro-combustion isotope ratio mass spectrometry. Archaeal ɛ values are calculated relative to DIC, TOC, and DOC to assess the activity of autotrophic and heterotrophic carbon assimilation pathways, while δ13C measurements of C16 fatty acids illuminate net isotope fractionation of the bacterial community. We examine the effects of environmental variables (e.g. pH, temperature, oxidation-reduction potential, geography) on ɛ ranges and contextualize our results with paired metagenomic analyses to examine the presence and activity of different carbon fixation pathways across different springs.
Elizabeth Sullivan, Lyle Nelson, Dana Polomski, Amanda Urist, Miquela Ingalls, Nabil Shawwa, Aksha Mehra, Peter Crockford
The first initial buildup of oxygen in the Earth’s atmosphere – the Great Oxidation Event (GOE) – started around 2.5 billion years ago, where oxygen may have reached levels comparable to today’s atmosphere. Following its debut, atmospheric oxygen levels quickly crashed, coinciding with a contraction of the global biosphere. The Orosirian (2.05 - 1.8 Ga) records Earth’s exit from oxygenation (“OXIT”) in addition to the emergence of Eukaryotes. Exceptionally well preserved and exposed post-GOE carbonates, from the ~1.9 Ga Pethei Group of Great Slave Lake, NWT, record unique reef-ramp-basin transitions. These alternating aggradational phases of reef and ramp formation can be observed stratigraphically within the group, making it a remarkable target for application of geochemical proxies. Stable carbon (δ13C) and oxygen (δ18O) isotopes measured throughout the sequence give new insights on carbon cycling in late Paleoproterozoic environments. Shifts in carbon cycling and how they manifest in terms of redox conditions (from previous reconstructions in the literature) are further elucidated. Carbonate associated phosphate (CAP) measurements provide key constraints on the important nutrient phosphate. Finally, iodine to calcium ratios (I/Ca), which record the degree of shallow water oxygenation, determine the specific magnitude and extent of post-GOE oxygenation within this basin. Regarded as one of the most critical atmospheric and biospheric intervals in Earth’s past, understanding how large-scale surface environments changed during the aftermath of Earth’s OXIT will reveal why eukaryogenesis occurred across this interval.
Michelle Stevens, Peter W. Crockford, Elizabeth Sullivan, Nabil A. Shawwa, Miquela Ingalls, Lyle L. Nelson
The Great Oxidation Event (GOE) spans a critical interval of Earth’s past. Here, a dramatic rise in atmospheric O2 is well documented and causal links have been drawn between biospheric evolution and global biogeochemical cycles. Constraints on the Earth system across the GOE have been predominantly based on the carbonate rock record, where marine carbonate carbon (δ13C) values 2.2-2.0 billion years ago host the largest positive carbon isotope excursion in all of Earth’s history termed the Lomagundi Jatuli Excursion (LJE). During the LJE reach carbonate δ13C values typically reach up to 10‰ in globally deposited strata representing a large departure from typical marine carbonate carbon values which have fluctuated around 0 per mille ‰. The Nash Fork Formation in Wyoming has been correlated to have been deposited within the LJE but bears the highest δ13C values ever recorded (+30‰). Such values are present at the base of the formation but fall to near 0‰ at the top. This stratigraphic variation enables for the exploration into what drives such extreme values within a single basin and explore the nature of this enrichment. Importantly, the exact cause of the extreme enrichment in the Nash Fork Fm. remains debated, bringing into question whether the Nash Fork isotopic record should be correlated to the global LJE. Here, new petrographic and geochemical data will be presented to evaluate the global, local, and diagenetic conditions that influenced the carbon isotope values of the Nash Fork Fm.
Annika Junek, Rizzieri Balestra, Lyle Nelson, Peter Crockford
The Pahrump Group of Death Valley, Eastern California, has been the subject of numerous studies attempting to constrain the age of the group and correlate it with other notable successions and events of the mid- to late Proterozoic. Within the Pahrump Group, the middle carbonate member of the Crystal Springs Formation has the potential to be correlated with other Mesoproterozoic carbonate successions in North America. The member is composed primarily of stromatolitic limestone with occasional chert nodules and has been constrained to >1080 Ma based on U-Pb baddeleyite dating of diabase sills that intrude the entire Crystal Springs Formation. Here, we will present new δ13C and δ18O isotope chemostratigraphy on dolomite and limestone in an effort to correlate the succession with other Mesoproterozoic carbonate units in North America, such as the Bylot Supergroup of Northern Canada and the Unkar Group in the Grand Canyon. δ13C and δ18O isotope data will add further insights into the Mesoproterozoic Earth system and set the foundation for further geochemical investigations.
Sydney Riemer, Spencer Moller, Emily Ellefson, Keith Dewing, Michael Melchin, Noah J. Planavsky, Ruth Blake, Erik Sperling, Lidya G. Tarhan
The emergence of vascular land plants with deep rooting systems during the late Silurian and Early Devonian periods is suggested to have mediated profound changes to the Earth system. Plant roots can increase both physical and chemical weathering, which can impact delivery of the key nutrient phosphorus (P) from the continents to the oceans. Apatite dissolution in soils can be enhanced by physical weathering from plant roots that increases mineral surface area, as well as by organic acids secreted from plant roots that lower soil pH. P can enter the ocean as either unreactive detrital apatite, or as bioavailable dissolved P, reflecting continental weathering conditions. This study tests the hypothesis that early vascular plants increased bioavailable P delivery to the oceans through increased continental apatite weathering during the Silurian-Devonian transition.
Here we present new P geochemistry data from a >700-meter succession of lower–middle Paleozoic marine shales from Bathurst Island, Nunavut, Canada. We highlight stratigraphic patterns contemporaneous with a shift from a pre-vascular plant baseline in the mid-upper Silurian to the Lower Devonian when vascular plants first emerged and radiated. We report P speciation data and P/Al to track detrital apatite fluxes, as well as chemical index of alteration data to constrain trends in chemical weathering intensity through this critical interval. Phosphorus speciation data, in particular, permits distinction between detrital and authigenic apatite, and brings new insights to the longstanding question of the extent to which the radiation of vascular land plants impacted continental nutrient fluxes or marine P cycling.
Katie M. Maloney, Steven T. LoDuca, Jean-Bernard Caron
Burgess Shale fossils provide a rare window into one of the most consequential biological events in Earth’s history, the rapid radiation of animal life during the Cambrian Period. This year the Royal Ontario Museum (ROM) is celebrating 50 years of Burgess Shale research (1975–2025), an effort that has produced the world's largest collection of Burgess Shale fossils with high-resolution stratigraphic control. The enigmatic Burgess Shale fauna has been the focus of considerable study, but the biota contains an exceptionally preserved macroalgal ("seaweed") flora as well that, despite occupying a critical ecological role at the base of the food chain, has received comparatively little attention. More recently several Burgess Shale species first thought to represent macroalgae were interpreted as animals (e.g., Yuknessia) and animal tubes (e.g., Margaretia) with many forms still needing a modern restudy. Macroalgal evolutionary trends in the Cambrian present something of a conundrum as macroalgae from this interval seem to maintain body plans from the Ediacaran while animal lineages are diversifying. This delayed diversification has been hypothesized to be related to herbivory, but it is difficult to test this hypothesis without additional information about Cambrian macroalgae. Here, we will summarize the current knowledge of Burgess Shale macroalgae using the ROM collections and aided by techniques such as SEM-BSE imaging. We will also provide an overview of two new species of non-calcified macroalgae from the Burgess Shale (Walcott Quarry, Tulip Beds and the Trilobite Beds, Yoho National Park, British Columbia, Canada), including aspects of their ecological importance, particularly in terms of sediment binding (via complex holdfasts) and benthic tiering, and their bearing on the "Cambrian seaweed conundrum."
Andrea Boscaini, Bianca R. Spiering, Ajani Bissick, Frederik J. Hilgen, Brandt M. Gibson, Peter R. Liberty, Marc Laflamme, Galen P. Halverson, Joshua H.F.L. Davies
The late Ediacaran Nama Group in southern Namibia comprises marine siliciclastic and carbonate rocks that bear evidence of different terminal Ediacaran biota and their disappearance at the Ediacaran-Cambrian boundary. Studying the depositional sequences of the Nama Group is thus crucial for understanding the evolution and preservation of early complex life preceding the Cambrian Explosion. High-precision geochronological data from volcanic ash beds, combined with sequence stratigraphic, cyclostratigraphic and magnetostratigraphic analyses suggest that the cyclic deposition of the Nama Group was influenced by climatic variations likely related to Milankovitch cycles. However, the link between orbital forcing and the deposition of the Nama Group remains unclear due to uncertainties in regional-scale stratigraphic correlations and the absence of consistent age models. In this study, we present preliminary results on the geochemical characterization of apatite separated from numerous silicified ash beds within the Nama Group. Electron microprobe analysis and laser ablation inductively coupled plasma spectrometry (LA-ICP-MS) are used to determine the volatiles (Cl, F, OH) and trace element concentrations of the apatite, respectively. Our results are used to explore the potential of apatite as a correlation tool for volcanic ash beds in Precambrian sedimentary successions. Temporal constraints for the formation of the ash beds in the Nama Group obtained using high-precision U-Pb zircon geochronology will serve as independent check of our findings from the geochemical characterization of apatite.
Ashley Rivas, Paul M. Myrow, Emily F. Smith, Lyle L. Nelson, Derek E.G. Briggs, and Lidya G. Tarhan
Recent studies indicate growing recognition of the diversity and abundance of tubular fossils in the Ediacaran stratigraphic record. Resolving the ecologies, affinities and modes of preservation of tubular fossils is therefore critically important to reconstructing the role of these organisms in Earth’s earliest communities of complex, macroscopic, multicellular life. Gaojiashania cyclus is an enigmatic tubular fossil and candidate index fossil found in upper Ediacaran strata worldwide. Nonetheless, previous study of Gaojiashania has focused chiefly on the Gaojiashan Lagerstätte of South China; the morphology, facies associations and fossilization of Gaojiashania in other deposits is largely unconstrained. Here we present petrographic and SEM-EDS data from Gaojiashania specimens found in the Ediacaran Dunfee Member of the Deep Spring Formation at Mount Dunfee, Nevada. Dunfee Gaojiashania specimens are preserved as ‘Ediacara-style’ external, internal, and composite molds in siltstone and sandstone with a clay mineral-rich matrix of both aluminosilicates and non-aluminous Mg- and Fe-rich silicate minerals. These silicates include phases which, on the basis of both composition and textural relationships, we identify as authigenic. Clay authigenesis, through the process of reverse weathering, may have been enhanced by the prevalence of both late Ediacaran silica-rich and ferruginous seawater conditions prior to the emergence of silica-biomineralizing organisms and the rise of ocean and atmospheric oxygen to modern levels. In this light, clay authigenesis may have played a critical role in facilitating multiple modes of Ediacaran and Cambrian exceptional fossilization, including the formation of Ediacara-style moldic fossils in heterolithic and compositionally immature sandy sediments.
Peter R. Liberty, Morgann G. Perrot, Joshua H.F.L. Davies, Brandt M. Gibson, Marc Laflamme
Zircon U-Pb geochronology is a widely used, robust method for determining the age of emplacement of igneous rocks, but its use in providing age information for sediments, and in particular fossils, is limited to either dating detrital zircon crystals in fossil-bearing beds, or zircons in older or younger interbedded ash layers. U-Pb dating of carbonate minerals potentially provides an alternative method of generating age information on fossils. Uranium can be incorporated into carbonate during crystallization while Pb concentration at the time of crystallization is usually relatively low. However, element mobility during diagenesis limits the use of this technique in heavily altered samples. Since fossils are often preserved as carbonates we tested the potential of direct U-Pb dating of carbonate minerals within shells to provide accurate dates for their time of crystallization. This would expand upon traditional U-Pb carbonate dating by directly dating carbonate fossil shells using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We selected minimally altered, exceptionally preserved fossils from the 76.4±0.4 Ma Campanian Coon Creek Formation in western Tennessee, including the ammonite Nostoceras sp., the bivalves Inoceramus sp. and Crassatella vadose, as well as the Permian index fossil Schwagerina huecoensis from the Hueco Mountains in Texas. Preliminary results of these age-confined samples are consistent with the age of the Campanian Coon Creek Formation and provide evidence of the viability of carbonate-fossil U-Pb dating. The continued use and development of carbonate-fossil U-Pb dating provides an avenue to define evolutionary developments to a more detailed resolution than previously understood.
Lucille Komar, Kelsey Doiron, Simon Brassell, Ann Pearson
An increase in greenhouse gases, notably the rise in atmospheric CO₂ levels resulting from human activity, has driven increased global temperatures associated with climate extremes, creating hotter, drier conditions in some regions. The changes in environmental conditions have amplified the intensity and frequency of wildfires in the twenty-first century, causing devastating impacts on ecosystems. Paleofire studies are essential to gain further understanding of how interactions between climate, terrestrial environments, and vegetation influence wildfires and their responses under different conditions, which is vital information for prediction of wildfires in future warming scenarios. Studies of the Cretaceous period, known as a ‘hothouse’ with elevated global temperatures and higher CO2 levels than the present day, provide an analog helpful to understanding Earth’s system during elevated greenhouse gas conditions. Polycyclic aromatic hydrocarbons (PAHs) are produced when vegetation burns and are preserved in sediment as biomarkers that provide records of past wildfire conditions, such as source material (angiosperms vs. gymnosperms), fire intensity (temperature), and burn frequency. In this study, we present a preliminary investigation of paleofire conditions recorded in sediment cores spanning the Late Cretaceous and Early Paleocene that were retrieved from the Transkei Basin (IODP U1581). By measuring the PAH composition throughout this sedimentary record, we seek to understand the history of wildfires recorded by temporal changes in the composition of burn fuel (i.e., angiosperms vs. gymnosperms) and its intensity.
Anais Mobarak, Julia Wilcots, Adam C. Maloof
The longstanding “Dolomite Problem” arises from the fact that although large volumes of dolomitic rocks are abundant throughout our planet’s history, dolomite sparsely forms today and has not been precipitated in laboratory studies without additional chemical agents. Importantly, dolomite constitutes a significant portion of the sedimentary rock record, and sedimentary carbonate rocks and the geochemical signals they carry serve as powerful tools for reconstructing Earth history. Uncertainty about whether dolomite forms as a primary precipitate or secondary mineral, however, complicates interpretations of signals measured in dolomite.
We investigate the question of dolomite precipitation by studying a modern analog, the Coorong region in southern Australia, in which several neighboring lakes precipitate Mg-carbonate minerals including dolomite and magnesite. To analyze dolomite precipitation, we constructed mineralogical and geochemical fingerprints for a series of samples collected from across six Coorong lakes, including both dolomite- and non-dolomite-precipitating lakes. In order to treat mineralogy as a quantitative variable in our analysis, we developed a method for estimating percent composition for minerals of interest by training a regression model between principal component scores from X-ray diffraction spectra and known mineral abundances for training mixtures. To geochemically characterize samples, we measured δ13C and δ18O, as well as the concentration of various major and trace elements. By integrating quantitative mineralogical and geochemical data, we examine how the natural process of dolomite formation translates into a measured geochemical signal to understand both how dolomite records environmental geochemistry and interrogate the relevant chemical mechanisms for formation.
Clara Danhof, David Jones
Although the maximum extent of the Laurentide Ice Sheet (LIS) is well-understood based on geomorphology, stratigraphy, and radiocarbon dating, estimates of its oxygen isotopic composition have great uncertainty. Reconstructing these values is made difficult by the convolution of influences in the available proxies. This study seeks to better constrain the temperature and oxygen isotope composition of a proglacial lake fed by the melting LIS, Glacial Lake Hitchcock (GLH) through geochemical analysis of the shells of ostracods recovered from varve sediment deposits from GLH. These organisms precipitated their CaCO3 shells in GLH, whose δ18O value was controlled by the δ18OLIS. We measured the Mg/Ca and Sr/Ca ratios in the shells in addition to their δ18O values. The Sr/Ca ratio of ostracod shells in proglacial lakes has previously been found to be a reliable proxy for lakewater temperature. Using this independent constraint on temperature, we are able to differentiate between the multiple factors influencing δ18O values of the ostracod shells, and thereby determine the oxygen isotopic composition of GLH. Preliminary results show that temperature in GLH was near 0℃ and δ18Owater values were around -20‰ VSMOW. Through further consideration of the regional hydroclimate, these data may be useful for reconstructing the δ18O of the Laurentide Ice Sheet. This information has significant implications for paleoclimate reconstructions of global temperature, typically reported by its proxy δ18Oforaminifera. As δ18Oforaminifera is influenced by both temperature and ice volume, an absence of constraints in global ice volume has prevented temperature reconstructions with higher certainty.
Scott, R.W., and Caron, J-C.
The middle (Wuliuan) Cambrian Burgess Shale of British Columbia provides an exceptional record of the Cambrian explosion and was designated a UNESCO World Heritage Site in 1980 in recognition of the preservation of diverse and abundant soft-bodied organisms. Trilobites are also present at the Burgess Shale but remain largely understudied. Out of more than 22,000 described trilobite species across the world, only about 40 preserve soft tissues of which Olenoides serratus from the Burgess Shale is one of the best known. This year, the Royal Ontario Museum (ROM) celebrates its 50th anniversary of Burgess Shale fieldwork, and over the previous half-century, has collected numerous trilobites, including many species with soft parts preserved in addition to new specimens of Olenoides with have not been redescribed in detail since 1975. New data from ROM collections will be invaluable for testing a range of ecological and evolutionary hypotheses, and ROM collections provide an unprecedented opportunity to understand trilobite evolution.
Session 2: 15:45 - 17:15
Lorelei Wolf, Ann Pearson, Susan Carter
The TEX86 paleotemperature proxy reconstructs sea surface temperatures using isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs), membrane-spanning lipid biomarkers, from the Nitrososphaerota. While the TEX86 proxy assumes temperature as the strongest control on lipid composition, several studies have shown that growth phase, growth rate, and electron-donor supply also affect ring synthesis. Therefore, comprehensive study into the effects of environmental growth stress factors on lipid composition is necessary to constrain more accurate sea surface paleotemperatures. This study sought to isolate the effects of oxidative stress on ring synthesis in N. maritimus, a model strain of the Nitrososphaerota. Batch culture experiments reflecting several permutations of oxidative stress conditions were run in triplicate and included both increases (hydrogen peroxide) and decreases (catalase) in extracellular reactive oxygen species. High-performance liquid chromatography-mass spectrometry (HPLC-MS) was used to identify and quantify the full suite of glycerol ether lipids produced in the lipid monolayer.
Results showed that oxidative stress prompted a modified lipid membrane for N. maritimus. Oxidative stress conditions resulted in lower biomass yield and a more permeable lipid membrane associated with decreased cyclization of core GDGTs. This lipid membrane modification directly impacts TEX86-derived sea surface temperature, leading to artificially low temperature approximations. Future research investigating the causal relationships between growth rate, ROS production, and membrane lipid synthesis in N. maritimus can provide further clarity for applying and interpreting the TEX86 paleothermometer throughout Earth’s history.
Olivia F. Pendas, Carolynn Harris, Tristan Caro, Amanda Calhoun, Maximiliano Amenabar, Jenny Blamey , Sebastian Kopf, Ann Pearson, William D. Leavitt
The distribution of lipid biomarkers produced by archaea can reflect environmental conditions during biosynthesis, including temperature, pH, and energy availability [1,2,3]. Archaeal lipids can survive in sediments for millions of years, and so provide insight into past environmental conditions, as well as microbial adaptations to extreme environments. However, the impact of a wide variety of environmental conditions on lipid structure is poorly constrained at neutral pHs and has yet to be studied at a Mars analog site. In this project we aim to establish a framework for interpreting the distribution of archaeal glycerol dibiphytanyl glycerol tetraether (GDGT) lipids, which can contain between 0 and 8 cyclopentane rings, with respect to the temperature and pH during biosynthesis. To do so we examined GDGT profiles from seven hot springs in the El Tatio hydrothermal field in Chile, spanning temperatures from 60 to 83°C, and pH 3 to 7. We recover GDGTs from all sites, with moieties ranging between 0 and 8 cyclopentane rings, where the ring index (RI; a measure of mean cyclization) ranges from 2.50 to 4.93. We observe a negative relationship between RI and pH for El Tatio springs, where variation in pH explains 55% of observed RI variation. Temperature, dissolved oxygen, and oxidation-reduction potential are not related to RI. We conclude that spring pH is the dominant environmental control on cyclopentane ring formation, consistent with previous studies on GDGTs in hot spring sediments in Yellowstone National Park [4,5].
Sugiyama, I., Santoro, A., Horner, T., and Saito, M.
Carbon and nitrogen are vital to marine ecosystems, and their uptake often relies on metals like Cu and Fe. Iron, a common limiting micronutrient, regulates processes such as photosynthesis, respiration, and nitrogen fixation in marine phytoplankton. Cu and Fe limitation in nitrite-oxidizing bacteria and ammonia-oxidizing archaea can disrupt the biosynthesis of metalloenzymes required for nitrification. Understanding Cu and Fe uptake in oxic and anoxic Fe-limited marine environments is key to interpreting metal demand by both autotrophic and chemolithotrophic communities. Here, we present results from at-sea incubation experiments conducted during the CliOMZ (AT50-10) cruise in the Eastern Tropical Pacific Ocean, aimed at studying the effects of trace metals on biological productivity and nitrification. Short-term incubations were performed on vertical profiles from surface waters to 800 m, spanning low-oxygen zones. Seawater was spiked with 65Cu and 57Fe to concentrations of ~100 pM and ~1 nM, respectively, and incubated for 24 hours. After incubation, samples were filtered (0.2 µm), digested, and analyzed using ICP-MS. Our results suggest previously unrecognized Fe-limitation zones in surface waters of the Eastern Tropical Pacific and indicate a potential microbial demand for Cu in the mesopelagic. These findings provide new insights into the relationship between microbial communities and biogeochemical metal cycling in low-oxygen marine environments.
June Rahman, Liam Cooper, Benjamin Acosta, Parker Mergelkamp, Amanda Ellis, Henry Holm, Sarah Hurley, Ana Gonzalez-Nayeck
The carbon isotopic composition of phytoplankton biomass (δ13Corg), analyzed in modern ecosystems and the sedimentary record, can reveal important information about ancient and present biogeochemical cycles, changing climatic environments, and the makeup of past photosynthetic communities. Modern marine phytoplankton exude between 2 and 50% of initially fixed carbon, primarily as mono- and poly- saccharides. Previous work has shown that mono- and poly-saccharides are relatively enriched in 13C compared to other cellular components. However, it’s unknown how sugar exudation impacts biomass δ13C. Here we hypothesize that cyanobacterial (Synechococcus PCC 7002) sugar exudation will decrease biomass δ13C as more sugar is exuded into the environment. We address this question by growing Synechococcus PCC 7002 under two light conditions to promote variable sugar excretion, and we report δ13C of biomass and relative amounts of sugar excretion. Our findings provide insight into how microbial carbon cycling influences the δ13C of marine biomass, improving interpretations of δ¹³Corg in both modern and ancient systems.
Chen A.E., Harris C.M., Amenabar M.J., Leavitt W.D., Palucis M.C.
Evidence of extinct or extant life are found as biosignatures, when an organic biomarker is lithified and survives diagenetic processes. Detecting life on Mars will offer insight into how life evolves and adapts to extreme environmental conditions. As one of the most arid regions in the world, the Atacama Desert has long been considered a valuable Mars analog. We focus on using salars to characterize how the abundance and diversity of lipids vary with mineralogy and environmental conditions. Physiochemical measurements of the salar brines were taken using a YSI probe, and a Hach spectrophotometer was used to quantify ion compositions of the water. Soil moisture and organic matter was determined by drying and mass loss on ignition, while the total organic carbon and nitrogen were analyzed on an elemental analyzer. To better understand how microbial life is influenced by the presence of water, we interpreted the relationship between aridity and total organic carbon. We compared the Atacama estimates to Martian sites to see if our terrestrial analogs are relevant to sites on Mars. Generally, in more arid environments we see a decrease in TOC, potentially due to water limitations affecting microbial biomass and slower decomposition rates due to reduced microbial activity. To better predict habitability in Mars analog environments, we will correlate our biological dataset with mineralogy through XRF and drone-scale imagery. This work will be key in identifying targets on Mars that are most likely to harbor preserved biomarkers and, ultimately, the search for life on other terrestrial bodies.
Mariam Nesterov, Mehreen Zahid, Ana Gonzalez-Nayeck
Marine phytoplankton exude fixed carbon as exopolysaccharides (EPS), providing a significant source of carbon for heterotrophic bacteria. Although the role of phytoplankton in carbon fixation is relatively well established, the contribution of EPS to the carbon cycle is less constrained. We hypothesize that the carbon isotope composition of EPS may be sufficiently distinct from other sources of organic carbon to quantify the proportion of a heterotrophic diet comprised of EPS. Current methods for measuring 13C in sugars are optimized for biomass or exopolysaccharides in benthic ecosystems. Here we develop and test the methods for 13C analysis of sugar exuded by planktic organisms, starting with the initial concentration of sugars in seawater, followed by isotopic quantification via GC-IRMS. EPS exudation by phytoplankton is a non-negligible process within the carbon cycle. The methodology presented will improve the ability to trace carbon flow in planktic environments.
Rizzieri Balestra, Peter Crockford, Lyle Nelson, Darrel Long, Keith Dewing
The Ediacaran Period (635 – ~535 Ma) marks a time when biogeochemical cycling underwent revolutionary changes that broadly coincided with the appearance of macroscopic, multicellular organisms. In northeastern Ellesmere Island, the lowest preserved stratigraphic units, the Kennedy Channel and Ella Bay formations, were putatively deposited during the Ediacaran, based on the preservation of Cambrian body and trace fossils in the overlying Ellesmere Group. These strata preserve a progradational (shallowing-upward) succession associated with the establishment of a NW-facing passive continental margin. This study presents carbon, oxygen and strontium isotopic measurements (δ13C, δ18O, and 87/86Sr) and petrographic observations of carbonate samples collected from six stratigraphic sections of the Kennedy Channel and Ella Bay formations along a N-S transect, oblique to the paleo-continental margin. The recognition of a large negative δ13C anomaly, with carbonate values reaching as low as -12‰, supports correlation to the globally recognized Shuram-Wonoka δ13C excursion (574.0 ± 4.7 – 567.3 ± 3.0 Ma), consistent with an Ediacaran age for this succession. While the Shuram-Wonoka δ13C excursion has been variably attributed to local or diagenetic controls, the diachroneity of carbonate facies along a transect of the Kennedy Channel and Ella Bay formations allow interrogation of the δ13C-facies-relationships predicted by these hypotheses. We find that the observed δ13C trends are instead consistent with a synchronous marine carbon cycle perturbation preserved on a progradational margin. These findings refine temporal and stratigraphic correlation of the Kennedy Channel and Ella Bay formations and contribute to understanding the largest negative carbon isotope excursion in Earth history.
Benjamin Mousseau, Jordan Wostbrock
Biogenic carbonate oxygen isotope ratios are a key proxy for paleotemperature reconstructions. However, they are limited in their temporal scope because the most commonly used fossils – foraminifera and brachiopods – only emerged in the Phanerozoic. Microbial carbonates like stromatolites and thrombolites exist from the Archaean to modern and are also frequently leveraged as paleotemperature proxies, especially in Precambrian rocks. However, there is some debate over whether microbial carbonates precipitate in oxygen isotope equilibrium with the water or whether kinetic effects impact their oxygen isotope ratios. In this work, we present δ13C, δ17O, δ18O, and Δ'17O values of carbonate sediment, thrombolitic bioherms, and water from Green Lake in Fayettville, New York, USA. In a 57-cm lake sediment core, we found a steady decrease in carbonate δ18O values going downcore. We find an increase in δ13C until 35 cm depth, followed by a decrease, reflecting oxidation of organic matter occurring below the sediment-water interface. Triple oxygen isotope values indicate that none of the carbonate is precipitating in oxygen isotope equilibrium with the sampled lake water. All carbonate samples have lower δ18O and Δ'17O values than expected for equilibrium. After modelling multiple precipitation scenarios, we conclude that carbonate precipitation within Green Lake is most likely driven by rapid changes in DIC driving authigenic carbonate precipitation. Future work will explore whether similar processes impact the oxygen isotope values in marine microbial carbonates and the implications for their use as a proxy for paleotemperatures.
Lauren E. Morrison, Sarah P. Slotznick, Paul E. Olsen, and Sean T. Kinney
Goethite, α-FeO(OH), is often found in soils and sedimentary rocks and has long been considered solely a modern weathering product of iron-bearing minerals. In paleomagnetic analyses of sedimentary rocks, goethite often records a primary geomagnetic field direction, corroborating a modern formation process. While a few unique field directions have been noted, primary goethite has yet to be rigorously identified based on magnetic properties. However, with a distinctive yellow color and mineral magnetic parameters, goethite has often been utilized in paleoclimate and paleoenvironmental reconstructions. This study will address whether or not ancient goethite exists in the rock record, and if whether or not it can preserve primary directional magnetic data. We will present preliminary rock magnetic data from samples from the Late Triassic Chinle Formation. Oriented samples were procured from two coring sites in Petrified Forest National Park that were drilled during the Colorado Plateau Coring Project, Phase I (CPCP-I). While goethite has yet to be identified in these rocks, its’ existence is implicitly indicated in paleomagnetic studies. The targeted section, the Mesa Redondo Member, contains significant amounts of yellow-colored sediment. These mudstones have distinct textures that suggest pedogenic goethite formation, which could record early paleomagnetic directions. By probing samples using rock magnetic techniques, we can confirm goethite’s presence and explore its’ mineralogical diversity in the context of paleoenvironments. This is the first step in our study testing goethite’s potential to be preserved in ancient rocks and soils.
Laurie A. Zielinski, Olivia C. Moehl, Sarah P. Slotznick
Laurentian paleogeography during the Proterozoic is constrained in part by paleomagnetic poles from red beds of the Belt Supergroup (Montana, Alberta, and British Columbia), which is home to the world’s third oldest macrofossil and a suite of eukaryotic microfossils. However, these data (Elston et al., 2002) are discrepant with time-equivalent data from elsewhere in Laurentia. Additional issues include coarse and incomplete demagnetization sequences, outdated analytical methods, failed sites, and unpublished data. Moreover, red beds record both detrital (primary) and chemical remanence (in situ mineral growth from early diagenesis or later processes). The measured paleomagnetic directions can therefore be complex, but the underlying components are distinguishable using high-resolution thermal demagnetization. Here, we present an updated pole for the 1.45 Ga Spokane Formation, incorporating data from the correlative Grinnell and underlying Appekunny Formations in Glacier National Park, Montana. Using a more detailed demagnetization sequence to higher temperatures (>680 ºC) and least squares fitting methods, we overcame overprints that were confined to lower temperatures and found steeper detrital hematite directional fits compared to the original data. Our high-quality sample-level data allow us to correct for inclination shallowing and to present an improved pole. These enhancements will help us address concerns about the Belt’s paleomagnetic data, as well as other archival datasets from red beds. Ultimately, this pole will provide better constraints on the Mesoproterozoic position of the Belt Supergroup, whose fossils document a pivotal period in the evolution of eukaryotes.
Daniel Havlat, Jordan A. G. Wostbrock
The Middle Devonian was an important interval in Earth’s history, seeing the emergence of the first tetrapods and deep-rooted terrestrial forests. It was also an interval of faunal turnover, with multiple instances of severe ocean anoxia causing both local and global extinctions, such as the Kačák Event and the Taghanic Event. Seawater temperatures have been calculated from both brachiopod calcite and conodont hydroxyapatite δ18O values across this interval, with significant discordance between the two proxies and anomalously high temperatures derived from brachiopod shell calcite. It remains unclear what may account for the high temperatures when using δ18O values of brachiopod calcite. However, calcite is generally thought to be more susceptible to diagenesis compared to hydroxyapatite. Triple oxygen isotope analysis, which incorporates δ17O, is a relatively new geochemical technique through which it is possible to back-calculate the impact of diagenetic alteration on shell calcite, elucidating true environmental temperatures during shell formation. We present the first triple oxygen measurements taken from brachiopod shell calcite from the Middle Devonian of western New York.
Clare O'Callaghan (advised by David Jones)
In the Late Cretaceous, 2-3 million years before the Cretaceous-Paleogene mass extinction, the Inoceramidea family, which were bivalves that existed throughout the world’s oceans, experienced an acme, a period of abundance, and then a staggered extinction. The causes of these events are unknown. The goal of this study is to use cyclostratigraphy to assess the potential impact that Milankovitch cycles had on the climate of the Late Cretaceous and investigate how these climatic variations may have affected the ecological and evolutionary history of the Inoceramids. We sampled an outcrop of pelagic limestone in Furlo Gorge, located in the central Apennine Mountains in Italy, which contained both the acme and extinction events. Then, using portable X-ray fluorescence (pXRF) and Inductively Coupled Plasma Optical Emissions Spectroscopy (ICP-OES), we analyzed the elemental composition of ~175 samples that spanned ~870,000 years and included time before, during, and after the acme and extinction events. We analyzed this data with a MATLAB script using Fast Fourier Transforms (FFTs) and a Monte Carlo Simulation to generate power spectra. We found significant spectral peaks for terrigenous elements aluminum, silicon, and titanium, in the eccentricity band. This suggests that increased insolation led to more wind moving these terrigenous materials into a pelagic depositional environment. Thus, our results support that eccentricity was a contributor to climatic changes during the Late Cretaceous. Our results provide evidence that astronomical forcing had an impact on the climate and may be implicated in the history of inoceramid populations.
Sophie Lewis, Laura Barnett, Meredith Kelly, Justin Sirico Stroup & Jeffrey Donnelly
Salt marshes sequester carbon and protect against coastal erosion; the survival of these ecosystems is critical to mitigate adverse effects of anthropogenic climate change. Extant marshes along the southern coast of Massachusetts formed during the late Holocene, mostly keeping pace with sea-level rise prior to the mid-20th century. Less is known about how marsh systems evolved post-deglaciation during the early-to-mid Holocene. In this study, we collected offshore sediment cores containing peat from a drowned salt marsh in Buzzards Bay. To establish a sea-level index point (SLIP) in the peat layer, we use foraminifera and stable isotope analyses. Our study adds 4 SLIPs, the oldest for the region, to a database for southern Massachusetts, which we use to generate a curve of sea-level rise for the entire Holocene. Preliminary results suggest that these marshes formed 7-7.5 ka BP and drowned in <500 years, indicating rapid rates of sea-level rise during the early-to-mid Holocene. Our further work seeks to estimate carbon accumulation rates for the sediment cores to investigate how salt marsh carbon sequestration changed as sea levels rose. Our study of the paleo salt marsh provides a possible analogue for how present-day salt marshes may be expected to respond to rising sea levels.
Julia Wilcots, Kristin D. Bergmann, Adam C. Maloof
At 717 Ma, tropical carbonate platforms around the world became covered in ice. The transition from ice-free to ice-covered shallow marine environments at the onset of this “snowball” glaciation appears abruptly and synchronously, but should have been preceded by some amount of cooling. The cause, duration, and magnitude of pre-snowball cooling — how and why our planet’s climate-regulating mechanism failed — represents one major outstanding problem in Earth history. We tackle the question of what caused snowball Earth by establishing the climatic boundary conditions prior to glacial onset using the only deep-time paleotemperature proxy, carbonate clumped isotopes.
Well-preserved carbonate rocks can preserve a geochemical record of their formation temperature — ideally the temperature of the water from which they precipitated — through their clumped isotope (Δ47) composition, but Δ47 is easily altered during diagenesis. We present 65 measurements of Δ47 from a tropical shallow-water dolomite succession deposited <100 Myr prior to the onset of snowball glaciation. We identify samples affected by early diagenetic alteration using multispectral petrographic imaging and demonstrate that the best-preserved samples record clumped temperatures as low as 15.4ºC. Our ~300 m-long record likely also preserves a signal of ~12-15ºC of cooling. This record suggests that Earth was cool — possibly similar to our modern icehouse climate — and cooling for millions of years prior to snowball onset. After long-term cooling from an already cold climate, even just a small perturbation could have tipped Earth into an ice-covered state; the planet was primed for snowball glaciation.
Reina Harding, Tianran Zhang, C. Brenhin Keller, and Justin V. Strauss
Neoproterozoic–Carboniferous strata in the southwestern Mackenzie Mountains of Canada record rifting of the supercontinent Rodinia, major perturbations to the global carbon cycle, and the first appearance datum (FAD) of Ediacaran fossils within the northern Cordilleran fold-thrust belt. While previous studies have placed final rifting of Rodinia between ~780-700 Ma, evidence for regional extension persists well into the early Paleozoic throughout the area, suggesting a younger development of Laurentia’s northwestern continental margin. Here we use an integrated subsidence and age-depth model, SubsidenceChron.jl, to assess the regional subsidence history and constrain the age of the rift-drift transition in NW Canada. SubsidenceChron.jl uses decompaction, backstripping, and McKenzie-style thermal subsidence techniques to estimate the age of each stratigraphic horizon in a given succession and propagates uncertainties using Monte Carlo Markov Chain methods. Here, we test the sensitivity of this method by comparing results from three scenarios: 1) only incorporating local age constraints from the same thrust sheet of the composite section, 2) integrating age constraints from NW Canada across different thrust sheets and paleoenvironmental regimes (e.g., slope vs. shelf), and 3) incorporating age constraints from globally correlated stratigraphic units. This allows us to assign age estimates with uncertainties to geologically significant events recorded in these strata—such as the FAD of Ediacaran fossils—even when radiometric age constraints are lacking.
Lyle L. Nelson, Emily F. Smith, Simon. A. F. Darroch, Iona Baillie, Jahandar Ramezani, John E. Almond, Roger Swart, Dana E. Polomski, Katherine A. Turk
The Nama Group (Kalahari Craton) is an archetypal stratigraphic record of the Ediacaran-Cambrian transition. The upper Schwarzrand Subgroup preserves key biostratigraphic markers of this interval, yet has a complex stratigraphic architecture due to deposition in a foreland basin. Here, we describe the stratigraphy of the upper Schwarzrand Subgroup of the Nama Basin, and collate sedimentologic, geochronologic, carbon isotope chemostratigraphic, and biostratigraphic data within this framework. While carbonates of the underlying Urusis Formation were deposited within shallow marine environments, the terminal Schwarzrand Subgroup records a transition to dominantly siliciclastic deposition, mostly below fair-weather wave base, and with extensive evidence of slope instability. We argue that distinct deltaic peritidal and shoreface strata that were previously correlated to this unit are part of the unconformably overlying molasse deposits of the Fish River Subgroup. These strata contain the stratigraphically lowest identified occurrences of Treptichnus pedum within the Nama Group, and thus the base of the Cambrian Period. These stratigraphic revisions solve several longstanding issues with regional correlation and revise the position of the Ediacaran-Cambrian boundary in the Witputs Subbasin. Accordingly, the upper Schwarzrand Subroup in the Witputs Subbasin (538.5 - <537.6 Ma) is Ediacaran as defined by biostratigraphy, supporting recent interpretations that the base of the Cambrian Period is younger than 537.6 Ma. With increasingly refined age-stratigraphic models for the Nama Group, the upper Schwarzrand Subgroup provides a high-resolution record of the evolution of increasingly complex benthic invertebrate behaviors in the terminal Ediacaran lead-up to the classical Cambrian radiation of biomineralized invertebrate phyla.
Rachel L. Surprenant, Padmaja Jonnalagedda, Bir Bhanu, Mary L. Droser
The Precambrian geologic record is a valuable source of information for developing understanding of the history of life in our Universe because it archives the origins and diversification of life on Earth and, in turn, provides a search image for past life and its sedimentological signatures on other rocky planets. Along with the preservation of the first single-cellular life and the first macroscopic, multicellular animals on Earth, the Precambrian preserves a remarkable abundance of organic mats, which played a pivotal role in shaping the sedimentological record. One way in which these organic mats impacted sedimentation was through the stabilization of storm-generated ripples on the seafloor which prevented the erosion of ripples and led depositional events to fill in ripples instead of eroding them as is typical in non-stabilized sediments. The result of this is a sedimentological record that has a clear fingerprint of past life and is characterized by stacks of successive, discrete sandstone bedforms, with no fine grained interbeds, that preserve ripples on their top-most and bottom-most surfaces. This type of bedform, known as palimpsest ripples, therefore represents a discrete biosignature that is readily detectable in images of geologic cross-section. This has potential to aid the search for past life on Mars via the development of automated methods for the remote detection of palimpsest ripples in imagery. Here, a novel automated computer vision method, Scene-aware Perception Augmentation Using Composite Embedding for Segmentation (SPACESeg2.0), is introduced and is found to detect palimpsest ripples in imagery with high accuracy.
Charlotte Spruzen, Katie M. Maloney, J. Wilder Greenman, Maxwell A. Lechte, Galen P. Halverson
Throughout much of Earth’s history, reefs have been crucial components of sedimentary systems, due to their role as cradles of evolution and ecosystem engineers, and their significant influence on the global carbon cycle. While the evolution of Phanerozoic reef systems has been extensively studied, particularly in the context of the succession of metazoans that have contributed to reef construction, our understanding of temporal changes in reef morphology in the Proterozoic is relatively limited. For example, the Tonian period (1000–720 Ma) may represent a critical transition in microbialite reef construction, with the emergence of reefs built predominantly by thrombolites and other framework-constructing microbialites, but our understanding of this transition in reef evolution through time is limited by a sparse record of detailed case studies. Here, we present a stratigraphic analysis of the ca. 850–800 Ma Reefal assemblage in the Ogilvie Mountains in Yukon, Canada. We find that this unit comprises a substantial, prograding platformal reef system, with alternating laminated and unlaminated microbialite building up on areas of uplifted paleotopography. In the adjacent depocentres, shale-to-carbonate sequences record periodic progradation and/or restriction. Recrystallization and silicification heavily obscure primary growth features in the majority of Reefal assemblage microbialite outcrop. However, we identify consistent microbialite textures at three different stages of preservation, both in outcrop and in petrographic thin section. We infer that the Reefal assemblage is predominantly built by framework-building thrombolites, with strong similarities to the approximately co-eval Little Dal Group of the Northwest Territories. The obliteration of thrombolite textures in the Reefal assemblage has implications for the microbialite record in deep time, as the sparse record of thrombolites in the Precambrian, particularly before the Neoproterozoic, may be a result of preservation-related obscurity rather than true absence.