Ceres’ regolith contains water ice that has receded in response to insolation-driven sublimation. Specially targeted, high spatial-resolution measurements of hydrogen by Dawn’s Gamma Ray and Neutron Detector reveal elevated hydrogen concentrations in and around Occator, a young, 90-km diameter, complex crater located at 19.82N where near-surface ice is not expected. The excess hydrogen is explained by impact excavation of water-rich outer crustal materials and their emplacement in the crater floor and ejecta blanket. This is supported by thermophysical models that show water ice could survive at sub-meter depths, given Occator’s relatively young age (~20 Myr). We hypothesize that the regolith can be replenished with ice from large impacts and that this process partially controls the distribution and depth of near surface ice. This is supported by results from Occator and similarities in the global distribution of hydrogen and the pattern of large craters (20-100 km diameter).
The current study presents new bed-by-bed brachiopod δ13C and δ18O records from Öland, Sweden, which together with previously published data from the East Baltic region, constitutes a high-resolution paired brachiopod and bulk rock carbon and oxygen isotope archive through the Lower to Upper Ordovician of Baltoscandia. This new dataset refines the temporal control on the global Ordovician δ18O-trend considerably, improving paleoenvironmental reconstructions through the main phase of the Great Ordovician Biodiversification Event (GOBE). The new brachiopod carbon and oxygen isotope records from Öland display strong similarity with the East Baltic records, elucidating the regional consistency as well as global correlation utility of the ensuing composite Baltoscandian Early to Middle Ordovician carbon and oxygen isotope record. The carbon isotope record from Öland indicates that prominent carbon cycle perturbations are recorded in both brachiopods and bulk carbonates, most notably the MDICE (Mid-Darriwilian Carbon Isotope Excursion). The oxygen isotope record reveals a long-term Early to Late Ordovician trend of increasingly heavier brachiopod δ18O values, with a pronounced increase during the Middle Ordovician Darriwilian Age. We interpret this trend as dominantly reflecting a paleotemperature signal indicating progressively cooler Early to Middle Ordovician climate with glacio-eustasy. Our Baltic δ18O values are therefore consistent with postulations that the biotic radiations during the GOBE and climatic cooling during the Darriwilian were strongly linked.
The Shuram excursion, an extremely negative and prolonged carbonate δ13C anomaly, is recorded globally in late Ediacaran shallow-water marine sedimentary sequences and coincided with a time of increasing ocean oxygenation. Marine planktonic microorganisms with organic cell walls, known as acritarchs, were common in the Ediacaran Period. The onset of the Shuram excursion occurred during a time of rapid acritarch cell wall diversification, and the excursion’s resolution was followed by the appearance of macroscopic calcium carbonate biomineralizing metazoans in the late Ediacaran. Accordingly, I consider that the Shuram excursion may be attributed to sedimentary accumulations of material sourced from weakly calcified acritarchs, which primitively biomineralized their cell walls by precipitating 13C-enriched marine carbonate onto 13C-depleted organic carbon. Decay of this organic carbon to authigenic carbonate after burial may have produced the low δ13Ccarb values. The carbon isotope mass balance of global carbon cycle reservoirs permits this effect to produce a Shuram excursion of any duration. An initial organic fraction of ~0.6 is required in the acritarch-derived phase, in agreement with fossil evidence that the earliest biomineralized structures contained a major fraction of organic carbon. I will discuss how fossil, petrographic and geochemical observations are consistent with this hypothesis. During the excursion, a peak globally averaged organic carbon burial fraction of ~0.4 is predicted. Burial sequestration of organic carbon in organic-rich biomineralized calcium carbonate could account for the rise in oxygen associated with the Shuram excursion.
Icy moons around the ice giant planets may contain subsurface oceans. Their oceans could be detected and characterized using measurements of magnetic fields induced by the host planet’s time-varying magnetospheric field. We explore the possibility of detecting and characterizing subsurface oceans among the five major moons of Uranus—with a particular focus on Ariel—using spacecraft magnetometry measurements. We find that the magnetic field at each moon is dominated by the synodic frequency with amplitudes ranging from ~4 nT at Oberon up to ~300 nT at Miranda. If these bodies contain oceans with sufficient thicknesses (>~6-100 km) and conductivities (>2 S m-1), the induced surface fields should have amplitudes exceeding the typical ~1 nT sensitivity of spacecraft magnetometry investigations. Furthermore, the magnetic field at the moons spans periods ranging from 1 to 103 h. This could enable long-term measurements to separately constrain ocean and ice thicknesses and ocean salinity.
Reconstructions of ocean primary productivity (PP) help to explain past and present biogeochemical cycles and climate changes in the oceans. We document PP variations over the last 50 kyr in a currently oligotrophic subtropical region, the Gulf of Cadiz (GoC). Data combine refined results from previous investigations on dinoflagellate cyst (dinocyst) assemblages, alkenones, and stable isotopes (18O, 13C) in planktonic (Globigerina bulloides) and endobenthic (Uvigerina mediterranea) foraminifera from cores MD04-2805 CQ and MD99-2339 with new isotopic measurements on epibenthic (Cibicidoides species) foraminifera and dinocyst-based estimates of PP using the new n = 1,968 modern database. We thus constrain paleoproductivity variations and export production by integrating qualitative information from micropaleontological bio-indicators with quantitative reconstructions of parameters such as dinocyst-based PP and seasonal sea-surface temperature (SST), as well as information about remineralization from the benthic Dd13C. We show that PP, carbon export, and remineralization were generally high in the NE subtropical Atlantic Ocean during the last glacial period and that the Last Glacial Maximum (LGM) had lower Dd13C than the Heinrich Stadials with sustained high PP, likely allowing enhanced carbon sequestration. This study also provides vital information on the dynamics PP regime changes, as the dataset includes alkenone-based SST and total organic carbon (TOC). We link these stimulated PP periods to seasonal intensification of upwelling, active almost year-round during stadials, but restricted to spring–summer during interstadials and LGM, like today. During interstadials, nutrient advection through freshwater inputs during autumn–winter rains need to be considered to fully understand PP regimes.
Using web standards including Schema.org and JSON-LD, the GeoCODES project extends Schema.org with Project 418's geoscience specific vocabulary. By embedding properly formatted and populated JSON-LD files in web sites serving geolocated datasets, search engines such as Google and Bing are able to parse and index these data sets and then to provide information concerning these datasets via standard web search tools. Due to the difficult nature of properly formatting and populating these JSON-LD structures, the GeoCODES User Interface was created to guide data providers through the process of describing the data and validating the descriptions against standard vocabularies. The result is user friendly and easily extensible web based, mobile device ready tool for automatically generating JSON-LD metadata for organizations and datasets. This ultimately allows the original data to be found and used by both scientists and the public.
Terrestrial hot springs have existed throughout Earth’s history and house some of the most ancient evidence of life on our planet. These settings are known for their high habitability and preservation potential, and are extensively studied as analog environments since hot spring deposits are thought to exist on the surface of Mars. Hot spring water commonly precipitates silica that coats microbial life dwelling in the hot spring outflow streams. This process can entomb microorganisms and preserve microbial remains over long timescales and with high morphological fidelity. Here we present research carried out on modern and sub-recent remains of microbial filaments from amorphous (unaltered) silica deposits in Yellowstone National Park. This work suggests that various elements sequestered by hot spring-dwelling organisms during life are preserved in microbial remains and persist over > 10,000 years. We also present findings from microfossils preserved in mid-Paleozoic terrestrial hot spring deposits which also show sequestrations of select elements in microfossil remains, suggesting that certain elements may persist even after several hundred million years and substantial host rock alteration. These elemental concentrations may be indicative of metabolic functioning during life and have application as biosignatures. Recent developments in analytical instrumentation now allow for even extremely low trace elemental abundances to be detected and mapped, regardless of sample complexity. This work is especially relevant to the search for life on Mars, as evidence of impact-induced hydrothermal activity may exist near the rim of Jezero Crater and may be sampled by the Perseverance rover. As a primary objective of the Mars 2020 mission is to search for evidence of past life on Mars, we suggest the application of this analytical technique to be valuable for potential samples returned to Earth by future Mars Sample Return missions. Distribution Statement A. Approved for public release: distribution unlimited.
Dob’s Linn (Scotland) is a location that has significantly influenced our understanding of how life evolved over the Ordovician to early Silurian. The current chronostratigraphic boundary between the Ordovician and Silurian periods is a Global Boundary Stratotype Section and Point (GSSP) at Dob’s Linn calibrated to 443.8±1.5 Ma, partly based on biostratigraphic markers, radiometric ages, and statistical modeling. Graptolites are used here as relative dating markers. We dated hundreds of zircon grains extracted from defined metabentonites from six horizons exposed at Dob’s Linn using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Each zircon was imaged using cathodoluminescence, and most show igneous zoning with minimal alteration. Sample locations range from 42 meters above to 5 meters below the recognized GSSP for the Ordovician-Silurian. Samples were responsibly collected and analyzed for paleontology and geochemistry in other work. Overall, many 238U-206Pb zircon ages from the section are significantly younger than expected. The youngest zircon in sample DL7, located 5 meters below the GSSP, yielded a 238U-206Pb age of 402±12 Ma (±2s, 5% disc). Nineteen spots on zircons from this sample are younger than the presently assigned GSSP age, including more concordant results of 426±8 Ma (0.8% disc) and 435±5 Ma (0.2% disc). The youngest zircon in sample 19DL12, < 1 m below the GSSP, is 377±8 Ma (2% disc) with a more concordant age of 443±7 Ma (0.6% disc). A sample located directly on the GSSP (19DL09) yields 327±5 Ma (0.8% disc). Eight spots on zircons from this sample are also younger than the presently assigned GSSP age. We also dated two samples (DL24 and BRS23) 8 meters above the GSSP, and the youngest, most concordant zircon ages in these samples are 400±11 Ma (5% disc) and 421±9 Ma (0.4% disc), respectively. Overall, the U-Pb ages would re-assign the Dob’s Linn chronostratigraphic section to Silurian-Devonian. The young age results could be attributed to Pb loss due to hydrothermal alteration during the Acadian and Alleghenian orogenies. Future work will implement Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry (CA-ID-TIMS) to obtain accurate U-Pb dating and evaluate the potential effects of Pb loss.
Carbon isotope (δ13C) records from marine sediments have been extensively used in Cenozoic chemostratigraphy. The early Paleogene interval in particular has received exceptional attention because negative carbon isotope excursions (CIEs) documented in the sedimentary record, e.g. at the Paleocene Eocene Thermal Maximum (PETM), ca ~56 Ma, are believed to reflect significant global carbon cycle perturbations during the warmest interval of the Cenozoic era. However, while bulk-carbonate δ13C values exhibit robust correlations across widely separated marine sedimentary sections, their absolute values and magnitude of CIEs vary spatially. Moreover, bulk-carbonates in open-marine environments are an ensemble of different components, each with a distinct isotopic composition. Consequently, a complete interpretation of the bulk δ13C record requires an understanding of co-evolution of these components. In this study, we dissect sediments, from early Paleogene interval, at ODP Site 1209, Shatsky Rise, Pacific Ocean to investigate how an evolving bulk-carbonate ensemble influences the overall carbon isotope record. A set of 45 samples were examined for δ13C and δ18O compositions, as bulk and individual size fractions. We find a significant increase in coarse-fraction abundance across PETM, driven by a changing community structure of calcifiers, modulating the size of CIE at Site 1209 and thus making it distinct from those recorded at other open-marine sites. These results highlight the importance of biogeography in marine stable-isotope record, especially when isotopic excursions are driven by climate- and/or carbon-cycle changes. In addition, community composition changes will alter the interpretation of weight percent coarse fraction as conventional proxy for carbonate dissolution.
Sedimentary records provide an invaluable background for understanding of complex phenomena that vary within multiple spatio--temporal scales, such as climate and the seismic cycle. Understanding the latter in southern Chile has yielded motivation to develop new tools to deal with such records, in order to build a comprehensive peleoseismic catalog from them. The region inherited an extensive chain of lakes from the pleistocene glaciations, and a strong tephrochronological framework has been developed during the last two decades. Lake deposits have been extensively studied and shown to contain an incredibly sensitive paleoseismic record in the form of lacustrine turbidites. The task is thus to build the best possible chronology making use of all available data. Age--depth modeling is now routinely done by means of bayesian techniques, by using a sedimentation model as prior information and a set of age determinations as data. This approach provides the best results for any single record, but not necessarily for a set of records taken together. This is the goal of the shared chronologies approach, to build the tools for estimating the best chronologies for a set of sedimentary records given some chronological data for each and a set of shared events or stratigraphic markers. We use for this purpose the fact that two or more of such layers should yield age differences close to zero, within the general age uncertainty. This fact is incorporated to the model as prior information, along with the sedimentation model. The idea is clearly usable in a wide range of contexts, and for this reason we would like to share the implementation in a very early stage of development in order to incorporate feedback into design decisions that could affect extensibility and modularity, and to forge collaboration. This contribution shares an early experiment against a simulated data set, as well as the current R implementation and future plans.
The usage of the term Knowledge Graph (KG) has gained significant popularity since 2012, when Google introduced its own knowledge graph, and how they used it to enhance their searches and question answering systems. While various definitions and interpretations for knowledge graphs have been presented, what remains consistent is that knowledge graphs are commonly used with reasonsers to make inferences about data, based on assertions and axioms written by human experts. But knowledge graphs, which store complex, multi-dimensional data contain hidden patterns and trends that cannot be explored simply using reasoners. In such a case it becomes necessary to extract parts of the knowledge graph (focusing on the instances related to one property at a time) and analyze them individually in order to conduct a focused but tractable exploration of the domain. In this presentation, we present one way to gain insights from knowledge graphs, using network science. To achieve this goal, we have formalised the partitioning of knowledge graphs to unipartite knowledge networks, and present various ways to explore and analyse such knowledge networks to form scientific hypotheses, gain scientific insights and make discoveries.