Now showing items 1-20 of 248

    • A 5-km-thick reservoir with > 380,000 km3 of magma within the ancient Earth's crust 

      Latypov, Rais; Chistyakova, Sofya; Hornsey, Richard A.; Costin, Gelu; van der Merwe, Mauritz (2022)
      Several recent studies have argued that large, long-lived and molten magma chambers may not occur in the shallow Earth’s crust. Here we present, however, field-based observations from the Bushveld Complex that provide evidence to the contrary. In the eastern part of the complex, the magmatic layering continuously drapes across a ~ 4-km-high sloping ...
    • A Framework for the Systematic Selection of Biosensor Chassis for Environmental Synthetic Biology 

      Sridhar, Swetha; Ajo-Franklin, Caroline M.; Masiello, Caroline A. (2022)
      Microbial biosensors sense and report exposures to stimuli, thereby facilitating our understanding of environmental processes. Successful design and deployment of biosensors hinge on the persistence of the microbial host of the genetic circuit, termed the chassis. However, model chassis organisms may persist poorly in environmental conditions. In ...
    • A Framework for Understanding Whole-Earth Carbon Cycling 

      Lee, Cin-Ty A.; Jiang, Hehe; Dasgupta, Rajdeep; Torres, Mark; Orcutt, Beth N.; (2019)
      Building from the base of knowledge presented in the preceding chapters, this chapter explores how the cycling of carbon in subduction zones and orogenic belts varies with supercontinent cycles and mountain building. It discusses the processes that link short-term and long-term carbon cycling and the timescales of these processes, such as the response ...
    • A novel and efficient engine for P-/S-wave-mode vector decomposition for vertical transverse isotropic elastic reverse time migration 

      Zhang, Lele; Liu, Lu; Niu, Fenglin; Zuo, Jiahui; Shuai, Da; (2022)
      Wave-mode decomposition plays a very important role in elastic reverse time migration (ERTM). Improved imaging quality can be achieved due to reduced wave-mode crosstalk artifacts. The current state-of-the-art methods for anisotropic wavefield separation are based on either splitting model strategy, low-rank approximation, or lower-upper (LU) ...
    • A perspective on climate model hierarchies 

      Jeevanjee, Nadir; Hassanzadeh, Pedram; Hill, Spencer; Sheshadri, Aditi (2017)
      To understand Earth's climate, climate modelers employ a hierarchy of climate models spanning a wide spectrum of complexity and comprehensiveness. This essay, inspired by the World Climate Research Programme's recent “Model Hierarchies Workshop,” attempts to survey and synthesize some of the current thinking on climate model hierarchies, especially ...
    • A subglacial hydrologic drainage hypothesis for silt sorting and deposition during retreat in Pine Island Bay 

      Schroeder, Dustin M.; MacKie, Emma J.; Creyts, Timothy T.; Anderson, John B. (2019)
      Late Holocene sediment deposits in Pine Island Bay, West Antarctica, are hypothesized to be linked to intensive meltwater drainage during the retreat of the paleo-Pine Island Ice Stream after the Last Glacial Maximum. The uppermost sediment units show an abrupt transition from ice-proximal debris to a draped silt during the late Holocene, which is ...
    • A zero-dimensional view of atmospheric degradation of levoglucosan (LEVCHEM_v1) using numerical chamber simulations 

      Suciu, Loredana G.; Griffin, Robert J.; Masiello, Caroline A. (2021)
      Here, we developed a zero-dimensional (0-D) modeling framework (LEVCHEM_v1) to provide insights into the atmospheric degradation of a key tracer emitted during biomass burning – levoglucosan (LEV), while additionally exploring its effects on the dynamics of secondary organic aerosols (SOA) and other gases. For this, we updated existing chemical ...
    • Absolute plate velocities from seismic anisotropy: Importance of correlated errors 

      Zheng, Lin; Gordon, Richard G.; Kreemer, Corné (2014)
      The errors in plate motion azimuths inferred from shear wave splitting beneath any one tectonic plate are shown to be correlated with the errors of other azimuths from the same plate. To account for these correlations, we adopt a two-tier analysis: First, find the pole of rotation and confidence limits for each plate individually. Second, solve for ...
    • Adjoint traveltime tomography unravels a scenario of horizontal mantle flow beneath the North China craton 

      Dong, Xingpeng; Yang, Dinghui; Niu, Fenglin; Liu, Shaolin; Tong, Ping (2021)
      The North China craton (NCC) was dominated by tectonic extension from late Cretaceous to Cenozoic, yet seismic studies on the relationship between crust extension and lithospheric mantle deformation are scarce. Here we present a three dimensional radially anisotropic model of NCC derived from adjoint traveltime tomography to address this issue. We ...
    • Aged black carbon in marine sediments and sinking particles 

      Coppola, Alysha I.; Ziolkowski, Lori A.; Masiello, Caroline A.; Druffel, Ellen R.M. (2014)
      We report measurements of oceanic black carbon (BC) to determine the sources of BC to abyssal marine sediments in the northeast Pacific Ocean. We find that the average 14C age of BC is older (by 6200 ± 2200 14C years) than that of the concurrently deposited non-BC sedimentary organic carbon. We investigate sources of aged BC to sediments by measuring ...
    • Airborne radar sounding evidence for deformable sediments and outcropping bedrock beneath Thwaites Glacier, West Antarctica 

      Schroeder, Dustin M.; Blankenship, Donald D.; Young, Duncan A.; Witus, Alexandra E.; Anderson, John B. (2014)
      The geologic and morphologic records of prior ice sheet configurations show evidence of rapid, back-stepping, meltwater intensive retreats. However, the potential for such a retreat in a contemporary glacier depends on the lithology of the current ice sheet bed, which lies beneath kilometers of ice, making its physical properties difficult to constrain. ...
    • An alternative formula for approximate extended Born inversion 

      Hou, Jie; Symes, William W. (2017)
      Various modifications of reverse time migration (RTM) provide asymptotic inverses to the subsurface offset extended Born modeling operator for constant-density acoustics. These approximate inverses have the same quality (asymptotic accuracy) as do generalized Radon transform pseudoinverses, but they can be computed without any ray tracing whatsoever. ...
    • An olivine cumulate outcrop on the floor of Jezero crater, Mars 

      Liu, Y.; Tice, M. M.; Schmidt, M. E.; Treiman, A. H.; Kizovski, T. V.; (2022)
      The geological units on the floor of Jezero crater, Mars, are part of a wider regional stratigraphy of olivine-rich rocks, which extends well beyond the crater. We investigated the petrology of olivine and carbonate-bearing rocks of the Séítah formation in the floor of Jezero. Using multispectral images and x-ray fluorescence data, acquired by the ...
    • Application of Frequency-dependent Traveltime Tomography and Full Waveform Inversion to Realistic Near-surface Seismic Refraction Data 

      Chen, Jianxiong; Zelt, Colin A. (2016)
      We present a synthetic test that uses a workflow consisting of a new frequency-dependent traveltime tomography (FDTT) method to provide a starting model for full waveform inversion (FWI) for near-surface seismic velocity estimation from refraction data. Commonly used ray-theory-based traveltime tomography methods may not be valid in the near surface ...
    • Aquifer Monitoring Using Ambient Seismic Noise Recorded With Distributed Acoustic Sensing (DAS) Deployed on Dark Fiber 

      Tribaldos, Verónica Rodríguez; Ajo-Franklin, Jonathan B. (2021)
      Groundwater is a critical resource for human activities worldwide, and a vital component of many natural ecosystems. However, the state and dynamics of water-bearing aquifers remain uncertain, mostly due to the paucity of subsurface data at high spatial and temporal resolution. Here, we show that analysis of infrastructure-generated ambient seismic ...
    • Artificial Soils Reveal Individual Factor Controls on Microbial Processes 

      Del Valle, Ilenne; Gao, Xiaodong; Ghezzehei, Teamrat A.; Silberg, Jonathan J.; Masiello, Caroline A. (2022)
      Soil matrix properties influence microbial behaviors that underlie nutrient cycling, greenhouse gas production, and soil formation. However, the dynamic and heterogeneous nature of soils makes it challenging to untangle the effects of different matrix properties on microbial behaviors. To address this challenge, we developed a tunable artificial soil ...
    • Assessing offsets between the δ13C of sedimentary components and the global exogenic carbon pool across early Paleogene carbon cycle perturbations 

      Sluijs, Appy; Dickens, Gerald R. (2012)
      [1] Negative stable carbon isotope excursions (CIEs) across the Paleocene–Eocene thermal maximum (PETM; ~56 Ma) range between 2‰ and 7‰, even after discounting sections with truncated records. Individual carbon isotope records differ in shape and magnitude from variations in the global exogenic carbon cycle through changes in (1) the relative abundance ...
    • Autocorrelation R2 on Mars 

      Deng, Sizhuang; Levander, Alan (2022)
      A purpose of the Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport (InSight) mission is to reveal the Martian interior structure with seismic data. In this work, ambient noise autocorrelation of the continuously recorded vertical-component seismic signals has extracted the Rayleigh waves that propagate around Mars for one ...
    • Autocorrelation Reflectivity of Mars 

      Deng, Sizhuang; Levander, Alan (2020)
      The seismic structure of the Martian interior can shed light on the formation and dynamic evolution of the planet and our solar system. The deployment of the seismograph carried by the InSight mission provides a means to study Martian internal structure. We used ambient noise autocorrelation to analyze the available vertical component seismic data ...
    • Avoiding unintentional eviction from integral projection models 

      Williams, Jennifer L.; Miller, Tom E.X.; Ellner, Stephen P. (2012-09)
      Integral projection models (IPMs) are increasingly being applied to study size-structured populations. Here we call attention to a potential problem in their construction that can have important consequences for model results. IPMs are implemented using an approximating matrix and bounded size range. Individuals near the size limits can be unknowingly ...