A method for inverting ratio–ratio data to estimate end-member compositions in mixing problems

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Chemical Geology 352 (2013): 63–69, doi:10.1016/j.chemgeo.2013.06.002.I discuss the general problem of fitting mixing models to ratio-ratio data, and derive formulae for applying non-linear Maximum Likelihood methods for parameter estimation. To estimate mixing model parameters in the under-determined inversion it is necessary to introduce prior constraints, which I implement by penalizing the likelihood function for variations from a starting model. I illustrate practical aspects of the inverse problem by applying the method to synthetic data for a ternary system of putative mantle reservoirs using Sr, Nd, and Pb isotope ratios. I fit the synthetic data using two different starting models to demonstrate the sensitivity of the gradient method used to solve the non-linear inverse to the starting model and the necessity of inspecting the final model to avoid spurious results. I include Matlab scripts to facilitate starting model selection and to perform binary and ternary ratio-ratio inversions as an Electronic Appendix

Sonic boom configuration minimization

The topics covered include the following: the sonic boom 'big picture'; current low boom technology; Mach number impact on gross weight; equal loudness equivalent areas; performance and sizing results; potential configuration modifications; equivalent area matching; and impact of nose bluntness on aerodynamic characteristics

Spectral analysis of vertical temperature profile time-series data in Yellowstone Lake sediments

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Water Resources Research 57(4), (2021): e2020WR028430, https://doi.org/10.1029/2020WR028430.We use yearlong vertical temperature profile time-series (seven thermistors at evenly spaced depth intervals from 10 to 70 cm) from five sites in and around the Deep Hole thermal area, southeast of Stevenson Island, Yellowstone Lake, to investigate heat and mass fluxes across the lake floor. The records demonstrate that thermal gradients in surficial sediments are modulated by a rich spectrum of bottom water temperature variations generated by hydrodynamic processes, and that sites inside the thermal area also respond to hydrothermal variations. We develop and implement a new method for estimating the sediment effective thermal diffusivity and pore fluid vertical flow rate that exploits the full spectrum of observed temperature variations to generate the parameter estimates, uncertainties, and metrics to assess statistical significance. Sediments at sites outside thermal areas have gradients of ∼7.5°C/m, in situ thermal diffusivities of ∼1.6 × 10−7 m2/s consistent with highly porous (80–90%) siliceous sediments, and experience hypolentic flow in the upper ∼20 cm. Sites inside the Deep Hole thermal area exhibit considerable spatial and temporal variability, with gradients of 1–32°C/m, and higher thermal diffusivities of ∼2–12 × 10−7 m2/s, consistent with hydrothermal alteration of biogenic silica to clays, quartz, and pyrite. Upward pore fluid flow at these sites is observed across multiple depth intervals, with maximum values of ∼3 cm/day. The observed spatial and temporal variability within the thermal area is consistent with upward finger flow combined with short wavelength convection within the porous sediments above a steam reservoir.This research was supported by the National Science Foundation Grants EAR-1516361 to Robert A. Sohn and EAR-1515283 to Robert N. Harris, and by the Independent Research and Development Program at the Woods Hole Oceanographic Institution (Robert A. Sohn). All work in Yellowstone National Park was completed under an authorized Yellowstone research permit (YELL-2018-SCI-7018)

Poroelastic response of mid-ocean ridge hydrothermal systems to ocean tidal loading : implications for shallow permeability structure

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 43 (2016): 1660–1668, doi:10.1002/2015GL066479.We use the time delay between tidal loading and exit-fluid temperature response for hydrothermal vents to model the poroelastic behavior and shallow upflow zone (SUZ) effective permeability structure of three mid-ocean ridge (MOR) sites with different spreading rates. Hydrothermal vents at Lucky Strike field exhibit relatively small phase lags corresponding to high SUZ effective permeabilities of ≥ ~10−10 m2, with variations that we interpret as resulting from differences in the extrusive layer thickness. By contrast, vents at East Pacific Rise site exhibit relatively large phase lags corresponding to low SUZ effective permeabilities of ≤ ~10−13 m2. Vents at Main Endeavour field exhibit both high and low phase lags, suggestive of a transitional behavior. Our results demonstrate that tidal forcing perturbs hydrothermal flow across the global MOR system, even in places where the tidal amplitude is very low, and that the flow response can be used to constrain variations in SUZ permeability structure beneath individual vent fields.This research was funded by Woods Hole Oceanographic Institution (USA). Thibaut Barreyre was supported by WHOI's Deep Ocean Exploration Institute (DOEI) postdoctoral scholarship.2016-08-2

OMP Peptides Activate the DegS Stress-Sensor Protease by a Relief of Inhibition Mechanism

In the E. coli periplasm, C-terminal peptides of misfolded outer-membrane porins (OMPs) bind to the PDZ domains of the trimeric DegS protease, triggering cleavage of a transmembrane regulator and transcriptional activation of stress genes. We show that an active-site DegS mutation partially bypasses the requirement for peptide activation and acts synergistically with mutations that disrupt contacts between the protease and PDZ domains. Biochemical results support an allosteric model, in which these mutations, active-site modification, and peptide/substrate binding act in concert to stabilize proteolytically active DegS. Cocrystal structures of DegS in complex with different OMP peptides reveal activation of the protease domain with varied conformations of the PDZ domain and without specific contacts from the bound OMP peptide. Taken together, these results indicate that the binding of OMP peptides activates proteolysis principally by relieving inhibitory contacts between the PDZ domain and the protease domain of DegS.United States. Dept. of Energy (Office of Basic Energy Sciences, contract DE-AC02-06CH11357))National Institutes of Health (U.S.) (NIH-NCRR award RR-15301)National Institutes of Health (U.S.) (NIH postdoctoral fellowship (F32AI-074245-01A1))National Institutes of Health (U.S.) (NIH grant AI-16892

Microearthquake evidence for reaction-driven cracking within the Trans-Atlantic Geotraverse active hydrothermal deposit

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 119 (2014): 822–839, doi:10.1002/2013JB010110.We detected 32,078 very small, local microearthquakes (average ML = −1) during a 9 month deployment of five ocean bottom seismometers on the periphery of the Trans-Atlantic Geotraverse active mound. Seismicity rates were constant without any main shock-aftershock behavior at ~243 events per day at the beginning of the experiment, 128 events per day after an instrument failed, and 97 events per day at the end of the experiment when whale calls increased background noise levels. The microearthquake seismograms are characterized by durations of <1 s and most have single-phase P wave arrivals (i.e., no S arrivals). We accurately located 6207 of the earthquakes, with hypocenters clustered within a narrow depth interval from ~50 to 125 m below seafloor on the south and west flanks of the deposit. We model the microearthquakes as reaction-driven fracturing events caused by anhydrite deposition in the secondary circulation system of the hydrothermal mound and show that under reasonable modeling assumptions an average event represents a volume increase of 31–58 cm3, yielding an annual (seismogenic) anhydrite deposition rate of 27–51 m3.This work was supported in part by the U.S. National Science Foundation, National Science and Engineering Graduate Fellowship, and the Woods Hole Oceanographic Institution Deep Ocean Exploration Institute.2014-09-1

Turbulence-induced bubble nucleation in hydrothermal fluids beneath Yellowstone Lake

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Caudron, C., Vandemeulebrouck, J., & Sohn, R. A. Turbulence-induced bubble nucleation in hydrothermal fluids beneath Yellowstone Lake. Communications Earth & Environment, 3(1), (2022): 103, https://doi.org/10.1038/s43247-022-00417-6.Volcanic systems generate large amounts of gas, and understanding gas fluxes is a fundamental aspect of volcanology and hazard mitigation. Volcanic gases can be challenging to measure, but acoustic methods hold promise in underwater environments because gas bubbles are powerful sound sources. We deployed an acoustic system to study the nature of gas discharge at a large (~30 MW) thermal field on the floor of Yellowstone Lake, which has experienced numerous hydrothermal explosions since the last glaciation (~13.4 ka). We find that small (<10 Pa) turbulent flow instabilities trigger the nucleation of CO2 bubbles in the saturated fluids. The observation of CO2 bubbles nucleating in hydrothermal fluids due to small pressure perturbations informs our understanding of hydrothermal explosions in Yellowstone Lake, and demonstrates that acoustic data in underwater environments can provide insight into the stability of gas-rich systems, as well as gas fluxes.This research was supported by the National Science Foundation grant EAR-1516361 to R.A.S. All work in Yellowstone National Park was completed under an authorized research permit (YELL-2018-SCI-7018). We also acknowledge the IRGA 2021 Volquan project (funded by Université Grenoble Alpes) and Thomas Jefferson Fund Face Foundation (project TJF20_009 ‘Quantifying underwater volcano degassing using novel seismo-acoustic approaches’)

Local seismicity of the Rainbow massif on the Mid‐Atlantic Ridge

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 123 (2018): 1615-1630, doi:10.1002/2017JB015288.The Rainbow massif, an oceanic core complex located in a nontransform discontinuity on the Mid‐Atlantic Ridge (36°N), is notable for hosting high‐temperature hydrothermal discharge through ultramafic rocks. Here we report results from a 9 month microearthquake survey conducted with a network of 13 ocean bottom seismometers deployed on and around the Rainbow massif as part of the MARINER experiment in 2013–2014. High rates (~300 per day) of low‐magnitude (average ML ~ 0.5) microearthquakes were detected beneath the massif. The hypocenters do not cluster along deeply penetrating fault surfaces and do not exhibit mainshock/aftershock sequences, supporting the hypothesis that the faulting associated with the exhumation of the massif is currently inactive. Instead, the hypocenters demarcate a diffuse zone of continuous, low‐magnitude deformation at relatively shallow (< ~3 km) depths beneath the massif, sandwiched in between the seafloor and seismic reflectors interpreted to be magmatic sills driving hydrothermal convection. Most of the seismicity is located in regions where seismic refraction data indicate serpentinized ultramafic host rock, and although the seismic network we deployed was not capable of constraining the focal mechanism of most events, our analysis suggests that serpentinization may play an important role in microearthquake generation at the Rainbow massif.NSF Grant Numbers: OCE‐0961680, OCE‐09611512018-07-2

Segment-scale variations in seafloor volcanic and tectonic processes from multibeam sonar imaging, Mid-Atlantic Ridge Rainbow region (35°45′–36°35′N)

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 17 (2016): 3560–3579, doi:10.1002/2016GC006433.Along-axis variations in melt supply and thermal structure can lead to significant variations in the mode of crustal accretion at mid-ocean ridges. We examine variations in seafloor volcanic and tectonic processes on the scale of individual ridge segments in a region of the slow spreading Mid-Atlantic Ridge (35°45′–36°35′N) centered on the Rainbow nontransform discontinuity (NTD). We use multibeam sonar backscatter amplitude data, taking advantage of multifold and multidirectional coverage from the MARINER geophysical study to create a gridded compilation of seafloor reflectivity, and interpret the sonar image within the context of other data to examine seafloor properties and identify volcanic flow fields and tectonic features. Along the spreading segments, differences in volcanic productivity, faulting, eruption style, and frequency correlate with inferred magma supply. Regions of low magma supply are associated with more widely spaced faults, and larger volcanic flow fields that are more easily identified in the backscatter image. Identified flow fields with the highest backscatter occur near the ends of ridge segments. Their relatively smooth topography contrasts with the more hummocky, cone-dominated terrain that dominates most of the neovolcanic zone. Patches of seafloor with high, moderately high, and low backscatter intensity across the Rainbow massif are spatially correlated with observations of basalt, gabbro and serpentinized peridotite, and sediment, respectively. Large detachment faults have repeatedly formed along the inside corners of the Rainbow NTD, producing a series of oceanic core complexes along the wake of the NTD. A new detachment fault is currently forming in the ridge segment just north of the now inactive Rainbow massif.National Science Foundation Grant Numbers: OCE-0961151, OCE-09616802017-03-0

Fluid oscillations in a laboratory geyser with a bubble trap

Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Rudolph, M. L., Sohn, R. A., & Lev, E.. Fluid oscillations in a laboratory geyser with a bubble trap. Journal of Volcanology and Geothermal Research, 368, (2018):100-110. doi:10.1016/j.jvolgeores.2018.11.003.Geysers are rare geologic features that episodically erupt water and steam. While it is understood that the eruptions are triggered by the conversion of thermal to kinetic energy during decompression of hot uids, geysers commonly exhibit a range of dynamic behaviors in-between and during eruptions that have yet to be adequately explained. In-situ measurements of temperature and pressure as well as remote geophysical techniques have revealed oscillatory behavior across a range of timescales, ranging from eruption cycles to impulsive bubble collapse events. Many geysers, including Old faithful in Yellowstone National Park, USA, are believed to have o set subsurface reservoirs (referred to as a `bubble trap') that can trap and accumulate noncondensable gas or steam entering the system. The impact of a bubble trap on the dynamic behaviors of the system, however, has not been fully established. We constructed a laboratory bubble trap and performed a series of experiments to study how uids oscillate back and forth between the eruption conduit and laterally-offseet reservoir in-between eruptions. We present a new theoretical model based on Hamiltonian mechanics that successfully predicts the oscillation frequencies observed in our experiments based on the conduit system geometry, the amount of gas that has accumulated in the bubble trap, and the amount of liquid water in the system. We demonstrate that when scaled to Old Faithful Geyser, this mechanism is capable of producing oscillations at the observed frequencies.The authors thank Paul Fucile and Glenn Macdonald for engineering support in designing and constructing the laboratory analog geyser rig. Funding for the laboratory geyser was provided by the US National Science Foundation grant EAR-1516361. EL was funded through a RISE award from Columbia University.2019-11-1