Earth, Environmental and Planetary Sciences Publications

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    Nature and Origin of Magnetic Lineations Within Valdivia Bank: Ocean Plateau Formation by Complex Seafloor Spreading
    (Wiley, 2023) Thoram, S.; Sager, W. W.; Gaastra, K.; Tikoo, S. M.; Carvallo, C.; Avery, A.; Del Gaudio, Arianna V.; Huang, Y.; Hoernle, K.; Höfig, T. W.; Bhutani, R.; Buchs, D. M.; Class, C.; Dai, Y.; Valle, G. Dalla; Fielding, S.; Han, S.; Heaton, D. E.; Homrighausen, S.; Kubota, Y.; Li, C.-F.; Nelson, W. R.; Petrou, E.; Potter, K. E.; Pujatti, S.; Scholpp, J.; Shervais, J. W.; Tshiningayamwe, M.; Wang, X. J.; Widdowson, M.
    Valdivia Bank (VB) is a Late Cretaceous oceanic plateau formed by volcanism from the Tristan-Gough hotspot at the Mid-Atlantic Ridge (MAR). To better understand its origin and evolution, magnetic data were used to generate a magnetic anomaly grid, which was inverted to determine crustal magnetization. The magnetization model reveals quasi-linear polarity zones crossing the plateau and following expected MAR paleo-locations, implying formation by seafloor spreading over ∼4 Myr during the formation of anomalies C34n-C33r. Paleomagnetism and biostratigraphy data from International Ocean Discovery Program Expedition 391 confirm the magnetic interpretation. Anomaly C33r is split into two negative bands, likely by a westward ridge jump. One of these negative anomalies coincides with deep rift valleys, indicating their age and mechanism of formation. These findings imply that VB originated by seafloor spreading-type volcanism during a plate reorganization, not from a vertical stack of lava flows as expected for a large volcano.
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    Measurements of Wave-Induced Attenuation in Saturated Metapelite and the Band-Limitation of Low-Frequency Earthquakes
    (Wiley, 2023) Fliedner, Céline; French, Melodie E.
    The most common explanation for the depletion of high frequency waves that defines low-frequency earthquakes (LFEs) and very low-frequency earthquakes (VLFEs) is that fault rupture and slip are slower than typical earthquakes. However, it is difficult to rule out the possibility that the high frequency waves are produced during slip, but attenuated near the LFE source. One reason this hypothesis has been poorly tested is that there are no measurements of attenuation on the relevant rocks. We present the results of forced oscillation experiments that measure the frequency-dependent attenuation of a chlorite-rich metapelitic schist, a lithology found along the subduction plate boundary where LFEs and VLFEs have been documented. Experiments were run on dry and water-saturated schist at effective pressures of 2–10 MPa and at frequencies of 2 × 10−5–30 Hz. We find that pore fluids and low effective pressure result in the attenuation of high frequencies. The frequency-dependent attenuation is consistent with the concomitant operation of two wave-induced fluid flow mechanisms, squirt flow, and patchy saturation. When the effects of these mechanisms are extrapolated to geologic conditions using rock physics models, our results predict that attenuation is capable of completely diminishing the frequencies depleted in LFEs and VLFEs. Therefore, LFEs and VLFEs may not necessarily record slow fault slip, but possibly the presence of high fluid pressure.
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    Using Dark Fiber and Distributed Acoustic Sensing to Characterize a Geothermal System in the Imperial Valley, Southern California
    (Wiley, 2023) Cheng, Feng; Ajo-Franklin, Jonathan B.; Nayak, Avinash; Tribaldos, Veronica Rodriguez; Mellors, Robert; Dobson, Patrick; Team, the Imperial Valley Dark Fiber
    The Imperial Valley, CA, is a tectonically active transtensional basin located south of the Salton Sea; the area hosts numerous geothermal fields, including significant hidden hydrothermal resources without surface manifestations. Development of inexpensive, rugged, and highly sensitive exploration techniques for undiscovered geothermal systems is critical for accelerating geothermal power deployment as well as unlocking a low-carbon energy future. We present a case study utilizing distributed acoustic sensing (DAS) and ambient noise interferometry for geothermal reservoir imaging, utilizing unlit fiber-optic telecommunication infrastructure (dark fiber). The study exploits two days of passive DAS data acquired in early November 2020 over a ∼28-km section of fiber from Calipatria, CA to Imperial, CA. We apply ambient noise interferometry to retrieve coherent signals from DAS records and develop a bin stacking technique to attenuate the effects from persistent localized noise sources and to enhance retrieval of coherent surface waves. As a result, we are able to obtain high-resolution two-dimensional (2D) S wave velocity (Vs) structure to 3 km depth, based on joint inversion of both the fundamental and higher overtones. We observe a previously unmapped high Vs and low Vp/Vs ratio feature beneath the Brawley geothermal system, which we interpret to be a zone of hydrothermal mineralization and lower porosity. This interpretation is consistent with a host of other measurements including surface heat flow, gravity anomalies, and available borehole wireline data. These results demonstrate the potential utility of DAS deployed on dark fiber for geothermal system exploration and characterization in the appropriate geological settings.
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    Widespread phosphorous excess in olivine, rapid crystal growth, and implications for magma dynamics
    (Presses universitaires de Strasbourg, 2022) Lee, Cin-Ty; Sun, Chenguang; Sharton-Bierig, Eytan; Phelps, Patrick; Borchardt, Jackson; Liu, Boda; Costin, Gelu; Johnston, A. Dana
    Trace element zoning is often used to unravel the crystallization history of phenocrysts in magmatic systems, but interpretation requires quantifying the relative importance of equilibrium versus disequilibrium. Published partition coefficients for phosphorous (P) in olivine vary by more than a factor of ten. After considering kinetic effects, a new equilibrium partition coefficient was extrapolated from a re-examination of natural and experimental systems, indicating that P partition coefficients in olivine are significantly over-estimated. These new partitioning constraints allow us to establish a theoretical P Equilibrium Fractionation Array (PEFA) for mid-ocean ridge basalts (MORBs), revealing that most olivines from MORBs have excess P (2–15 times PEFA) and are thus in disequilibrium. Using an independent case study of natural dendritic olivines, we show that such P enrichments can be explained by diffusion-limited incorporation of P during rapid crystal growth. If growth rate can be related to cooling, the rapid growth rates of olivines have implications for magma system dynamics, such as the size of magma bodies or where crystallization occurs within the body.
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    Understanding Subsurface Fracture Evolution Dynamics Using Time-Lapse Full Waveform Inversion of Continuous Active-Source Seismic Monitoring Data
    (Wiley, 2023) Liu, Xuejian; Zhu, Tieyuan; Ajo-Franklin, Jonathan
    Predicting the behavior, geometry, and flow properties of subsurface fractures remains a challenging problem. Seismic models that can characterize fractures usually suffer from low spatiotemporal resolution. Here, we develop a correlative double-difference time-lapse full waveform inversion of continuous active source seismic monitoring data for determining high-spatiotemporal-resolution time-lapse Vp models of in-situ fracture evolution at a shallow contamination site in Wyoming, USA. Assisted by rock physics modeling, we find that (a) rapidly increasing pore pressure initializes and grows the fracture, increasing the porosity slightly (from ∼13.7% to ∼14.6%) in the tight clay formation, thus decreasing Vp (∼50 m/s); (b) the fluid injection continues decreasing Vp, likely through the introduction of gas bubbles in the injectate; and (c) final Vp reductions reach over ∼150 m/s due to a posited ∼4.5% gas saturation. Our results demonstrate that high-resolution Vp changes are indicative of mechanical and fluid changes within the fracture zone during hydrofracturing.
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    Compactive deformation of incoming calcareous pelagic sediments, northern Hikurangi subduction margin, New Zealand: Implications for subduction processes
    (Elsevier, 2023) Wang, Maomao; Barnes, Philip M.; Morgan, Julia K.; Bell, Rebecca E.; Moore, Gregory F.; Wang, Ming; Fagereng, Ake; Savage, Heather; Gamboa, Davide; Harris, Robert N.; Henrys, Stuart; Mountjoy, Joshu; Tréhu, Anne M.; Saffer, Demian; Wallace, Laura; Petronotis, Katerina
    Calcareous rocks are commonly found in subduction zones, but few studies have investigated the consolidation and compactive deformation of these rocks prior to subduction, and their potential effects on subduction and accretionary processes are thus poorly understood. Using drilling data obtained during International Ocean Discovery Program (IODP) Expeditions 372 and 375 combined with 2D and 3D seismic reflection data, the structure, growth history, and slip rates of normal faults identified in the incoming pelagic sedimentary sequences of the Hikurangi Margin were investigated. A seismic coherence depth slice and vertical profiles show that these faults exhibit polygonal structure that has rarely been documented at subduction margins. The polygonal faults are closely spaced and layer-bound within sequences dominated by pelagic carbonate and calcareous mudstone of Paleocene-Pliocene age. Kinematic modeling and 2D displacement analysis reveal that fault throws decrease toward the upper and lower tipline. In detail, two groups of throw profiles are defined by locations of displacement maxima, possibly reflecting lateral variations in physical properties. The polygonal fault system (PFS) likely formed by syneresis processes that involve diagenetically induced shear failure and volumetric contraction of the pelagic unit associated with fluid escape. Fault growth sequences reveal multiple, weakly correlated intervals of contemporaneous seafloor deformation and sedimentation and allow estimates of fault slip rates. We find evidence for a significant increase in typical slip rates from 0.5-3 m/Ma during pelagic sedimentation to >20 m/Ma following the onset of terrigenous sedimentation. These observations suggest that rapid loading of the pelagic sediments by the trench-wedge facies was associated with renewed and faster growth of the PFS. The PFS will eventually be transported into the base of the accretionary wedge, enhancing geometric roughness and heterogeneity of materials along the megathrust, and providing inherited zones of weakness. Selective fault reactivation may facilitate deformation and episodic vertical fluid migration in the lower wedge associated with microearthquakes, tremor, and slow slip events.
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    Viscous relaxation as a probe of heat flux and crustal plateau composition on Venus
    (PNAS, 2023) Nimmo, Francis; Mackwell, Stephen
    It has recently been suggested that deformed crustal plateaus on Venus may be composed of felsic (silica-rich) rocks, possibly supporting the idea of an ancient ocean there. However, these plateaus have a tendency to collapse owing to flow of the viscous lower crust. Felsic minerals, especially water-bearing ones, are much weaker and thus lead to more rapid collapse, than more mafic minerals. We model plateau topographic evolution using a non-Newtonian viscous relaxation code. Despite uncertainties in the likely crustal thickness and surface heat flux, we find that quartz-dominated rheologies relax too rapidly to be plausible plateau-forming material. For plateaus dominated by a dry anorthite rheology, survival is possible only if the background crustal thickness is less than 29 km, unless the heat flux on Venus is less than the radiogenic lower bound of 34 mW m −2 mW m − 2 . Future spacecraft determinations of plateau crustal thickness and mineralogy will place firmer constraints on Venus’s heat flux.
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    Reconstructing Holocene temperatures in time and space using paleoclimate data assimilation
    (Copernicus Publications, 2022) Erb, Michael P.; McKay, Nicholas P.; Steiger, Nathan; Dee, Sylvia; Hancock, Chris; Ivanovic, Ruza F.; Gregoire, Lauren J.; Valdes, Paul
    Paleoclimatic records provide valuable information about Holocene climate, revealing aspects of climate variability for a multitude of sites around the world. However, such data also possess limitations. Proxy networks are spatially uneven, seasonally biased, uncertain in time, and present a variety of challenges when used in concert to illustrate the complex variations of past climate. Paleoclimatic data assimilation provides one approach to reconstructing past climate that can account for the diverse nature of proxy records while maintaining the physics-based covariance structures simulated by climate models. Here, we use paleoclimate data assimilation to create a spatially complete reconstruction of temperature over the past 12 000 years using proxy data from the Temperature 12k database and output from transient climate model simulations. Following the last glacial period, the reconstruction shows Holocene temperatures warming to a peak near 6400 years ago followed by a slow cooling toward the present day, supporting a mid-Holocene which is at least as warm as the preindustrial. Sensitivity tests show that if proxies have an overlooked summer bias, some apparent mid-Holocene warmth could actually represent summer trends rather than annual mean trends. Regardless, the potential effects of proxy seasonal biases are insufficient to align the reconstructed global mean temperature with the warming trends seen in transient model simulations.
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    Tropospheric Ozone During the Last Interglacial
    (Wiley, 2022) Yan, Yuzhen; Banerjee, Asmita; Murray, Lee T.; Tie, Xin; Yeung, Laurence Y.
    The history of tropospheric O3, an important atmospheric oxidant, is poorly constrained because of uncertainties in its historical budget and a dearth of independent records. Here, we estimate the mean tropospheric O3 burden during the Last Interglacial period (LIG; 115 to 130 thousand years ago) using a record of the clumped isotopic composition of O2 (i.e., Δ36 values) preserved in Antarctic ice. The measured LIG Δ36 value is 0.03 ± 0.02‰ (95% CI) higher than the late pre-industrial Holocene (PI; 1,590–1,850 CE) value and corresponds to a modeled 9% reduction in LIG tropospheric O3 burden (95% CI: 3%–15%), caused in part by a substantial reduction in biomass burning emissions during the LIG relative to the PI. These results are consistent with the hypothesis that late-Pleistocene megafaunal extinctions caused woody and grassy fuels to accumulate on land, leading to enhanced biomass burning in the preindustrial Holocene.
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    Insights on Formation of the Gulf of Mexico by Rayleigh Surface Wave Imaging
    (Wiley, 2022) Nguyen, Luan C.; Levander, Alan; Niu, Fenglin; Morgan, Julia; Li, Guoliang
    We used cross-correlation of ambient noise records from seismic stations in the US, Mexico, and Cuba to extract dispersion data of Rayleigh surface wave. Our derived 3D shear-wave velocity model of the greater Gulf of Mexico (GOM) region captures variations in the crustal and lithospheric structures across the continental margins of the US Gulf Coast and Yucatan, Mexico. The model shows a zone of reduced velocity in the mantle lithosphere underlying the extended continental margin of the northwestern GOM. We attributed this velocity reduction to extensional deformation and melt-induced weakening of the lithosphere during the Triassic continental rifting that preceded the seafloor spreading that formed the GOM. Melt extraction might have been hindered by the greater lithospheric thickness in the western region along the US Gulf Coast margin that resulted in the westward decrease of rift-related volcanism/magmatism reported from previous studies. The clear asymmetry between the US Gulf Coast and its conjugate Yucatan margin suggests extension along a shear-zone that focused more deformation on the North American plate prior to breakup. In contrast to the counterclockwise rotation of the Yucatan block during seafloor-spreading, our analyses using deformable plate models demonstrate that continental rifting occurred in a predominantly northwest-southeast direction. This change in plate motion is attributed to the development of mantle shear-zones in the western part of the rift. We estimated the depth of the lithosphere-asthenosphere boundary and determined that the extended continental and oceanic lithospheres have mostly regained their thickness since the time of breakup.
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    A Pliocene Precipitation Isotope Proxy-Model Comparison Assessing the Hydrological Fingerprints of Sea Surface Temperature Gradients
    (Wiley, 2022) Knapp, Scott; Burls, Natalie J.; Dee, Sylvia; Feng, Ran; Feakins, Sarah J.; Bhattacharya, Tripti
    The Pliocene offers insights into future climate, with near-modern atmospheric pCO2 and global mean surface temperature estimated to be 3–4°C above pre-industrial. However, the hydrological response differs between future global warming and early Pliocene climate model simulations. This discrepancy results from the use of reduced meridional and zonal sea surface temperature (SST) gradients, based on foraminiferal Mg/Ca and Alkenone proxy evidence, to force the early Pliocene simulation. Subsequent, SST reconstructions based on the organic proxy TEX86, have found warmer temperatures in the warm pool, bringing the magnitude of the gradient reductions into dispute. We design an independent test of Pliocene SST scenarios and their hydrological cycle “fingerprints.” We use an isotope-enabled General Circulation Model, iCAM5, to model the distribution of water isotopes in precipitation in response to four climatological SST and sea-ice fields representing modern, abrupt 4 × CO2, late Pliocene and early Pliocene climates. We conduct a proxy-model comparison with all the available precipitation isotope proxy data, and we identify target regions that carry precipitation isotopic fingerprints of SST gradients as priorities for additional proxy reconstructions. We identify two regions with distinct precipitation isotope (D/H) fingerprints resulting from reduced SST gradients: the Maritime Continent (D-enriched due to reduced convective rainfall) and the Sahel (wetter, more deep convection, D-depleted). The proxy-model comparison using available plant wax reconstructions, mostly from Africa, is promising but inconclusive. Additional proxy reconstructions are needed in both target regions and in much of the world for significant tests of SST scenarios and dynamical linkages to the hydrological cycle.
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    Sharp Changes of Crustal Seismic Anisotropy Across the Central Tanlu Fault Zone in East China
    (Wiley, 2023) Miao, Wenpei; Niu, Fenglin; Chen, Haichao
    Both seismic and geodetic data suggested that the ∼120-km long Weifang segment of the Tanlu fault zone, a large-scale active strike-slip system at east China, is a seismic gap with no obvious along-strike shear motion at surface. Measuring crustal deformation around the segment is crucial to constrain stress/strain buildup and potential seismic risk at the fault. We measured crustal and upper mantle seismic anisotropy using P-to-S converted waves at the Moho (Pms) and core-mantle boundary (SKS) recorded by broadband arrays across the Weifang fault segment. The measured crustal anisotropy inside the fault zone shows a fast direction of ∼NNE, parallel to the fault orientation. Right east to the fault zone, the fast axis rotates by almost 90° to ESE. The crustal anisotropy within the fault zone could be caused by aligned microcracks and foliated minerals due to long-lasting shear motion inside the fault zone.
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    Master event based backazimuth estimation and its application to downhole microseismic monitoring
    (Elsevier, 2022) Meng, Xiao-Bo; Chen, Hai-Chao; Niu, Feng-Lin; Du, Yi-Jing
    Microseismic monitoring provides a valuable tool for evaluating the effectiveness of hydraulic fracturing operations. However, robust detection and accurate location of microseismic events are challenging due to the low signal to noise ratio (SNR) of their signals on seismograms. In a downhole monitoring setting, P-wave polarization direction measured from 3-component records is usually considered as the backazimuth of the microseismic event, i.e., the direction of the event. The direction and arrival time difference between the P and S waves is used to locate the seismic event. When SNR is low, an accurate estimate of event backazimuth becomes very challenging with the traditional covariance matrix method. Here we propose to employ a master event and use a grid search method to find the backazimuth of a target event that maximizes the dot product of the two backazimuthal vectors of the master and target events. We compared the backazimuths measured with the proposed grid-search and the conventional covariance-matrix methods using a large synthetic dataset. We found that the grid-search method yields more accurate backazimuth estimates from low SNR records when measurements are made at single geophone level. When array data are combined, the proposed method also has some advantage over the covariance-matrix method, especially when the number of geophones is low. We also applied the method to a microseismic dataset acquired by a hydraulic fracturing project at a shale play site in southwestern China and found that the relocated microseismic events tend to align along existing faults more tightly than those in the original catalog.
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    Kolmogorov n–width and Lagrangian physics-informed neural networks: A causality-conforming manifold for convection-dominated PDEs
    (Elsevier, 2023) Mojgani, Rambod; Balajewicz, Maciej; Hassanzadeh, Pedram
    We make connections between complexity of training of physics-informed neural networks (PINNs) and Kolmogorov n-width of the solution. Leveraging this connection, we then propose Lagrangian PINNs (LPINNs) as a partial differential equation (PDE)-informed solution for convection-dominated problems. PINNs employ neural-networks to find the solutions of PDE-constrained optimization problems with initial conditions and boundary conditions as soft or hard constraints. These soft constraints are often blamed to be the sources of the complexity in the training phase of PINNs. Here, we demonstrate that the complexity of training (i) is closely related to the Kolmogorov n-width associated with problems demonstrating transport, convection, traveling waves, or moving fronts, and therefore becomes apparent in convection-dominated flows, and (ii) persists even when the boundary conditions are strictly enforced. Given this realization, we describe the mechanism underlying the training schemes such as those used in eXtended PINNs (XPINN), curriculum learning, and sequence-to-sequence learning. For an important category of PDEs, i.e., governed by non-linear convection–diffusion equation, we propose reformulating PINNs on a Lagrangian frame of reference, i.e., LPINNs, as a PDE-informed solution. A parallel architecture with two branches is proposed. One branch solves for the state variables on the characteristics, and the second branch solves for the low-dimensional characteristics curves. The proposed architecture conforms to the causality innate to the convection, and leverages the direction of travel of the information in the domain, i.e., on the characteristics. This approach is unique as it reduces the complexity of convection-dominated PINNs at the PDE level, instead of optimization strategies and/or schedulers. Finally, we demonstrate that the loss landscapes of LPINNs are less sensitive to the so-called “complexity” of the problems, i.e., convection, compared to those in the traditional PINNs in the Eulerian framework.
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    Buffering of mantle conditions through water cycling and thermal feedbacks maintains magmatism over geologic time
    (Springer Nature, 2022) Seales, Johnny; Lenardic, Adrian; Richards, Mark
    The Earth has remained magmatically and volcanically active over its full geologic history despite continued planetary cooling and a lack of thermal equilibrium in the mantle. Here we investigate this conundrum using data-constrained numerical models of deep-water cycling and thermal history. We find that the homologous temperature - the ratio of upper mantle to melting temperatures - initially declined but has been buffered at a nearly constant value since 2.5-2.0 billion years ago. Melt buffering is a result of the dependence of melting temperature and mantle viscosity on both mantle temperature and water content. We show that thermal and water cycling feedbacks lead to a self-regulated mantle evolution, characterised by a near-constant mantle viscosity. This occurs even though the mantle remains far from thermal equilibrium. The added feedback from water-dependent melting allows magmatism to be co-buffered over geological time. Thus, we propose that coupled thermal and water cycling feedbacks have maintained melting on Earth and associated volcanic/magmatic activity.
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    The Exoplanet Radius Valley from Gas-driven Planet Migration and Breaking of Resonant Chains
    (IOP Publishing, 2022) Izidoro, André; Schlichting, Hilke E.; Isella, Andrea; Dasgupta, Rajdeep; Zimmermann, Christian; Bitsch, Bertram
    The size frequency distribution of exoplanet radii between 1 and 4R ⊕ is bimodal with peaks at ∼1.4 R ⊕ and ∼2.4 R ⊕, and a valley at ∼1.8 R ⊕. This radius valley separates two classes of planets—usually referred to as “super-Earths” and “mini-Neptunes”—and its origin remains debated. One model proposes that super-Earths are the outcome of photoevaporation or core-powered mass loss stripping the primordial atmospheres of the mini-Neptunes. A contrasting model interprets the radius valley as a dichotomy in the bulk compositions, where super-Earths are rocky planets and mini-Neptunes are water-ice-rich worlds. In this work, we test whether the migration model is consistent with the radius valley and how it distinguishes these views. In the migration model, planets migrate toward the disk’s inner edge, forming a chain of planets locked in resonant configurations. After the gas disk dispersal, orbital instabilities “break the chains” and promote late collisions. This model broadly matches the period-ratio and planet-multiplicity distributions of Kepler planets and accounts for resonant chains such as TRAPPIST-1, Kepler-223, and TOI-178. Here, by combining the outcome of planet formation simulations with compositional mass–radius relationships and assuming the complete loss of primordial H-rich atmospheres in late giant impacts, we show that the migration model accounts for the exoplanet radius valley and the intrasystem uniformity (“peas in a pod”) of Kepler planets. Our results suggest that planets with sizes of ∼1.4 R ⊕ are mostly rocky, whereas those with sizes of ∼2.4 R ⊕ are mostly water-ice-rich worlds. Our results do not support an exclusively rocky composition for the cores of mini-Neptunes.
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    Enhanced continental weathering activity at the onset of the mid-Cenomanian Event (MCE)
    (European Association of Geochemistry, 2022) Yobo, L. Nana; Brandon, A.D.; Lauckner, L.M.; Eldrett, J.S.; Bergman, S.C.; Minisini, D.
    The emplacement of a Large Igneous Province (LIP) is implicated in the triggering of the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2). Evidence for a similar initiation mechanism for the mid-Cenomanian Event (MCE) is unclear. In this study, a reconstruction of mid-Cenomanian seawater 187Os/188Os, the first for the Western Interior Seaway, tests the competing roles of LIP versus continental weathering activity in triggering the MCE. The absence of a prolonged unradiogenic Os isotope excursion (low 187Os/188Os) at the onset of the MCE interval argues against LIP involvement in the event’s initiation. Rather, more radiogenic 187Os/188Os at the onset, that continues to rise to the middle of the MCE, indicates that the event was triggered by increased continental weathering. The combination of decreasing 187Os/188Os from the middle of the MCE onward, coincident with a 40Ar/39Ar age of 96.4 Ma of basalts from Ellesmere Island, Canada, is consistent with High Arctic LIP-related volcanic activity that may have contributed to the end of the MCE. These new data on the MCE thus indicate that LIP activity is not always the trigger for carbon cycle perturbation and associated climate change.
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    An olivine cumulate outcrop on the floor of Jezero crater, Mars
    (AAAS, 2022) Liu, Y.; Tice, M.M.; Schmidt, M.E.; Treiman, A.H.; Kizovski, T.V.; Hurowitz, J.A.; Allwood, A.C.; Henneke, J.; Pedersen, D.A.K.; VanBommel, S.J.; Jones, M.W.M.; Knight, A.L.; Orenstein, B.J.; Clark, B.C.; Elam, W.T.; Heirwegh, C.M.; Barber, T.; Beegle, L.W.; Benzerara, K.; Bernard, S.; Beyssac, O.; Bosak, T.; Brown, A.J.; Cardarelli, E.L.; Catling, D.C.; Christian, J.R.; Cloutis, E.A.; Cohen, B.A.; Davidoff, S.; Fairén, A.G.; Farley, K.A.; Flannery, D.T.; Galvin, A.; Grotzinger, J.P.; Gupta, S.; Hall, J.; Herd, C.D.K.; Hickman-Lewis, K.; Hodyss, R.P.; Horgan, B.H.N.; Johnson, J.R.; Jørgensen, J.L.; Kah, L.C.; Maki, J.N.; Mandon, L.; Mangold, N.; McCubbin, F.M.; McLennan, S.M.; Moore, K.; Nachon, M.; Nemere, P.; Nothdurft, L.D.; Núñez, J. I.; O’Neil, L.; Quantin-Nataf, C.M.; Sautter, V.; Shuster, D.L.; Siebach, K.L.; Simon, J.I.; Sinclair, K.P.; Stack, K.M.; Steele, A.; Tarnas, J.D.; Tosca, N.J.; Uckert, K.; Udry, A.; Wade, L.A.; Weiss, B.P.; Wiens, R.C.; Williford, K.H.; Zorzano, M.-P.
    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 Perseverance rover, we performed a petrographic analysis of the Bastide and Brac outcrops within this unit. We found that these outcrops are composed of igneous rock, moderately altered by aqueous fluid. The igneous rocks are mainly made of coarse-grained olivine, similar to some martian meteorites. We interpret them as an olivine cumulate, formed by settling and enrichment of olivine through multistage cooling of a thick magma body.
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    Rates of Future Climate Change in the Gulf of Mexico and the Caribbean Sea: Implications for Coral Reef Ecosystems
    (Wiley, 2022) Lawman, A.E.; Dee, S.G.; DeLong, K.L.; Correa, A.M.S.
    Rising temperatures and ocean acidification due to anthropogenic climate change pose ominous threats to coral reef ecosystems in the Gulf of Mexico (GoM) and the western Caribbean Sea. Unfortunately, the once structurally complex coral reefs in the GoM and Caribbean have dramatically declined since the 1970s; relatively few coral reefs still exhibit a mean live coral cover of >10%. Additional work is needed to characterize future climate stressors on coral reefs in the GoM and the Caribbean Sea. Here, we use climate model simulations spanning the period of 2015–2100 to partition and assess the individual impacts of climate stressors on corals in the GoM and the western Caribbean Sea. We use a top-down modeling framework to diagnose future projected changes in thermal stress and ocean acidification and discuss its implications for coral reef ecosystems. We find that ocean temperatures increase by 2°C–3°C over the 21st century, and surpass reported regional bleaching thresholds by mid-century. Whereas ocean acidification occurs, the rate and magnitude of temperature changes outpace and outweigh the impacts of changes in aragonite saturation state. A framework for quantifying and communicating future risks in the GoM and Caribbean using reef risk projection maps is discussed. Without substantial mitigation efforts, the combined impact of increasing ocean temperatures and acidification are likely to stress most existing corals in the GoM and the Caribbean, with widespread economic and ecological consequences.
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    Autocorrelation Reflectivity of Mars
    (Wiley, 2020) Deng, Sizhuang; Levander, Alan
    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 to recover the reflectivity beneath the Insight lander. We identify the noise that is approximately periodic with the Martian sol as daily lander operations and the diurnal variation in Martian weather and tides. To investigate the seismic discontinuities at different depths, the autocorrelograms are filtered and stacked into different frequency bands. We observe prominent reflection signals probably corresponding to the Martian Moho, the olivine-wadsleyite transition in the mantle, and the core-mantle boundary in the stacked autocorrelograms. We estimate the depths of these boundaries as ~35, 1,110–1,170, and 1,520–1,600 km, consistent with other estimates.