Geology Research Works

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A Better Understanding of Atmospheric Methane Sources Using 13CH3D and 12CH2D2 Clumped Isotopes
(2024-09) Haghnegahdar, Mojhgan A.
We evaluate the use of clumped isotopes of methane (CH4) to fingerprint local atmospheric sources of methane. We focus on a regenerative stormwater conveyance (RSC) stream wetland site running through the University of Maryland campus, which emits methane due to its engineering. Air samples in the RSC were collected at different heights above the surface and at different times of the day including both early in the morning, after methane accumulated below the nocturnal boundary layer, and late in the afternoon when convection mixed air to the cloud layer. Measured Δ12CH2D2 values of air samples record mixing between locally produced methane with low D/H and ambient air. The Δ12CH2D2 of the near surface air collected at the RSC during the early morning ranges from ~+23‰ to ~+35‰ which is lower than the ~+50‰ values of tropospheric air. Mixing between background air (with Δ12CH2D2 ~+50‰) and methane captured from chamber and bubble samples, as well as produced in incubation (all with negative Δ12CH2D2), explains the observed values of Δ12CH2D2 and Δ13CH3D of near surface RSC air samples. The effect of mixing with biogenic sources on Δ13CH3D is much smaller. The findings demonstrate how methane isotopologues can be used as a tool not only to fingerprint local contributions to these greenhouse gas emissions but also to identify sources of near-surface methane hot spots.
Snowfall Replenishes Groundwater Loss in the Great Basin of the Western United States, but Cannot Compensate for Increasing Aridification
(Wiley, 2024-03-20) Hall, Dorothy K.; Loomis, Bryant D.; DiGirolamo, Nicolo E.; Forman, Barton A.
There has been an acceleration of groundwater loss in the Great Basin (GB) of the western U.S. as determined from total water storage (TWS) measurements from the GRACE/FO satellite missions. From 2002 to 2023, there was a loss of TWS in the GB of ∼68.7 km3 which is more than six times the current volume of the Lake Mead Reservoir. In this arid/semi-arid region, groundwater is the primary factor contributing to the decade-scale decline in TWS. Stronger declining trends are found in the western versus the eastern GB. Snow loading is the major cause of seasonal fluctuations of TWS in the GB. Despite annual replenishment of groundwater by snow, the downward trend persists even in notable snow years. Likely causes include declining snow mass, upstream water diversions and increased evaporation/sublimation due to increasing temperatures. Dire consequences for humans and wildlife are associated with this large loss of groundwater.
Chemical and genetic characterization of the ungrouped pallasite Lieksa
(Wiley, 2023-11-03) Chiappe, Emily M.; Ash, Richard D.; Luttinen, Arto; Lukkari, Sari; Kuva, Jukka; Hilton, Connor D.; Walker, Richard J.
The meteorite Lieksa was found in 2017 in Löpönvaara, Finland, and later donated to the Finnish Museum of Natural History. Here, we report siderophile element concentrations, genetic isotopic data, and a metal–silicate segregation age for the meteorite. The ~280 g Lieksa is ~80% metal and ~20% silicate and oxide inclusions by volume, with the inclusions consisting primarily of Fe-rich olivine. Due to Lieksa's silicate content, coupled with a texture characterized by metal enclosing the silicates, it has been classified as a pallasite. Lieksa's olivine and bulk chemical characteristics are distinct from those of the known pallasite and iron meteorite groups, consistent with its classification as ungrouped. The meteorite exhibits a flat, chondrite-normalized highly siderophile element pattern, consistent with an origin as an early crystallization product from a metallic melt with chondritic relative abundances. Molybdenum, Ru, and 183W isotopic data indicate that Lieksa formed in the non-carbonaceous (NC) domain of the solar nebula. Radiogenic 182W abundances for Lieksa yield a model metal–silicate segregation age of 1.5 ± 0.8 Myr after calcium-aluminum-rich inclusion formation, which is within the range established for other NC-type pallasite and iron meteorite parent bodies.
The Hunga Tonga-Hunga Ha'apai Volcanic Eruption as Seen in Satellite Microwave Observations and MiRS Temperature Retrievals
(Wiley, 2023-12-06) Lee, Yong-Keun; Hindley, Neil; Grassotti, Christopher; Liu, Quanhua
The strongest volcanic eruption since the 19th century occurred on 15 January 2022 at Hunga Tonga-Hunga Ha'apai, generating unprecedented atmospheric waves not seen before in observations. We used satellite microwave observations from (a) Advanced Technology Microwave Sounder (ATMS) on board the National Oceanic and Atmospheric Administration (NOAA)-20 and the Suomi-National Polar-orbiting Partnership (SNPP) and (b) Advanced Microwave Sounding Unit (AMSU)-A on board Meteorological operational satellite (MetOp)-B/MetOp-C to study these waves in the stratosphere immediately after the eruption. The NOAA Microwave Integrated Retrieval System (MiRS) was applied to these microwave observations to produce atmospheric temperature profiles. The atmospheric Lamb wave and fast-traveling gravity waves are clearly revealed in both the brightness temperatures and the MiRS retrieved temperatures, revealing their vertical phase structures. This study is the first attempt to perform a detailed analysis of the stratospheric impact of the Tonga eruption on operational satellite microwave observations and the corresponding MiRS retrievals.
Oxygen Fugacity of Global Ocean Island Basalts
(Wiley, 2024-01-27) Willhite, Lori N.; Arevalo, Ricardo Jr.; Piccoli, Philip; Lassiter, John C.; Rand, Devin; Jackson, Matthew G.; Day, James M. D.; Nicklas, Robert W.; Locmelis, Marek; Ireland, Thomas J.; Puchtel, Igor S.
Mantle plumes contain heterogenous chemical components and sample variable depths of the mantle, enabling glimpses into the compositional structure of Earth's interior. In this study, we evaluated ocean island basalts (OIB) from nine plume locations to provide a global and systematic assessment of the relationship between fO2 and He-Sr-Nd-Pb-W-Os isotopic compositions. Ocean island basalts from the Pacific (Austral Islands, Hawaii, Mangaia, Samoa, Pitcairn), Atlantic (Azores, Canary Islands, St. Helena), and Indian Oceans (La Réunion) reveal that fO2 in OIB is heterogeneous both within and among hotspots. Taken together with previous studies, global OIB have elevated and heterogenous fO2 (average = +0.5 ∆FMQ; 2SD = 1.5) relative to prior estimates of global mid-ocean ridge basalts (MORB; average = −0.1 ∆FMQ; 2SD = 0.6), though many individual OIB overlap MORB. Specific mantle components, such as HIMU and enriched mantle 2 (EM2), defined by radiogenic Pb and Sr isotopic compositions compared to other OIB, respectively, have distinctly high fO2 based on statistical analysis. Elevated fO2 in OIB samples of these components is associated with higher whole-rock CaO/Al2O3 and olivine CaO content, which may be linked to recycled carbonated oceanic crust. EM1-type and geochemically depleted OIB are generally not as oxidized, possibly due to limited oxidizing potential of the recycled material in the enriched mantle 1 (EM1) component (e.g., sediment) or lack of recycled materials in geochemically depleted OIB. Despite systematic offset of the fO2 among EM1-, EM2-, and HIMU-type OIB, geochemical indices of lithospheric recycling, such as Sr-Nd-Pb-Os isotopic systems, generally do not correlate with fO2.
Characterization of Regolith And Trace Economic Resources (CRATER): An Orbitrap-based laser desorption mass spectrometry instrument for in situ exploration of the Moon
(Wiley, 2024-02-11) Ray, Soumya; Arevalo, Ricardo Jr.; Southard, Adrian; Willhite, Lori; Bardyn, Anais; Ni, Ziqin; Danell, Ryan; Grubisic, Andrej; Gundersen, Cynthia; Llano, Julie; Yu, Anthony; Fahey, Molly; Hernandez, Emanuel; Graham, Jacob; Lee, Jane; Ersahin, Akif; Briois, Christelle; Thirkell, Laurent; Colin, Fabrice; Makarov, Alexander
Rationale Characterization of Regolith And Trace Economic Resources (CRATER), an Orbitrap™-based laser desorption mass spectrometry instrument designed to conduct high-precision, spatially resolved analyses of planetary materials, is capable of answering outstanding science questions about the Moon's formation and the subsequent processes that have modified its (sub)surface. Methods Here, we describe the baseline design of the CRATER flight model, which requires <20 000 cm3 volume, <10 kg mass, and <60 W peak power. The analytical capabilities and performance metrics of a prototype that meets the full functionality of the flight model are demonstrated. Results The instrument comprises a high-power, solid-state, pulsed ultraviolet (213 nm) laser source to ablate the surface of the lunar sample, a custom ion optical interface to accelerate and collimate the ions produced at the ablation site, and an Orbitrap mass analyzer capable of discriminating competing isobars via ultrahigh mass resolution and high mass accuracy. The CRATER instrument can measure elemental and isotopic abundances and characterize the organic content of lunar surface samples, as well as identify economically valuable resources for future exploration. Conclusion An engineering test unit of the flight model is currently in development to serve as a pathfinder for near-term mission opportunities.
Stabilizing Effect of High Pore Fluid Pressure on Fault Growth During Drained Deformation
(Wiley, 2023-07-21) Zega, Zachary; Zhu, Wenlu
Dilatant hardening is an accepted model for the stabilizing effect of high pore fluid pressure on fault slip and operates when deformation is undrained. To test whether high pore fluid pressure impedes fault propagation under drained conditions, we deformed highly permeable Darley Dale sandstone using strain rates of 10−4 s−1, 10−5 s−1, and 10−6 s−1, respectively. For each strain rate, we compared the inelastic behaviors and faulting styles among rocks deformed under different pore fluid pressures (Pf) (2–180 MPa). The confining pressure (Pc) was attuned to the pore fluid pressure throughout deformation to maintain a constant differential pressure (Pc − Pf) of 10 MPa. In samples deformed at 10−4 s−1 and 10−5 s−1, faulting behaviors were similar regardless of the magnitude of pore fluid pressure. However, when the strain rate was lowered to 10−6 s−1, we observed prolonged stress drops and slower slip velocities in samples deformed under high pore fluid pressures. In samples deformed at 10−6 s−1, we demonstrate that chemically assisted subcritical crack growth played an important role during faulting. A quantitative microstructural analysis revealed that slow faulting at slow strain rates was accompanied by pervasive microcracking and diffuse shear bands, which suggests pervasive subcritical cracking enabled slow faulting under drained conditions at the sample length scale. High pore fluid pressure may have facilitated slow faulting chemically by increasing the rate of subcritical cracking, mechanically via localized dilatant hardening, or both. Our results provide insight into the mechanics of faulting in natural settings where subcritical cracking is prevalent.
182W and HSE constraints from 2.7 Ga komatiites on the heterogeneous nature of the Archen mantle
(Elsevier, 2018-03-02) Puchtel, I.S.; Blichert-Toft, J.; Touboul, M.; Walker, Richard J.
While the isotopically heterogeneous nature of the terrestrial mantle has long been established, the origin, scale, and longevity of the heterogeneities for different elements and isotopic systems are still debated. Here, we report Nd, Hf, W, and Os isotopic and highly siderophile element (HSE) abundance data for the Boston Creek komatiitic basalt lava flow (BCF) in the 2.7 Ga Abitibi greenstone belt, Canada. This lava flow is characterized by strong depletions in Al and heavy rare earth elements (REE), enrichments in light REE, and initial e143Nd = +2.5 ± 0.2 and initial e176Hf = +4.2 ± 0.9 indicative of derivation from a deep mantle source with time-integrated suprachondritic Sm/Nd and Lu/Hf ratios. The data plot on the terrestrial Nd-Hf array suggesting minimal involvement of early magma ocean processes in the fractionation of lithophile trace elements in the mantle source. This conclusion is supported by a mean mu142Nd = -3.8 ± 2.8 that is unresolvable from terrestrial standards. By contrast, the BCF exhibits a positive 182W anomaly (mu182W = +11.7 ± 4.5), yet is characterized by chondritic initial g187Os = +0.1 ± 0.3 and low inferred source HSE abundances (35 ± 5% of those estimated for the present-day Bulk Silicate Earth, BSE). Collectively, these characteristics are unique among Archean komatiite systems studied so far. The deficit in the HSE, coupled with the chondritic Os isotopic composition, but a positive 182W anomaly, are best explained by derivation of the parental BCF magma from a mantle domain characterized by a predominance of HSE-deficient, differentiated late accreted material. According to the model presented here, the mantle domain that gave rise to the BCF received only ~35% of the present-day HSE complement in the BSE before becoming isolated from the rest of the convecting mantle until the time of komatiite emplacement at 2.72 Ga. These new data provide strong evidence for a highly heterogeneous Archean mantle in terms of absolute HSE abundances and W isotopic composition, and also indicate slow mixing, on a timescale of at least 1.8 billion years. Additionally, the data are consistent with a stagnant-lid plate tectonic regime in the Hadean and Archean, prior to the onset of modern-style plate tectonics.
Oceanic and continental lithospheric mantle in the 1.95 Ga Jormua Ophiolite Complex, Finland: implications for mantle and crustal evolution
(Oxford, 2023-10-31) Finlayson, Valerie; Haller, Mitchell; Day, James M.D.; Ginley, Stephen; O'Driskoll, Brian; Kontinen, Asko; Hanski, Eero; Walker, Richard J.
The ca. 1.95 Ga Jormua Ophiolite Complex (JOC), Finland, is a rare Paleoproterozoic ophiolite that preserves a record of diverse upper mantle materials and melting processes. Meter-scale grid sampling of four JOC outcrops, as well as non-grid samples, permits evaluation of meter- to kilometer-scale mantle heterogeneity within the JOC. Significant heterogeneity is observed between the four grids, and also among a number of the non-grid samples examined. Variations in the concentrations of fluid-mobile elements are particularly large among different samples and locations. New whole-rock major, lithophile trace, and highly siderophile element data (HSE: Os, Ir, Ru, Pt, Pd, Re), including 187Re-187Os isotopic data, for serpentinized harzburgites indicate the presence of two distinct compositional types and probable modes of origin within the JOC. This is consistent with prior findings. Type 1 is similar to modern refractory abyssal-type mantle. Type 2 is more highly refractory than Type 1, and most likely represents samples from sub-continental lithospheric mantle (SCLM). Type 1 mantle is moderately heterogeneous with respect to chemical and Os isotopic compositions at both the meter and kilometer scales. By contrast, Type 2 mantle is considerably more homogeneous than Type 1 grids at the meter scale, but is more heterogeneous at the kilometer scale. The median initial γOs value for Type 1 mantle, calculated for 1.95 Ga, is ~-2.0 (where γOs is the % deviation in 187Os/188Os relative to a chondritic reference calculated for a specified time). This isotopic composition is consistent with a moderate, long-term decrease in Re/Os relative to the estimate for Primitive Mantle, prior to JOC formation. The similarity in this γOs value to the value for the modern abyssal mantle, as well as the initial values for several Phanerozoic ophiolites suggests that the upper mantle achieved a Re/Os ratio similar to the chondritic reference by ~2 Ga, then evolved along a subparallel trajectory to the chondritic reference since then. For this to occur, only limited Re could have been permanently removed from the upper mantle since at least the time the JOC formed. A localized secondary metasomatic event at ~2 Ga, concurrent with the estimated obduction age for the JOC and subsequent Svecofennian Orogeny, affected the HSE systematics of some Type 1 samples. By contrast, late Archean Os TRD model ages for Type 2 rocks indicate a depletion event superimposed upon the long-term Re depletion of the abyssal mantle. This event was established no later than ~2.6 Ga and may have occurred during a period of significant, well-documented crustal production in the Karelia craton at ~2.7 Ga.
In Search of Late-Stage Planetary Building Blocks
(Elsevier, 2015-07-03) Walker, Richard J.; Bermingham, Katherine; Liu, Jingao; Puchtel, Igor S.; Touboul, Mathieu; Worsham, Emily A.
Genetic contributions to the final stages of planetary growth, including materials associated with the giant Moon-forming impact, late accretion, and late heavy bombardment are examined using siderophile elements. Isotopic similarities between the Earth and Moon for both lithophile and siderophile elements collectively lead to the suggestion that the genetics of the building blocks for Earth, and the impactor involved in the Moon-forming event were broadly similar, and shared some strong genetic affinities with enstatite chondrites. The bulk genetic fingerprint of materials subsequently added to Earth by late accretion, defined as the addition of ~0.5 wt.% of Earth's mass to the mantle, following cessation of core formation, was characterized by 187Os/188Os and Pd/Ir ratios that were also similar to those in some enstatite chondrites. However, the integrated fingerprint of late accreted matter differs from enstatite chondrites in terms of the relative abundances of certain other HSE, most notably Ru/Ir. The final ≤0.05 wt.% addition of material to the Earth and Moon, believed by some to be part of a late heavy bombardment, included a component with much more fractionated relative HSE abundances than evidenced in the average late accretionary component. Heterogeneous 182W/184Wisotopic compositions of some ancient terrestrial rocks suggest that some very early formed mantle domains remained chemically distinct for long periods of time following primary planetary accretion. This evidence for sluggish mixing of the early mantle suggests that if late accretionary contributions to the mantle were genetically diverse, it may be possible to isotopically identify the disparate primordial components in the terrestrial rock record using the siderophile element tracers Ru and Mo.
High-Precision Tungsten Isotopic Analysis by Multicollection Negative Thermal Ionization Mass Spectrometry Based on Simultaneous Measurement of W and 18O/16O Isotope Ratios for Accurate Fractionation Correction
(American Chemical Society, 2016-01-11) Trinquier, Anne; Touboul, Mathieu; Walker, Richard J.
Determination of the 182W/184W ratio to a precision of ±5 ppm (2σ) is desirable for constraining the timing of core formation and other early planetary differentiation processes. However, WO3 − analysis by negative thermal ionization mass spectrometry normally results in a residual correlation between the instrumental-mass-fractionation-corrected 182W/184W and 183W/184W ratios that is attributed to mass-dependent variability of O isotopes over the course of an analysis and between different analyses. A second-order correction using the 183W/184W ratio relies on the assumption that this ratio is constant in nature. This may prove invalid, as has already been realized for other isotope systems. The present study utilizes simultaneous monitoring of the 18O/16O and W isotope ratios to correct oxide interferences on a per-integration basis and thus avoid the need for a double normalization of W isotopes. After normalization of W isotope ratios to a pair of W isotopes, following the exponential law, no residual W−O isotope correlation is observed. However, there is a non-ideal mass bias residual correlation between 182W/iW and 183W/iW with time. Without double normalization of W isotopes and on the basis of three or four duplicate analyses, the external reproducibility per session of 182W/184W and 183W/184W normalized to 186W/183W is 5−6 ppm (2σ, 1−3 μg loads). The combined uncertainty per session is less than 4 ppm for 183W/184W and less than 6 ppm for 182W/184W (2σm) for loads between 3000 and 50 ng.
Widespread tungsten isotope anomalies and W mobility in crustal and mantle rocks of the Eoarchean Saglek Block, northern Labrador, Canada: Implications for early Earth processes and W recycling
(Elsevier, 2016-08-15) Liu, Jingao; Touboul, Mathieu; Ishikawa, Akira; Walker, Richard J.; Pearson, D. Graham
Well-resolved 182W isotope anomalies, relative to the present mantle, in Hadean–Archean terrestrial rocks have been interpreted to reflect the effects of variable late accretion and early mantle differentiation processes. To further explore these early Earth processes, we have carried out W concentration and isotopic measurements of Eoarchean ultramafic rocks, including lithospheric mantle rocks, metakomatiites, a layered ultramafic body and associated crustal gneisses and amphibolites from the Uivak gneiss terrane of the Saglek Block, northern Labrador, Canada. These analyses are augmented by in situ W concentration measurements of individual phases in order to examine the major hosts of W in these rocks. Although the W budget in some rocks can be largely explained by a combination of their major phases, W in other rocks is hosted mainly in secondary grain-boundary assemblages, as well as in cryptic, unidentified W-bearing ‘nugget’ minerals. Whole rock W concentrations in the ultramafic rocks show unexpected enrichments relative, to elements with similar incompatibilities. By contrast, W concentrations are low in the Uivak gneisses. These data, along with the in situ W concentration data, suggest metamorphic transport/re-distribution of W from the regional felsic rocks, the Uivak gneiss precursors, to the spatially associated ultramafic rocks. All but one sample from the lithologically varied Eoarchean Saglek suite is characterized by generally uniform ∼+11 ppm enrichments in 182W relative to Earth’s modern mantle. Modeling shows that the W isotopic enrichments in the ultramafic rocks were primarily inherited from the surrounding 182W-rich felsic precursor rocks, and that the W isotopic composition of the original ultramafic rocks cannot be determined. The observed W isotopic composition of mafic to ultramafic rocks in intimate contact with ancient crust should be viewed with caution in order to plate constraints on the early Hf–W isotopic evolution of the Earth’s mantle with regard to late accretionary processes. Although 182W anomalies can be erased via mixing in the convective mantle, recycling of 182W-rich crustal rocks into the mantle can produce new mantle sources with anomalous W isotopic compositions that can be tapped at much later times and, hence, this process should be considered as a mechanism for the generation of 182W-rich rocks at any subsequent time in Earth history.
Age, genetics, and crystallization sequence of the group IIIE iron meteorites
(Elsevier, 2023-06-14) Chiappe, Emily M.; Ash, Richard; Walker, Richard J.
Chemical and isotopic data were obtained for ten iron meteorites classified as members of the IIIE group. Nine of the IIIE irons exhibit broadly similar bulk siderophile element characteristics. Modeling of highly siderophile element abundances suggests that they can be related to one another through simple crystal-liquid fractionation of a parent melt. Our preferred model suggests initial S, P, and C concentrations of approximately 12 wt%, 0.8 wt %, and 0.08 wt%, respectively. The modeled IIIE parent melt composition is ~4 times more enriched in highly siderophile elements than a non-carbonaceous (NC) chondrite-like parent body, suggesting a core comprising ~22% of the mass of the parent body. Although chemically distinct from the other IIIE irons, formation of the anomalous IIIE iron Aletai can potentially be accounted for under the conditions of this model through the nonequilibrium mixing of an evolved liquid and early formed solid. Cosmic ray exposure-corrected nucleosynthetic Mo, Ru, and W isotopic compositions of four of the bona fide IIIE irons and Aletai indicate that they originated from the non-carbonaceous (NC) isotopic domain. Tungsten-182 isotopic data for the IIIE irons and Aletai yield similar model metal-silicate segregation ages of 1.6 ± 0.8 Myr and 1.2 ± 0.8 Myr, respectively, after calcium aluminum-rich inclusion (CAI) formation. These ages are consistent with those reported for other NC-type iron meteorite parent bodies. The IIIE irons are chemically and isotopically similar to the much larger IIIAB group. Despite some textural, mineralogical, and chemical differences, such as higher C content, the new results suggest they may have originated from a different crystallization sequence on the same or closely-related parent body.
Geodynamic implications of ophiolitic chromitites in the La Cabaña ultramafic bodies, Central Chile
(Taylor & Francis, 2014-07-18) González-Jiménez, José María; Barra, Fernando; Walker, Richard J.; Reich, Martin; Gervilla, Fernando
Chromitites (>80% volume chromite) hosted in two ultramafic bodies (Lavanderos and Centinela Bajo) from the Palaeozoic metamorphic basement of the Chilean Coastal Cordillera were studied in terms of their chromite composition, platinum group element (PGE) abundances, and Re-Os isotopic systematics. Primary chromite (Cr# = 0.64–0.66; Mg# = 48.71–51.81) is only preserved in some massive chromitites from the Centinela Bajo ultramafic body. This chemical fingerprint is similar to other high-Cr chromitites from ophiolite complexes, suggesting that they crystallized from arc-type melt similar to high-Mg island-arc tholeiites (IAT) and boninites in supra-subduction mantle. The chromitites display enrichment in IPGE (Os, Ir, Ru) over PPGE (Rh, Pt, Pd), with PGE concentrations between 180 and 347 ppb, as is typical of chromitites hosted in the mantle of supra-subduction zone (SSZ) ophiolites. Laurite (RuS2)-erlichmanite (OsS2) phases are the most abundant inclusions of platinum-group minerals (PGM) in chromite, indicating crystallization from S-undersaturated melts in the subarc mantle. The metamorphism associated with the emplacement of the ultramafic bodies in the La Cabaña has been determined to be ca. 300 Ma, based on K-Ar dating of fuchsite. Initial 187Os/188Os ratios for four chromitite samples, calculated for this age, range from 0.1248 to 0.1271. These isotopic compositions are well within the range of chromitites hosted in the mantle section of other Phanaerozoic ophiolites. Collectively, these mineralogical and geochemical features are interpreted in terms of chromite crystallization in dunite channels beneath a spreading centre that opened a marginal basin above a supra-subduction zone. This implies that chromitite-bearing serpentinites in the metamorphic basement of the Coastal Cordillera are of oceanic-mantle origin and not oceanic crust as previously suggested. We suggest that old subcontinental mantle underlying the hypothetical Chilenia micro-continent was unroofed and later altered during the opening of the marginal basin. This defined the compositional and structural framework in which the protoliths of the meta-igneous and meta-sedimentary rocks of the Eastern and Western Series of the Chilean Coastal Cordillera basement were formed.
Preservation of Earth-forming events in the W isotopic 1 composition of modern flood basalts
(Science Magazine, 2016-05-13) Rizo, Hanika; Walker, Richard J.; Carlson, Richard W.; Horan, Mary F.; Mukhopadhyay, Sujoy; Manthos, Vicky; Francis, Don; Jackson, Matthew G.
How much of Earth's compositional variation dates to processes that occurred during planet formation remains an unanswered question. High-precision tungsten isotopic data from rocks from two large igneous provinces, the North Atlantic Igneous Province and the Ontong Java Plateau, reveal preservation to the Phanerozoic of tungsten isotopic heterogeneities in the mantle. These heterogeneities, caused by the decay of hafnium-182 in mantle domains with high hafnium/tungsten ratios, were created during the first ~50 million years of solar system history, indicating that portions of the mantle that formed during Earth’s primary accretionary period have survived to the present.
Using Satellite Data to Represent Tropical Instability Waves (TIWs)-Induced Wind for Ocean Modeling: A Negative Feedback onto TIW Activity in the Pacific
(MDPI, 2013-05-24) Zhang, Rong-Hua; Li, Zhongxian; Min, Jinzhong
Recent satellite data and modeling studies indicate a pronounced role Tropical Instability Waves (TIW)-induced wind feedback plays in the tropical Pacific climate system. Previously, remotely sensed data were used to derive a diagnostic model for TIW-induced wind stress perturbations (τTIW), which was embedded into an ocean general circulation model (OGCM) to take into account TIW-induced ocean-atmosphere coupling in the tropical Pacific. While the previous paper by Zhang (2013) is concerned with the effect on the mean ocean state, the present paper is devoted to using the embedded system to examine the effects on TIW activity in the ocean, with τTIW being interactively determined from TIW-scale sea surface temperature (SSTTIW) fields generated in the OGCM, written as τTIW = αTIW·F(SSTTIW), where αTIW is a scalar parameter introduced to represent the τTIW forcing intensity. Sensitivity experiments with varying αTIW (representing TIW-scale wind feedback strength) are performed to illustrate a negative feedback induced by TIW-scale air-sea coupling and its relationship with TIW variability in the ocean. Consistent with previous modeling studies, TIW wind feedback tends to have a damping effect on TIWs in the ocean, with a general inverse relationship between the τTIW intensity and TIWs. It is further shown that TIW-scale coupling does not vary linearly with αTIW: the coupling increases linearly with intensifying τTIW forcing at low values of αTIW (in a weak τTIW forcing regime); it becomes saturated at a certain value of αTIW; it decreases when αTIW goes above a threshold value as the τTIW forcing increases further. This work presents a clear demonstration of using satellite data to effectively represent TIW-scale wind feedback and its multi-scale interactions with large-scale ocean processes in the tropical Pacific.
Urban Evolution: The Role of Water
(MDPI, 2015-07-27) Kaushal, Sujay S.; McDowell, William H.; Wollheim, Wilfred M.; Newcomer Johnson, Tamara A.; Mayer, Paul M.; Belt, Kenneth T.; Pennino, Michael J.
The structure, function, and services of urban ecosystems evolve over time scales from seconds to centuries as Earth’s population grows, infrastructure ages, and sociopolitical values alter them. In order to systematically study changes over time, the concept of “urban evolution” was proposed. It allows urban planning, management, and restoration to move beyond reactive management to predictive management based on past observations of consistent patterns. Here, we define and review a glossary of core concepts for studying urban evolution, which includes the mechanisms of urban selective pressure and urban adaptation. Urban selective pressure is an environmental or societal driver contributing to urban adaptation. Urban adaptation is the sequential process by which an urban structure, function, or services becomes more fitted to its changing environment or human choices. The role of water is vital to driving urban evolution as demonstrated by historical changes in drainage, sewage flows, hydrologic pulses, and long-term chemistry. In the current paper, we show how hydrologic traits evolve across successive generations of urban ecosystems via shifts in selective pressures and adaptations over time. We explore multiple empirical examples including evolving: (1) urban drainage from stream burial to stormwater management; (2) sewage flows and water quality in response to wastewater treatment; (3) amplification of hydrologic pulses due to the interaction between urbanization and climate variability; and (4) salinization and alkalinization of fresh water due to human inputs and accelerated weathering. Finally, we propose a new conceptual model for the evolution of urban waters from the Industrial Revolution to the present day based on empirical trends and historical information. Ultimately, we propose that water itself is a critical driver of urban evolution that forces urban adaptation, which transforms the structure, function, and services of urban landscapes, waterways, and civilizations over time.
Mesozoic subduction shaped lower mantle structures beneath the East Pacific Rise
(2024) Wang, Jingchuan; Lekic, Vedran; Schmerr, Nicholas; Gu, Yu Jeffrey; Guo, Yi; Lin, Rongzhi; Lekic, Vedran; Schmerr, Nicholas
The morphology of the Large Low Shear Velocity Provinces (LLSVPs) has been a subject of debate for decades. Large-scale features of the Pacific LLSVP, as revealed by cluster analysis of global tomographic models, suggest three distinct portions. Notably, the East Pacific Anomaly and the Superswell Anomaly are characterized by a ~20 deg wide gap. The cause of the structural gap remains unclear, and there has been no direct evidence for a subduction episode beneath the region. In this study, we take advantage of an up-to-date SS precursor data set that samples the Nazca Plate and investigate the high-resolution seismic structure at mantle transition zone (MTZ) depths. We find that much of the southern East Pacific Rise is underlain by a thin MTZ due to the depressed 410 by up to 15 km, which suggests along-ridge temperature variations extending into the MTZ. East of the East Pacific Rise, the MTZ is characterized by anomalous thickening and fast seismic velocities from seismic tomography, consistent with the presence of cold subducted slab material intersecting the MTZ. Furthermore, recent global tomographic models reveal a slab-like structure throughout the MTZ and lower mantle, which is also evidenced by tomographic vote maps, albeit with less visibility. The observations reconcile with Mesozoic intraoceanic subduction beneath the present-day Nazca Plate, which is predicted by an earlier plate reconstruction model of proto-Pacific Ocean. The subduction initiated ~250 Myr ago and ceased before 120 Myr ago. The implications of this discovery are that the shape of the eastern portion of the Pacific LLSVP was separated by downwelling associated with this ancient subducted slab.
Nutrient Retention in Restored Streams and Rivers: A Global Review and Synthesis
(MDPI, 2016-03-25) Newcomer Johnson, Tamara A.; Kaushal, Sujay S.; Mayer, Paul M.; Smith, Rose M.; Sivirichi, Gwen M.
Excess nitrogen (N) and phosphorus (P) from human activities have contributed to degradation of coastal waters globally. A growing body of work suggests that hydrologically restoring streams and rivers in agricultural and urban watersheds has potential to increase N and P retention, but rates and mechanisms have not yet been analyzed and compared across studies. We conducted a review of nutrient retention within hydrologically reconnected streams and rivers, including 79 studies. We developed a typology characterizing different forms of stream and river restoration, and we also analyzed nutrient retention across this typology. The studies we reviewed used a variety of methods to analyze nutrient cycling. We performed a further intensive meta-analysis on nutrient spiraling studies because this method was the most consistent and comparable between studies. A meta-analysis of 240 experimental additions of ammonium (NH4+), nitrate (NO3−), and soluble reactive phosphorus (SRP) was synthesized from 15 nutrient spiraling studies. Our results showed statistically significant relationships between nutrient uptake in restored streams and specific watershed attributes. Nitrate uptake metrics were significantly related to watershed surface area, impervious surface cover, and average reach width (p < 0.05). Ammonium uptake metrics were significantly related to discharge, velocity, and transient storage (p < 0.05). SRP uptake metrics were significantly related to watershed area, discharge, SRP concentrations, and chl a concentrations (p < 0.05). Given that most studies were conducted during baseflow, more research is necessary to characterize nutrient uptake during high flow. Furthermore, long-term studies are needed to understand changes in nutrient dynamics as projects evolve over time. Overall analysis suggests the size of the stream restoration (surface area), hydrologic connectivity, and hydrologic residence time are key drivers influencing nutrient retention at broader watershed scales and along the urban watershed continuum.
Satellite Climate Data Records: Development, Applications, and Societal Benefits
(MDPI, 2016-04-15) Yang, Wenze; John, Viju O.; Zhao, Xuepeng; Lu, Hui; Knapp, Kenneth R.
This review paper discusses how to develop, produce, sustain, and serve satellite climate data records (CDRs) in the context of transitioning research to operation (R2O). Requirements and critical procedures of producing various CDRs, including Fundamental CDRs (FCDRs), Thematic CDRs (TCDRs), Interim CDRs (ICDRs), and climate information records (CIRs) are discussed in detail, including radiance/reflectance and the essential climate variables (ECVs) of land, ocean, and atmosphere. Major international CDR initiatives, programs, and projects are summarized. Societal benefits of CDRs in various user sectors, including Agriculture, Forestry, Fisheries, Energy, Heath, Water, Transportation, and Tourism are also briefly discussed. The challenges and opportunities for CDR development, production and service are also addressed. It is essential to maintain credible CDR products by allowing free access to products and keeping the production process transparent by making source code and documentation available with the dataset.

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