A document by Meiyun Lin. Click on the document to view its contents.

A connection between the quasi-biennial oscillation (QBO), the 11-yr solar cycle (SC), and the short-term convective climate oscillation, the Madden-Julian Oscillation (MJO), in boreal winter has been found in observational data, yet is generally lacking in current global climate models (GCMs). The extent to which a proposed mechanism for producing this connection is simulated in a series of GCMs participating in the Coupled Model Intercomparison Project 6 (CMIP6) is investigated. The models are found to be often lacking complete representation of several elements of this mechanism, with particular issues being QBOs that are westerly-biased and weak in the lower stratosphere, weak solar stratospheric temperature and zonal wind signals, insufficient solar or QBO-modulation of extratropical wave activity (the Holton-Tan effect), too weak reductions in equatorial tropopause static stability in response to extratropical wave forcing, and MJOs that in some cases do not respond to these reductions. Through by-passing many of these deficiencies via data selection, it is demonstrated that effects on the MJO that resemble those found in observations (strengthening of the MJO following early-winter sudden stratospheric warmings and during easterly QBO winters) can be simulated by a subset of the models. This supports operation of the proposed mechanism, and points to needed model improvements, although additional feedbacks may be needed to reproduce the full modulation.

Clumped isotope thermometry (T(∆47)) of soil carbonates provides an estimate of soil temperature at the time of mineral formation. Historically, that temperature has been interpreted to represent a warm-season soil temperature based on modern calibration studies largely done in (very) coarse-grained soils. Additionally, T(∆47) gives us an estimate of the oxygen isotope composition of soil water (δ18Ow) in the past, but previous calibration work has not generated independent δ18Ow datasets with which to understand these archives. Here, we present a modern calibration study of pedogenic carbonate clumped isotope thermometry in three soils in Colorado and Nebraska, USA, that have a fine-medium grain size, contain clay, and are representative of many carbonate-bearing paleosols preserved in the rock record. At two of the three sites, Briggsdale, CO and Seibert, CO, T(∆47) overlaps with mean annual air temperature (MAAT), and the calculated δ18Ow overlaps within uncertainty with measured δ18Ow at carbonate bearing depths. At the third site in Oglala National Grassland, NE, mean T(∆47) is 9 – 10°C warmer than MAAT, and the calculated δ18Ow has a significantly higher isotope value than any observations of δ18Ow. At all three sites, even in the fall season, δ18Ow values at carbonate bearing depths indicate little to no evaporative enrichment of heavy isotopes. Moreover, δ18Ow values overlap with precipitation isotope values from spring precipitation. Altogether, these data indicate that soil grain size affects pedogenic carbonate formation, and highlight a need for continued research in modern systems that emulate key features of the geologic record.

The Arctic sea ice, in particular the ice pack, acts as an insulator between the atmosphere and the ocean. Leads, commonly found in the Arctic, facilitate ocean-atmosphere flux exchanges. Local observations have captured heat fluxes through some leads one order of magnitude larger than those outside of the leads, leading to the speculation that air-sea exchanges through leads contribute significantly to the Arctic Ocean surface buoyancy forcing. Here, we quantify the magnitude and impact on the ocean surface of the leads using SEDNA, a subkilometer pan-Arctic hindcast. Leads account for 22% of the sea ice cover surface, and within them, there is approximately 25% of the total surface water mass transformation. In other words, the water mass transformation in leads is similar to those underneath the surrounding ice-covered oceans. Thus, the present estimate indicates that leads have a small contribution to Arctic Ocean dynamics, contrary to previous hypotheses.

Paleointensity observations from meteorites provide insights into planetary formation and evolution. Meteoritic samples are usually dominated by Fe-rich kamacite, which is capable of faithfully recording the ancient dynamo activity of meteorites’ parent body. To retrieve paleointensity estimates, experimental protocols assume that samples are dominated by uniformly magnetized particles. However, most magnetic carriers observed in extraterrestrial samples are non-uniformly magnetized. This inconsistency represents a major impediment in reliably reconstructing paleointensities from meteorites. Here we present the State Group Algorithm (SGA); a micromagnetic based model capable of efficiently simulating thermoremance acquisition of magnetic particles with a single-vortex domain state. The results show that iron particles can acquire thermoremance that is linear with the external field up to ∼100 µT. Single-vortex cooling rate effects are generally weaker than those of single-domain particles, providing more accurate paleointensity estimates. A small number of particles exhibit inverse cooling rate effects, leading to underestimates in paleointensity.

The north-south seismic belt of China poses a high risk of earthquakes, necessitating the need for accurate and rapid prediction of intensity measures (IMs) to prevent and mitigate potential damage. We have developed a new multi-task model, CRAQuake, to predict IMs for the north-south seismic belt of China. Using initial arrival seismic waves recorded at a single station as input, CRAQuake simultaneously predicts six IMs without relying on pre-configured parameters such as earthquake source, path, and location. The model was trained on 4281 sets of strong motion records datasets at 822 stations and tested to show highly correlated results with the target IMs. The prediction performance continues to improve as the input initial arrival seismic wave time window increases. CRAQuake promises to enhance the accuracy and timeliness of IMs prediction in the north-south seismic belt of China.

Human populations are increasingly impacted by climate change, especially in the Arctic, where Polar Amplification is accelerating climate impacts to more than four times the global average. The complex, interconnected risks that result from climate change need to be measured, tracked and prioritized, to characterize highly impacted areas. We reviewed a cross section of published vulnerability indices developed to characterize change in the Alaskan Arctic, including ecosystem dynamics like permafrost thaw, water availability, animal habitat and migration, and anthropogenic risks from marine & aviation infrastructure, and oil spill impacts. Further, we evaluated the spatiotemporal relationship of vulnerability indices within the context of industrial development in the Arctic, including shipping, mining, and energy extraction. While this cross section offers a diversity of analysis, the accessibility of the indices to Arctic communities needs improvement. Increasing accessibility of these tools will allow further evaluation of these interconnected vulnerabilities, and understanding feasibility and limitations.

In Distributed Acoustic Sensing (DAS), a fiber-optic cable is used as a distributed seismic sensor, with channels representing successive short sections of the fiber, spaced at defined intervals along the 1D fiber axis. Typically, the positions of these channel are assumed to be known and to coincide with the cable´s position. In reality, a fiber-optic cable contains many fibers that are not perfectly straight and are thus longer than the cable itself. Additionally, the cable may feature some degree of curvature even though it was deployed with the intention of a straight line. Consequently, the real channel spacing differs from the theoretical one and may vary alongside the cable axis. On land usually a tap test is carried out before the start of the DAS acquisition to determine the exact channel locations. DAS with marine horizontal cables has recently been used for various offshore applications including seismic imaging. To avoid errors in the seismic image, a precise receiver location is required. For many marine fiber optic cables, the position is known to some extent but may be subject to inaccuracies. In this paper, we propose a traveltime-based inversion workflow to determine a more accurate fiber position on the seafloor. Moreover, we show that we can resolve an unknown time shift, between the acquisition and the recording system, in addition to the fiber position.

Satellite altimetry has successfully monitored inland waters for more than 30 years and is increasingly important as the demand for freshwater grows and climate change accelerates. Launched in December 2022, the Surface Water and Ocean Topography (SWOT) satellite is the first to provide 2D spatially distributed elevation measurements, with a nominal 21-day revisit time and better coverage depending on latitude. Here, we evaluate the SWOT L2 HR PIXC 2.0 data product for constructing water surface elevation (WSE) time series at 40 Danish lakes with a surface area above 0.25km2 via the summary measures RMSE and Pearson Correlation Coefficient (PCC). Two methods to derive the bias between the SWOT-based WSE and the gauge water level were tested; a constant bias and a newly proposed acquisition-specific bias. Based on the 40 gauged lakes we find a median RMSE of 5.76cm and 8.87cm and PCC of 0.93 and 0.76, for the acquisition-specific bias and constant bias, respectively.   Additionally, we examined the spatial variations of the water surface elevations in the L2 HR PIXC 2.0 data product. Compared with ICESat-2, we found that the spatially distributed variations in SWOT data were unlikely to represent real physical phenomena. Our findings highlight the potential of SWOT for generating high-accuracy WSE time series, for small lakes. SWOT’s broad spatial coverage offers far greater temporal frequency (for Danish lakes: usually 3 to 4 acquisitions per 21-day orbit) compared to traditional satellite altimeters, enabling new insights into water level dynamics that were previously unattainable.

A document by Jingwei ZHANG. Click on the document to view its contents.

The shared tectonic history of southwestern Australia and East Antarctica facilitates the exchange of geological insights between the regions. In this study, we present coupled susceptibility and density models obtained through the joint inversion of magnetic and gravity data. By assuming a common geological source for both signals, our coupling method minimizes misfits and variation in information, thereby enhancing the correlation between susceptibility and density. The resulting anomalies demonstrate structural continuity between the continents, aligning closely with major shear zones and seismic reflectors. Combining these results with machine learning, geochemical, and petrophysical databases, we predict a high-resolution ($10$ km) heat production map for East Antarctica. Utilizing a Markov Chain Monte Carlo (MCMC) algorithm, we further develop a geothermal heat flow map with greater spatial variability than previous studies, yielding an average of $55\,$mW/m$^2$ in East Antarctica and $46\,$mW/m$^2$ in southwestern Australia. Our results provide a crucial high-resolution boundary condition for ice sheet simulations, enabling more realistic estimates of basal meltwater production and ice temperatures.

In the nightside region of Earth’s magnetosphere, buoyancy modes have been associated with low entropy bubbles. These bubbles form in the plasma sheet, particularly during substorm expansion, and move rapidly earthward and come to rest in the inner plasma sheet or inner magnetosphere. They often exhibit damped oscillations with periods of a few minutes and have been associated with Pi2 pulsations. In previous work, we used the thin filament approximation to compare the frequencies and modes of buoyancy waves using three approaches: magnetohydrodynamic (MHD) ballooning theory, classic interchange theory, and an idealized formula. Interchange oscillations differ from the more general MHD oscillations in that they assume a constant pressure on each magnetic field line. It was determined that the buoyancy and interchange modes are very similar for field lines that extend into the plasma sheet but differ for field lines that map to the inner magnetosphere. In this paper, we create a small region of entropy depletion in an otherwise stable entropy background profile of the magnetotail to represent the presence of a plasma bubble and determine the properties of the buoyancy modes using the same 3 approaches. In the bubble region, we find that in some regions the interchange and buoyancy modes overlap resulting in frequencies that are much lower than the background. In other regions within the bubble, we find interchange unstable modes while in other locations MHD normal mode predicts an MHD slow mode wave solution which is not found in the pure interchange solution.

The ACES-II sounding rocket mission launched two payloads from Andøya Rocket Range into a post-dusk discrete auroral arc and observed field-aligned electron dispersions near inverted-V precipitation. Five repetitive suprathermal electron bursts (STEBs) associated with low frequency (< 8 Hz) Earth-ward traveling Alfvén waves are observed at 400 km altitude. The electron bursts occur both coincident and outside inverted-V electrons, with those nearest to inverted-V precipitation displaying higher peak energy and differential flux values than events further away. We interpret the events as wave-particle acceleration via inertial Alfvén waves along near-Earth field lines and employ time-of-flight methods to gauge source altitudes. We show the differences in STEB behavior are better explained by changes in the resonant source population and not from significant variation in Alfvén wave parameters, a result that agrees with previous simulated predictions.

The inductive component of the magnetospheric electric field, which is associated with the temporal change of magnetic field, provides an additional means of local plasma energization and transport in addition to the electrostatic counterpart. This study examines the detailed response of the inner magnetosphere to inductive electric fields and the associated electric-driven convection corresponding to different solar wind conditions. A novel modeling capability is employed to self-consistently simulate the electromagnetic and plasma environment of the entire magnetospheric cavity. The explicit separation of the electric field by source (inductive vs. electrostatic) and subsequent implementation of inductive effects in the ring current model allow us to investigate, for the first time, the effect of the inductive electric field on the kinetics and evolution of the ring current system. The simulation results presented in this study demonstrate that the inductive component of the electric field is capable of providing an additional source for long-lasting plasma drifts, which in turn significantly alter the trajectories of both thermal and energetic particles. Such changes in the plasma drift, which arise due to the inductive electric fields, further reshape the storm-time ring current morphology and alter the degree of the ring current asymmetry, as well as the timing and the peak of the ion pressure. The total ion energy is increasing at a faster rate than the supply of energetic ions to the ring current, suggesting that the inductive electric field provides effective and accumulative local energization for the trapped ring current population without confining additional particles.

A document by Dandy Calla Choque. Click on the document to view its contents.

We estimate the global impact of storms on the global structure and dynamics of the nightside plasma sheet (PS) from observations by the NASA mission THEMIS. We focus on an intense storm occurring in December 2015 triggered by interplanetary coronal mass ejections (ICMEs). It starts with a storm sudden commencement (SSC) phase (SYM-H~+50nT) followed by a growth phase (SYM-H~-188nT at the minimum) and then a long recovery phase. We investigate THEMIS observations when the spacecraft were located in the midnight sector of the PS at distances typically between 8 and 13RE. It is found that the PS has been globally compressed up to a value of about~>4nPa during the SSC and main phases, i.e. 8 times larger than its value during the quiet phase before the event. This compression occurs during periods of high dynamic pressure in the ICME (20nPa) about one order of magnitude larger than its value in the pristine solar wind. We infer a global increase of the lobe magnetic field from 30nT to 100nT, confirmed by THEMIS data just outside the PS. During the SSC and main phases, the PS is found thinner by a factor of 2 relative to its thickness at quiet times, while the Tsyganenko T96 magnetic field model shows very stretched magnetic field lines from inner magnetospheric regions toward the nightside. During the recovery phase, whereas the interplanetary pressure has dropped off, the PS tends to gradually recover its quiet phase characteristics (pressure, thickness, magnetic configuration, etc) during a long recovery phase.

This work introduces a physically-based modeling framework to capture the spatio-temporal dynamics of dune vegetation under stochastic environmental disturbances. In analogy with other transitional disturbed environments, the model evaluates vegetation cover, within a cross-shore dimensionless framework, in response to random wind speed and runup. The wind speed is modeled as a compound Poisson process with Gamma-distributed properties, facilitating the computation of up-crossing times for various thresholds. The dune topography is represented by a swash zone with a Gaussian shape and a monotonic landward increase, parameterized by slope, wavelength, and height. Key disturbance conditions affecting vegetation---runup-induced flooding in the swash zone and wind-induced scour on the backshore and crest---are addressed through threshold-based analysis. The model uses a state-dependent dichotomic process for vegetation dynamics, where growth and decay are influenced by external forcing and vegetation state. Analytical solutions of the master equation for the vegetation distributions reveal the impact of stochastic factors on vegetation growth and stability. Sensitivity analysis identifies dune steepness, forcing magnitude and variability, and relative roughness as critical parameters. These factors significantly affect vegetation distribution, with increased steepness leading to higher vegetation density at the backshore and reduced density at the shorefront. Also, a Suitability Index to assess analytically dune stability based on disturbance and topographic features is introduced. Validation against satellite imagery and high-resolution real elevation data from the U.S. coastline confirms robustness and accuracy of the proposed approach. The results enhance understanding of dune vegetation dynamics and offer a framework for coastal restoration strategies.

Coincident shifts in riparian ground-active arthropod diversity and soil nutrients under an introduced symbiotic N2-fixing treeBenjamin D. Duval1*, Evangelina Carabotta1, Sergio de Tomas-Marin1, David Lightfoot21Biology Department, New Mexico Institute of Mining and Technology, Socorro, NM 878012Museum of Southwestern Biology, University of New Mexico, Albuquerque, NM 87131*corresponding author, ORCID 0000-0001-7692-4400Biology Department801 Leroy PlaceNew Mexico Institute of Mining and Technology01-575-835-5820, [email protected] nitrogen-fixing plants such as Russian olive, can significantly impact soil chemistry and invertebrate biodiversity in riparian ecosystems. Here, the effects of Russian olive on soil chemical properties and invertebrate communities in riparian zones of the southwestern U.S. were investigated. Russian olive stands were compared to native cottonwood stands and restoration sites by analyzing soil nitrogen (N), phosphorus (P) and moisture levels, and arthropod diversity and abundance. Sites where Russian olive is present led to a net increase in soil nitrogen, a decrease in soil phosphorus, and greater soil moisture compared to both native cottonwood stands and restoration sites. Native cottonwood stands showed lower soil N and higher P levels, as well as higher arthropod diversity. This increased diversity could be linked to the soil’s nutrient stoichiometry, as there is a negative correlation between taxonomic diversity and the soil N:P ratio. Moreover, there was a greater abundance of detritivorous arthropods in Russian olive stands compared to native vegetation. Soil nitrate (NO3-) levels showed a strong positive correlation with detritivorous arthropod abundance, but only a moderate correlation with herbivores, and NO3- was unrelated to predator abundance. These results suggest that Russian olive stands can alter soil chemistry in ways that disproportionately benefit detritivores, potentially disrupting the balance of arthropod communities and reducing overall biodiversity in riparian ecosystems. The study underscores the need for careful management of invasive, symbiotic N2-fixing plant species to preserve the ecological integrity of riparian habitats.Keywords: nitrate, phosphate, Rio Grande, Russian olive, soilINTRODUCTIONA persistent question in invasive species ecology is what are the functional roles of the invaders and their effect in the biodiversity and functional structure and composition of the recipient community (Renault et al., 2022; Galán Díaz et al., 2023). Invasive species can have cascading effects through different trophic levels and alter ecosystem functions, processes and services (McCary et al., 2016; Castro Díez and Alonso Fernández, 2017). One of the main effects of invasive plant species is the disruption of nutrient cycling and availability (Weidenhamer and Callaway, 2010; Afzal et al., 2023) which is especially relevant in invasions produced by woody and N2-fixing plants (Liao et al. 2008).Trees in symbiotic relationships with N2-fixing actinobacteria are globally reliable as invasive species and known to induce substantial effects on the N cycle relative to native vegetation (Vitousek et al. 1987, Nsikani et al. 2018, Collette and Pither 2015). These trees typically increase soil mineral N pools relative to native vegetation, and should be considered part of the ongoing anthropogenic global disruption of the nitrogen (N) cycle (Galloway, 1998; Galloway et al., 2008). Given that increased N is occurring with relatively less change to phosphorus (P) cycling, ecosystem responses are best understood in the context of increased N:P of major biotic and abiotic components (Penuelas et al., 2020).The ratio of N to P in leaves has long been understood to impact decomposition processes and nutrient cycling (Koerselman and Meuleman, 1996; Güsewell and Freeman, 2005). As part of the initial decomposition processes, soil and surface-active arthropods physically and chemically alter litter, and multiple experiments have demonstrated food preferences for litter based on a variety of chemical and structural properties (David, 2014). The direct mechanisms by which microbial use of arthropod frass contributes to soil organic material cycling are not fully clear, but there is evidence that microbial litter colonization directly increases litter palatability to arthropods when microbes increase litter nutritive value (Gerlach et al., 2012), or indirectly when microbes detoxify plant secondary compounds that hinder arthropod consumption and digestion of said litter (David 2014). Another established link between arthropods and soil microbes is that N mineralization is consistently increased following arthropod litter processing (David, 2014). Therefore, it is reasonable to assume that altered litter and soil N:P are filters on arthropod communities, which is plausible given that arthropods are likely phylogenetically constrained in their stoichiometry and feeding guilds (Martinson et al., 2008; Ross et al., 2022), and different community assemblages and functional groups are expected to inhabit this chemically shifted environment (Tie et al., 2021; Deng et al., 2022; Nessel et al., 2023). If detritivores, and to some extent herbivores, increase in abundance from higher N litter, feedbacks to the soil system may promote further increases in N:P via decomposed frass and dung inputs (Wolters, 2000), and increased N mineralization rates (David 2014). Changes in litter input can also change soil moisture quantity and dynamics, which would feedback to the above scenarios (Wang et al., 2020; Liu et al., 2021). Thus, an invader with impacts on soil N dynamics may be expected to also alter arthropod communities in ways that further change soil N pools and transformations.Invasive N2-symbiont trees therefore provide a natural experiment to evaluate the effect of N:P shifts on surface-active arthropod diversity and potential feedbacks to soil. Arid riparian zones in the southwestern USA have been significantly altered by the establishment of non-native vegetation (Dukes and Mooney, 2004; Harms and Hiebert, 2006), including by a tree with N2-fixing actinobacterial symbionts, Russian olive (Elaeagnus angustifolia ; Bertrand and Lalonde 1985). This species was introduced to riparian woodlands along the Rio Grande of New Mexico, USA, between 1900 and 1915 (Hink and Ohmart 1984). A major ecological disruption in the form ofreduced disturbance was a consequence of dams, levees and diversions that altered dynamic flood regimes of the river, and the relatively static channels of the Rio Grande are less suitable habitat for vegetation communities evolved to frequent overbank flooding and sedimentation (Rood and Mahoney, 1990; Shah and Dahm, 2008). The tree rapidly spread throughout the Rio Grande and became a dominant component of riparian vegetation by 1960 (Campbell and Dick-Peddie 1964). Native N2-fixing symbiotic trees are known in the region (Shepherdia argentea ; silver buffaloberry) but are locally rare and exhibit much lower fixation rates than Russian olive (Petrides 1998, Follstad Shah et al. 2010).Several reports document N cycling alterations following Russian olive invasion, including increased N loss from litter mass decomposed compared to cottonwood (Simons and Seastedt 1999). De Cant (2008) isotopically demonstrated N2-fixation from Russian olive in a Rio Grande bosque, and ~5-fold increase in foliar N compared to adjacent cottonwoods (Populus deltoides var.wislizenii ), but the native trees did not utilize increased soil N from fixation inputs. Decomposing Russian olive litter (C:N = 13) was observed to produce spikes in N2O not observed from cottonwood litter (C:N = 22) under laboratory conditions (Duval et al. 2020). That study also reports increased N-processing enzyme (leucine amino peptidase, LAP) activity from cottonwood soils, suggesting potential microbial N limitation not found with Russian olive soils. However, Russian olive soils exhibited slightly higher acid phosphatase activity compared to cottonwood (Duval et al. 2020), suggesting P limitation.Russian olive introductions clearly have impacts on soil N inputs and cycling, and recent evidence suggests the presence or removal of the tree alters riparian tree-dwelling arthropod communities (West et al., 2023). Ground-dwelling arthropods are excellent taxa to explore invasive tree effects on ecosystem processes, because they are sensitive to fine-scale environmental conditions, and these conditions themselves are vital contributors to decomposition and nutrient cycling in riparian areas (Perry and Herms 2017). Indeed, detritivorous arthropods generally respond well with increased nitrogen and phosphorus levels, with isopods increasing in abundance (Coccia and Fariña 2022). Ellis et al. (1999) found the species composition and richness of middle Rio Grande bosque ground-dwelling arthropods to be similar between native cottonwood and saltcedar habitats, but cottonwood habitats supported greater densities of non-native isopods. However, it is generally unknown what the arthropod community looks like in areas dominated by Russian olive and areas where it has been removed. To improve our knowledge of the ecosystem-level impacts of Russian olive, we designed a study to compare ground dwelling arthropod relative abundance and diversity (taxonomic and functional) in Russian olive dominated stands versus native cottonwood woodlands, and the effect of restoration efforts by comparing Russian olive stands with plots where the tree had been mechanically removed. This allows us to evaluate longer-term (decadal) influence of an invasive tree compared to historic vegetation, as well as short-term impacts on the arthropod community driven by physical removal of plants (and associated ecosystem effects) where the soil chemistry has perhaps not yet appreciably changed.Because we are centering our work on shifting stoichiometry due to a plant invasion, we quantify functional (feeding) diversity of surface-active arthropods as well as taxonomic diversity. We hypothesize that cottonwood stands will have significantly different arthropod communities (beta diversity; taxonomic and functional diversity) than Russian olive stands, and those will be related to soil chemical changes induced by the invasive tree, such as greater N pools and increased N:P (DeCant 2008; Peñuelas et al. 2020). Stands where Russian olive has been removed are predicted to be chemically similar to extant Russian olive stands, but arthropod communities will differ between these areas due to physical character alterations from plant removal (moisture retention, soil temperature). Addressing these questions will provide additional insight into the ecosystem effects of altered N:P on biogeochemically relevant biota, and feedbacks related to invasive, symbiotic N2-fixing vegetation in an arid riparian zone.MATERIALS & METHODS