地球科学最新文献

Ocean Alkalinity Enhancement (OAE) is an emerging carbon dioxide removal approach that aims to store additional atmospheric CO₂ as (bi)carbonate in seawater. OAE can be realized through a variety of pathways, one of which is the dispersal of alkaline mineral sand on beaches where wave energy shall accelerate alkalinity formation. Here, we built a “Beach-Machine” to simulate a gradient of wave energy and test its effect on alkalinity formation by olivine, a widely considered mineral for OAE. We find that wave energy strongly (linearly) increases alkalinity formation from olivine when energy input is beyond a certain threshold. However, when olivine is mixed with organic-poor sand, energy input also increases the loss of alkalinity possibly by promoting precipitation reactions thereby canceling out the benefits of waves on alkalinity formation. Our experiments show that the effects of wave energy on OAE efficiency are dependent on the sediment where olivine-based OAE is applied.

Plant responses to water stress is a major uncertainty to predicting terrestrial ecosystem sensitivity to drought. Different approaches have been developed to represent plant water stress. Empirical approaches (the empirical soil water stress (or Beta) function and the supply-demand balance scheme) have been widely used for many decades; more mechanistic based approaches, that is, plant hydraulic models (PHMs), were increasingly adopted in the past decade. However, the relationships between them—and their underlying connections to physical processes—are not sufficiently understood. This limited understanding hinders informed decisions on the necessary complexities needed for different applications, with empirical approaches being mechanistically insufficient, and PHMs often being too complex to constrain. Here we introduce a unified framework for modeling transpiration responses to water stress, within which we demonstrate that empirical approaches are special cases of the full PHM, when the plant hydraulic parameters satisfy certain conditions. We further evaluate their response differences and identify the associated physical processes. Finally, we propose a methodology for assessing the necessity of added complexities of the PHM under various climatic conditions and ecosystem types, with case studies in three typical ecosystems: a humid Midwestern cropland, a semi-arid evergreen needleleaf forest, and an arid grassland. Notably, Beta function overestimates transpiration when VPD is high due to its lack of constraints from hydraulic transport and is therefore insufficient in high VPD environments. With the unified framework, we envision researchers can better understand the mechanistic bases of and the relationships between different approaches and make more informed choices.

Fluxes of carbon dioxide (CO₂) and methane (CH₄) from open water bodies are critical components of carbon-climate feedbacks in high latitudes. Processes governing the spatial and temporal variability of these aquatic greenhouse gas (GHG) fluxes are still highly uncertain due to limited observational data sets and lack of modeling studies incorporating comprehensive thermal and biochemical processes. This research investigates how slight variations in climate propagate through the biogeochemical cycles of ponds and resulting impacts on GHG emissions. We examine the thermal and biogeochemical dynamics of two ponds in the Yukon–Kuskokwim Delta, Alaska, under varying climatic conditions to study the impacts on CO₂, CH₄, and oxygen (O₂) concentrations and fluxes. We performed multiple numerical experiments, using the LAKE process-based model and field measurements, to analyze how these ponds respond to variations in air temperature, shortwave radiation, and snow cover. Our study demonstrates that ice cover duration and water temperature are primary climatic drivers of GHG fluxes. Climate experiments led to reductions in ice cover duration and increased water temperatures, which subsequently enhanced CH₄ and CO₂ gas emissions from two study ponds. On average, cumulative CH₄ and CO₂ emissions were 5% and 10% higher, respectively, under increases in air temperature and shortwave radiation. Additionally, we uncovered a need to incorporate groundwater influxes of dissolved gases and nutrients in order to fully represent processes governing aquatic biochemical activity. Our work highlights the importance of understanding local-scale processes in predicting future Arctic contributions to GHG emissions.

This study systematically evaluates the performance of the Mellor-Yamada-Nakanishi-Niino-Eddy-Diffusion-Mass-Flux planetary boundary layer (PBL) scheme within the Weather Research and Forecasting (WRF) model in simulating near-surface wind speeds across various topographies in New York State (NYS). Simulated wind speeds are compared with in-situ measurements from 22 surface sites, grouped into six topographic categories: continental plain (CT), lakeside (LS), river valley (RV), Long Island (LI), Block Island (BI), and offshore ocean (OO). A quantitative evaluation based on Relative Euclidean Distance shows that wind speeds at the OO site are the most accurately reproduced, followed by those at LI sites, while the model performs less accurately for the remaining topographic groups. Wind speeds over CT sites tend to be overestimated by approximately 1 m/s, although their diurnal variability (DV) is well captured. In contrast, the model underestimates wind DV at LS, RV, LI, and BI sites, with the largest biases occurring at LI and BI, resulting in underestimated daytime wind speed and/or overestimated nighttime wind speed. The OO winds exhibit minimal diurnal variation, accurately captured by our WRF model. The surface wind diurnal variation is closely linked to PBL development. Among the indicators of PBL development, surface potential temperature biases most strongly correlate with wind speed biases. Our WRF model faces challenges in capturing the distinctions between winds influenced by local circulations and those over continental plains, and the significantly stronger winds at OO compared to BI. Potential causes for these biases are discussed, offering pathways for improving surface wind simulations in future.

We combine lidar temperature observations onboard a research aircraft with numerical simulations in the framework of the SOUTHTRAC (Southern Hemisphere Transport, Dynamics, and Chemistry) Campaign. Deep propagation of gravity waves (GW) from the troposphere to the lower mesosphere is studied above the Southern Andes during two flights in September 2019. We use the Weather Research and Forecasting (WRF) model with a configuration for the simulations that has been validated in a previous study of this campaign. Strong orographic GW were detected during both flights that were conceived for different latitudes. The observational and numerical data reveal the presence of significant GW attenuation, breaking and secondary wave generation above the stratopause due to the development of convective and dynamic instability as well as conditions for wave evanescence. The GW generated by topography were not able to alter the stable structure of the stratosphere, but the scenario was quite different in the lower mesosphere. The disturbed zones in that layer were produced by the combined effect on lapse rate of the background temperature variation and the perturbations associated with GW, which together may induce large vertical gradients. As a consequence, areas of reduced stability (with low or even negative buoyancy parameter) emerge above the stratopause. The existence of these GW self-induced attenuation layers in the mesosphere where temperature perturbations produce large negative gradients may lead to an amplitude growth control mechanism for the upward propagating waves.

The Mars 2020 rover, Perseverance, encountered a range of basaltic igneous rocks on the floor of Jezero crater, two of which are olivine cumulates, formed by accumulation of olivine crystals from basaltic magma. These olivine cumulates lie in a geomorphically distinct region, named Séítah, on the Jezero crater floor. To understand the origin of the olivine cumulates and their relationship with the adjacent basalts of the Máaz formation, we calculated the composition of the parent magma of one of the olivine cumulates, named Brac, based on chemical analyses and mineralogic interpretations from the Planetary Instrument for X-ray Lithochemistry (PIXL) instrument. Acceptable Brac/Dourbes parent magmas are olivine tholeiite basalts with SiO₂ ∼ 45%, MgO ∼ 8%, FeO_Tot ∼ 27%, Al₂O₃ ∼ 6%, and total alkali oxides of ∼2.8% weight. These compositions are similar to one of the Máaz basalts, the rock Rimplas, which is stratigraphically close to Séítah, but chemically distinct from other Máaz basalts. Rimplas could (within uncertainty) be a sample of the Brac parent magma, but it is more likely that Rimplas and Brac had a common (or similar) parent magma. Geochemical similarities between Rimplas and the other Máaz basalts thus suggest that Brac (and other olivine-rich rocks of Séítah) and the Máaz basalts could be geochemically related; they could have been cogenetic and possibly contemporaneous, or could have been derived (at different times) from similar or related mantle source(s).

The increase in the number of objects in Low-Earth Orbit has heightened the demand for high-accuracy orbital prediction models driven by dependable measurements of thermospheric mass density (TMD). Given the added cost and complexity burden of equipping satellites with high precision accelerometers, recent attention has focused on alternative techniques for observing TMD such as “GNSS accelerometry,” which involves harnessing spacecraft as instruments themselves to quantify thermospheric density vis-à-vis orbital decay. This work demonstrates how the Energy Dissipation Rate (EDR) technique utilizes the change in spacecraft orbital energy to recover density measurements at cadences ranging from a single orbital period down to as small as a quarter of such periods. After presenting a framework for applying the EDR method to the elliptical orbit of the Communications/Navigation Outage Forecasting System (C/NOFS) satellite, “effective” TMD measurements integrated over a continuous “orbit arc” are recovered for C/NOFS during January 2011. The merits of the EDR method, especially in its heightened sensitivity to solar/geomagnetic activity, are underscored by investigating a minor geomagnetic storm on 7 January 2011 and contrasting the results with those obtained from processing Two-Line Element sets (TLEs) or the output from NRLMSISE-00 and HASDM. Furthermore, this study introduces the novel application of fractional-orbit average EDR integration tailored for satellites with eccentric orbits, demonstrating its efficacy in offering nuanced insights into thermospheric conditions. The results demonstrate the ability of physics-based techniques and readily accessible data sets to estimate thermospheric density and provide insight into aeronomy and space weather science.

Equatorial Layered Deposits (ELDs) are sedimentary landforms found at equatorial latitudes of Mars showing repetitive bedding and commonly associated with hydrous minerals. These deposits are important archives of Mars' past aqueous conditions yet in most cases their formation mechanisms are still debated and elusive. Here we provide a detailed characterization of the mineralogy and stratigraphy of three different exposures of ELDs in Meridiani Planum, where such formations are found within small impact craters and are dated back to the Noachian-Hesperian boundary. Our analysis highlights a varying degree of mixture between polyhydrated Mg sulfates and Fe/Mg phyllosilicates within the beds of all three chosen targets, with several alternating strata of sulfate-rich and phyllosilicate-rich materials. In one case, Al-phyllosilicates are also found along with their Fe/Mg counterpart. This is a much more varied mineral assemblage than previously reported for ELDs in this area. We propose a formation mechanism which explains the observed interbedding as a result of surface ponding of groundwaters, aqueous alteration of atmospherically-sourced basaltic materials and water table/pH oscillations (wet/dry cycles) leading to recurrent sulfate precipitation. Our findings show how local environments play a substantial role in recording small-scale variations of complex aqueous processes, generally not observed at regional and global scales on Mars.