Reviews of Geophysics最新文献

The Pliocene Epoch (∼5.3–2.6 million years ago, Ma) was characterized by a warmer than present climate with smaller Northern Hemisphere ice sheets, and offers an example of a climate system in long-term equilibrium with current or predicted near-future atmospheric CO₂ concentrations (pCO₂). A long-term trend of ice-sheet expansion led to more pronounced glacial (cold) stages by the end of the Pliocene (∼2.6 Ma), known as the “intensification of Northern Hemisphere Glaciation” (iNHG). We assessed the spatial and temporal variability of ocean temperatures and ice-volume indicators through the late Pliocene and early Pleistocene (from 3.3 to 2.4 Ma) to determine the character of this climate transition. We identified asynchronous shifts in long-term means and the pacing and amplitude of shorter-term climate variability, between regions and between climate proxies. Early changes in Antarctic glaciation and Southern Hemisphere ocean properties occurred even during the mid-Piacenzian warm period (∼3.264–3.025 Ma) which has been used as an analog for future warming. Increased climate variability subsequently developed alongside signatures of larger Northern Hemisphere ice sheets (iNHG). Yet, some regions of the ocean felt no impact of iNHG, particularly in lower latitudes. Our analysis has demonstrated the complex, non-uniform and globally asynchronous nature of climate changes associated with the iNHG. Shifting ocean gateways and ocean circulation changes may have pre-conditioned the later evolution of ice sheets with falling atmospheric pCO₂. Further development of high-resolution, multi-proxy reconstructions of climate is required so that the full potential of the rich and detailed geological records can be realized.

Subtropical gyres cover 26%–29% of the world's surface ocean and are conventionally regarded as ocean deserts due to their permanent stratification, depleted surface nutrients, and low biological productivity. Despite tremendous advances over the past three decades, particularly through the Hawaii Ocean Time-series and the Bermuda Atlantic Time-series Study, which have revolutionized our understanding of the biogeochemistry in oligotrophic marine ecosystems, the gyres remain understudied. We review current understanding of upper ocean biogeochemistry in the North Pacific Subtropical Gyre, considering other subtropical gyres for comparison. We focus our synthesis on spatial variability, which shows larger than expected dynamic ranges of properties such as nutrient concentrations, rates of N₂ fixation, and biological production. This review provides new insights into how nutrient sources drive community structure and export in upper subtropical gyres. We examine the euphotic zone (EZ) in subtropical gyres as a two-layered vertically structured system: a nutrient-depleted layer above the top of the nutricline in the well-lit upper ocean and a nutrient-replete layer below in the dimly lit waters. These layers vary in nutrient supply and stoichiometries and physical forcing, promoting differences in community structure and food webs, with direct impacts on the magnitude and composition of export production. We evaluate long-term variations in key biogeochemical parameters in both of these EZ layers. Finally, we identify major knowledge gaps and research challenges in these vast and unique systems that offer opportunities for future studies.

Over the past decades, the scientific community has made significant efforts to simulate flooding conditions using a variety of complex physically based models. Despite all advances, these models still fall short in accuracy and reliability and are often considered computationally intensive to be fully operational. This could be attributed to insufficient comprehension of the causative mechanisms of flood processes, assumptions in model development and inadequate consideration of uncertainties. We suggest adopting an approach that accounts for the influence of human activities, soil saturation, snow processes, topography, river morphology, and land-use type to enhance our understanding of flood generating mechanisms. We also recommend a transition to the development of innovative earth system modeling frameworks where the interaction among all components of the earth system are simultaneously modeled. Additionally, more nonselective and rigorous studies should be conducted to provide a detailed comparison of physical models and simplified methods for flood inundation mapping. Linking process-based models with data-driven/statistical methods offers a variety of opportunities that are yet to be explored and conveyed to researchers and emergency managers. The main contribution of this paper is to notify scientists and practitioners of the latest developments in flood characterization and modeling, identify challenges in understanding flood processes, associated uncertainties and risks in coupled hydrologic and hydrodynamic modeling for forecasting and inundation mapping, and the potential use of state-of-the-art data assimilation and machine learning to tackle the complexities involved in transitioning such developments to operation.

Reviews of Geophysics (RoG) is the top-rated journal in geochemistry and geophysics (Florindo et al., 2023) and it could not exist without your investment of time and effort. Your expertise ensures that the papers published in this journal meet the standards that the research community expects. We sincerely appreciate the time you spent reading and commenting on manuscripts, and we are very grateful for your willingness and readiness to serve in this role.

RoG published 22 review papers and an editorial in 2022, covering most of the American Geophysical Union section topics, and for this, we were able to rely on the efforts of 69 dedicated reviewers who freely donated their expertise to the journal. Many reviewers answered the call multiple times, as RoG received 82 reviews in 2022. Thank you all again for your awesome efforts, your insights, and your service on behalf of the Earth and space science community.

We look forward to a 2023 of exciting advances in the field and communicating those advances to our community and the broader public. If you have comments regarding the RoG or its peer review process, we invite you to contact the journal at [email protected].

Dynamics of flowing air in partially water-saturated, porous geological formations are governed by a wide range of forces and parameters. These dynamics are reviewed in the contexts of flow patterns that arise and the corresponding applicability of diverse modeling approaches. The importance of reliable gas-liquid flow models draws from the key role gases play in earth systems, and the various engineering practices involving air injection into geological formations. Here, we focus on air flow in water-wet porous media. We survey the factors that affect flow patterns and phase configurations, and the measures that quantify them. For single-phase flow in saturated media (i.e., air flow in dry media or water flow in water-saturated media), the continuum approach (Darcy's law) is generally applicable and offers a good interpretive tool. However, the coupled two-phase flow continuum approach appears appropriate only for phase-saturation degrees that allow both phases to be continuous in the flow domain. Furthermore, air flow in wet media is highly unstable. As a result, air commonly flows in preferential pathways or in the form of bubbles and ganglia, which are not amenable to continuum modeling. On the other hand, pore-scale models that account for the complex geometries and interfaces between the fluids and the media require extreme computational efforts, and generally inaccessible details on medium characteristics. Other stochastically-based representations, such as percolation theory, have value in the conceptualization of complex flow problems but demonstrate limited success in interpreting phase configurations, saturation degrees, and relative permeabilities.

Aerosol forcing uncertainty represents the largest climate forcing uncertainty overall. Its magnitude has remained virtually undiminished over the past 20 years despite considerable advances in understanding most of the key contributing elements. Recent work has produced modest increases only in the confidence of the uncertainty estimate itself. This review summarizes the contributions toward reducing the uncertainty in the aerosol forcing of climate made by satellite observations, measurements taken within the atmosphere, as well as modeling and data assimilation. We adopt a more measurement-oriented perspective than most reviews of the subject in assessing the strengths and limitations of each; gaps and possible ways to fill them are considered. Currently planned programs supporting advanced, global-scale satellite and surface-based aerosol, cloud, and precursor gas observations, climate modeling, and intensive field campaigns aimed at characterizing the underlying physical and chemical processes involved, are all essential. But in addition, new efforts are needed: (a) to obtain systematic aircraft in situ measurements capturing the multi-variate probability distribution functions of particle optical, microphysical, and chemical properties (and associated uncertainty estimates), as well as co-variability with meteorology, for the major aerosol airmass types; (b) to conceive, develop, and implement a suborbital (aircraft plus surface-based) program aimed at systematically quantifying the cloud-scale microphysics, cloud optical properties, and cloud-related vertical velocities associated with aerosol-cloud interactions; and (c) to focus much more research on integrating the unique contributions of satellite observations, suborbital measurements, and modeling, to reduce the persistent uncertainty in aerosol climate forcing.

Heat waves (HWs) can cause large socioeconomic and environmental impacts. The observed increases in their frequency, intensity and duration are projected to continue with global warming. This review synthesizes the state of knowledge and scientific challenges. It discusses different aspects related to the definition, triggering mechanisms, observed changes and future projections of HWs, as well as emerging research lines on subseasonal forecasts and specific types of HWs. We also identify gaps that limit progress and delineate priorities for future research. Overall, the physical drivers of HWs are not well understood, partly due to difficulties in the quantification of their interactions and responses to climate change. Influential factors convey processes at different spatio-temporal scales, from global warming and the large-scale atmospheric circulation to regional and local factors in the affected area and upwind regions. Although some thermodynamic processes have been identified, there is a lack of understanding of dynamical aspects, regional forcings and feedbacks, and their future changes. This hampers the attribution of regional trends and individual events, and reduces the ability to provide accurate forecasts and regional projections. Sustained observational networks, models of diverse complexity, narrative-based methodological approaches and artificial intelligence offer new opportunities toward process-based understanding and interdisciplinary research.

Reviews of Geophysics is an AGU journal, first established in February 1963. It is a hybrid open access invitation-only journal that publishes comprehensive review articles across various disciplines within the Earth and Space Sciences. The selection criteria are rigorous and many submissions are declined without review. The journal is the highest ranked in the fields of Geochemistry and Geophysics, with a high Journal Impact Factor (JIF₂₀₂₁ = 24.9), which is indicative of its high visibility and influence within the scientific community. The journal's published review papers, beyond a mere summary of literature, provide crucial context for current work, and establish the framework for comprehensive understanding of research progress, challenges, and interconnections between different communities, so that research may be appreciated by a broad audience. We emphasize the importance of publishing studies that provide a comprehensive overview and synthesis of the current state of knowledge in a field, especially in the case of geophysics, where knowledge is rapidly developing, increasing and becoming more specialized.

Risks associated with dust hazards are often underappreciated, a gap between the knowledge pool and public awareness that can be costly for impacted communities. This study reviews the emission sources and chemical, physical, and biological characteristics of airborne soil particles (dust) and their effects on human and environmental health and safety in the Pan-American region. American dust originates from both local sources (western United States, northern Mexico, Peru, Bolivia, Chile, and Argentina) and long-range transport from Africa and Asia. Dust properties, as well as the trends and interactions with criteria air pollutants, are summarized. Human exposure to dust is associated with adverse health effects, including asthma, allergies, fungal infections, and premature death. In the Americas, a well-documented and striking effect of soil dust is its association with Coccidioidomycosis, commonly known as Valley fever, an infection caused by inhalation of soil-dwelling fungi unique to this region. Besides human health, dust affects environmental health through nutrients that increase phytoplankton biomass, contaminants that diminish water supply and affect food (crops/fruits/vegetables and ready-to-eat meat), spread crop and marine pathogens, cause Valley fever among domestic and wild animals, transport heavy metals, radionuclides and microplastics, and reduce solar and wind power generation. Dust is also a safety hazard to road transportation and aviation, in the southwestern US where blowing dust is one of the deadliest weather hazards. To mitigate the harmful effects, coordinated regional and international efforts are needed to enhance dust observations and prediction capabilities, soil conservation measures, and Valley fever and other disease surveillance.

Wildfires affect 40% of the earth's terrestrial biome, but much of our knowledge of wildfire activity is limited to the satellite era. Improved understanding of past fires is necessary to better forecast how fire regimes might change with future climate change, to understand ecosystem resilience to fire, and to improve data-model comparisons. Environmental proxy archives can extend our knowledge of past fire activity. Speleothems, naturally occurring cave formations, are widely used in paleoenvironmental research as they are absolutely dateable, occur on every ice-free continent, and include multiple proxies. Recently, speleothems have been shown to record past fire events (Argiriadis et al., 2019, https://doi.org/10.1021/acs.analchem.9b00767; McDonough et al., 2022, https://doi.org/10.1016/j.gca.2022.03.020; Homann et al., 2022, https://doi.org/10.1038/s41467-022-34950-x). Here we present a review of this emerging application in speleothem paleoenvironmental science. We give a concise overview of fire regimes and common paleofire proxies, describe past attempts to use stalagmites to investigate paleofire, and describe the physical basis through which speleothems can record past fires. We then describe the ideal speleothem sample for paleofire research and offer a summary of applicable laboratory and statistical methods. Finally, we present four case studies from southwest Australia which: (a) explore the geochemistry of ash leachates, (b) detail how sulfate isotopes may be a proxy for post fire ecological recovery, (c) demonstrate how a catastrophic paleofire was linked to changes in climate and land management, and (d) investigate whether deep caves can record past fire events. We conclude the paper by outlining future research directions for paleofire applications.