AGU Advances最新文献

{"title":"More Than Marine Heatwaves: A New Regime of Heat, Acidity, and Low Oxygen Compound Extreme Events in the Gulf of Alaska","authors":"Claudine Hauri,&nbsp;Rémi Pagès,&nbsp;Katherine Hedstrom,&nbsp;Scott C. Doney,&nbsp;Sam Dupont,&nbsp;Bridget Ferriss,&nbsp;Malte F. Stuecker","doi":"10.1029/2023AV001039","DOIUrl":"https://doi.org/10.1029/2023AV001039","url":null,"abstract":"<p>Recent marine heatwaves in the Gulf of Alaska have had devastating impacts on species from various trophic levels. Due to climate change, total heat exposure in the upper ocean has become longer, more intense, more frequent, and more likely to happen at the same time as other environmental extremes. The combination of multiple environmental extremes can exacerbate the response of sensitive marine organisms. Our hindcast simulation provides the first indication that more than 20% of the bottom water of the Gulf of Alaska continental shelf was exposed to quadruple heat, positive hydrogen ion concentration [H⁺], negative aragonite saturation state (Ω_arag), and negative oxygen concentration [O₂] compound extreme events during the 2018–2020 marine heat wave. Natural intrusion of deep and acidified water combined with the marine heat wave triggered the first occurrence of these events in 2019. During the 2013–2016 marine heat wave, surface waters were already exposed to widespread marine heat and positive [H⁺] compound extreme events due to the temperature effect on the [H⁺]. We introduce a new Gulf of Alaska Downwelling Index (GOADI) with short-term predictive skill, which can serve as indicator of past and near-future positive [H⁺], negative Ω_arag, and negative [O₂] compound extreme events near the shelf seafloor. Our results suggest that the marine heat waves may have not been the sole environmental stressor that led to the observed ecosystem impacts and warrant a closer look at existing in situ inorganic carbon and other environmental data in combination with biological observations and model output.</p>","PeriodicalId":100067,"journal":{"name":"AGU Advances","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023AV001039","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139435230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Systematic Underestimation of Canopy Conductance Sensitivity to Drought by Earth System Models","authors":"J. K. Green,&nbsp;Y. Zhang,&nbsp;X. Luo,&nbsp;T. F. Keenan","doi":"10.1029/2023AV001026","DOIUrl":"https://doi.org/10.1029/2023AV001026","url":null,"abstract":"&lt;p&gt;The response of vegetation canopy conductance (&lt;i&gt;g&lt;/i&gt;&lt;sub&gt;&lt;i&gt;c&lt;/i&gt;&lt;/sub&gt;) to changes in moisture availability (&lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msubsup&gt;\u0000 &lt;mi&gt;γ&lt;/mi&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;g&lt;/mi&gt;\u0000 &lt;mi&gt;c&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mi&gt;m&lt;/mi&gt;\u0000 &lt;/msubsup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${gamma }_{gc}^{m}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt;) is a major source of uncertainty in climate projections. While vegetation typically reduces stomatal conductance during drought, accurately modeling how and to what degree stomata respond to changes in moisture availability at global scales is particularly challenging, because no global scale &lt;i&gt;g&lt;/i&gt;&lt;sub&gt;&lt;i&gt;c&lt;/i&gt;&lt;/sub&gt; observations exist. Here, we leverage a collection of satellite, reanalysis and station-based near-surface air and surface temperature estimates, which are physically and statistically linked to &lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msubsup&gt;\u0000 &lt;mi&gt;γ&lt;/mi&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;g&lt;/mi&gt;\u0000 &lt;mi&gt;c&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mi&gt;m&lt;/mi&gt;\u0000 &lt;/msubsup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${gamma }_{gc}^{m}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; due to the local cooling effect of &lt;i&gt;g&lt;/i&gt;&lt;sub&gt;&lt;i&gt;c&lt;/i&gt;&lt;/sub&gt; through transpiration, to develop a novel emergent constraint of &lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msubsup&gt;\u0000 &lt;mi&gt;γ&lt;/mi&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;g&lt;/mi&gt;\u0000 &lt;mi&gt;c&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mi&gt;m&lt;/mi&gt;\u0000 &lt;/msubsup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${gamma }_{gc}^{m}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; in an ensemble of Earth System Models (ESMs). We find that ESMs systematically underestimate &lt;math&gt;\u0000 &lt;semantics&gt;\u0000 &lt;mrow&gt;\u0000 &lt;msubsup&gt;\u0000 &lt;mi&gt;γ&lt;/mi&gt;\u0000 &lt;mrow&gt;\u0000 &lt;mi&gt;g&lt;/mi&gt;\u0000 &lt;mi&gt;c&lt;/mi&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;mi&gt;m&lt;/mi&gt;\u0000 &lt;/msubsup&gt;\u0000 &lt;/mrow&gt;\u0000 &lt;annotation&gt; ${gamma }_{gc}^{m}$&lt;/annotation&gt;\u0000 &lt;/semantics&gt;&lt;/math&gt; by ∼33%, particularly in grasslands, croplands, and savannas in semi-arid and bordering regions of the Central United States, Central Europe, Southeastern South America, Southern Africa, Eastern Australia, and parts of East Asia. We show that this underestimation occurs because ESMs inadequately reduce &lt;i&gt;g&lt;/i&gt;&lt;sub&gt;&lt;i&gt;c","PeriodicalId":100067,"journal":{"name":"AGU Advances","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-01-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023AV001026","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139109946","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multi-Layer Evolution of Acoustic-Gravity Waves and Ionospheric Disturbances Over the United States After the 2022 Hunga Tonga Volcano Eruption","authors":"P. A. Inchin,&nbsp;A. Bhatt,&nbsp;S. A. Cummer,&nbsp;S. D. Eckermann,&nbsp;B. J. Harding,&nbsp;D. D. Kuhl,&nbsp;J. Ma,&nbsp;J. J. Makela,&nbsp;R. Sabatini,&nbsp;J. B. Snively","doi":"10.1029/2023AV000870","DOIUrl":"10.1029/2023AV000870","url":null,"abstract":"<p>The Hunga-Tonga Hunga-Ha'apai volcano underwent a series of large-magnitude eruptions that generated broad spectra of mechanical waves in the atmosphere. We investigate the spatial and temporal evolutions of fluctuations driven by atmospheric acoustic-gravity waves (AGWs) and, in particular, the Lamb wave modes in high spatial resolution data sets measured over the Continental United States (CONUS), complemented with data over the Americas and the Pacific. Along with &gt;800 barometer sites, tropospheric observations, and Total Electron Content data from &gt;3,000 receivers, we report detections of volcano-induced AGWs in mesopause and ionosphere-thermosphere airglow imagery and Fabry-Perot interferometry. We also report unique AGW signatures in the ionospheric D-region, measured using Long-Range Navigation pulsed low-frequency transmitter signals. Although we observed fluctuations over a wide range of periods and speeds, we identify Lamb wave modes exhibiting 295–345 m s⁻¹ phase front velocities with correlated spatial variability of their amplitudes from the Earth's surface to the ionosphere. Results suggest that the Lamb wave modes, tracked by our ray-tracing modeling results, were accompanied by deep fluctuation fields coupled throughout the atmosphere, and were all largely consistent in arrival times with the sequence of eruptions over 8 hr. The ray results also highlight the importance of winds in reducing wave amplitudes at CONUS midlatitudes. The ability to identify and interpret Lamb wave modes and accompanying fluctuations on the basis of arrival times and speeds, despite complexity in their spectra and modulations by the inhomogeneous atmosphere, suggests opportunities for analysis and modeling to understand their signals to constrain features of hazardous events.</p>","PeriodicalId":100067,"journal":{"name":"AGU Advances","volume":"4 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2023AV000870","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138822605","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Instabilities Across the Agulhas Current Enhance Upward Nitrate Supply in the Southwest Subtropical Indian Ocean","authors":"Tanya A. Marshall,&nbsp;Lisa Beal,&nbsp;Daniel M. Sigman,&nbsp;Sarah E. Fawcett","doi":"10.1029/2023AV000973","DOIUrl":"https://doi.org/10.1029/2023AV000973","url":null,"abstract":"<p>The Agulhas Current, like other western boundary currents (WBCs), transports nutrients laterally from the tropics to the subtropics in a subsurface “nutrient stream.” These nutrients are predominantly supplied to surface waters by seasonal convective mixing, to fuel a brief period of productivity before phytoplankton become nutrient-limited. Episodic mixing events characteristic of WBC systems can temporarily alleviate nutrient scarcity by vertically entraining deep nutrients into surface waters. However, our understanding of these nutrient fluxes is lacking because they are spatio-temporally limited, and once they enter the sunlit layer, the nutrients are rapidly consumed by phytoplankton. Here, we use a novel application of nitrate Δ(15–18), the difference between the nitrogen and oxygen isotope ratios of nitrate, to characterize three (sub)mesoscale events of upward nitrate supply across the Agulhas Current in winter: (1) mixing at the edges of an anticyclonic eddy, (2) inshore upwelling associated with a submesoscale meander of the Agulhas Current, and (3) overturning at the edge of the current core driven by submesoscale instabilities. All three events manifest as upward injections of high-Δ(15–18) nitrate into the thermocline and surface where nitrate Δ(15–18) is otherwise low; these entrainment events are not always apparent in the other co-collected data. The dynamics driving the nitrate supply events are common to all WBCs, implying that nutrient entrainment facilitated by WBCs is quantitatively significant and supports productivity in otherwise oligotrophic subtropical surface waters. A future rise in energy across WBC systems may increase these nutrient fluxes, partly offsetting the predicted stratification-induced decrease in subtropical ocean fertility.</p>","PeriodicalId":100067,"journal":{"name":"AGU Advances","volume":"4 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2023AV000973","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138678760","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemical and Photochemical Constraints on S[IV] Concentrations in Natural Waters on Prebiotic Earth","authors":"Sukrit Ranjan,&nbsp;Khaled Abdelazim,&nbsp;Gabriella G. Lozano,&nbsp;Sangita Mandal,&nbsp;Cindy Y. Zhou,&nbsp;Corinna L. Kufner,&nbsp;Zoe R. Todd,&nbsp;Nita Sahai,&nbsp;Dimitar D. Sasselov","doi":"10.1029/2023AV000926","DOIUrl":"https://doi.org/10.1029/2023AV000926","url":null,"abstract":"<p>Aqueous S[IV] species (<math>\u0000 <semantics>\u0000 <mrow>\u0000 <msubsup>\u0000 <mrow>\u0000 <mi>H</mi>\u0000 <mi>S</mi>\u0000 <mi>O</mi>\u0000 </mrow>\u0000 <mn>3</mn>\u0000 <mo>−</mo>\u0000 </msubsup>\u0000 </mrow>\u0000 <annotation> ${mathrm{H}mathrm{S}mathrm{O}}_{3}^{-}$</annotation>\u0000 </semantics></math>, <math>\u0000 <semantics>\u0000 <mrow>\u0000 <msubsup>\u0000 <mrow>\u0000 <mi>S</mi>\u0000 <mi>O</mi>\u0000 </mrow>\u0000 <mn>3</mn>\u0000 <mrow>\u0000 <mn>2</mn>\u0000 <mo>−</mo>\u0000 </mrow>\u0000 </msubsup>\u0000 </mrow>\u0000 <annotation> ${mathrm{S}mathrm{O}}_{3}^{2-}$</annotation>\u0000 </semantics></math>) derived from volcanogenic atmospheric SO₂ are important to planetary habitability through their roles in proposed origins-of-life chemistry and influence on atmospheric sulfur haze formation, but the early cycling of S[IV] is poorly understood. Here, we combine new laboratory constraints on S[IV] disproportionation kinetics with a novel aqueous photochemistry model to estimate the concentrations of S[IV] in natural waters on prebiotic Earth. We show that S[IV] disproportionation is slow in pH ≥ 7 waters, with timescale <i>T</i> ≥ 1 year at room temperature, meaning that S[IV] was present in prebiotic natural waters. However, we also show that photolysis of S[IV] by UV light on prebiotic Earth limited [S[IV]] &lt; 100 µM in global-mean steady-state. Because of photolysis, [S[IV]] was much lower in natural waters compared to the concentrations generally invoked in laboratory simulations of origins-of-life chemistry (≥10 mM), meaning further work is needed to confirm whether laboratory S[IV]-dependent prebiotic chemistries could have functioned in nature. [S[IV]] ≥ 1 µM in terrestrial waters for: (a) SO₂ outgassing ≥20× modern, (b) pond depths &lt;10 cm, or (c) UV-attenuating agents present in early waters or the prebiotic atmosphere. Marine S[IV] was sub-saturated with respect to atmospheric SO₂, meaning that atmospheric SO₂ deposition was efficient and that, within the constraints of present knowledge, UV-attenuating sulfur hazes could only have persisted on prebiotic Earth if sulfur emission rates were very high (≳100× modern). Our work illustrates the synergy between planetary science, geochemistry and synthetic organic chemistry toward understanding the emergence and maintenance of life on early Earth.</p>","PeriodicalId":100067,"journal":{"name":"AGU Advances","volume":"4 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2023AV000926","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138678762","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Search for Slow Sulfur Sinks","authors":"Sonny Harman","doi":"10.1029/2023AV001064","DOIUrl":"https://doi.org/10.1029/2023AV001064","url":null,"abstract":"&lt;p&gt;Earth's earliest epochs are shrouded by billions of years of planetary and biological evolution. As a result, many questions surround the origins of life, ranging from what surface conditions prevailed to where and how key prebiotic precursors formed and combined to give rise to life as we know it. Stanley Miller and Harold Urey performed some of the first laboratory explorations of those questions with their spark discharge experiments (Miller, &lt;span&gt;1953&lt;/span&gt;, &lt;span&gt;1955&lt;/span&gt;; Miller &amp; Urey, &lt;span&gt;1959&lt;/span&gt;). Six decades on, researchers are describing plausible mechanisms that can form the building blocks of life (e.g., Becker et al., &lt;span&gt;2019&lt;/span&gt;) from molecules anticipated to exist in a prebiotic atmosphere (Cleaves et al., &lt;span&gt;2008&lt;/span&gt;) and ocean (Rimmer &amp; Shorttle, &lt;span&gt;2019&lt;/span&gt;). These advances are all important components of the long voyage toward discovering how life originated on Earth. And while the ultimate destination is set, the route is not fully mapped, nor has the ship been fully assembled.&lt;/p&gt;&lt;p&gt;Part of that missing map is due to the limits in our understanding of sulfur, as is discussed by Ranjan et al. Sulfur is thought to play critical roles in prebiotic chemistry, volatile cycling, and climate in large part due to its ability to gain and lose electrons and participate in chemistry as a gas, dissolved in liquids, or as a solid. Sulfur aerosols, formed from either sulfuric acid (H&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt;) or elemental sulfur (&lt;i&gt;S&lt;/i&gt;&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt;), contribute to the present-day climates of both Venus (e.g., Taylor &amp; Grinspoon, &lt;span&gt;2009&lt;/span&gt;) and Earth (e.g., Storelvmo et al., &lt;span&gt;2016&lt;/span&gt;), and substantial hazes may have appeared at multiple points in Earth's (e.g., Kasting et al., &lt;span&gt;1989&lt;/span&gt;) and Mars' (e.g., Tian et al., &lt;span&gt;2010&lt;/span&gt;) histories.&lt;/p&gt;&lt;p&gt;The work of Ranjan et al. helps to draw a more complete map and furnishing a seaworthy vessel in three ways. First, their efforts are advancing our understanding of the earliest part of Earth's history. Because of the potential effect sulfate and elemental sulfur have on the climate of the early Earth, as well as the secondary effect that those species have on other sulfur-bearing molecules in the atmosphere (e.g., Kasting et al., &lt;span&gt;1989&lt;/span&gt;), understanding how sulfite reacts is an important region of the molecular map. Sulfate is also critical in several proposed pathways to form prebiotic molecules (e.g., Becker et al., &lt;span&gt;2019&lt;/span&gt;), making it a vital component of the vessel traversing the abiotic to biotic seascape.&lt;/p&gt;&lt;p&gt;Second, the experiments described are neither quick nor easy to perform, which matters when many of the remaining problems are difficult to accomplish on “graduate student lifetime” timescales. Of all the atoms that stock the prebiotic shipyard, including carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur, sulfur is perhaps the thorniest. Given its moderate electronegativ","PeriodicalId":100067,"journal":{"name":"AGU Advances","volume":"4 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2023AV001064","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138678761","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Europa's Ocean Translates Interior Tidal Heating Patterns to the Ice-Ocean Boundary","authors":"D. G. Lemasquerier,&nbsp;C. J. Bierson,&nbsp;K. M. Soderlund","doi":"10.1029/2023AV000994","DOIUrl":"https://doi.org/10.1029/2023AV000994","url":null,"abstract":"<p>The circulation in Europa's ocean determines the degree of thermal, mechanical and chemical coupling between the ice shell and the silicate mantle. Using global direct numerical simulations, we investigate the effect of heterogeneous tidal heating in the silicate mantle on rotating thermal convection in the ocean and its consequences on ice shell thickness. Under the assumption of no salinity or ocean-ice shell feedbacks, we show that convection largely transposes the latitudinal variations of tidal heating from the seafloor to the ice, leading to a higher oceanic heat flux in polar regions. Longitudinal variations are efficiently transferred when boundary-driven thermal winds develop, but are reduced in the presence of strong zonal flows and may vanish in planetary regimes. If spatially homogeneous radiogenic heating is dominant in the silicate mantle, the ocean's contribution to ice shell thickness variations is negligible compared to tidal heating within the ice. If tidal heating is instead dominant in the mantle, the situation is reversed and the ocean controls the pole-to-equator thickness contrast, as well as possible longitudinal variations.</p>","PeriodicalId":100067,"journal":{"name":"AGU Advances","volume":"4 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2023AV000994","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138634050","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Strong Physical Contrasts Across Two Mid-Lithosphere Discontinuities Beneath the Northwestern United States: Evidence for Cratonic Mantle Metasomatism","authors":"Tianze Liu,&nbsp;Emily J. Chin,&nbsp;Peter Shearer","doi":"10.1029/2023AV001014","DOIUrl":"https://doi.org/10.1029/2023AV001014","url":null,"abstract":"<p>Mid-lithosphere discontinuities are seismic interfaces likely located within the lithospheric mantle of stable cratons, which typically represent velocities decreasing with depth. The origins of these interfaces are poorly understood due to the difficulties in both characterizing them seismically and reconciling the observations with thermal-chemical models of cratons. Metasomatism of the cratonic lithosphere has been reported by numerous geochemical and petrological studies worldwide, yet its seismic signature remains elusive. Here, we identify two distinct mid-lithosphere discontinuities at ∼87 and ∼117 km depth beneath the eastern Wyoming craton and the southwestern Superior craton by analyzing seismic data recorded by two longstanding stations. Our waveform modeling shows that the shallow and deep interfaces represent isotropic velocity drops of 2%–8% and 4%–9%, respectively, depending on the contributions from changes in radial anisotropy and density. By building a thermal-chemical model including the regional xenolith thermobarometry constraints and the experimental phase-equilibrium data of mantle metasomatism, we show that the shallow interface probably represents the metasomatic front, below which hydrous minerals such as amphibole and phlogopite are present, whereas the deep interface may be caused by the onset of carbonated partial melting. The hydrous minerals and melts are products of mantle metasomatism, with CO₂-H₂O-rich siliceous melt as a probable metasomatic reagent. Our results suggest that mantle metasomatism is probably an important cause of mid-lithosphere discontinuities worldwide, especially near craton boundaries, where the mantle lithosphere may be intensely metasomatized by fluids and melts released by subducting slabs.</p>","PeriodicalId":100067,"journal":{"name":"AGU Advances","volume":"4 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2023AV001014","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138564876","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Maximum Supersaturation in the Marine Boundary Layer Clouds Over the North Atlantic","authors":"Xianda Gong,&nbsp;Yang Wang,&nbsp;Hua Xie,&nbsp;Jiaoshi Zhang,&nbsp;Zheng Lu,&nbsp;Robert Wood,&nbsp;Frank Stratmann,&nbsp;Heike Wex,&nbsp;Xiaohong Liu,&nbsp;Jian Wang","doi":"10.1029/2022AV000855","DOIUrl":"https://doi.org/10.1029/2022AV000855","url":null,"abstract":"<p>The maximum supersaturation (<i>S</i>_x) in clouds is a key parameter affecting the cloud's microphysical and radiative properties. We investigate the <i>S</i>_x of the marine boundary layer clouds by combining airborne and surface observations in the Eastern North Atlantic. The cloud droplet number concentration (<i>N</i>_c) in the least diluted cloud cores agrees well with the number concentration of particles larger than the Hoppel Minimum (HM) (<i>N</i>_&gt;HM) below clouds, indicating that the HM represents the average size threshold above which particles are activated to form cloud droplets. The <i>S</i>_x values derived from surface observations vary from 0.10% to 0.50% from June 2017 to June 2018, with a clear seasonal variation exhibiting higher values during winter. Most of the <i>S</i>_x variance (∼60%) can be explained by the cloud condensation nuclei (CCN) concentration and updraft velocity (<i>w</i>), with the CCN concentration playing a more important role than <i>w</i> in explaining the variation of <i>S</i>_x. The influence of CCN concentration on <i>S</i>_x leads to a buffered response of <i>N</i>_c to aerosol perturbations. The response of <i>N</i>_c to low aerosol concentration during winter is further buffered by the high <i>w</i>. The global Community Earth System Model (CESM) simulated <i>S</i>_x values in the Azores have a positive bias compared to measured <i>S</i>_x, likely due to overestimated <i>w</i> and underestimated CCN concentration. The CESM simulated <i>S</i>_x exhibits higher values further north over the North Atlantic Ocean, which is attributed to stronger <i>w</i>. The suppression of <i>S</i>_x by aerosol is also evident in regions with high CCN concentrations.</p>","PeriodicalId":100067,"journal":{"name":"AGU Advances","volume":"4 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2022AV000855","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138432042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"RECCAP2 Future Component: Consistency and Potential for Regional Assessment to Constrain Global Projections","authors":"Chris D. Jones,&nbsp;Tilo Ziehn,&nbsp;Jatin Anand,&nbsp;Ana Bastos,&nbsp;Eleanor Burke,&nbsp;Josep G. Canadell,&nbsp;Manoel Cardoso,&nbsp;Yolandi Ernst,&nbsp;Atul K. Jain,&nbsp;Sujong Jeong,&nbsp;Elizabeth D. Keller,&nbsp;Masayuki Kondo,&nbsp;Ronny Lauerwald,&nbsp;Tzu-Shun Lin,&nbsp;Guillermo Murray-Tortarolo,&nbsp;Gert-Jan Nabuurs,&nbsp;Mike O’Sullivan,&nbsp;Ben Poulter,&nbsp;Xiaoyu Qin,&nbsp;Celso von Randow,&nbsp;Marcos Sanches,&nbsp;Dmitry Schepaschenko,&nbsp;Anatoly Shvidenko,&nbsp;T. Luke Smallman,&nbsp;Hanqin Tian,&nbsp;Yohanna Villalobos,&nbsp;Xuhui Wang,&nbsp;Jeongmin Yun","doi":"10.1029/2023AV001024","DOIUrl":"10.1029/2023AV001024","url":null,"abstract":"<p>Projections of future carbon sinks and stocks are important because they show how the world's ecosystems will respond to elevated CO₂ and changes in climate. Moreover, they are crucial to inform policy decisions around emissions reductions to stay within the global warming levels identified by the Paris Agreement. However, Earth System Models from the 6th Coupled Model Intercomparison Project (CMIP6) show substantial spread in future projections—especially of the terrestrial carbon cycle, leading to a large uncertainty in our knowledge of any remaining carbon budget (RCB). Here we evaluate the global terrestrial carbon cycle projections on a region-by-region basis and compare the global models with regional assessments made by the REgional Carbon Cycle Assessment and Processes, Phase 2 activity. Results show that for each region, the CMIP6 multi-model mean is generally consistent with the regional assessment, but substantial cross-model spread exists. Nonetheless, all models perform well in some regions and no region is without some well performing models. This gives confidence that the CMIP6 models can be used to look at future changes in carbon stocks on a regional basis with appropriate model assessment and benchmarking. We find that most regions of the world remain cumulative net sources of CO₂ between now and 2100 when considering the balance of fossil-fuels and natural sinks, even under aggressive mitigation scenarios. This paper identifies strengths and weaknesses for each model in terms of its performance over a particular region including how process representation might impact those results and sets the agenda for applying stricter constraints at regional scales to reduce the uncertainty in global projections.</p>","PeriodicalId":100067,"journal":{"name":"AGU Advances","volume":"4 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2023AV001024","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135474623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}