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Tidal forcing is a dominant physical forcing mechanism on the Northwest European Shelf (NWES) that regulates the mixing-stratification status of the water column and thus acts as a major control for biological productivity and air-sea CO2 exchange. Tides further influence the marine carbon cycle on the shelf by affecting benthic-pelagic coupling, vertical mixing and the large-scale residual circulation. The cumulative tidal impact on oceanic uptake of atmospheric CO2 on the NWES, however, remains largely unexplored. We use a coupled physical-biogeochemical ocean model to gain quantitative understanding of the tidal impacts on the air-sea CO2 exchange of the NWES by comparing hindcast simulations with and without tidal forcing. Our results show that tidal forcing weakens the annual oceanic CO2 uptake on the NWES by 0:15 Tmol C yr-1, corresponding to a ~13% stronger CO2 sink in the experiment without tidal forcing. The tide-induced increase in marine primary production demonstrated in earlier studies, which primarily enhances biological carbon fixation in shallow inner-shelf regions of the NWES, does not significantly affect net air-sea CO2 exchange. Instead, we find tidal mixing, tide-induced baroclinic circulation and the tidal impact on benthic-pelagic coupling to be dominant controls of air-sea CO2 exchange. Tidal mixing in the permanently mixed shelf regions accounts for the majority (~40%) of the weakening effect on CO2 uptake, while the modulation of water mass composition in the Celtic Sea by tide-induced baroclinic circulation reduces the uptake further (~33% of the difference in annual mean CO2 uptake). In terms of the shelf carbon budget, the tidal response of airsea CO2 exchange is primarily mediated by changes to the pelagic DIC reservoir (~73%; - 0:11 Tmol C yr-1). Tidal impacts on off-shelf carbon export to the North Atlantic only account for ~20% (- 0:03 Tmol C yr-1) of the tidal impact on shelf CO2 uptake, and changes in sedimentation of particulate organic carbon account for the remaining ~7% (- 0:01 Tmol C yr-1). [ABSTRACT FROM AUTHOR]

We introduce an novel approach to compare Earth System Model output using a causality-based approach. The method is based on the PCMCI+ algorithm, which identifies causal relationships between multiple variables. We aim to investigate the causal relationships between atmospheric (North Atlantic Oscillation – NAO), oceanic (gyre strength, stratification, circulation), and biogeochemical variables (nitrate, iron, silicate, net primary production) in the North Atlantic subpolar gyre, a critical region for the global climate system with a well characterised multi-year variability in physical and biogeochemical properties in response to the North Atlantic Oscillation. We test a specific multivariate conceptual scheme, involving causal links between these variables. Applying the PCMCI+ method allows us to differentiate between the influence of vertical mixing and horizontal advection on nutrient concentrations, spring bloom intensity, as well as to highlight model-specific dynamics. The analysis of the causal links suggests a dominant contribution of vertical mixing to peak spring bloom intensity compared to transport. The strength of the links is variable among models. Stratification is identified as an important factor controlling spring bloom NPP in some, but not all, models. Horizontal transport also significantly influences biogeochemistry. However, horizontal transport generally exhibits lower contributions than vertical mixing. Most of the links found are model-specific, hence likely contributing to inter-model spread. The limitations of the method are discussed and directions for future research are suggested. [ABSTRACT FROM AUTHOR]

Long path length FTIR‐smog chamber techniques were used to study the title reactions in 650 Torr of N2, oxygen, or air diluent at 296 ± 3 K. Values of k(Cl + (Z)‐CF2HCF = CHCl)═(6.6 ± 0.7) × 10−11 and k(OH + (Z)‐CF2HCF═CHCl)═(4.1 ± 0.7) × 10−12 cm3 molecule−1 s−1 were measured. The IR spectrum of (Z)‐CF2HCF═CHCl is reported. The atmospheric lifetime of (Z)‐CF2HCF═CHCl is determined by the reaction with OH and is approximately 2.8 days. Reaction of (Z)‐CF2HCF═CHCl with Cl atoms gives HC(O)Cl and CF2HC(O)F as major primary products. Under environmental conditions, the OH radical initiated oxidation gives CF2HC(O)F and HC(O)Cl in yields of (98 ± 8)% and (100 ± 4)%, respectively. Accounting for non‐uniform horizontal and vertical mixing leads to a 100‐year time‐horizon global warming potential value for (Z)‐CF2HCF═CHCl of essentially zero. [ABSTRACT FROM AUTHOR]

Tokyo Bay is one of the most productive coastal systems in the world. Surrounded by a growing urban metropolis, the bay has experienced large fluctuations in water quality over the past decades due to eutrophication and regulatory requirements for wastewater treatment. However, the spatial and temporal variability of chlorophyll a (Chl a) and associated environmental factors remains unclear. In this study, water temperature, salinity, light condition, Chl a and nutrient concentrations was investigated monthly at three stations in the inner area from November 2016 to October 2020. In the surface water, the Chl a and nutrient concentrations largely fluctuated seasonally. In the summer season (May–September), with sufficient nutrient input from rivers and wastewater treatment plants, Chl a concentration in the northwestern part of the bay (St. AO) was positively correlated with water temperature with extremely high concentration (mean, 90.5 µg L−1). On the other hand, those in the northern (St. CB) and central (St. F3) areas were negatively correlated with nutrient concentrations, especially DIP and DSi which sometimes decreased to below the detection limit (BDL). In the winter–spring season (January–April), the Chl a concentration was relatively high at St. CB (mean, 25.9 µg L−1), which could be attributed to light availability, sufficient light penetration to the bottom, and vertical mixing of the entire water column. These results indicated that the factors controlling Chl a differed among areas and seasons in the bay. [ABSTRACT FROM AUTHOR]

The study of upper ocean mixing processes, including their dynamics and thermodynamics, has been a primary focus for oceanographers and meteorologists. Wave breaking in deep water is believed to play a significant role in these processes, affecting air–sea interactions and contributing to the energy dissipation of surface waves. This, in turn, enhances the transfer of gas, heat, and mass at the ocean surface. In this paper, we use the FVCOM-SWAVE coupled wave and current model, which is based on the MY-2.5 turbulent closure model, to examine the response of upper ocean turbulent kinetic energy (TKE) and temperature to various wave breaking parametric schemes. We propose a new parametric scheme for wave breaking energy at the sea surface, which is based on the correlation between breaking wave parameter R B and whitecap coverage. The impact of this new wave breaking parametric scheme on the upper ocean under typhoon conditions is analyzed by comparing it with the original parametric scheme that is primarily influenced by wave age. The wave field simulated by SWAVE was verified using Jason-3 satellite altimeter data, confirming the effectiveness of the simulation. The simulation results for upper ocean temperature were also validated using OISST data and Argo float observational data. Our findings indicate that, under the influence of Typhoon Nanmadol, both parametric schemes can transfer the energy of sea surface wave breaking into the seawater. The new wave breaking parameter R B scheme effectively enhances turbulent mixing at the ocean surface, leading to a decrease in sea surface temperature (SST) and an increase in mixed layer depth (MLD). This further improves upon the issue of uneven mixing of seawater at the air–sea interface in the MY-2.5 turbulent closure model. However, it is important to note that wave breaking under typhoon conditions is only one aspect of wave impact on ocean disturbances. Therefore, further research is needed to fully understand the impact of waves on upper ocean mixing, including the consideration of other wave mechanisms. [ABSTRACT FROM AUTHOR]

This study examines the influence of shallow cumulus clouds on the excessive summertime heat in the Houston‐Galveston metropolitan area, a coastal urban area in the warm Southeast United States. Specifically, it aims to improve our understanding of how both the clouds and the relatively cool, moist afternoon sea breeze impact the Urban Heat Island (UHI) and Heat Index (HI). During the warm season, the afternoon sea breeze phenomenon in this coastal city acts as a natural air conditioner for city residents, facilitating the dispersion of moisture, heat, and pollutants. To investigate the relationship among urbanization, clouds, and land‐sea interactions, we conducted cloud‐ and urban‐resolving simulations at a 900 m grid resolution and perform simulation scenarios aiming to isolate urbanization, clouds and land‐sea circulations. Results show that urbanization correlates with the presence of shallow cumulus clouds, higher cloud bases, and increased cloud duration over the Galveston‐Houston region compared to rural areas. These urban clouds benefit from the enhanced moist static energy that is favored by intensifying vertical mixing and moisture flux convergence. Urbanization raises the mean HI while mitigating its afternoon HI high. We found that the urban circulation dome overwhelms the sensitivity of the sea breeze to the urbanization. Instead, the influence of urbanization on cloud enhancement emerges as a crucial pathway responsible for reducing the high afternoon HI values. Moreover, uncertainties in SSTs are closely linked to the sensitivities of land‐sea circulations, which in turn modulate UHI and HI. Plain Language Summary: Urbanization influences the meteorology by creating a warmer environment that enhances excessive heat during the summer. Additionally, the warmer environment and the urban buildings increase friction, leading to more mixing and in turn favoring the development of low‐level clouds. We developed computer simulations aiming to understand these processes and their interaction with the sea‐breeze in this coastal city, and we found that these clouds help ameliorate the excessive heat during the afternoon. Key Points: Urbanization correlates with the presence of shallow cumulus cloudsUrban clouds are driven by the enhanced sensible heat and dynamic drag imparted by the urban landscapeUrbanization cloud enhancement emerges as a crucial pathway responsible for reducing the afternoon Heat Index values [ABSTRACT FROM AUTHOR]

Plastic pollution in aquatic environments is a growing concern, with rivers recognized as major pathways. However, rivers themselves are also subject to pollution. Hence, understanding riverine plastic transport dynamics is essential for mitigating environmental impacts. Although plastic-related research focus has shifted from marine environments towards rivers, challenges remain in standardizing methods for monitoring and integrating spatiotemporal variabilities of riverine plastic occurrence into flux determination. This study addresses these challenges by adopting established methods from sediment research. Utilizing data from a net-based cross-sectional multi-point approach, it examines spatio-temporal and discharge-dependent variations. It comprehensively analyzes the complex dynamics of plastic transport in the Danube River, contrasting an impounded section near Aschach, Austria, with a free-flowing reach near Hainburg, Austria. The paper emphasizes the significance of applying these methodologies for accurate flux determination and underscores the risks of neglecting them. By incorporating average microplastic particle weights, we aim to overcome limitations in prior methodologies that solely emphasize qualitative aspects or rely on item numbers. Spatial distribution analysis revealed a pronounced stratification at low flow and a more variable distribution in the free-flowing section, attributed to higher turbulence. As discharge increased, vertical mixing occurred, along with distinct lateral patterns displaying increased concentrations toward the riverbanks. Encountering plastic particles throughout the river profile underscores their properties of both suspended and floating matter, emphasizing the importance of hydro-morphology and multi-point cross-sectional measurement approaches. Microplastic loads were calculated to be <6.9 t a-1 in Aschach and <17.1 t a-1 in Hainburg, compared to total plastic loads of <14.3 t a-1 in Aschach and <41.6 t a-1 in Hainburg. Consequently, plastic loads were doubled to tripled within the Austrian section of the Danube River. The study contributes valuable insights into the complex nature of plastic transport in river systems, emphasizing comprehensive spatial, temporal and discharge-dependent assessments for characterizing and managing plastic pollution. It suggests that rivers can function as sources, pathways and sinks of plastic pollution, contingent upon hydro-morphological conditions. This underscores the need for longitudinal, basin-wide assessments to accurately understand plastic transport dynamics. [ABSTRACT FROM AUTHOR]

The article "WESTERN BOUNDARY CURRENT-SUBTROPICAL CONTINENTAL SHELF INTERACTIONS" discusses the interactions between western boundary currents and subtropical continental shelves, focusing on the transport of heat, nutrients, and biota. The workshop held in Savannah, Georgia in May 2023 brought together researchers to discuss observational strategies, modeling systems, cross-shelf exchange, ecosystem properties, and future climate-related impacts. The article emphasizes the need for interdisciplinary collaboration, improved observational strategies, and accurate modeling to understand and predict the consequences of environmental change in WBC-STCS systems. [Extracted from the article]

This study utilizes Deep Neural Networks (DNN) to improve the K‐Profile Parameterization (KPP) for the vertical mixing effects in the ocean's surface boundary layer turbulence. The deep neural networks were trained using 11‐year turbulence‐resolving solutions, obtained by running a large eddy simulation model for Ocean Station Papa, to predict the turbulence velocity scale coefficient and unresolved shear coefficient in the KPP. The DNN‐augmented KPP schemes (KPP_DNN) have been implemented in the General Ocean Turbulence Model (GOTM). The KPP_DNN is stable for long‐term integration and more efficient than existing variants of KPP schemes with wave effects. Three different KPP_DNN schemes, each differing in their input and output variables, have been developed and trained. The performance of models utilizing the KPP_DNN schemes is compared to those employing traditional deterministic first‐order and second‐moment closure turbulent mixing parameterizations. Solution comparisons indicate that the simulated mixed layer becomes cooler and deeper when wave effects are included in parameterizations, aligning closer with observations. In the KPP framework, the velocity scale of unresolved shear, which is used to calculate ocean surface boundary layer depth, has a greater impact on the simulated mixed layer than the magnitude of diffusivity does. In the KPP_DNN, unresolved shear depends not only on wave forcing, but also on the mixed layer depth and buoyancy forcing. Plain Language Summary: The uppermost tens of meters of the ocean, known as the ocean surface boundary layer, are rich in intricate and chaotic fine‐scale (cm to 100s m) ocean currents referred to as turbulence. These currents, spanning from centimeters to hundreds of meters, play pivotal roles in shaping the oceanic environment and influencing Earth's climate dynamics. Despite their significance, simulating these fine‐scale ocean currents remains beyond the capabilities of current and foreseeable supercomputing resources. Consequently, simplified formulas derived from fundamental principles are commonly employed to approximate these currents in ocean and climate models. However, these approximations still cannot cover all types of choppy currents and uncertainties in these approximations represent a substantial source of bias in contemporary ocean and climate modeling endeavors. In this study, we enhance one of the prevalent physics‐based approximations of fine‐scale turbulent currents using machine learning techniques. Our tests show that integrating machine learning in physics‐based approximation is stable and efficient and is suitable for use in ocean and climate models. Key Points: New versions of K‐Profile Parameterization (KPP), augmented by deep neural networks (DNNs) (KPP_DNN), were developedThe KPP_DNN schemes were trained using Large Eddy Simulations and implemented in the General Ocean Turbulence ModelThe KPP_DNN schemes are stable for long‐term integration and as efficient as the physics‐based KPP schemes [ABSTRACT FROM AUTHOR]

The Turkana low-level jet stream (TJ) is important to climatic conditions over northern Kenya and East Africa. The representation of the TJ in climate models varies due to the TJ interaction with Turkana channel that is influenced by model resolution and influences the model representation of the regional climate. This study compares features of the TJ in CMIP6 AMIP model simulations with ERA5. Models reveal climatological wind speeds that match those of the reanalysis from the ERA5 at the jet entrance (13 m/s) but lower magnitudes of wind speed and vertical shears compared to ERA5 within the Turkana channel. The models with slowest wind speeds, have a flattened Turkana channel and fail to exhibit the terrain constriction at 37° E which otherwise aids in accelerating winds to form a jet core. Furthermore, they fail to represent the narrowing of the channel as in ERA5, thereby forming blocking walls in the channel, forcing vertical ascent and mixing, and weakening shear. This boosting of ascent motion promotes rainfall formation and enhances wet anomalies at the exit of the TJ when the jet stream is weaker. By applying a new narrowing index, we demonstrate the need to improve topography details in the CMIP6 models, particularly those with resolution coarser than 1.5°, in order to properly simulate the TJ and the observed rainfall over the northwestern areas of eastern Africa. [ABSTRACT FROM AUTHOR]

Methane (CH4) is a powerful greenhouse gas that is produced by a diverse set of natural and anthropogenic emission sources. Biogenic methane sources generally involve anaerobic decay processes such as those occurring in wetlands, melting permafrost, or the digestion of organic matter in the guts of ruminant animals. Thermogenic CH4 sources originate from the breakdown of organic material at high temperatures and pressure within the Earth's crust, a process which also produces more complex trace hydrocarbons such as ethane (C2H6). Here, we present the development and deployment of an uncrewed aerial system (UAS) that employs a fast (1 Hz) and sensitive (1–0.5 ppbs-1) CH4 and C2H6 sensor and ultrasonic anemometer. The UAS platform is a vertical-takeoff, hexarotor drone (DJI Matrice 600 Pro, M600P) capable of vertical profiling to 120 m altitude and plume sampling across scales up to 1 km. Simultaneous measurements of CH4 and C2H6 concentrations, vector winds, and positional data allow for source classification (biogenic versus thermogenic), differentiation, and emission rates without the need for modeling or a priori assumptions about winds, vertical mixing, or other environmental conditions. The system has been used for direct quantification of methane point sources, such as orphan wells, and distributed emitters, such as landfills and wastewater treatment facilities. With detectable source rates as low as 0.04 and up to ∼ 1500 kgh-1 , this UAS offers a direct and repeatable method of horizontal and vertical profiling of emission plumes at scales that are complementary to regional aerial surveys and localized ground-based monitoring. [ABSTRACT FROM AUTHOR]

Wave-induced mixing can enhance vertical mixing in the upper ocean, facilitating the exchange of heat and momentum between the surface and deeper layers, thereby influencing ocean circulation and climate patterns. Building on previous research, this study proposes a wave-induced mixing parameterization scheme (referred to as EXP3) specifically designed for typhoon periods. This scheme was integrated into the fully coupled ocean–wave–atmosphere model COAWST and applied to analyze Typhoon In-Fa (2021) as a case study. The simulation results were validated against publicly available data, demonstrating a good overall match with observed phenomena. Subsequently, a comparative analysis was conducted between the EXP3 scheme, the previous scheme (EXP2) and the original model scheme (EXP1). Validation against Argo and Drifter buoy data revealed that both EXP2 and EXP3, which include wave-induced mixing effects, resulted in a decrease in the simulated mixed layer depth (MLD) and mixed layer temperature (MLT), with EXP3 showing closer alignment with the observed data. Compared to the other two experiments, EXP3 enhanced vertical motion in the ocean due to intensified wave-induced mixing, leading to increased upper-layer water divergence and upwelling, a decrease in sea surface temperature and accelerated rightward deflection of surface currents. This phenomenon not only altered the temperature structure of the ocean surface layer but also significantly impacted the regional ocean dynamics. [ABSTRACT FROM AUTHOR]

In this study, we simulated the tropical cyclone (TC) Wutip, which originated in the South China Sea in 2013, using three planetary boundary layer (PBL) parameterized schemes within the Weather Research and Forecasting model, i.e., Medium-Range Forecast (MRF), Yonsei University scheme (YSU), and Asymmetric Convective Model Version 2 (ACM2), with different vertical mixing mechanisms. We investigated the effects of different PBL mixing mechanisms on the simulation of TC track, intensity, structure, and precipitation. The results reveal that the surface flux and vertical mixing of PBL jointly influenced the TC throughout its lifecycle, and the simulated TC intensity was closely correlated with the eyewall structure. These three schemes were all first-order and nonlocal closure schemes. However, the MRF scheme was over-mixed, which led to a relatively dryer and warmer near-surface layer, a wetter and colder upper PBL, and thus a simulated eyewall with the smallest wet static energy and weaker convection. Moreover, the MRF scheme produced the smallest 10-m wind speed, which was closest to the observation, and the weakest TC warm-core structure and intensity. The YSU scheme was similar to the MRF scheme, yet it distinguished itself by incorporating an explicit treatment of the entrainment process at the top of the PBL and developing thermal-free convection above the PBL of the eyewall, which significantly increased the wet static energy over the TC eyewall. Thus, the simulated eyewall was more contracted and steeper with stronger upward motion while the eye area became even warmer, finally leading to the strongest TC. The precipitation distribution simulated by the YSU scheme was the most consistent with the observation. The ACM2 scheme used the nonlocal upward and local downward mixed asymmetric convection modes, which reduced the excessive development of thermal-free convection at the eyewall, and avoided restricting the dynamically forced turbulent motion outside the eyewall, leading to a larger radius of the maximum wind speed, and thus more reasonable structural characteristics of PBL and TC intensity. In summary, compared with the YSU scheme and the MRF scheme, the ACM2 scheme demonstrated superior performance in capturing the structure, track, and intensity of Typhoon Wutip. It is important to note that this analysis was based on a specific case study, which might have inherent limitations due to its modest focus. [ABSTRACT FROM AUTHOR]

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During the Last Glacial Maximum (LGM), tidal dissipation was about 3-fold higher than today, which could have led to a considerable increase in vertical mixing. This increase might have enhanced the glacial Atlantic Meridional Overturning Circulation (AMOC), contradicting the shoaled AMOC indicated by paleoproxies. Here, we conduct ocean model simulations to investigate the impact of background climate conditions and tidal mixing on the AMOC during the LGM. We successfully reproduce the stratified ocean characteristics of the LGM by accurately simulating the elevated salinity of the deep sea and the rapid temperature decrease in the ocean's upper layers. Our findings indicate that the shoaled glacial AMOC is mainly due to strong glacial-ocean stratification, regardless of enhanced tidal dissipation. However, glacial tidal dissipation plays a critical role in the intensification of Antarctic Bottom Water (AABW) during the LGM. Given the critical role of the AMOC in (de-)glacial climate evolution, our results highlight the complex interactions of ocean stratification and tidal dissipation that have been neglected so far. [ABSTRACT FROM AUTHOR]

Climate change and anthropogenic impacts drastically affect the biogeochemical regime of the Black Sea, which contains the largest volume of sulphidic water in the world. The Sea's oxygen inventory depends on vertical mixing that transports dissolved oxygen (DO) from the upper euphotic layer to deeper layers and on dissolved oxygen consumption for the oxidation of organic matter (OM) and reduced species of S, Fe, and Mn. Here we use a vertical one-dimensional transport model, 2DBP, forced by Copernicus data, that was coupled with the FABM-family N-P-Si-C-O-S-Mn-Fe Bottom RedOx Model BROM. The research objective of this study was to analyze the oxygen budget in the upper 350 m of the Sea and demonstrate the role of the parameterization of the acceleration of the sinking of particles covered by precipitated Mn(IV). The analysis of the oxygen budget revealed distinct patterns in oxygen consumption within different depths. In the oxic zone, the primary sink for DO is the mineralization of organic matter, whereas in the suboxic zone, dissolved Mn(II) oxidation becomes the predominant sink. The produced Mn(IV) sinks down and reacts with hydrogen sulphide several meters below, making possible the existence of the suboxic layer without detectable concentrations of DO and H2S. [ABSTRACT FROM AUTHOR]

Tropical cyclones (TCs) are known to trigger chlorophyll bloom and boost local primary productivity. The characteristics of ocean ecological responses to TCs and their feedback on physical fields in the northeastern Pacific are investigated using a coupled ocean general circulation model‐ocean ecosystem model. A case study is carried out on Hurricane Fernanda (2017), which formed in the northeastern tropical Pacific. TC‐induced mixing and upwelling act to transport subsurface cold and nutrient‐rich waters into the mixed layer, leading to surface cooling and chlorophyll (CHL) bloom. The phytoplankton budget analyses indicate that the CHL bloom is dominated by small phytoplankton (PS) growth term, which is modulated by biological consumption terms (i.e., small zooplankton grazing and PS mortality) and physical processes‐related terms (i.e., advection and vertical mixing); biological consumption terms and physical processes tend to mainly offset the contributions from the PS growth term. Furthermore, CHL is found to exert feedback on physical fields. The CHL bloom mainly contributes to a decrease in surface temperature, thereby enhancing the temperature structure induced physically by TCs. This biofeedback on physical fields involves two mechanisms: a direct heating (OBH) due to ocean biology‐induced effect, and an indirect cooling effect due to dynamic processes associated with vertical mixing and advection. In particular, the CHL bloom‐induced sea surface temperature cooling is dominated by vertical mixing and modulated by the OBH effect and advection. These findings offer novel perspectives on TC‐induced ecological responses, as well as the related mechanisms for biofeedback on physical fields. Plain Language Summary: Tropical cyclones (TCs) are powerful and potentially destructive weather systems. They are characterized by strong winds, heavy precipitation, and active heat exchange at the air‐sea interface. The combined effects due to these atmospheric forcings can induce strong physical and ecological responses in the upper ocean, whose complicated interplays are still not well understood. A case study is carried out on Hurricane Fernanda (2017), which formed in the northeastern tropical Pacific. When the Fernanda passed by, distinct surface cooling and chlorophyll (CHL) bloom emerged, which are attributed to TC‐induced physical and ecological processes and their interactions. For example, TC‐induced increasing nutrient supply in the euphotic layer is conducive to small phytoplankton growth (i.e., the CHL bloom). Furthermore, CHL is found to exert feedback on physical fields. For example, the CHL bloom induces heat redistribution, vertical mixing, and currents, mainly contributing to surface cooling and thereby enhancing the temperature structure induced by TCs. These findings offer novel perspectives on TC‐induced physical and ecological responses, as well as related biofeedback on the physical fields. Key Points: Tropical cyclone (TC) triggers chlorophyll (CHL) bloom, which is attributed to the increased nutrient supply in the euphotic layerThe CHL bloom is dominated by small phytoplankton growth term, which is modulated by physical and biological consumption termsThe CHL‐related effects cause differences in physics (heat redistribution, mixing, and currents), mainly contributing to surface cooling [ABSTRACT FROM AUTHOR]

Greenland's marine‐terminating glaciers connect the ice sheet to the ocean and provide a critical boundary where heat, freshwater, and nutrient exchanges take place. Buoyant freshwater runoff from inland ice sheet melt is discharged at the base of marine‐terminating glaciers, forming vigorous upwelling plumes. It is understood that subglacial plumes modify waters near glacier fronts and increase submarine glacier melt by entraining warm ambient waters at depth. However, ocean observations along Greenland's coastal margins remain biased toward summer months which limits accurate estimation of ocean forcing on glacier retreat and acceleration. Here, we fill a key observational gap in northwest Greenland by describing seasonal hydrographic variation at glacier fronts in Melville Bay using in situ observations from moorings deployed year‐round, CTDs, and profiling floats. We evaluated local and remote forcing using remote sensing and reanalysis data products alongside a high‐resolution ocean model. Analysis of the year‐round hydrographic data revealed consistent above‐sill seasonality in temperature and salinity. The warmest, saltiest waters occurred in spring (April–May) and primed glaciers for enhanced submarine melt in summer when meltwater plumes entrain deep waters. Waters were coldest and freshest in early winter (November–December) after summer melt from sea ice, glacier ice, and icebergs provided cold freshwater along the shelf. Ocean variability was greatest in the summer and fall, coincident with increased freshwater runoff and large wind events before winter sea ice formation. Results increase our mechanistic understanding of Greenland ice‐ocean interactions and enable improvements in ocean model parameterization. Plain Language Summary: Many of Greenland's glaciers terminate in the ocean and form an important boundary between coastal waters and the ice sheet. During summer months, meltwater from the ice sheet flows out below glaciers that terminate in the ocean. The less‐dense meltwater rises to the surface as a plume, increasing near‐glacier ocean mixing and submarine glacier melt. Understanding processes at the glacier‐ocean interface, including how plumes modify nearshore waters, requires sustained observations near glacier termini. However, ocean measurements are largely taken during the summer and do not necessarily represent the total variability observed in the system. Here, we fill an important knowledge gap by presenting year‐round measurements of temperature and salinity near glacier fronts in Northwest Greenland. We found the warmest, saltiest waters in the spring and coldest, freshest waters in early winter at all sites. Warm waters in the spring prime deep glaciers for submarine melt during summer. Increased winds in the fall initiated vertical mixing in nearshore waters before winter sea ice created a surface barrier, stabilizing the water column. Results advance our understanding of the ocean's role in the acceleration and retreat of Greenland's glaciers, which is important for estimating large‐scale ocean circulation and Greenland's ice sheet mass loss. Key Points: Moored hydrographic observations at glacier fronts in NW Greenland revealed consistent above‐sill seasonality in temperature and salinityOcean temperatures reached a maximum in spring, priming deep glaciers for submarine melt during summerRemote forcing supplied the renewal of warm, salty water in the spring and local forcing controlled increased variability in the summer/fall [ABSTRACT FROM AUTHOR]

Typhoons, fueled by warm sea surface waters, heighten concern as they increasingly interact with frequent Marine Heatwaves (MHWs) in a changing climate. Typhoon Hinnamnor (2022) weakened and re‐intensified as it approached the Korean Strait, interacting with an underlying MHW in the northern East China Sea (nECS). In‐situ observations and reanalysis products revealed a significant increase in latent heat loss from the nECS during the MHW period, contributing to the typhoon re‐intensification. Strong sea surface wind forcing with the typhoon enhanced vertical mixing and upwelling, resulting in a pronounced (0.90°C) sea surface cooling after the typhoon passage, facilitating MHW disappearance with reduced thermal stratification. During MHWs, increased background stratification increases temperature oscillations associated with semidiurnal internal tides. Furthermore, post‐typhoon changes in stratification weakened semidiurnal internal tides due to unfavorable conditions for generation from a nearby source. These findings highlight the importance of continuous time‐series observations to monitor interactions among climatic extremes. Plain Language Summary: Typhoons, powered by warm ocean waters, are causing more concern as they increasingly interact with frequent episodes of extremely warm sea conditions known as Marine Heatwaves (MHWs) in a changing climate. This study focuses on Typhoon Hinnamnor in 2022, which went through a weakening and then strengthened as it moved to the Korean Strait and encountered an MHW in the northern East China Sea (nECS). By using in‐situ data collected in the nECS and additional data analysis, we discovered a significant increase in heat loss from the nECS during the MHW, contributing to the intensification of typhoon. The powerful winds from the typhoon caused enhanced mixing and cooling of the sea surface after it passed, helping to cause the disappearance of the MHW and reduce the layering of temperatures in the ocean. During MHW, strong layering strengthens the temperature oscillation linked with the semidiurnal internal tides in the ocean. After typhoon passage there is a decrease in the layering in the ocean, thus weakening the internal tide. The study emphasizes the importance of continuous observations to understand and monitor these interactions in our changing climate. Key Points: Typhoon Hinnamnor (2022) re‐intensified after interacting with the underlying Marine Heatwave (MHW) in the East China SeaTyphoon wind‐driven mixing caused the disappearance of the underlying MHWStratification change accompanied by MHW, and typhoon reduced the local activities of semidiurnal internal tides [ABSTRACT FROM AUTHOR]

Marine‐terminating glacier fjords play a central role in the transport of oceanic heat toward ice sheets, regulating their melt. Mixing processes near glacial termini are key to this circulation but remain poorly understood. We present new summer measurements of circulation and mixing near a marine‐terminating glacier with active sub‐glacial discharge. 65% of the fjord's vertical overturning circulation is driven by the buoyant plume, however we newly report intense vertical and horizontal mixing in the plume's horizontal spreading phase, accounting for the remaining 35%. Buoyant plume theory supports 2%–5% of total glacial melt. Thus, most of the heat associated with vertical overturing short‐circuits the glacial front. We find however that turbulence in the horizontal spreading phase redistributes the short‐circuited heat back into the surface waters of the near‐glacial zone. Our findings highlight the need for further research on the complex mixing processes that occur near the glacier terminus. Plain Language Summary: Melting of glacial ice is the single largest contributor to global sea‐level rise. Many glaciers flow into the ocean where the near‐vertical ice wall is bathed in relatively warm sea water. Freshwater from ice surface melting seeps down through cracks and crevasses in the glacier to be discharged at the base of the ice wall, many tens to hundreds of meters below the sea surface. This fresh water rises from the depths as a highly turbulent plume, drawing in and pushing upwards the surrounding seawater, eventually spreading horizontally as a mixture of fresh discharge and mixed‐in seawater. Few measurements exist in the dangerous zone where iceberg often calve. Using data from a robotic platform we show that the vertical rise and the horizontal spreading of fresh water both play important roles in the total ocean‐induced melting of the glacial face in this type of system. Key Points: Entrainment into the buoyant plume drives ∼65% of fjord vertical overturning circulationIntense turbulent mixing in the horizontal spreading phase of the plume drives the remaining ∼35%95%–98% of the heat in the rising plume short‐circuits the glacier, to be redistributed into glacial proximal waters by horizontal mixing [ABSTRACT FROM AUTHOR]

Ponds are characterized by high biodiversity, intense biogeochemical cycling, and susceptibility to anthropogenic impacts. Yet few studies have quantified the water velocities responsible for vertical mixing or lateral transport in ponds. We used high‐resolution observations of velocity to examine mixing and transport during summer in a 50‐m‐long, 2.7‐m‐deep temperate pond. Many observed transport and mixing processes resembled those found in larger stratified lakes. A surface mixed layer was observed, whose depth ranged between ~ 1 m at night and < 0.3 m during the day. Turbulence was usually sufficient to vertically mix the surface layer in 4–12 min, but no turbulence was observed in the hypolimnion. Persistent (2.5‐h‐averaged) currents usually flowed downwind near the surface and returned upwind near the mixed layer base. Surface currents were proportional to windspeed, with root‐mean‐squared speed of 8×10−3ms−1$$ 8\times {10}^{-3}\ \mathrm{m}\;{\mathrm{s}}^{-1} $$ (persistent hypolimnion currents were much weaker). Superposed on persistent currents were 30‐ to 100‐min‐period fluctuations resulting from internal seiches. These fluctuations were comparable in magnitude to more persistent currents in the mixed layer and dominated in the hypolimnion. Seiches did not advect particles far across the pond, but did contribute to production of mixed layer turbulence. Seiches also contributed to shear dispersion, which was sufficient to mix near‐surface tracers across the pond in 2–4 d. Theory suggests that hypolimnion bottom boundary layers were laminar during the downslope phase of seiche motion, but became turbulent during the upslope phase as near‐bed water flows created unstable stratification. [ABSTRACT FROM AUTHOR]

We present an atmospheric retrieval analysis of the Y0 brown dwarf WISE J035934.06−540154.6 using the low-resolution 0.96–12 μ m James Webb Space Telescope (JWST) spectrum presented in Beiler et al. We obtain volume number mixing ratios of the major gas-phase absorbers (H2O, CH4, CO, CO2, PH3, and H2S) that are three to five times more precise than previous work that used Hubble Space Telescope (HST) spectra. We also find an order-of-magnitude improvement in the precision of the retrieved thermal profile, a direct result of the broad wavelength coverage of the JWST data. We used the retrieved thermal profile and surface gravity to generate a grid of chemical forward models with varying metallicity, (C/O)atm, and strengths of vertical mixing as encapsulated by the eddy diffusion coefficient K zz. Comparison of the retrieved abundances with this grid of models suggests that the deep atmosphere of WISE 0359−54 shows signs of vigorous vertical mixing with K zz = 109 [cm2 s−1]. To test the sensitivity of these results to our five-knot spline thermal profile model, we performed a second retrieval using the Madhusudhan & Seager thermal profile model. While the results of the two retrievals generally agree well, we do find differences between the retrieved values of mass and volume number mixing ratio of H2S with fractional differences of the median values of −0.64 and −0.10, respectively. In addition, the five-knot thermal profile is consistently warmer at pressure between 1 and 70 bar. Nevertheless, our results underscore the power that the broad-wavelength infrared spectra obtainable with the JWST have to characterize the atmospheres of cool brown dwarfs. [ABSTRACT FROM AUTHOR]

The model representation of dry intrusions (DIs) and the marine boundary layer (MBL) is analyzed in the European Centre for Medium‐Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS). For this purpose, a DI classification at the Azores is combined with observation, short‐term background forecast and analysis data from the IFS data assimilation system. The background exhibits a cold bias in the descending DI, which is possibly related to a cold bias in the MBL below through vertical mixing. At the surface, simulated wind speeds are underestimated and directions are veered compared to the observations. The errors are reduced in the analysis except for near‐surface wind and humidity biases. We hypothesize that these biases are connected through underestimated surface latent heat fluxes. Such persistent biases potentially influence local weather and midlatitude weather evolution as cyclones are supplied with moisture from the cold sector influenced by DIs. Plain Language Summary: The representation of descending dry intrusion airstreams and the marine boundary layer at the Azores is investigated in a global numerical weather prediction model. Specifically, radiosonde observations are compared with short‐term forecast and analysis data to identify biases. The diagnosed underestimated temperature, specific humidity, and wind speed in the lower troposphere are important as they can influence the evolution of mid‐latitude weather. Key Points: Forecast and analysis errors within dry intrusions (DIs) above the Azores are studied using data assimilation (DA) outputDIs and the boundary layer beneath exhibit a cold bias and near‐surface wind and humidity underestimationLow‐level wind speed and humidity biases are not reduced through DA with possible implications for midlatitude weather [ABSTRACT FROM AUTHOR]

Arctic sea ice mediates atmosphere-ocean momentum transfer, which drives upper ocean circulation. How Arctic Ocean surface stress and velocity respond to sea ice decline and changing winds under global warming is unclear. Here we show that state-of-the-art climate models consistently predict an increase in future (2015–2100) ocean surface stress in response to increased surface wind speed, declining sea ice area, and a weaker ice pack. While wind speeds increase most during fall (+2.2% per decade), surface stress rises most in winter (+5.1% per decade) being amplified by reduced internal ice stress. This is because, as sea ice concentration decreases in a warming climate, less energy is dissipated by the weaker ice pack, resulting in more momentum transfer to the ocean. The increased momentum transfer accelerates Arctic Ocean surface velocity (+31–47% by 2100), leading to elevated ocean kinetic energy and enhanced vertical mixing. The enhanced surface stress also increases the Beaufort Gyre Ekman convergence and freshwater content, impacting Arctic marine ecosystems and the downstream ocean circulation. The impacts of projected changes are profound, but different and simplified model formulations of atmosphere-ice-ocean momentum transfer introduce considerable uncertainty, highlighting the need for improved coupling in climate models. The authors use climate models and show that projected declining and weakening Arctic sea ice, combined with stronger winds, will enhance ocean surface stress. This increased momentum transfer will spin up surface currents, leading to a more energetic Arctic Ocean in the future. [ABSTRACT FROM AUTHOR]

Ocean stratification on Arctic shelves critically influences nutrient availability, essential for primary production. However, discerning the changes in stratification and their drivers is challenging. Through the use of a highresolution ocean-sea-ice model, this study investigates the variability in stratification within the northeastern Chukchi Sea over the period from 1987 to 2016. Our analysis, validated against available observations, reveals that summers with weak stratification are marked by a warmer water column that features a saltier upper layer and a fresher lower layer, thereby diminishing the vertical density gradient. In contrast, summers with strong stratification are characterized by a cooler column with a fresher upper layer and a saltier lower layer, resulting in an increased density gradient. This variability is primarily driven by the timing of sea-ice retreat and the consequent variations in meltwater flux, with early retreat leading to less meltwater and saltier surface conditions. This factor significantly outweighs the influence of changes in circulation and associated lateral freshwater transport driven by the Bering Strait inflow. We also find that the synchronization of sea-ice retreat and Bering Strait inflow intensity is linked to the timing and strength of the Aleutian Low's westward shift from the Gulf of Alaska to the Aleutian Basin in the early winter. These insights are crucial for understanding nutrient dynamics and primary production in the region. Furthermore, monitoring sea-ice retreat timing could serve as a useful proxy for predicting subsequent summer stratification changes. [ABSTRACT FROM AUTHOR]

A total solar eclipse provides an unparalleled opportunity to study the changes in the atmosphere's planetary boundary layer (PBL) due to changes in radiative heating. Although previous eclipse studies have demonstrated that significant changes occur, few studies have explored the evolution of these changes. To better understand the changes in the lowest layers of the PBL during an eclipse, a multi-sensor sampling approach was taken. Radiosonde launches were used to explore the depth of the column, while Unmanned Aerial Vehicles (UAVs) were used to document with high-resolution the brief changes in the vertical structure of the PBL caused by the eclipse. These changes highlighted differences from previous studies that relied solely on radiosonde and/or mesonet data alone. Higher-resolution sampling of the lower PBL showed a delay in the local vertical mixing as well as changes in the PBL height from pre- to post-eclipse. Slow responses were noted at the top of the PBL while very rapid changes to the PBL profile were captured in the near-surface layer. These changes highlighted differences from previous studies that relied solely on radiosonde and/or mesonet data alone. A preliminary analysis of the collected data highlighted a slow response to the eclipse near the top of the planetary boundary layer (radiosonde data) with very rapid changes noted in the near surface layer (UAV data). Preliminary results show that PBL heights remained nearly constant until well after third contact when a 35 hPa lowering of the PBL heights was observed and were limited to the lowest 25 hPa. The UAV soundings demonstrated the development of a strong inversion where the air below 990 hPa rapidly cooled with a nearly 1 °C drop in temperature observed. These observed changes raise interesting questions about how the lower and upper parts of the planetary boundary layer interact. [ABSTRACT FROM AUTHOR]

Information about estuarine mixing and its control of sediment transport is crucial to elucidating the dynamics and evolution of estuaries. Here, the microtidal and funnel-shaped Zhenhai Estuary, located in the southwestern Pearl River Delta of China, is used to investigate the characteristics and mechanisms of water mixing and sediment transport based on observations from three spring tides. The results reveal that the studied estuary remains well mixed during spring tides from 2013–2022 despite its microtidal regime. Tidal stirring, which is enhanced by tidal energy convergence and benefits from the funnel-shaped geometry and shallow bathymetry, favors vertical mixing, contributing to the formation of strong mixing in the estuary. Due to the well-mixed regime, sediment transport in the estuary is dominated by the advective term, followed by a moderate tidal pumping term and minor estuarine circulation term. Accordingly, sediments within the estuary tend to be transported landward owing to the regulation of the funnel-shaped geometry, and a gradual but slow infilling trend is predictable. This paper deepens our understanding of hydrodynamics and sediment transport in microtidal estuaries. [ABSTRACT FROM AUTHOR]

This paper presents a discussion on observations of nonlinear internal waves (NLIWs) in the coastal zone of the Sea of Japan, based on the mooring of thermostring clusters in different seasons of 2022. For statistical evaluation of the frequency of event occurrence and determination of NLIW movement direction, we use our observations of the past 12 years. We present the NLIW structures, observed in spring, summer, and autumn of 2022, which are typical for this shelf area. Two types of nonlinear waves are described—solitary and undular bores, with or without strong vertical mixing behind the front. We demonstrate spatial transformation of an undular bore as it moves over the shelf. A mathematical model based on the second-order shallow water approximation is proposed for numerical simulation. To simplify calculations, the authors limit themselves to two- and three-layer shallow water models. We investigate the possibility of spatiotemporal reconstruction of internal nonlinear structures between thermostrings using experimental data and proposed models. The authors show that at distances of up to several kilometers between thermostrings, the wave fields of strongly nonlinear and nonstationary structures can be successfully reconstructed. Water flow induced by NLIWs can be reconstructed from the data of even one thermostring. [ABSTRACT FROM AUTHOR]

This study investigates the rain-initiated mixing and variability in the mixing ratio of selected trace gases in the atmosphere over the central Amazon rain forest. It builds on comprehensive data from the Amazon Tall Tower Observatory (ATTO), spanning from 2013 to 2020 and comprising the greenhouse gases (GHGs) carbon dioxide (CO2) and methane (CH4); the reactive trace gases carbon monoxide (CO), ozone (O3), nitric oxide (NO), and nitrogen dioxide (NO2); and selected volatile organic compounds (VOCs). Based on more than 1000 analyzed rainfall events, the study resolves the trace gas mixing ratio patterns before, during, and after the rain events, along with vertical mixing ratio gradients across the forest canopy. The assessment of the rainfall events was conducted independently for daytime and nighttime periods, which allows us to elucidate the influence of solar radiation. The mixing ratios of CO2 , CO , and CH4 clearly declined during rainfall, which can be attributed to the downdraft-related entrainment of pristine air from higher altitudes into the boundary layer, a reduction of the photosynthetic activity under increased cloud cover, and changes in the surface fluxes. Notably, CO showed a faster reduction than CO2 , and the vertical gradient of CO2 and CO is steeper than for CH4. Conversely, the O3 mixing ratio increased across all measurement heights in the course of the rain-related downdrafts. Following the O3 enhancement by up to a factor of 2, NO , NO2 , and isoprene mixing ratios decreased. The temporal and vertical variability of the trace gases is intricately linked to the diverse sink and source processes, surface fluxes, and free-troposphere transport. Within the canopy, several interactions unfold among soil, atmosphere, and plants, shaping the overall dynamics. Also, the mixing ratio of biogenic VOCs (BVOCs) clearly varied with rainfall, driven by factors such as light, temperature, physical transport, and soil processes. Our results disentangle the patterns in the trace gas mixing ratio in the course of sudden and vigorous atmospheric mixing during rainfall events. By selectively uncovering processes that are not clearly detectable under undisturbed conditions, our results contribute to a better understanding of the trace gas life cycle and its interplay with meteorology, cloud dynamics, and rainfall in the Amazon. [ABSTRACT FROM AUTHOR]

The estuarine exchange flow increases the longitudinal dispersion of passive tracers and trap sinking particles, potentially creating an estuarine turbidity maximum (ETM): a localized maximum of suspended particulate matter concentration in an estuary. The ETM can have many implications: dead zones due to increased turbidity or hypoxia from organic matter decomposition, naval navigation challenges, and other water quality problems. Using timescales, we investigate how the interaction between exchange flow and particle sinking leads to ETMs by modeling a sinking tracer in an idealized box model of the Total Exchange Flow (TEF) first developed by Parker MacCready. Results indicate that the balance of particle sinking and vertical mixing is critical to determining ETM size and location. We then focus on the role of ecology in ETM formation through the use of the Peter–Parker Model, a new biophysical model which combines the TEF box model with a Nutrient–Phytoplankton–Zooplankton–Detritus (NPZD) model, the likes of which were first developed by Peter J.S. Franks. Detritus sinking rates similarly influence detritus peak concentration and location (an ETM), but detritus ETMs occur in a different location than the sinking tracer due to the influence of biological factors, which create a time lag of about 1 day. Lastly, we characterize the flow of the models with a dimensionless parameter that compares timescales and summarizes the dynamics of the sinking tracer in ETM formation and that can be used across systems. [ABSTRACT FROM AUTHOR]

Upper layer thickness (mixing depth) is an essential parameter for estimating the dissolved inorganic carbon and carbon flux at the water surface based on their association with the vertical flux of dissolved inorganic carbon. Previous studies quantified the mixing depth without SAV meadow or penetration depth in the SAV meadow without stratification and wind stress. However, mixing depth related to interaction with submerged aquatic vegetations (SAVs), stratification, and wind stress has yet to be quantified in the previous studies. Our study is the first to quantify the theoretical mixing depth with SAVs according to wind stress, SAV height, and drag coefficient. Theoretical mixing depth was quantified from modeled vertical temperature profile, vertical profile of horizontal velocity, and gradient Richardson number (Rig,veg). We found that mixing depth at a Rig,veg of 100 demonstrated good agreement with numerical results on average, with the mixing depth estimated in this study (hU,this study) showing high applicability to observations at Komuke Lagoon. Moreover, hU,this study increased with the increasing wind stress and decreasing drag coefficient and SAV height. Further, we found that SAV meadows with stratification and wind stress could be divided into four hydrodynamic regimes: non‐vegetated layers, upper vegetated layers, thermoclines, and benthic boundary layers. Our findings help us estimate mixing depth or vertical flux without complicated numerical simulation and understand flow interaction with SAV, wind stress, and stratification. Plain Language Summary: Upper layer thickness (mixing depth) and flow fields are important to estimate the carbon flux (e.g., "blue carbon") and the transportation of dissolved materials (e.g., dissolved oxygen, dissolved inorganic carbon, dissolved inorganic nitrogen, etc) in submerged aquatic vegetation (SAV) meadows. However, it may not be easy to estimate mixing depth without complex numerical simulations. Additionally, we have not understood the interaction of SAV meadows with stratification, currents, or waves. Our study is the first to quantify the mixing depth analytically and to show the hydrodynamic regimes in SAV meadows with stratification. Our finding helps us to estimate carbon flux and the transportation rate of dissolved materials easily without complicated numerical simulation. Key Points: Mixing depth with submerged aquatic vegetation (SAV) meadows was estimated using an average gradient Richardson number 100SAV meadows with stratification and wind stress were divided into four hydrodynamic regimesWind stress, SAV, and stratification effects were used to accurately estimate the mixing depth [ABSTRACT FROM AUTHOR]

Utilizing an 11‐year (2011–2021) data set, we report surface‐ocean pCO2 in Baffin Bay during the open‐water season (June–October) to establish a baseline understanding of surface seawater carbon dynamics in this region. We found pCO2 was strongly undersaturated (70–130 μatm below saturation, depending on year), albeit with substantial regional variability. Though temperature was found to be a generally strong control of pCO2, sea‐ice dynamics and other non‐thermal drivers controlled pCO2 at certain times and in certain regions. The Baffin Island Current region (western Baffin Bay) experienced relatively high pCO2 during instances of high sea‐ice cover, usually in early spring. Average pCO2 was comparatively lower in the West Greenland Current region (eastern Baffin Bay) which is ice‐free substantially longer (by 3–4 months) and where temperature acted as the dominant control to pCO2. With respect to temporal variations, June had the lowest pCO2 of the open‐water season, coinciding with active sea‐ice melt. Surface‐ocean pCO2 then increased month‐to‐month through July and August due to warming and decreased meltwater dilution, increasing again into September before stabilizing into October. Generally, non‐thermal controls acted to decrease pCO2 during mid‐summer (possibly primary production, sea‐ice melt, and circulation), but acted to increase pCO2 during early fall (vertical mixing). Despite spatial and temporal variation over the open‐water season, persistent undersaturation suggests that Baffin Bay is a potentially strong CO2 sink, even in comparison to other uptake regions across the western Arctic. Plain Language Summary: When the surface‐ocean partial pressure of CO2 (pCO2) is less than the atmospheric pCO2, the ocean absorbs CO2 from the atmosphere. Surface‐ocean pCO2 varies greatly in space and time and has been poorly documented in difficult‐to‐access Arctic regions. By measuring surface‐ocean pCO2 over an eleven ‐year period, we have shown for the first time that the Baffin Bay region is consistently undersaturated in CO2 over the open‐water season (June–October). The variations in surface‐ocean pCO2 between regions across the bay are strongly related to the differences in sea ice and temperature, with lower pCO2 in eastern than in western Baffin Bay. As a whole, the surface of Baffin Bay is most undersaturated in June due to active sea‐ice melt. Surface‐ocean pCO2 increases over July and August, before stabilizing at slightly higher values in September and October, before freeze‐up. Based on these results, Baffin Bay appears to be a large atmospheric CO2 sink, even in comparison to other uptake regions of the western Arctic. Key Points: Baffin Bay surface waters are strongly undersaturated in pCO2 relative to atmospheric values during the open‐water seasonOverall, pCO2 in Baffin Bay was lowest in June, increasing from July to September, before stabilizing in OctoberTemperature and sea‐ice dynamics are important controls of pCO2 in Baffin Bay [ABSTRACT FROM AUTHOR]

The diurnal cycles of near‐surface velocity and temperature, also known as diurnal jet and diurnal warm layer (DWL), are ubiquitous in the tropical oceans, affecting the heat and momentum budget of the ocean surface layer, air‐sea interactions, and vertical mixing. Here, we analyze the presence and descent of near‐surface diurnal shear and stratification in the upper 20 m of the equatorial Atlantic as a function of wind speed using ocean current velocity and hydrographic data taken during two trans‐Atlantic cruises along the equator in October 2019 and May 2022, data from three types of surface drifters, and data from Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) moorings along the equator. The observations during two seasons with similar mean wind speeds but varying surface heat fluxes reveal similar diurnal jets with an amplitude of about 0.11 m s−1 and similar DWLs when averaging along the equator. We find that higher wind speeds lead to earlier diurnal peaks, deeper penetration depths, and faster descent rates of DWL and diurnal jet. While the diurnal amplitude of stratification is maximum for minimal wind speeds, the diurnal amplitude of shear is maximum at 6 m depth for moderate wind speeds of about 5 m s−1. The inferred wind dependence of the descent rates of DWL and diurnal jet is consistent with the earlier onset of deep‐cycle turbulence for higher wind speeds. The DWL and the diurnal jet not only trigger deep‐cycle turbulence but are also observed to modify the wind power input and thus the amount of energy available for mixing. Plain Language Summary: During daytime, solar radiation leads to the formation of a thin warm layer at the ocean surface which can trap heat and wind‐forced momentum. Both heat and momentum are transported in the deeper ocean during the evening and night by turbulent mixing. The associated diurnal variation of temperature, current velocity, and their vertical gradients, stratification and velocity shear, are thus relevant for understanding ocean‐atmosphere interactions. This study investigates how the diurnal variation in stratification and velocity shear is influenced by the wind speed. For that, basin‐scale observations of velocity and temperature, which were collected in the equatorial Atlantic during two trans‐Atlantic equatorial cruises and by instruments installed at long‐term moorings along the equator, are analyzed. These observations reveal that the wind speed influences the amplitude, the timing, and the vertical structure of the diurnal variation in stratification and velocity shear. Wind speed also influences how deep and how fast this variation propagates from the surface downward. The study concludes that the diurnal variation of stratification and velocity shear impacts first the input of mechanical energy from the atmosphere into the ocean and second the process of turbulent mixing below the night‐time mixed layer. Key Points: Basin‐scale in‐situ data show the evolution of diurnal warm layer and diurnal jet in the upper 15 m of the equatorial Atlantic OceanHigher wind speeds lead to earlier diurnal peaks, deeper penetration depths, and faster descent rates of the diurnal jetWind speed dependence of descent rates of diurnal shear and stratification can explain the varying onset of deep‐cycle turbulence [ABSTRACT FROM AUTHOR]

Four underwater glider missions were carried out to sample the physical and bio‐optical properties inside a Loop Current Eddy (LCE) in the Gulf of Mexico, to investigate whether the winter deepening of the mixed‐layer and erosion of the nitracline stimulates phytoplankton growth. Recent coupled physical‐biogeochemical numerical models support this mechanism, but observations using profiling floats suggest that there is no seasonal cycle on integrated phytoplankton biomass. Here, data collected by underwater gliders during a full seasonal cycle and inside the LCE Poseidon support the idea of an increase in phytoplankton biomass during winter, consistent with nutrient entrainment into the euphotic zone. The changes in fluorescence emission per chlorophyll‐a unit and their implications for interpreting bio‐optical variability were also assessed. Linear regressions between in vivo chlorophyll‐a fluorescence and satellite chlorophyll‐a concentration show the largest (smallest) slopes during winter (summer), suggesting a shift in the phytoplankton community along the year or photoacclimation. Although the glider data set is convolved by temporal and spatial variability, and chlorophyll‐a fluorescence is affected by multiple factors, the concomitant enhancement of particle backscattering coefficient and chlorophyll‐a observed during winter supports the occurrence of a seasonal cycle in phytoplankton biomass. Deep vertical mixing in winter inside the core of the LCE, can promote fertilization through vertical diffusion of nutrients. Poseidon was an extraordinary, large, and strong, LCE that prompted phytoplankton blooms in winter highlighting their relevance for primary production and in general for biogeochemical processes. Plain Language Summary: Recent technological advancements have revolutionized our ability to monitor changes in the marine primary producers. Specialized robots are nowadays capable of measuring bio‐optical properties, such as chlorophyll‐a fluorescence and the particle backscattering coefficient even during severe climate conditions. However, interpreting chlorophyll‐a fluorescence measurements can be challenging, as they are influenced by multiple factors, including phytoplankton community shifts, and nutritional status. Here, we used data acquired by remotely controlled platforms to track a large coherent rotating oceanic eddy as it propagated westward through the Gulf of Mexico. Near the center of the eddy, the upper 170 m of the water column were mixed thoroughly by strong winds during winter, redistributing particles from deeper layers toward the upper ones including nutrients required for phytoplankton growth. The data set revealed a correlation between the winter mixing and the increase in both, the chlorophyll‐a concentration and particle backscattering. Therefore, nutrient injection stimulated phytoplankton growth during winter. We also found that fluorescence per chlorophyll‐a concentration changes dramatically during the year, presumably because there is a shift in the composition of the phytoplankton community along the seasons. Observed high‐frequency phytoplankton response to winds in this data set needs to be analyzed and will be the basis for future work. Key Points: Optical data suggest changes in the phytoplankton taxonomic composition along a seasonal cycleThe seasonal cycle explains most of the variability of bio‐optical properties near the eddy coreThe entrainment of nutrients into the euphotic zone during winter supports the seasonal signal of phytoplankton biomass [ABSTRACT FROM AUTHOR]

The diurnal cycle of dust aerosols on Mars is studied by analyzing lidar observations at the Phoenix landing site under cloud‐ and fog‐free conditions and in the absence of elevated, long‐range transported dust layers. There is a pronounced diurnal cycle in the dust‐layer height with minimum heights of 4–6 km occurring between 11:00 and 17:00 local time. The ratio of the aerosol optical depth (AOD) within the lowermost 2 km to the total AOD reaches peak values at the same time. This can be explained by local dust emissions driven by the diurnal cycle of heating and cooling in the boundary layer. Analysis of wind and pressure measurements show that the gustiness of surface winds and the frequency of convective vortices undergo diurnal variations resembling those of AOD, indicating that these processes are the main drivers for local dust emissions. Plain Language Summary: Dust particles suspended in air are important for the radiative energy budget of Mars. By interacting with solar radiation, these aerosols impact the temperature, dynamics, and composition of the atmosphere, as well as the surface temperature of Mars. Dust aerosols are produced by wind‐lifting processes ranging from small‐scale eddies to planetary‐scale dust storms, resulting in spatially and temporally varying concentrations. Here the focus is on the diurnal cycle of dust emissions as observed by the Phoenix lander. By jointly analyzing light‐scattering observations by a lidar instrument and measurements of wind speed and air pressure, one can correlate the concentration of aerosols in air in proximity to the ground to meteorological processes. The results reveal distinct maxima in aerosol loads, the intensity of wind gusts, and the frequency of dust devils around local noon and early afternoon, and corresponding minima around midnight. This indicates that gustiness and dust devils, both fueled by solar heating during the day, are among the main causes for local dust emissions. During daytime the aerosols are concentrated at altitudes of 4–6 km. This can provide us with an indication for the degree of vertical mixing in the planetary boundary layer of Mars. Key Points: Diurnal variation of local dust emissions, wind gustiness, and convective vortices are analyzed for the entire Phoenix missionPeak values are observed in early afternoon, indicating that gustiness and convective vortices are main drivers for local dust emissionsTypical dust‐layer heights in early afternoon are 4–6 km, consistent with typical boundary‐layer heights [ABSTRACT FROM AUTHOR]

The distribution of tropical cyclone (TC) eye cloud heights is documented for the first time using compact Raman lidar (CRL) measurements with high spatial resolution. These cloud heights act as tracers for low‐level vertical mixing in the eye region. Cloud height distributions using all available data from nine Atlantic TCs in 2021 and 2022 show significant vertical variance, dispelling the notion of a flat stratiform eye cloud deck. Eye cloud widths are multiscale, with shallow convective clouds dominating CRL returns. Data from Hurricane Sam (2021) highlight the evolution of shallow convective clouds in the TC eye and their associated temperature inversions. The frequent appearance of convective eye clouds, along with observed vertical wind fluctuations, suggests that vertical mixing from the boundary layer frequently occurs in the TC eye, even beneath strong inversions. This strong vertical mixing should be accurately portrayed by TC simulations and forecasts. Plain Language Summary: While the temperature inversion and associated clouds within the tropical cyclone (TC) eye region are essential elements of storm structure, observing eye cloud heights remains a challenge, and the vertical distribution of these clouds is poorly constrained. This study documents TC eye cloud characteristics using a new aircraft‐based remote sensing technique for the first time, with a focus on cloud height distributions. Both case study and statistical approaches confirm that most of these clouds are convective in nature, not stratiform. The formation of shallow convective clouds within TC eyes is driven by shallow upward mixing as documented by aircraft flight level vertical wind measurements. Vertical mixing across the eye inversion layer changes inner core thermodynamics, highlights a potential pathway for intensity change, and emphasizes why this process must be captured in high resolution TC forecast models. Key Points: New, aircraft‐based compact Raman lidar cloud, temperature, and water vapor measurements detail tropical cyclone inner core structureCase studies and statistics demonstrate how shallow convective clouds with high spatial variability are the most common eye cloud typeVertical velocity and cloud height analyses suggest that low level vertical mixing drives shallow convective eye cloud formation [ABSTRACT FROM AUTHOR]

With four companions at separations from 16 to 71 au, HR 8799 is a unique target for direct imaging, presenting an opportunity for a comparative study of exoplanets with a shared formation history. Combining new VLTI/GRAVITY observations obtained within the ExoGRAVITY program with archival data, we performed a systematic atmospheric characterisation across all four planets. We explored different levels of model flexibility to understand the temperature structure, chemistry, and clouds of each planet using both petitRADTRANS atmospheric retrievals and fits to self-consistent radiative–convective equilibrium models. Using Bayesian model averaging to combine multiple retrievals (a total of 89 across all four planets), we find that the HR 8799 planets are highly enriched in metals, with [M/H] ≳1, and have stellar to superstellar atmospheric C/O ratios. The C/O ratio increases with increasing separation from 0.55−0.10+0.12 for d to 0.78−0.04+0.03 for b, with the exception of the innermost planet, which has a C/O ratio of 0.87 ± 0.03. Such high metallicities are unexpected for these massive planets, and challenge planet-formation models. By retrieving a quench pressure and using a disequilibrium chemistry model, we derive vertical mixing strengths compatible with predictions for high-metallicity, self-luminous atmospheres. Bayesian evidence comparisons strongly favour the presence of HCN in HR 8799 c and e, as well as CH4 in HR 8799 c, with detections at > 5σ confidence. All of the planets are cloudy, with no evidence of patchiness. The clouds of c, d, and e are best fit by silicate clouds lying above a deep iron cloud layer, while the clouds of the cooler HR 8799 b are more likely composed of Na2S. With well-defined atmospheric properties, future exploration of this system is well positioned to unveil further details of these planets, extending our understanding of the composition, structure, and formation history of these siblings. [ABSTRACT FROM AUTHOR]

Microplastics in the environment are considered complex pollutants as they are chemical and corrosive-resistant, non-biodegradable and ubiquitous. These microplastics may act as vectors for the dissemination of other pollutants and the transmission of microorganisms into the water environment. The currently available literature reviews focus on analysing the occurrence, environmental effects and methods of microplastic detection, however lacking a wide-scale systematic review and classification of the mathematical microplastic modelling applications. Thus, the current review provides a global overview of the modelling methodologies used for microplastic transport and fate in water environments. This review consolidates, classifies and analyses the methods, model inputs and results of 61 microplastic modelling studies in the last decade (2012–2022). It thoroughly discusses their strengths, weaknesses and common gaps in their modelling framework. Five main modelling types were classified as follows: hydrodynamic, process-based, statistical, mass-balance and machine learning models. Further, categorisations based on the water environments, location and published year of these applications were also adopted. It is concluded that addressed modelling types resulted in relatively reliable outcomes, yet each modelling framework has its strengths and weaknesses. However, common issues were found such as inputs being unrealistically assumed, especially biological processes, and the lack of sufficient field data for model calibration and validation. For future research, it is recommended to incorporate macroplastics' degradation rates, particles of different shapes and sizes and vertical mixing due to biofouling and turbulent conditions and also more experimental data to obtain precise model inputs and standardised sampling methods for surface and column waters. [ABSTRACT FROM AUTHOR]

Tropopause-overshooting convection in the midlatitudes provides a rapid transport pathway for air from the lower troposphere to reach the upper troposphere and lower stratosphere (UTLS) and can result in the formation of above-anvil cirrus plumes (AACPs) that significantly hydrate the stratosphere. Such UTLS composition changes alter the radiation budget and impact climate. Novel in situ observations from the NASA Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign are used in this study to examine UTLS impacts from AACP-generating overshooting convection. Namely, a research flight on 31 May 2022 sampled active convection over the state of Oklahoma for more than 3 h with the NASA ER-2 high-altitude research aircraft. An AACP was bisected during this flight, providing the first such extensive in situ sampling of this phenomenon. The convective observations reveal pronounced changes in air mass composition and stratospheric hydration up to altitudes of 2.3 km above the tropopause and concentrations more than double background levels. Unique dynamic and trace gas signatures were found within the AACP, including enhanced vertical mixing near the AACP edge and a positive correlation between water vapor and ozone. Moreover, the water vapor enhancement within the AACP was found to be limited to the saturation mixing ratio of the low temperature overshoot and AACP air. Comparison with all remaining DCOTSS flights demonstrates that the 31 May 2022 flight had some of the largest tropospheric tracer and water vapor perturbations in the stratosphere and within the AACP. [ABSTRACT FROM AUTHOR]

Summer monsoon southwest wind induces the South Vietnam Upwelling (SVU) over four main areas along the southern and central Vietnamese coast: upwelling offshore of the Mekong shelf (MKU), along the southern and northern coasts (SCU and NCU), and offshore (OFU). Previous studies have highlighted the roles of wind and ocean intrinsic variability (OIV) in intraseasonal to interannual variability in the SVU. The present study complements these results by examining the influence of tides and river discharges and investigates the physical mechanisms involved in MKU functioning. MKU is driven by non-chaotic processes, explaining its negligible intrinsic variability. It is triggered first by the interactions of currents over marked topography. The surface convergence of currents over the southwestern slope of the Mekong shelf induces a downwelling of the warm northeastward alongshore current. It flows over the shelf and encounters a cold northwestward bottom current when reaching the northeastern slope. The associated bottom convergence and surface divergence lead to an upwelling of cold water, which is entrained further north by the surface alongshore current. Tides strengthen this circulation-topography-induced MKU through two processes. First, tidal currents weaken the current over the shallow coastal shelf by enhancing the bottom friction. This increases the horizontal velocity gradient and hence the resulting surface convergence and divergence and the associated downwelling and upwelling. Second, they reinforce the surface cooling upstream and downstream of the shelf through lateral and vertical tidal mixing. This tidal reinforcement explains 72 % of MKU intensity on average over the summer and is partly transmitted to SCU through advection. Tides do not significantly influence OFU and NCU intensity. Mekong waters slightly weaken MKU (by 9 % of the annual average) by strengthening the stratification but do not significantly influence OFU, NCU, and SCU. Last, tides and rivers do not modify the chronology of upwelling in the four areas. [ABSTRACT FROM AUTHOR]

In this work, the seasonal variations of the carbonate system and air‐sea CO2 fluxes were investigated by two cruises in the southern Yellow Sea (SYS) and the East China Sea (ECS), which were significantly influenced by the Changjiang riverine inputs across seasons. Biological‐mediated change of dissolved inorganic carbon (DIC) was first quantitated through a three end‐member mixing model from winter to spring. Our modeling results suggested that DIC addition through biological remineralization persisted in the SYS during winter and spring, while DIC removal was evident in the Changjiang River Plume and the offshore ECS triggered by river inputs in spring. Horizontal and vertical mixing together constituted the largest contribution to the interseasonal variability of partial pressure of CO2 (pCO2) in the SYS (−69.5%), the river plume (−59.3%), and the ECS offshore (−43.8%), followed by temperature effects in the plume area (29.4%), and biological processes in the ECS offshore (24.1%) and the SYS (−7.7%), with air‐sea CO2 exchange contributing the least in both three subregions. The SYS, the river plume, and the ECS offshore all acted as atmospheric CO2 sinks in both winter and spring. Furthermore, their ability to absorb atmospheric CO2 increased from winter to spring, as reflected in a ∼1.8‐fold increase in the overall spring air‐sea CO2 flux compared to winter estimation. Plain Language Summary: The carbonate system has played an essential role in regulating the ocean carbon cycle due to its buffer capacity for ocean acidification, especially in continental shelf seas. However, complex biological and physical processes present difficulties in assessing the seasonal dynamics of the carbonate system and following air‐sea CO2 fluxes. In this study, seasonal variations of the carbonate system were identified in the southern Yellow Sea (SYS) and the East China Sea (ECS). From winter to spring, biological DIC addition happened in the SYS, while DIC removal by biological production exceeded the addition by remineralization and caused most springtime DIC consumption in the river plume and the ECS offshore. We also quantified pCO2 variations from winter to spring, revealing the importance of physical mixing in controlling the ocean carbon cycle. Our study regions acted as atmospheric CO2 sinks in winter and spring, and their sink capacity was strengthened from winter to spring. Key Points: Dissolved inorganic carbon (DIC) addition occurred in the southern Yellow Sea (SYS) during winter and spring, while springtime DIC removal occurred in the river plume and the East China Sea (ECS) offshorePhysical mixing became the primary factor in regulating the interseasonal variation of pCO2The capacity of coastal waters in absorbing atmospheric CO2 was enhanced from winter to spring [ABSTRACT FROM AUTHOR]

North Atlantic subtropical mode water (NASTMW) serves as a major conduit for dissolved carbon to penetrate into the ocean interior by its wintertime outcropping events. Prior research on NASTMW has concentrated on its physical formation and destruction, as well as Lagrangian pathways and timescales of water into and out of NASTMW. In this study, we examine how dissolved inorganic carbon (DIC) concentrations are modified along Lagrangian pathways of NASTMW on subannual timescales. We introduce Lagrangian parcels into a physical‐biogeochemical model and release these parcels annually over two decades. For different pathways into, out of, and within NASTMW, we calculate changes in DIC concentrations along the path (ΔDIC), distinguishing contributions from vertical mixing and biogeochemical processes. The strongest ΔDIC is during subduction of water parcels (+101 μmol L−1 in 1 year), followed by transport out of NASTMW due to increases in density in water parcels (+10 μmol L−1). While the mean ΔDIC for parcels that persist within NASTMW in 1 year is relatively small at +6 μmol L−1, this masks underlying dynamics: individual parcels undergo interspersed DIC depletion and enrichment, spanning several timescales and magnitudes. Most DIC enrichment and depletion regimes span timescales of weeks, related to phytoplankton blooms. However, mixing and biogeochemical processes often oppose one another at short timescales, so the largest net DIC changes occur at timescales of more than 30 days. Our new Lagrangian approach complements bulk Eulerian approaches, which average out this underlying complexity, and is relevant to other biogeochemical studies, for example, on marine carbon dioxide removal. Plain Language Summary: Mode waters are relatively thick water masses with homogeneous properties, such as temperature and salinity. The North Atlantic subtropical mode water (NASTMW), found in the Sargasso Sea, is one such water mass. Lying underneath the ocean surface, it comes into contact with the atmosphere during winter, when the surface layer is vigorously mixed due to strong winds, causing the mixed layer to connect with NASTMW. This way, NASTMW can buffer atmospheric temperature and carbon anomalies during the summer, when there is no surface connection. It is also a conduit for carbon to penetrate beneath the ocean's upper mixed layer, with the potential to sequester it. We study NASTMW from the viewpoint of a water parcel that moves with the currents and see how carbon concentrations in the water parcels change along different NASTMW pathways. For each pathway, the carbon concentration changes due to an interplay of vertical mixing and biogeochemical processes, for example, related to plankton growth and decay. These processes can unfold over different timescales and may counteract or enhance themselves or one another. The largest change in carbon concentration is found when a parcel moves from the upper ocean mixed layer into NASTMW, mostly due to vertical mixing. Key Points: Carbon transformations along pathways of North Atlantic Subtropical Mode Water are split into mixing and biogeochemical contributionsAlong paths into, within, and out of this mode water, mixing and biogeochemistry alter carbon in water parcels over a range of timescalesEnrichment is highest during mixed layer subduction, which few parcels undergo annually; persistence in mode water is the dominant pathway [ABSTRACT FROM AUTHOR]

Mesoscale eddies are found almost everywhere in global ocean. They can last for weeks to months with scales up to over 100 km and play important roles in global biogeochemical cycles. In this study, we analyzed the phylogenetic and pigment type composition of Synechococcus in a cyclonic eddy (CE, cold eddy) and an anticyclonic eddy (ACE, warm eddy) located in western South China Sea in summer, 2018. Nutrients pumping enhanced Synechococcus abundance markedly in the upper euphotic layers of CE. High diversity of both phylogenetic clades and pigment types of Synechococcus were discovered in the sampling area, with clear composition difference between CE and ACE. The chromatic acclimating pigment type (PT) 3dA dominated in CE while PT 3dB dominated in ACE. The potential weak chromatic acclimator PT 3eA contributed a significant proportion in both CE and ACE. To better understand the difference of PT composition in CE and ACE, we further investigated the phylogenetic composition of Synechococcus in CE and ACE. Clade CRD 1, which were the main strains in upwelling regions, were dominant in CE, where cooler and nutrient rich subsurface water was pumped to the upper layers. Warm water adapted clade II and clade III dominated in ACE. Our study, for the first time, indicated that chromatic acclimation was important in shaping the vertical profile of Synechococcus community in mesoscale eddies of the subtropical oceans. Plain Language Summary: We analyzed the phylogenetic and pigment type composition of Synechococcus, tiny cyanobacteria that are global significant primary producers, in a cyclonic eddy (CE, cold eddy) and an anticyclonic eddy (ACE, warm eddy) located in western South China Sea in summer, 2018. The upward nutrients pumping in CE enhanced Synechococcus abundance remarkably. Chromatic acclimators, those that can change their pigment composition in responding to changes in light spectrum, dominated in mesoscale eddies, resulted from their great advantage over Synechococcus with a fixed pigmentation in water columns where light spectrum changes dramatically due to vertical mixing. Both pigment types and phylogenetic composition were highly diverse and displayed clear niche segregation in cold and warm eddies. Chromatic acclimators that are typically found in cold waters dominated in the cold eddy, while those prevailing in tropical and subtropical waters were abundant in the warm eddy. We also tried to link the two distinctive subgroups of chromatic acclimators to corresponding phylogenetic clades. Our study reveals that the physical and chemical characteristics of mesoscale eddies, including light, temperature and nutrients, shaped the community structure and biomass of Synechococcus. Key Points: Nutrients pumping enhanced Synechococcus abundance remarkably in the upper euphotic layers of cyclonic eddiesThe chromatic acclimating Synechococcus dominated in mesoscale eddies resulting from dynamic vertical mixingWe observed clear niche segregation of both pigment types and phylogenetic clades in CE and ACE resulted from the unique physical and chemical properties [ABSTRACT FROM AUTHOR]

Previous studies have primarily focused on the impact of human activities on coastal dissolved organic matter (DOM) cycles, while neglecting the role of dynamic processes. This limits our comprehensive understanding of the dynamic processes of coastal DOM, particularly in coastal waters affected by multiple dynamic processes. In this study, the dynamics of DOM in the northwestern South China Sea (SCS) were investigated using DOM‐related parameters and a three end‐member mixing model, which accounted for the effects of coastal currents and upwelling during the spring, summer, and winter seasons. Our results demonstrated that the net addition of DOM was predominantly observed in the nearshore during all seasons, owing to strong coastal currents that induced phytoplankton production and particle desorption. However, owing to weaker coastal currents and upwelling in spring and winter, DOM removal induced by decomposition was observed in the western offshore area. This observation can be attributed to the abundance of microorganisms in spring and increased vertical water mixing in winter. Conversely, in summer, stronger upwelling provided more bio‐refractory DOM, limiting its decomposition, whereas stronger coastal currents stimulated productivity and particle desorption, resulting in the net addition of DOM during this period. In the eastern offshore area, DOM decomposition was the primary mechanism for eliminating DOM owing to weak or absent coastal currents and upwelling. Our study revealed that DOM decomposition is widespread in the coastal regions of the northwestern SCS and that stronger coastal currents and upwelling facilitate the net addition of DOM. Plain Language Summary: Dissolved organic matter (DOM) is a significant component of the global carbon cycles. However, our understanding of the dynamics of DOM in coastal waters with multiple dynamic processes, such as coastal currents and upwelling, remains limited. In this study, DOM‐related parameters were investigated to address this issue in the northwestern South China Sea (SCS) during spring, summer, and winter. These results revealed that the dynamic processes of DOM in the northwestern SCS were regulated by coastal currents and upwelling. Strong coastal currents facilitate the net addition of DOM, and strong upwelling provides more bio‐refractory DOM, limiting its decomposition. Decomposition was the dominant process during periods of weaker coastal currents and upwelling. Key Points: Coastal currents lead to the addition of dissolved organic matter (DOM) by promoting phytoplankton production and particle desorptionThe upwelling with depleted and bio‐refractory DOM may contribute to a dilution in DOM levelDOM decomposition is primarily observed in offshore areas characterized by weak or absent upwelling and coastal currents [ABSTRACT FROM AUTHOR]

Anthropogenic perturbations from fossil fuel burning, nuclear bomb testing, and chlorofluorocarbon (CFC) use have created useful transient tracers of ocean circulation. The atmospheric 14C/C ratio (∆14C) peaked in the early 1960s and has decreased now to pre‐industrial levels, while atmospheric CFC‐11 and CFC‐12 concentrations peaked in the early 1990s and early 2000s, respectively, and have now decreased by 10%–20%. We present the first analysis of a decade of new observations (2007 to 2018–2019) and give a comprehensive overview of the changes in ocean ∆14C and CFC concentration since the WOCE surveys in the 1990s. Surface ocean ∆14C decreased at a nearly constant rate from the 1990–2010s (20‰/decade). In most of the surface ocean ∆14C is higher than in atmospheric CO2 while in the interior ocean, only a few places are found to have increases in ∆14C, indicating that globally, oceanic bomb 14C uptake has stopped and reversed. Decreases in surface ocean CFC‐11 started between the 1990 and 2000s, and CFC‐12 between the 2000–2010s. Strong coherence in model biases of decadal changes in all tracers in the Southern Ocean suggest ventilation of Antarctic Intermediate Water was enhanced from the 1990 to the 2000s, whereas ventilation of Subantarctic Mode Water was enhanced from the 2000 to the 2010s. The decrease in surface tracers globally between the 2000 and 2010s is consistently stronger in observations than in models, indicating a reduction in vertical transport and mixing due to stratification. Plain Language Summary: The ocean contains many dissolved gases that can be measured by sampling ocean water from ships. Some of these dissolved gases are changing over time because their atmospheric concentrations are changing. By measuring these changes in the ocean, we can learn about ocean transport and mixing, which is an important factor regulating climate change. We describe ocean measurements from the past three decades of radiocarbon in dissolved inorganic carbon, that was affected by nuclear bomb testing, and of chlorofluorocarbon gases, CFCs, that were banned in the 1990s due to their destructive effects on the ozone layer. The measurements show how their oceanic distributions have changed, as a result of their atmospheric histories and the patterns of ocean uptake and transport. By comparing the measurements with ocean models, we can identify biases in the models that affect how well future climate change can be predicted. In the most recent decade, the presence of all three tracers is shown to be decreasing in the upper ocean, a reversal of the preceding decades. Also in the most recent decade, the decrease in surface tracers is stronger in the observations than the models, suggesting a change to upper ocean mixing and stratification. Key Points: Recent trends in upper ocean Δ14C, pCFC‐11, and pCFC‐12 are negative, reflecting their decreasing atmospheric trendsIncreases in ∆14C are only observed in a few places over 2000–2010s, showing oceanic bomb 14C uptake has stopped and reversedModel‐data Δ14C and chlorofluorocarbon differences could be consistent with decadal ventilation changes and large‐scale stratification or model errors [ABSTRACT FROM AUTHOR]

Lower Pliensbachian hemipelagic successions from the northern Iberian palaeomargin are characterized by the occurrence of organic-rich calcareous rhythmites of decimetre-thick limestone and marl beds as well as thicker black shale intervals. Understanding the genetic mechanisms of the cyclic lithologies and processes involved along with the nature of the carbon cycle is of primary interest. This cyclostratigraphic study, carried out in one of the black shale intervals exposed in Santiurde de Reinosa (Basque–Cantabrian Basin), reveals that the calcareous rhythmites responded to periodic environmental variations in the Milankovitch-cycle band and were likely driven by eccentricity-modulated precession. The main environmental processes that determined the formation of the rhythmite were deduced on the basis of the integrated sedimentological, mineralogical, and geochemical study of an eccentricity bundle. The formation of precession couplets was controlled by variations in carbonate production and dilution by terrigenous supplies, along with periodic changes in bottom-water oxygenation. Precessional configurations with marked annual seasonality increased terrigenous input (by rivers or wind) to marine areas and boosted organic productivity in surface water. The great accumulation of organic matter on the seabed eventually decreased bottom-water oxygenation, which might also be influenced by reduced ocean ventilation. Thus, deposition of organic-rich marls and shales occurred when annual seasonality was maximal. On the contrary, a reduction in terrestrial inputs at precessional configurations with minimal seasonality diminished shallow organic productivity, which, added to an intensification of vertical mixing, contributed to increasing the oxidation of organic matter. These conditions also favoured greater production and basinward export of carbonate mud in shallow marine areas, causing the formation of limy hemipelagic beds. Short eccentricity cycles modulated the amplitude of precession-driven variations in terrigenous input and oxygenation of bottom seawater. Thus, the amplitude of the contrast between successive precessional beds increased when the Earth's orbit was elliptical and diminished when it was circular. The data also suggest that short eccentricity cycles affected short-term sea level changes, probably through orbitally modulated aquifer eustasy. [ABSTRACT FROM AUTHOR]

A study on the dynamics of Radon and meteorological parameters was conducted in Bengaluru (12056′44'' N, 77030′25″ E, 840 m AMSL) during monsoon of 2014. All measured parameters exhibited a clear diurnal pattern, except for pressure, and are attributed to morning temperature inversion and afternoon enhanced vertical mixing. Concentration of Radon is higher during north eastern monsoon compared with south western monsoon and is due to the presence of continental air mass from north east of India. Monthly average Radon activity has exhibited a positive link with long wave radiation while displaying a negative correlation with ambient temperature, accumulated rainfall and soil temperature. During the study, ambient gamma dose rate of 190.8 nSv hour−1, shortwave radiation of 184.4 Wm−2, longwave radiation of −40.4 Wm−2, soil temperature (at 10 cm) of 26.3°C, humidity of 62.9%, pressure of 918.1 mbar and radon activity of 8.4 ± 0.5 Bq m−3 were recorded. [ABSTRACT FROM AUTHOR]

The Fast Fourier Transform (FFT) analysis of the activity concentration of radon and selected meteorological parameters was carried out at Department of Physics, Bangalore University, Bengaluru (12056′44"N, 77030′25″E, 840 m above MSL). All of the measured parameters, with the exception of pressure, showed a clear diurnal trend, which can be explained by the presence of typical atmospheric processes such as temperature inversion in the morning and greater vertical mixing in the afternoon. Radon's time series has a latent memory of sub-diurnal cycles, as shown via FFT analysis. The monthly average radon has higher levels of activity during winter months compared with monsoon and summer months. Days during the monsoon season had the lowest radon activity, which may be ascribed to the fact that less radon was being exhaled from the soil as a result of the rain. Radon was recorded at 8.06 ± 0.56 Bq/m3, temperature at 28.9 °C, humidity at 55.2% and pressure at 918 mbar. [ABSTRACT FROM AUTHOR]

The Venusian atmosphere hosts a 10 km deep convective layer that has been studied by various spacecrafts. However, the impact of the strong vertical mixing on the chemistry of this region is still unknown. This study presents the first realistic coupling between resolved small‐scale turbulence and a chemical network. The resulting vertical mixing is different for each species: those with longer chemical timescales will tend to be well‐mixed. Vertical eddy diffusion due to resolved convection motions was estimated, ranging from 102 to 104 m2/s for the 48–55 km convective layer, several orders of magnitude above the typically used value. In the 48–55 km convective layer, the impact of the small‐scale turbulence on the cloud layer boundaries was between 200 m and 1 km. The impact of turbulence on cloud chemistry is consistent with Venus Express/Visible and Infrared Thermal Imaging Spectrometer observations. The observability at the cloud‐top of small‐scale turbulence by VenSpec‐U spectrometer would be challenging. Plain Language Summary: Venus hosts a global sulfuric acid cloud layer between 45 and 70 km. A convective layer is present between roughly 50 and 60 km, with its variability in latitude and local time assessed by observation, with a thicker layer at high latitude and at night. One question that remains unclear is how this turbulence mixes momentum, heat, and chemical species. Especially, the impact of the strong vertical mixing on the chemistry of this region is still unknown. To investigate this topic, we use a convection‐resolving model coupled for the first time with a realistic chemical network. The resulting vertical mixing is different for each species: those with longer chemical timescales will tend to be well‐mixed. 1D and global circulation models use the so‐called vertical eddy diffusion approach to represent turbulent motion, quantified in our model and underestimated in chemistry models. The small‐scale turbulence in the cloud layer causes a variation in the altitude of the top and bottom boundaries of the cloud. Our model shows that the impact of turbulence on cloud chemistry corresponds well to what has been observed by satellites. In the future, the EnVision mission will be able to observe chemical species at the small turbulence scales. Key Points: Estimation for the first time of the spatial and temporal variability of chemical species due to vertical mixingQuantification of the vertical eddy diffusion coefficient, order of magnitude above typical used valuesCloud‐top altitudes change by 0.2–1 km due to vertical convective mixing and gravity waves [ABSTRACT FROM AUTHOR]

Over the past century, rapid urbanization has greatly altered landscapes and affected atmospheric conditions causing impacts across a wide range of sectors including human welfare, infrastructure, and ecosystems. As a result, there is a growing imperative to improve understanding of urbanization impacts on local and regional weather events and hydroclimates. This study investigates how urbanization affects precipitation and cloud fraction (CF) in the vicinity of Indianapolis. We employ multi‐month simulations using the Weather Research and Forecasting model to: (a) assess the impact of an urban area on precipitation and CF, (b) quantify how this impact varies with urban growth, and (c) examine the main mechanisms through which the city alters the local hydroclimate. Specifically, two perturbed simulations, where the urban land cover is either replaced by croplands or is increased in size, are also performed for the two rainiest months. Comparisons of the control run with no city against the perturbed runs indicate statistically significant impacts of the urban area in enhancing precipitation amounts, frequency and low‐level CF, particularly within the first 100 km radius downwind of the city boarder. The urban environment is found to increase precipitation efficiency over the city and in downwind regions. Temperature at 2 m height, planetary boundary layer height, turbulent kinetic energy, and convective available potential energy, are also enhanced in the perturbed runs and drive changes in vertical mixing, downwind precipitation amounts, frequency and low‐level height CF. All these changes appear to be a non‐linear function of the city size. Plain Language Summary: Over the past century, rapid urbanization has reshaped landscapes, influencing atmospheric circulation, and leaving profound impacts on human welfare, infrastructure, and ecosystems. Recognizing the urgency to comprehend these effects, this study contributes to an improved understanding of the influence of urbanization on precipitation amounts and cloud fraction (CF) in the surrounding areas of a metropolitan area in the United States. This work utilizes a modeling approach based on an ensemble of simulations of the Weather Research and Forecasting model. The design of our modeling experiment allows us to investigate the role of different degrees of urbanization and to decouple the urban signature from the background climate in terms of precipitation and cloud properties. Our findings reveal a statistically significant increase in low‐level CF and precipitation, particularly within the first 100 km radius downwind of the city border. Further, we identify a non‐linear relationship between size of the urban area and the associated changes in precipitation amounts, frequency, and CF. Key Points: Urban areas may modify the regional climate by altering cloud fraction (CF), rainfall patterns, and rain efficiencyStatistically significant increases in downwind low‐level CF, precipitation amounts, intensity, and frequency are identifiedUrban areas enhance turbulent mixing, convective available potential energy and rain efficiency, over the city, and in downwind regions [ABSTRACT FROM AUTHOR]