Unveiling fDOM dynamics in shallow lakes via a coupled "spectral-thermal" XGBoost-SHAP retrieval framework: Implications for water diversion management in Lake Honghu.

COVID-19 induced reduction of fossil-fuel emissions in 2020 altered the seasonal cycle of atmospheric CO2 at high latitudes

Abstract Anthropogenic climate change is projected to intensify the global hydrological cycle, posing substantial risks to human societies. However, monitoring these changes through direct observations remains challenging, particularly over the oceans. Since long‐term shifts in the hydrological cycle are expected to alter ocean salinity distribution, understanding the processes governing its evolution is essential. Salinity distribution is known to result from a balance between freshwater fluxes, which broaden the distribution, and mixing processes, which narrow it. Using a novel diagnostic based on the mean salinity variance budget applied to the Estimating the Circulation and Climate of the Ocean (ECCO), we estimate that the large‐scale salinity flux—primarily driven by the seasonal cycle—contributes approximately 23% to this mixing. Our framework also enables us to understand the regional balances, and to identify the regions where these balances are most significant. Our results suggest that accurately representing the seasonal salinity cycle in ocean and climate models is important for simulating the ocean salinity distribution.

ABSTRACT This study employs statistical analysis to examine the impact of urban morphology on land surface temperature (LST). The findings reveal notable differences in LST across various Local Climate Zone (LCZ) types. The LST of building LCZs is significantly higher than natural LCZs. Additionally, SHapley Additive exPlanation analysis highlights that the influence of urban morphology on LST shows clear seasonal and diurnal patterns. In daytime, Floor Area Ratio is the most significant contributor to temperature variation. In contrast, at nighttime, Normalized Difference Vegetation Index and Building Height play a more dominant role. Interestingly, BH exhibits a bidirectional regulatory effect across different seasonal and diurnal cycles. Furthermore, the application of Multiscale Geographically Weighted Regression (MGWR) confirms that the relationship between urban morphology and LST is subject to spatial heterogeneity. Among the LCZs, LCZ9 shows the greatest variability in factor contribution, indicating the need for tailored interventions, while LCZ4 exhibits more homogeneous effects. This research integrates Light Gradient Boosting Machine with MGWR models, challenging the traditional static approach to studying the urban thermal environment and underscoring the importance of seasonal and spatial variations. The results provide valuable insights for urban thermal environment planning and suggest strategies for mitigating Urban Heat Island effects.

Accurate forecasting of lottery sales is crucial for strategic planning in volatile consumer markets driven by trend shifts, multi-scale seasonality, and calendar effects. This study proposes a Diagnostic Decomposition–Correction Hybrid (DDC-Hybrid) framework integrating Prophet and SARIMA through a residual diagnostics and correction pipeline. Specifically, Prophet is employed to model long-term trend changes and interpretable holiday impacts, while SARIMA is subsequently used to correct the residual series, capturing short-range temporal dependence that remains statistically significant after decomposition. From an information-theoretic perspective, the framework can be viewed as a two-stage uncertainty reduction process, where decomposition extracts low-frequency informative components and residual correction harvests remaining predictive information. Using monthly lottery sales in China (2008–2025), we conduct a comprehensive evaluation of SARIMA, Prophet, and the proposed hybrid approach. The DDC-Hybrid demonstrates improved predictive accuracy, yielding the lowest error rates. Beyond predictive accuracy, we further examine varying holiday effects through statistical testing. We also find that lottery sales contain a pronounced quadrennial (48-month) seasonal cycle associated with mega-sport events, which improves long-horizon stability. The results suggest that the proposed diagnostic hybrid modeling approach enhances forecasting accuracy and provides practical insights for lottery sales management.

Abstract Increasing atmospheric CO 2 seasonal cycle amplitudes in boreal regions have been attributed to climate-driven changes in land ecosystems, but terrestrial biosphere models (TBMs) are unable to replicate observations, leading to large uncertainties in future predictions of carbon cycle changes. Accurately partitioning net ecosystem exchange into its component fluxes—gross primary production (GPP) and respiration—is essential for understanding impacts of changing climate on the Arctic and boreal carbon balance, yet these component fluxes cannot be measured directly. Carbonyl sulfide (OCS) has been used to infer GPP at site to global scales, because its one-way uptake by plants is an analog for photosynthesis. However, expanding site-level process understanding to regional scales remains challenging. Here, we use atmospheric OCS mole fraction observations representative of Alaskan boreal forests to evaluate simulations of OCS fluxes in a state-of-the-science TBM. We use TBM-estimated OCS fluxes and surface influence functions on the order of 100–1000 km to simulate OCS mole fractions at the NOAA Global Monitoring Laboratory’s CRV tower site in central Alaska. By comparing with atmospheric observations, we can evaluate the TBM over much larger scales than is possible using eddy covariance data while still providing valuable information about underlying mechanisms. Comparisons reveal a missing ecosystem sink corresponding to a concentration difference of 22.3 ± 9.1 ppt OCS for July–November relative to observed concentrations of 433 ± 26 ppt at CRV. Solely improving the temperature sensitivity of apparent mesophyll conductance reduces the July–November mismatch between modeled and observed OCS concentration data by ∼5.3 ± 2.7 ppt. Consideration of alternate land cover maps provides an additional ∼5.3 ± 3.0 ppt towards the mismatch. These results demonstrate a strong decoupling of OCS and GPP, especially after the end of the growing season. Our analyzes demonstrate the limitations of using OCS as a proxy for GPP and highlight potential missing processes that need to be incorporated into future OCS modeling efforts to maximize its potential as a photosynthetic tracer.

Impact of soil compaction and seasonal freeze-thaw cycles on the microstructural evolution and aggregate stability of Mollisol

Understanding fish behaviour and activity patterns is essential for interpreting their ecology and the processes that shape population dynamics, yet such information remains limited for wild fishes because observing individuals in situ is challenging. Recent technological advances make it possible to collect high-resolution movements and activity data over extended periods, opening the door to detailed descriptions of fine-scale behaviours and their temporal variability. We evaluated the coarse and fine-scale activity patterns of 25 Atlantic halibut (Hippoglossus hippoglossus) individuals throughout a complete seasonal cycle in the Gulf of St. Lawrence using acceleration data at a resolution of 5 s extracted from 25 pop-up satellite archival tags (PSAT). We sought to classify individuals into behavioural contingents within the population and to identify specific behaviours that could be identified with the fine resolution of the available data using dynamic factor analysis, visual representations and variance partitioning. Despite some common general patterns of activity during reproduction, the data were characterized by a high level of individual variability in the amount and patterns of activity, with each halibut exhibiting a unique activity profile across the year. Periodic daily behaviours (diurnal and nocturnal) were identified for several individuals but with no clear pattern in their recurrence over time within individuals or coherence between individuals. Overall, individual variability in activity dominated over the common patterns detected, with little evidence of distinct activity contingents among individuals. The high-frequency activity data available from PSATs in this study challenge the traditional view of halibut and flatfish in general, as passive bottom dwellers exhibiting simple, perhaps periodic behaviours, instead supporting growing evidence that fish exhibit substantial individual behavioural differences.

Abstract. Precipitation stable isotopes are critical tracers for understanding climate variability and the hydrological cycle, as they enable the tracing of moisture sources, air mass mixing, and evaporation vs. condensation mechanisms. In mid-latitude regions such as South Korea, which are influenced by tropical and extratropical circulation, long-term isotope records remain scarce. Here, we analyze stable isotopes in precipitation collected bi-weekly in Seoul, South Korea, from 2016 to 2020. The oxygen isotope composition (δ18O) ranged widely from 1.15 ‰ to −18.21 ‰, hydrogen isotope composition (δ2H) varied from 3.3 ‰ to −132.0 ‰, the deuterium excess (d-excess) ranged from 23.7 ‰–2.1 ‰ and the 17O-excess (Δ′17O) ranged from 69 to −28 per meg. All three primary isotopes exhibited a coherent sinusoidal seasonal cycle, with the most depleted values in winter, gradual enrichment through spring, and sharp depletion during the summer monsoon, reflecting the combined influence of temperature and the amount effect. The d-excess was highest during cold, dry months and lowest in humid, rainy months, reflecting shifts in near-surface relative humidity at the moisture source region and associated kinetic fractionation. Meanwhile, Δ′17O exhibited a similar season trend with a smaller amplitude, indicating a reduced sensitivity to seasonal variations in relative humidity compared to d-excess and suggesting additional modulation by large-scale transport and water vapor mixing. The local meteoric water line closely matches the global line but winter samples show a higher intercept and a slightly steeper δ17O–δ18O slope, suggesting enhanced kinetic fractionation under continental air masses. A consistently negative δ18O–Δ′17O relationship was observed except in winter when it weakened. This integrated analysis of δ18O, d-excess, and Δ′17O provides a comprehensive picture of source humidity, transport dynamics, and seasonal precipitation processed in a mid-latitude East Asia, and offers a valuable reference for refining isotope-enabled climate models over East Asia. The dataset is publicly available at https://doi.org/10.1594/PANGAEA.983390 (Kim et al., 2025).

Diatoms are major primary producers in productive polar oceans, where cold temperatures and high CO2 solubility raise questions as to whether they rely on the CO2-concentrating mechanism (CCM) to saturate photosynthesis. Knowledge of CCM function will help better predict the sensitivity of diatom primary production to warming and acidifying polar oceans. Here, we characterized the CCM in the polar diatom, Fragilariopsis cylindrus, using membrane inlet mass spectrometry (MIMS) and a numerical model. Quantification of the role of external carbonic anhydrase (eCA) was enabled through the addition of a surface boundary layer to the numerical model. We found that F. cylindrus displayed an active CCM across a wide range of inorganic carbon availability, but that the CCM was not required under air-equilibrated CO2 concentrations. eCA was an essential component of the CCM, facilitating HCO3 - uptake. When eCA was inhibited, CO2 was the primary carbon source. The eCA role in supporting HCO3 - uptake was independent of temperature changes. eCA-supported HCO3 - transport is likely a mechanism for F. cylindrus to cope with fluctuating concentrations of inorganic carbon over a dynamic seasonal cycle in polar oceans. Our work challenges the hypothesis that CCMs are not required at cold temperatures.

The purpose of the study is to identify the key components of specialized training during the pre-competition period in qualified saber fencers. Research methods and organization. A total of 12 athletes from the Russian national saber fencing team were observed. The research program included: analysis of scientific and methodological literature on the topic; analysis of the competition calendar with identification of events of varying significance throughout the season; observation of training and competitive processes with recording of match outcomes; analysis of athletes’ actions during bouts; and analysis of coaches’ and athletes’ opinions through a structured questionnaire. Additionally, mathematical and statistical methods were employed for data processing. Research results and conclusions. In constructing a training plan for saber fencers leading up to major competitions within the annual cycle, it is essential to operate with core load indicators—volume and intensity—applied appropriately to each training phase. When planning training intensity, in addition to the motor component, psychological strain must be taken into account, given its interdependence with physical load. Rational management of fencers’ sports preparation contributes significantly to optimizing competitive performance at the peak of the seasonal cycle. Training planning for qualified saber fencers during the immediate pre-competition phase should be based on eight key factors: technique-tactical skill development exercises; physical and functional readiness of the fencer; readiness to compete under match conditions; intensity of training exercises; number of bouts per day; competitive effectiveness; minimum acceptable number of bouts per day; characteristics of recovery processes.

Abstract With the operation of JWST, atmospheric characterization has now extended to low-mass exoplanets. In compact multiplanetary systems, secular spin-orbital resonance may preserve high obliquities and asynchronous rotation even for tidally despinning, low-mass planets, potentially leading to unique atmospheric circulation patterns. To understand the impact on the atmospheric circulation and to identify the potential atmospheric observational signatures of such high-obliquity planets, we simulate the three-dimensional circulation of a representative mini-Neptune K2-290 b, whose obliquity may reach about 67°. Whether synchronously rotating or not, the planet’s slow rotation, moderate temperature, and radius result in a global weak temperature gradient (WTG) behavior with moderate horizontal temperature contrasts. Under synchronous rotation, broad eastward superrotating jets efficiently redistribute heat. Circulation in an asynchronous rotation exhibits a seasonal cycle driven by high obliquity, along with quasiperiodic oscillations in winds and temperatures with a period of ∼70 orbital periods. These oscillations, driven by wave–mean flow interactions, extend from low- to midlatitudes due to the slow planetary rotation. Higher atmospheric metallicity strengthens radiative forcing, increasing temperature contrasts and jet speeds. Clouds have minimal impact under synchronous rotation but weaken jets under nonsynchronous rotation by reducing temperature contrasts. In all cases, both thermal emission and transmission spectra exhibit moderate observational signals at a level of 100 ppm, and high-obliquity effects contribute differences at the ∼10 ppm level. Our results are also applicable to a range of potential high-obliquity exoplanets, which reside in the WTG regime and likely exhibit nearly homogeneous horizontal temperature patterns.

Abstract. Hydrogen is a potential candidate for an alternate energy source and carrier. As usage of hydrogen in industry rises, leakages into the atmosphere may occur, causing an increase in the global atmospheric hydrogen concentration. Hydrogen is an indirect greenhouse gas, known to increase methane, stratospheric water vapour, and tropospheric ozone. Methane and hydrogen are closely coupled, with the main atmospheric destructive pathway of both species being via reaction with the hydroxyl radical (OH). Currently, most earth system models (ESMs) simulate hydrogen or methane with a prescribed lower boundary condition, which suppresses chemical feedbacks at the surface. In this work, we implement hydrogen emissions and a hydrogen soil uptake scheme into an ESM with free-running methane to demonstrate the capability of a fully interactive hydrogen and methane emissions-driven ESM. We show that the model is able to capture long term trends and seasonal cycles of both species when compared to observations, and find that the inclusion of both fluxes does not impact other chemical species in the model, such as tropospheric ozone. We show that the model can be used under pre-industrial conditions and present day scenarios. The ESM with fully coupled hydrogen and methane chemistry has great potential to be used in future scenarios and to estimate a more accurate global warming potential of hydrogen.

Oberon Reservoir (OR), a temperate monomictic water body in Australia, displays strong seasonal stratification that has intensified over the past decade in response to climate change. In this study, a nine-year dataset (2016-2025) from OR reveals pronounced seasonal cycles characterised by stable summer stratification with a thermocline near 10m, isolating bottom waters and restricting mixing, thereby intensifying hypolimnetic oxygen depletion. Surface water temperatures (WTs) peaked at 20°C, while hypoxic conditions prevailed in deeper layers. Vertical pH gradients emerge, driven by surface photosynthetic CO₂ uptake, leading to alkalinization, in contrast to bottom-water acidification due to respiratory CO₂ accumulation. These redox conditions promote elevated concentrations of iron (Fe) and manganese (Mn) in anoxic bottom waters through reductive dissolution of metal oxides, concurrently releasing soluble Fe2+, Mn2+, inorganic phosphorus (P), and ammonium (NH₄+-N), thereby intensifying internal nutrient loading. Regression analysis confirmed strong correlations between thermocline strength index (TSI) and chemical stratification index (IC-i), indicating tight coupling between thermal and chemical stratification. Although winter mixing temporarily restored homogeneity, it did not counteract the cumulative effects of prolonged stratification. Analysis of the past decade of data shows a steady increase in reservoir surface temperatures accompanied by a consistent decline in bottom dissolved oxygen. Seasonal Autoregressive Integrated Moving Average (SARIMA) forecasting further projects intensified thermal stratification, with surface warming of approximately +2.5°C by 2030, raising concerns about worsening hypoxia, enhanced nutrient and metal release, and increased acidification. Model performance for WT, DO, pH, Fe, Mn, inorganic P, and NH₄+-N demonstrated strong predictive accuracy, evidenced by low mean error (ME), root mean square error (RMSE), and mean absolute error (MAE) values, symmetric mean absolute percentage errors (SMAPE) generally below 10% (and<20% for highly variable constituents), mean absolute scaled errors (MASE) <1 across all models, and negligible residual autocorrelation (ACF₁≈0). These findings highlight that climate warming intensifies both thermal and chemical stratification in OR, underscoring the need for integrated long-term monitoring and predictive modelling, with adaptive reservoir management, such as artificial destratification techniques, to safeguard water quality.

Urchin herbivory is a key function in temperate reef ecosystems. Some urchin species overgraze macroalgal forests, leading to their collapse into barren states. In Australia, climate change is enabling the poleward range extension of urchin species, resulting in increased barrens formation at the cool-edge of their distribution. Despite their ecological importance and association with warming, broad-scale effects of temperature on sea-urchin feeding ecology remain unknown. We characterise in-situ feeding rates of two barrens-forming urchin species, one range-extender (Centrostephanus rodgersii), the other range-persistent (Heliocidaris erythrogramma), across a temperature range of 8°C and 12 degrees of latitude, as well as over seasonal cycles. We assess the extent to which ecological drivers (temperature, macroalgal nutrition, urchin size/weight metrics) explain grazing patterns. We find contrasting patterns in, and drivers of, performance between urchin species. C. rodgersii shows a peak in grazing and abundance at its range-centre, and temperature is shown to be an important driver of grazing rates for this species. For H. erythrogramma, gonad index and macroalgal nutrition are key drivers of grazing rates, which display no significant change across latitude. These contrasting patterns suggest each species occupies different thermal niches, providing key insights into how their ecological impacts may change across their distribution and in response to ocean warming.

ABSTRACT This study provides a comprehensive evaluation of the latest generation of climate models in simulating the dynamics of the Australian summer monsoon over northern Australia. The analysis focuses on both spatial and temporal characteristics of precipitation, low‐level circulation, monsoon onset and retreat as well as the representation of El‐Niño Southern Oscillations (ENSO) teleconnections. Using multiple observational datasets and standard performance metrics, including correlation, root mean square error, standard deviation and bias, models are assessed and ranked based on their ability to simulate observed monsoon features. The results reveal persistent model biases, including overestimated precipitation, underestimated wind intensity, delayed monsoon onset and retreat (by up to 2 weeks in some models), a weak or overly uniform simulation of ENSO influence and in some cases interannual rainfall variability is more than double the observed value. These limitations affect the models' ability to capture the seasonal cycle and interannual variability of the monsoon. Importantly, performance varies significantly even among models from the same modelling institution, underscoring the need for individual model evaluation. Using a subset of high‐performing models that accurately capture key monsoon features leads to more consistent and robust projections. These high‐performing models simulate increased rainfall in northeast Australia (+15 to +20%) by the late 21st century under a high emissions scenario. In contrast, low‐performing models simulate much weaker increases (0 to +5%). This study highlights both the progress and ongoing challenges in current‐generation climate models, contributing to improved understanding and model selection for future monsoon projections across northern Australia.

Perennial trees in temperate regions precisely coordinate the timing of seasonal growth cessation and dormancy with environmental cues, primarily photoperiod. While the roles of abscisic acid (ABA) in dormancy regulation are well-established, its function in growth cessation remains less defined. ABSCISIC ACID-INSENSITIVE 5 (ABI5) is a basic leucine zipper transcription factor that plays a central role in ABA-mediated development and abiotic stress responses, yet its roles in photoperiodic regulation of growth cessation and its coordination with radial stem growth remain unknown. Here, we demonstrate that in poplar (Populus tomentosa) trees, exogenous ABA application exacerbated short-day (SD)-induced growth inhibition, accelerated bud set, and strongly suppressed secondary xylem formation. We identified a Populus ABI5 homolog, PtoABI5, whose expression is induced by both ABA and SDs. Overexpression of PtoABI5 phenocopied and enhanced SD responses, leading to premature growth cessation and a pronounced inhibition of cambial division and wood formation under SDs. Conversely, PtoABI5 suppressed the expression of the GA biosynthesis gene, while it enhanced the expression of GA catabolic genes. Exogenous GA application partially rescued both the apical growth defects and the impaired secondary xylem development in PtoABI5-overexpressing plants. Our findings establish PtoABI5 as a central integrator, linking ABA and GA signaling pathways to coordinately arrest shoot apical growth and seasonal wood formation, thereby fine-tuning the seasonal growth cycle in perennial trees.

Abstract The large annual carbon source over northern tropical Africa (NTA), inferred from satellite CO 2 , remains highly debated. Using observing system simulation experiments with Orbiting Carbon Observatory‐2 (OCO‐2) sampling, we show that seasonally dependent sampling can lead to overestimated annual fluxes. These biases arise when prior flux seasonal cycle differs from the assumed truth. Since OCO‐2 provides more observations during the non‐growing season, posterior fluxes are more constrained in that period. When prior fluxes underestimate the seasonal amplitude, the posterior carbon sink during the growing season is underestimated, leading to a net positive bias. This effect is supported by real OCO‐2 data, where we hypothesize that underestimating fire emissions during non‐growing season and weaker seasonality of prior fluxes may contribute to overestimated annual fluxes. Our results highlight the need to improve prior flux estimates and expand observational coverage during the growing season to reduce biases in regional carbon budget assessments over NTA.

Abstract The circulation of the Caspian Sea, the largest enclosed aquatic basin in the world, is still somewhat mysterious. Recent studies have largely relied on numerical circulation models forced by global wind reanalysis products. Many of these papers lament the lack of any long-term observations of currents for comparison, and this is especially true in the southern basin. However, from late 2012 to early 2014, a series of field studies were conducted by the Iranian Ports and Maritime Authority in the southern basin of the Caspian, with currents measured at 5 sites, and a high-resolution gridded regional wind product was created for the same period. Here we use this combined dataset to describe the monthly-to-seasonal scales of variability of currents and winds near the coast. These low-frequency currents on the shelf are mostly barotropic at speeds of 0 to 10 cm s −1 , while low-frequency winds are as high as 3 m s −1 . Although the 14 month period of observations, containing a single seasonal cycle, is not enough to provide an unambiguous link, seasonal cycles in spatially-variable shelf currents are consistent in phase and magnitude with local forcing by seasonally and spatially-variable local winds, balanced by bottom friction. These local winds are heavily influenced by the surrounding topography, being steered sharply eastwards near the coast by the Alborz mountains in a manner not reflected in global reanalyses, and are also affected on regional scales by land heating in some of the coastal plains. In consequence of this local balance with spatially-variable winds the coastal currents will have convergences and divergences along the coastline that may in turn affect large-scale basin circulation patterns. In addition, flow dynamics are more complicated near Cape Sefidrood as the coastal current often separates from the coast there to form eddies.

Mangroves form an integral habitat component for species of the southern Arabian Gulf, yet their role in supporting fish remains limited. This study investigated habitat use by fish in mangroves to determine the diversity, abundance, size, and whether microhabitat complexity and environmental conditions influence fish assemblage. Fish were surveyed using an underwater visual census among mangrove habitat types across seasonal cycles. Results revealed 1137 individuals belonging to eleven families and fourteen species, a majority being juveniles with Gerres longirostris (44.59%) the most abundant. High-commercial-value species were documented, including Lutjanus ehrenbergii (dominance 18.65%) and Lutjanus argentimaculatus (dominance 15.48%). To date, this study reports the first evidence of Epinephelus coioides in the mangroves of this region. Results showed significant variation in fish assemblage among habitat types and seasons, with markedly higher abundance and diversity during the summer and in mangroves close to structural habitats. Seawater temperature emerged as the most influential environmental variable for fish. Together, structurally complex habitat settings and seawater temperatures were the key drivers shaping the fish assemblage in mangroves. Future investigations would benefit from diel and tidal sampling within multiple habitats near mangroves to better understand fish populations. Findings may guide research and conservation strategies by integrating coastal habitats and fish populations.