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Tide effects on the structure of the near‐field Changjiang River plume and on the extension of the far‐field plume have often been neglected in analysis and numerical simulations, which is the focus of this study. Numerical experiments highlighted the crucial role of the tidal forcing in modulating the Changjiang River plume. Without the tidal forcing, the plume results in an unrealistic upstream extension along the Jiangsu coast. With the tidal forcing, the vertical mixing increases, resulting in a strong horizontal salinity gradient at the northern side of the Changjiang River mouth along the Jiangsu coast, which acts as a dynamic barrier and restricts the northward migration of the plume. Furthermore, the tidal forcing produces a bidirectional plume structure in the near field, and the plume separation is located at the head of the submarine canyon. A significant bulge occurs around the head of the submarine canyon and rotates anticyclonically, which carries a large portion of the diluted water toward the northeast and merges into the far‐field plume. A portion of the diluted water moves toward the southeast, which is mainly caused by tidal rectification. This bidirectional plume structure is more evident under certain wind conditions. During the neap tide with the reduced tidal energy, the near‐field plume extends farther offshore, and the bulge becomes less evident. These dynamic behaviors are maintained and are fundamentally important in the region around the river mouth even under the summer monsoon and the shelf currents, although in the far field the wind forcing and shelf currents eventually dominate the plume extension. Key Points Key role of tide in determing the extension of Changjiang plume in near field Tide‐induced mixing arrests the upstream extension of plume Tide helps to produce the bidirectional structure of Changjiang plume

Periods of high astronomically generated tides contribute to the occurrence of extreme sea levels. Over interannual time scales, two precessions associated with the orbit of the Moon cause systematic variation of high tides. A global assessment of when these tidal modulations occur allows for the prediction of periods when the enhanced risk of coastal flooding is likely in different parts of the world. This paper uses modeled tides to assess the influence of the 18.61 year lunar nodal cycle and the 8.85 year cycle of lunar perigee (which affects high tidal levels as a quasi 4.4 year cycle) on high tidal levels on a global scale. Tidal constituents from the TPXO7.2 global tidal model are used, with satellite modulation corrections based on equilibrium tide expectations, to predict multidecadal hourly time series of tides on a one‐quarter degree global grid. These time series are used to determine the amplitude and phase of tidal modulations using harmonic analysis fitted to 18.61, 9.305, 8.85, and 4.425 year sinusoidal signals. The spatial variations in the range and phase of the tidal modulations are related to the global distribution of the main tidal constituents and tidal characteristics (diurnal or semidiurnal and tidal range). Results indicate that the 18.61 year nodal cycle has the greatest influence in diurnal regions with tidal ranges of >4 m and that the 4.4 year cycle is largest in semidiurnal regions where the tidal range is >6 m. The phase of the interannual tidal modulations is shown to relate to the form of the tide. Key Points Interannual tidal modulations influence extreme sea levels and coastal flooding This paper maps the range and phase of the tidal modulations on a global scale Determine where the modulations contribute largest to high tidal levels

Repeating earthquakes, which occur on overlapping rupture patches with the same focal mechanisms, provide insights into fault creep, earthquake cycle dynamics, triggering, and predictability. Recently, earthquakes with highly anti-correlated waveforms have been systematically reviewed. However, most studies have only observed a small number of anti-repeating earthquake pairs or noted reversals in earthquake focal mechanisms, without connecting these observations to underlying earthquake physics processes. Here we show 37 anti-repeating earthquake pairs ( M : 0.18–1.88) in Sierra Valley deep (~ 32 km) earthquake sequence based on regional waveform analysis. Our high-precision location analysis shows that these anti-repeating earthquake pairs occur on adjacent faults (separated by ~ 240 m), with focal mechanisms indicating that normal and thrust earthquakes can occur within short time intervals. Furthermore, tidal modulation of seismicity in this region suggests a low effective normal stress. We suggest small-scale stress heterogeneity is the mechanism of anti-repeating earthquakes. These findings underscore the necessity of considering both positive and negative components of cross correlation in earthquake studies to better understand the mechanics of fault systems and improve seismic hazard assessment. Graphical abstract

Tidal-scale wave modulation is a critical yet complex process in macro-tidal estuaries. This study investigates semidiurnal wave modulations in the Changjiang River Estuary (CRE) using unique, long-term in situ observations and high-resolution ADCIRC–SWAN coupled simulations. Pronounced semidiurnal signals are identified in significant wave height (Hs), mean wave period, and wave direction. Observational results demonstrate that the modulation intensity is highest in Hangzhou Bay and the CRE mouth, decreasing gradually offshore. A key finding is that semidiurnal Hs maxima systematically coincide with peak flood currents and precede high water by approximately three hours. Long-term records confirm that this modulation persists year-round and intensifies during energetic events such as typhoons. The expression of the tidal signal depends on wave composition: wind-sea-dominated conditions exhibit stronger period modulation, whereas swell-dominated conditions favor coherent Hs modulation as kinematic tidal effects remain more apparent in the absence of strong local wind forcing. Numerical sensitivity experiments demonstrate that tidal currents are the primary driver of the observed wave modulation, while water-level effects are largely confined to shallow shoals. The results highlight that accurately reproducing the observed frequency–directional structure requires the inclusion of current-induced Doppler shifts and refraction. Beyond the classical following-current effects, the analysis suggests that the spatial deceleration of currents along the wave path acts as a kinematic trap that focuses wave action and sustains Hs intensification. This mechanism provides a physically plausible explanation for the observed phase relationship and points to the non-local nature of estuarine wave dynamics, where the wave state appears as an integrated response to cumulative current gradients along the propagation path. These findings emphasize the necessity of incorporating wave–current coupling in future coastal modeling and hazard forecasting.

This work shows a 3-year climatology of the horizontal components of the solar diurnal tide, obtained from wind measurements made by a multistatic specular meteor radar (SIMONe) located in Jicamarca, Peru (12∘S, 77∘W). Our observations show that the meridional component is more intense than the zonal component, and that it exhibits its maxima shifted with respect to the equinox times (i.e., the largest peak occurs in August–September, and the second one in April–May). The zonal component only shows a clear maximum in August–September. This observational climatology is compared to a climatology obtained with the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X). Average comparisons indicate that the model amplitudes are 50% smaller than the observed ones. The WACCM-X results are also used in combination with observed altitude profiles of the tidal phases to understand the relative contributions of migrating and non-migrating components. Based on this, we infer that the migrating diurnal tide (DW1) dominates in general, but that from June until September (November until July) the DE3 (DW2) may have a significant contribution to the zonal (meridional) component. Finally, applying wavelet analysis to the complex amplitude of the total diurnal tide, modulating periods between 5 and 80 days are observed in the SIMONe measurements and the WACCM-X model. These modulations might be associated to planetary waves and intraseasonal oscillations in the lower tropical atmosphere.

Methane emissions from cold seeps play an important role in oceanic carbon cycling and climate regulation, yet their temporal dynamics and controlling mechanisms remain poorly understood. We conducted long-term in situ monitoring at the Formosa Ridge (Site F), southwest of Taiwan, using a self-developed ocean observation platform that integrates an acoustic Doppler current profiler (ADCP), conductivity–temperature–depth (CTD) sensors, current meters, and other instruments, enabling multi-parameter correlation analysis. The observations revealed pronounced temporal variability in gas emissions, with emission intensity closely correlated with bottom pressure fluctuations controlled by tidal cycles. The results suggest that hydrostatic pressure changes promote or inhibit hydraulic fracturing, thereby modulating gas release. These findings support a conceptual model of the seep’s fluid system, characterized by a constant subsurface methane supply and tidally modulated episodic bubble discharge, a mechanism likely applicable to other cold seep environments globally and offering new insights into the dynamics of marine methane emissions.

Urban estuarine environments face increasing water safety risks due to microbial contamination from combined sewer overflows (CSOs), particularly during heavy rainfall events. In megacities like Tokyo, where waterfronts are widely used for recreation, such contamination poses significant public health risks. The challenge is compounded by the variability in both intensity and spatial distribution of rainfall across the catchment, combined with complex tidal dynamics making effective water quality management difficult. To address this challenge, we conducted a series of hydrodynamic–microbial fate simulations to examine the spatial and vertical behavior of Escherichia coli (E. coli) under different rainfall–tide conditions. Focusing on the Sumida River estuary, rainfall data from eight drainage areas were classified into six event types using cluster analysis. Two contrasting events were selected for detailed analysis: a light rainfall (G2, 15 mm over 13 h) and an intense event (G6, 272 mm over 34 h). Vertical water quality profiling was performed along an 8.5 km transect from the Kanda–Sumida River confluence to the Tokyo Bay Tunnel, illustrating E. coli and salinity. The results showed that the rainfall intensity and tidal phase at the event onset are critical in shaping both the magnitude and vertical distribution of microbial contamination. The intense event (G6) led to deep microbial intrusion (up to 6–7 m) and major salinity disruption, while the lighter event (G2) showed surface-layer confinement. Salinity gradients were more strongly affected during G6, indicating freshwater intrusion. Tidal phase also influenced transport: the flood-high condition retained E. coli, whereas ebb-low tides facilitated downstream flushing. These findings highlight the influence of rainfall intensity and tidal timing on microbial distribution and support the use of vertical profiling in estuarine water quality management. They also support the development of dynamic, event-based water quality risk assessment tools. With appropriate local calibration, the modeling framework is transferable to other urban estuarine systems to support proactive and adaptive water quality management.

To understand the process-response relations among physical forcing and biogeochemical properties of suspended particles (SPs) in the river-dominated northern South China Sea shelf, a 5-day shipboard observation was conducted at a fixed location on the dispersal pathway of the Zhujiang (Pearl) River plume (ZRP) in the summer of 2016. Instrumented moorings were deployed near the sampling site to record the flow and wave fields every 10 minutes. Hydrographic properties were measured hourly to identify different water masses. Water and SPs samples at the surface (3 m) and near the bottom (3 m above the bed) were taken every 3 h for the analyses of nutrients, chlorophyll-a (Chl-a), and particulate organic matter (POM including POC, PN, and δ 13 C POC ). Meanwhile, the grain-size composition of SPs and seafloor sediment were also analyzed. Results showed that monsoon winds drove cold upwelling and ZRP waters at the surface. Both the upwelling and ZRP regimes contained newly produced marine phytoplankton based on low POC/Chl-a ratio (PC ratio) and enriched δ 13 C POC. However, SPs in the ZRP regime were smaller (<153 µm), having denser particle bulk density, and less enriched δ 13 C POC , indicating different bio-communities from the upwelling regime. EOF analysis of the surface data suggested that mixing processes and the dispersal of the ZRP regime were mainly controlled by far-field storm winds, tidal modulation, and strength of mixing. On the other hand, a bottom nepheloid layer (BNL) was observed, mainly consisting of SPs<63 μm with higher bulk density than SPs at the surface. POM in the BNL was degraded and δ 13 C POC -depleted according to the PC ratio and δ 13 C POC . EOF analysis of the near-bottom data indicated that the dominant physical processes influencing the biogeochemical properties of SPs in the BNL were jointly the upwelling-associated lateral transport (first order) and tide-related resuspension (second order). Our study identified the contrast between the surface and near-bottom regimes with the coupling patterns among physical forcing and physiochemical properties of SPs using good constraints on particle dynamics and particle sources.

The tidal signal and its long‐term variation in the Caribbean Sea is analyzed on the basis of hourly records from thirteen tide gauges five of which span more than 20 years. The seven larger tidal constituents are studied, namely the fortnightly term Mf, diurnal K1, O1, and P1, and semidiurnal M2, S2 and N2. The 18.61 year nodal modulation is clearly identifiable in almost all the examined constituents of lunar origin. However, its signal in M2 is less clear while it is almost imperceptible in N2, where the 8.85 year cycle caused by the eccentricity of the Moon's orbit and the orientation of its major axis variation dominates the long‐term variability. The effect of the nodal variation in the amplitude and phase lag of the various tidal constituents is in agreement (within the 95% error limits) with the theoretical gravitational estimate, with the exception of the 8.85 year cycle in N2, where larger values are found. Overall, in the Caribbean the net effect of the low frequency cycles can change the maximum tidal range from 16.5% to 23.5% in a nodal cycle. Although the Caribbean is a micro‐tidal environment this still results in changes of the range of up to 8.4 cm. Significant, spatially coherent trends are found for the amplitude of S2 (2.3 to 8.8 mm/cy). Key Points Significant, spatially coherent positive trends for the amplitude of S2 Long term modulations consistent with the tide‐generating potential Mean tidal constituents for thirteen ports in the Caribbean using long series

Among the many deep low‐frequency earthquakes (LFEs) recently discovered worldwide, LFEs beneath Osaka Bay, western Japan, are especially unusual. Their waveforms are monochromatic, resembling those of some volcanic LFEs, but there are no active volcanoes around. The area is close to but clearly distinct from a belt of tectonic LFEs, and is near the site of a large inland earthquake (the 1995 Kobe earthquake). To characterize the activity of these LFEs, we present an extensive catalog constructed using a matched filter analysis on continuous seismic records with template LFEs determined by the Japan Meteorological Agency. The relocated catalog of 1378 events over a period of 5 years shows spatially concentrated activity in two volumetric zones, with several active periods including successive tremor‐like events. The magnitude–frequency statistics satisfy the Gutenberg–Richter law with a b‐value of 2. Unlike tectonic LFEs, which are highly sensitive to tidal stress, the LFEs beneath Osaka Bay show no spectral peak in activity at tidal periods, and the overall pattern of the spectrum is similar to that of volcanic LFEs beneath Sakurajima, Japan. These findings suggest that the Osaka Bay LFEs are almost same as volcanic LFEs in origin, or at least related to fluid upwelling from the mantle. Key Points Many monochromatic LFEs and tremor‐like episodes were found beneath Osaka Bay These LFEs are similar to volcanic LFEs as a result of the new rich catalog These LFEs must be related to water upwelling from the mantle in this area