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While nonlinear internal wave (NLIW) trains are known to influence near‐sea bed suspended sediment dynamics, the mechanisms remain a topic of debate. We present near‐sea bed observations of suspended sediment concentration C$C$and estimates of vertical sediment flux, at high vertical‐ and temporal‐resolution, during trains of NLIW of depression. We quantify the contributions of vertical advection and turbulent mixing to C$C$ . Vertical advection was important during the leading wave and the turbulent mixing flux was important over the entire wave train. Maximum C$C$was highly correlated with the maximum horizontal current speed squared and was only weakly correlated with the maximum vertical velocity. Boundary layer‐induced turbulence was thus inferred to be the key driver of net vertical sediment flux over wave trains of this type. Estimating the maximum total horizontal speed (i.e., wave‐induced plus background) is sufficient for modeling sediment vertical dynamics in shelf‐scale modeling studies.

Nonlinear internal waves are found in many parts of the world ocean. Their widespread distribution is a result of their origin in the barotropic tide and in the variety of ways they can be generated, including by lee waves, tidal beams, resonance, plumes, and the transformation of the internal tide. The differing generation mechanisms and diversity of generation locations and conditions all combine to produce waves that range in scale from a few tens of meters to kilometers, but with all properly described by solitary wave theory. The ability of oceanic nonlinear internal waves to persist for days after generation and the key role internal waves play in connecting large-scale tides to smaller-scale turbulence make them important for understanding the ocean environment.

We present multi-sensor measurements from satellites, unmanned aerial vehicle, marine radar, thermal profilers, and repeated conductivity–temperature–depth casts made in the Kara Gates strait connecting the Barents and the Kara Seas during spring tide in August 2021. Analysis of the field data during an 18-h period from four stations provides evidence that a complex sill in the Kara Gates is the site of regular production of intense large-amplitude nonlinear internal waves. Satellite data show a presence of a relatively warm northeastward surface current from the Barents Sea toward the Kara Sea attaining 0.8–0.9 m/s. Triangle-shaped measurements using three thermal profilers revealed pronounced vertical thermocline oscillations up to 40 m associated with propagation of short-period nonlinear internal waves of depression generated by stratified flow passing a system of shallow sills in the strait. The most intense waves were recorded during the ebb tide slackening and reversal when the background flow was predominantly supercritical. Observed internal waves had wavelengths of ~100 m and traveled northeastward with phase speeds of 0.8–0.9 m/s. The total internal wave energy per unit crest length for the largest waves was estimated to be equal to 1.0–1.8 MJ/m.

In the equatorial Indian Ocean, strong westerly and easterly wind anomaly can drive eastward downwelling and upwelling Kelvin waves, respectively, which play an important role in determining the circulations and thermal structures near the equator. Kelvin waves can propagate into the Andaman Sea, a marginal sea located to the northeast of the Indian Ocean. In the Andaman Sea, nonlinear internal waves (NLIWs) that are crucial in facilitating the mixing in the ocean interior and maintaining the ecosystem are found to be extremely active. Although both equatorial Kelvin waves and NLIWs have been well known in oceanography, the influence of equatorial Kelvin waves on NLIWs in the Andaman Sea remains unclear. In this study, based on long-term mooring measurements in the southern Andaman Sea, it is found that the NLIW amplitude shows remarkable intraseasonal and seasonal variances, and these variances can be mostly explained by the occurrence of equatorial Kelvin waves. Downwelling Kelvin waves can deepen the thermocline depth by tens of meters, so that the NLIW amplitude can be reduced up to 22%. Meanwhile, upwelling Kelvin waves can notably uplift the thermocline depth and the NLIW amplitude can be enhanced up to 32%. These discoveries provide credible evidence that basin-scale waves from the open ocean can remotely modulate small-scale internal waves in marginal seas.

Ship and mooring data collected off the coast of New Jersey are used to describe the nonlinear internal wave (NLIW) field and the background oceanographic conditions that formed the waveguide on the shelf. The subinertial, inertial, and tidal circulation are described in detail, and the background fluid state is characterized using the coefficients of the extended Korteweg–de Vries equation. The utility of this type of analysis is demonstrated in description of an amplitude‐limited, flat wave. NLIWs observed over most of the month had typical displacements of −8 m, but waves observed from 17–21 August were almost twice as large with displacements near −15 m. During most of the month, wave packets occurred irregularly at a fixed location, and often more than one packet was observed per M2 tidal period. In contrast, the arrival times of the large‐amplitude wave groups observed over 17–21 August were more closely phased with the barotropic tide. The time span in which the largest NLIWs were observed corresponded to neap barotropic conditions, but when the shoreward baroclinic energy flux was elevated. During the time of large NLIWs, near‐inertial waves were a dominate contributor to the internal motions on the shelf and apparently regulated wave formation, as destructive/constructive modulation of the M2 internal tide by the inertial wavefield at the shelf break corresponded to stronger/weaker NLIWs on the shelf.

The baroclinic response to barotropic tidal forcing in the Camarinal Sill area, within the Strait of Gibraltar, is investigated with a three‐dimensional, fully nonlinear, nonhydrostatic numerical model. The aim of numerical efforts was the assessment of three‐dimensional effects, which are potentially significant in the area because of rather irregular bottom topography, variable background stratification, and complex structure of barotropic tides. Model results reveal a complex baroclinic response under relatively moderate flood tidal currents, which includes the formation of internal hydraulic jumps upstream of the sill, internal cross waves close to the channel walls, and a plunging pycnocline at the lee side of the sill crest. These structures exhibit significant cross‐channel spatial dependence and may appear to be aligned together across the channel. This fact makes their identification difficult from the surface pattern captured by remote sensing images. Under strong barotropic forcing (spring tides) the upstream hydraulic jumps are shifted to the lee side of Camarinal Sill, where a single internal hydraulic jump is formed. Significant first‐ and second‐mode hydraulic jumps are also generated near smaller secondary sills in Tangier basin, thus extending the occurrence of intense water mixing and energy dissipation to other zones of the strait. Key Points Three‐dimensional baroclinic response to tidal forcing in the Camarinal Sill Different baroclinic response under moderate to strong tidal forcing Generation of multiple internal hydraulic jumps in secondary sills

Laboratory observations are presented showing the structure and dynamics of the turbulent bottom boundary layer beneath nonlinear internal waves (NLIWs) of depression shoaling upon sloping topography. The adverse pressure gradient beneath the shoaling waves causes the rear face to steepen, flow separation to occur, and wave‐induced near‐bottom vortices to suspend bed material. The resuspension is directly attributed to the near‐bed viscous stress and to near‐bed patches of elevated positive Reynolds stress generated by the vortical structures. These results are consistent with published field observations of resuspension events beneath shoaling NLIWs. Elevated near‐bed viscous stresses are found throughout the domain at locations that are not correlated to the resuspension events. Near‐bed viscous stress is thus required for incipient sediment motion but is not necessarily a precursor for resuspension. Resuspension is dependent on the vertical velocity field associated with positive Reynolds stress and is also found to occur where the mean (wave‐averaged) vertical velocity is directed away from the bed. The results are interpreted by analogy to the eddy‐stress and turbulent bursting resuspension models developed for turbulent channel flows.

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.

Tidal currents in Luzon Strait south of Taiwan generate some of the largest internal waves anywhere in the ocean. Recent collaborative efforts between oceanographers from the United States and Taiwan explored the generation, evolution, and characteristics of these waves from their formation in the strait to their scattering and dissipation on Dongsha Plateau and the continental slope of mainland China. Nonlinear internal waves affect offshore engineering, navigation, biological productivity, and sediment resuspension. Observations within Luzon Strait identified exceptionally large vertical excursions of density (as expressed primarily in temperature profiles) and intense turbulence as tidal currents interact with submarine ridges. In the northern part of the strait, the ridge spacing is close to the internal semidiurnal tidal wavelength, allowing wave generation at both ridges to contribute to amplification of the internal tide. Westward radiation of semidiurnal internal tidal energy is predominant in the north, diurnal energy in the south. The competing effects of nonlinearity, which tends to steepen the stratification, and rotational dispersion, which tends to disperse energy into inertial waves, transform waves traveling across the deep basin of the South China Sea. Rotation inhibits steepening, especially for the internal diurnal tide, but despite the rotational effect, the semidiurnal tide steepens sufficiently so that nonhydrostatic effects become important, leading to the formation of a nonlinear internal wave train. As the waves encounter the continental slope and Dongsha Plateau, they slow down, steepen further, and are modified and scattered into extended wave trains. At this stage, the waves can \"break,\" forming trapped cores. They have the potential to trap prey, which may account for their attraction to pilot whales, which are often seen following the waves as they advance toward the coast. Interesting problems remain to be explored and are the subjects of continuing investigations.

Nonlinear internal waves (NLIWs) exhibit robust dynamic submesoscale motions, connecting large-scale tides to small-scale shear instabilities in the ocean. Previous studies have mainly focused on their generation mechanisms and evolution along their paths. Considering their global distribution resulting from the primary origin in tide-topography interaction, there is an increasing cross-disciplinary interest in understanding how these energetic and ubiquitous NLIWs contribute to sediment redistribution in the ocean. This paper presents fundamental theories on NLIWs and comprehensively reviews triggering mechanisms, different types of instability, and sediment responses by summarizing recent theoretical parameterizations, numerical simulations, laboratory experiments, and in-situ observations. We specifically focus on elucidating various types of instability along with their impact on sediment dynamic processes. Finally, we outline several unresolved issues that require further exploration for a quantitative investigation into NLIW-induced sediment transfer in the ocean.