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Abstract. Ice shelf calving constitutes roughly half of the total mass loss from the Antarctic ice sheet. Although much attention is paid to calving of giant tabular icebergs, these events are relatively rare. Here, we investigate the role of frontal melting and stresses at the ice shelf front in driving bending and calving on the scale of ∼100 m, perpendicular to the ice edge. We focus in particular on how buoyant underwater “feet” that protrude beyond the above-water ice cliff may cause tensile stresses at the base of the ice. Indirect and anecdotal observations of such feet at the Ross Ice Shelf front suggest that the resulting bending may be widespread and can trigger calving. We consider satellite observations together with an elastic beam model and a parameterization of wave erosion to better understand the dynamics at the ice shelf front. Our results suggest that on average frontal ablation rather consistently accounts for 20±5 m yr−1 of ice loss at Ross Ice Shelf, likely mostly due to wave erosion and smaller-scale, 𝒪(100 m), foot-induced calving. This constitutes only ∼2 % of the total frontal mass loss (since near-front ice velocities are ∼1000 m yr−1). Observational evidence suggests that sporadic larger events can skew this rate (we document one foot-induced calving event of size ∼1 km). Stresses from foot-induced bending are likely not sufficient to initiate crevassing but rather act to propagate existing crevasses. In addition, our results support recent findings by Buck (2024) that additional bending moments, likely due to temperature gradients in the ice, may play a role in driving frontal deflections. The highly variable environment, irregularity of pre-existing crevasse spacing, and complex rheology of the ice continue to pose challenges in better constraining the drivers behind the observed deformations and resulting calving rates. 

Abstract We report on a laboratory study of wave‐swash interactions, which occur in the very nearshore environment of a beach when the shallow swash flow of a breaking wave interacts with a subsequent wave. Wave‐swash interactions have been observed in the field, hypothesized to be important for nearshore transport processes, and categorized into different qualitative types, but quantitative descriptions of their dynamics have remained elusive. Using consecutive solitary waves with different wave heights and separations, we generate a wide variety of wave‐swash interactions with large flow velocities and vertical accelerations. We find that wave‐swash interactions can be quantitatively characterized in terms of two dimensionless parameters. The first of them corresponds to the wave height ratio for consecutive waves, and the second is a dimensionless measure of the time separation between consecutive wave crests. Using measurements of bed pressure and free‐surface displacement, we estimate the total vertical accelerations and focus on the peak upward‐directed acceleration. We find that wave‐swash interactions can generate vertical accelerations that can easily exceed gravity, despite occurring in very shallow water depths. The large vertical accelerations are upward‐directed and are quickly followed by onshore‐directed horizontal velocities. Together, our findings suggest that wave‐swash interactions are capable of inducing large material suspension events of sediment or solutes in sediment pores, and transporting them onshore. While the data are from a single location making it difficult to generalize the findings across the swash zone, the results clearly demonstrate the importance of large vertical accelerations in wave‐swash interactions. 

We report an investigation into random-jet-stirred homogeneous turbulence generated in a vertical octagonal prism-shaped tank where there are jet arrays on four of the eight vertical faces. We show that the turbulence is homogeneous at all scales in the central region of the tank that span multiple integral scales in all directions. The jet forcing from four sides in the horizontal direction guarantees isotropy in horizontal planes but leads to more energy in the horizontal fluctuations com- pared with the vertical fluctuations. This anisotropy between the horizontal and vertical fluctuations decreases at smaller scales, so that the inertial and dissipation range statistics show isotropic behavior. Using four jet arrays allows us to achieve higher turbulence intensity and Reynolds number with a shorter jet merging distance compared to previous facilities with two-facing arrays. By changing the array-to-array distance, the parameters of the algorithm that drives random-jet stirring, and attachments to the exits of each jet, we show that we are able to vary the turbulence scales and Reynolds number. We provide scaling relations for the turbulent fluctuation velocity, integral scale, and dissipation rate, and we show how these scales of motion are primarily determined by the properties of individual jets and the diffusion of their momentum with distance from the nozzles. Finally, we examine the signatures of individual jets in the turbulent velocity spectra and report the conditions under which individual jet flows, not fully mixed with the background turbulence, produce a spectral peak and the corresponding frequency associated with the jet forcing timescale. 

In this work, we conduct controlled experiments in a wave flume to represent different wave-wave interactions occurring in the swash zone. Using solitary waves as the forcing condition, we combined different wave amplitudes with separation times between the wave events. Experimental results show that interactions developing in the swash zone present three main stages: A jet slamming, an induced splash, and a region where the flow becomes fully 3D turbulent. We identified that the location where the interactions occur and the type of interaction depends on two main factors, the relationship between the wave amplitudes and the separation time between these wave events. Additionally, we were able to mimic the wave-wave interactions observed in real-case scenarios. Our goal is to relate these findings to the sediment transport processes in the swash zone, where interactions could develop a potential impact on the sediment transport mechanism and possible morphological changes. 

In fluid dynamics applications that involve flow adjacent to a porous medium, there exists some ambiguity in how to model the interface. Despite different developments, there is no agreed upon boundary condition that should be applied at the interface. We present a new analytical solution for laminar boundary layers over permeable beds driven by oscillatory free stream motion where flow in the permeable region follows Darcy's law. We study the fluid boundary layer for two different boundary conditions at the interface between the fluid and a permeable bed that was first introduced in the context of steady flows: a mixed boundary condition proposed by Beavers and Joseph [“Boundary conditions at a naturally permeable bed,” J. Fluid Mech. 30, 197–207 (1967)] and the velocity continuity condition proposed by Le Bars and Worster [“Interfacial conditions between a pure fluid and a porous medium: Implications for binary alloy solidification,” J. Fluid Mech. 550, 149–173 (2006)]. Our analytical solution based on the velocity continuity condition agrees very well with numerical results using the mixed boundary condition, suggesting that the simpler velocity boundary condition is able to accurately capture the flow physics near the interface. Furthermore, we compare our solution against experimental data in an oscillatory boundary layer generated by water waves propagating over a permeable bed and find good agreement. Our results show the existence of a transition zone below the interface, where the boundary layer flow still dominates. The depth of this transition zone scales with the grain diameter of the porous medium and is proportional to an empirical parameter that we fit to the available data. 

Particulate matter in the environment, such as sediment, marine debris and plankton, is transported by surface waves. The transport of these inertial particles is different from that of fluid parcels described by Stokes drift. In this study, we consider the transport of negatively buoyant particles that settle in flow induced by surface waves as described by linear wave theory in arbitrary depth. We consider particles that fall under both a linear drag regime in the low Reynolds number limit and in a nonlinear drag regime in the transitional Reynolds number range. Based on an analysis of typical applications, we find that the nonlinear regime is the most widely applicable. From an expansion in the particle Stokes number, we find kinematic expressions for inertial particle motion in waves, and from a multiscale expansion in the dimensionless wave amplitude, we find expressions for the wave-averaged drift velocities. These drift velocities are analogous to Stokes drift and can be used in large-scale models that do not resolve surface waves. We find that the horizontal drift velocity is reduced relative to the Stokes drift of fluid parcels and that the vertical drift velocity is enhanced relative to the particle terminal settling velocity. We also demonstrate that a cloud of settling particles released simultaneously will disperse in the horizontal direction. Finally, we discuss the accuracy of our expressions by comparing against numerical simulations, which show excellent agreement, and against experimental data, which show the same trends.