A basic framework characterising the interaction between aquatic flows and permeable sediment beds is presented here. Through the permeability Reynolds number ( $Re_{K}=\sqrt{K}u_{\ast }/\unicode[STIX]{x1D708}$ , where $K$ is the sediment permeability, $u_{\ast }$ is the shear velocity and $\unicode[STIX]{x1D708}$ is the fluid viscosity), the framework unifies two classical flow typologies, namely impermeable boundary layer flows ( $Re_{K}\ll 1$ ) and highly permeable canopy flows ( $Re_{K}\gg 1$ ). Within this range, the sediment–water interface (SWI) is identified as a transitional region, with $Re_{K}$ in aquatic systems typically $O(0.001{-}10)$ . As the sediments obstruct conventional measurement techniques, experimental observations of interfacial hydrodynamics remain extremely rare. The use of refractive index matching here allows measurement of the mean and turbulent flow across the SWI and thus direct validation of the proposed framework. This study demonstrates a strong relationship between the structure of the mean and turbulent flow at the SWI and $Re_{K}$ . Hydrodynamic characteristics, such as the interfacial turbulent shear stress, velocity, turbulence intensities and turbulence anisotropy tend towards those observed in flows over impermeable boundaries as $Re_{K}\rightarrow 0$ and towards those seen in flows over highly permeable boundaries as $Re_{K}\rightarrow \infty$ . A value of $Re_{K}\approx 1{-}2$ is seen to be an important threshold, above which the turbulent stress starts to dominate the fluid shear stress at the SWI, the penetration depths of turbulence and the mean flow into the sediment bed are comparable and similarity relationships developed for highly permeable boundaries hold. These results are used to provide a new perspective on the development of interfacial transport models at the SWI.

Molecular diffusion, dispersion, and turbulent diffusion can all contribute to the transport of mass across the sediment‐water interface (SWI). Flow observations across the SWI are critical in the description of these transport processes but are currently very limited as the sediment bed is inaccessible in most experimental approaches. We overcome this constraint by combining refractive‐index matching (RIM) with particle‐tracking velocimetry (PTV). Using measurements of the flow dynamics across the SWI, we propose a mechanistic model that describes the interfacial mass transport over a wide and relevant parameter space. We show there are three transport regimes where molecular, dispersive, or turbulent transport dominates the mass flux of a passive tracer across the SWI. Transitions between these regimes are defined by the permeability Reynolds number, whereKis the sediment permeability,is the shear velocity, andνis the fluid viscosity. In the molecular regime (), mass transport is described by the molecular diffusion coefficient (D). In both the dispersive () and turbulent regimes (), the mass diffusivity is directly proportional to. The model is strongly supported by an extensive data set of published interfacial mass flux observations and provides a tool for describing fluxes across the SWI in aquatic system models.

There is a wide consensus within the polar science, meteorology, and oceanography communities that more in situ observations of the ocean, atmosphere, and sea ice are required to further improve operational forecasting model skills. Traditionally, the volume of such measurements has been limited by the high cost of commercially available instruments. An increasingly attractive solution to this cost issue is to use instruments produced in-house from open-source hardware, firmware, and postprocessing building blocks. In the present work, we release the next iteration of our open-source drifter and wave-monitoring instrument, which follows these solution aspects. The new design is significantly less expensive (typically by a factor of 5 compared with our previous, already cost-effective instrument), much easier to build and assemble for people without specific microelectronics and programming competence, more easily extendable and customizable, and two orders of magnitude more power-efficient (to the point where solar panels are no longer needed even for long-term deployments). Improving performance and reducing noise levels and costs compared with our previous generation of instruments is possible in large part thanks to progress from the electronics component industry. As a result, we believe that this will allow scientists in geosciences to increase by an order of magnitude the amount of in situ data they can collect under a constant instrumentation budget. In the following, we offer (1) a detailed overview of our hardware and software solution, (2) in situ validation and benchmarking of our instrument, (3) a fully open-source release of both hardware and software blueprints. We hope that this work, and the associated open-source release, will be a milestone that will allow our scientific fields to transition towards open-source, community-driven instrumentation. We believe that this could have a considerable impact on many fields by making in situ instrumentation at least an order of magnitude less expensive and more customizable than it has been for the last 50 years, marking the start of a new paradigm in oceanography and polar science, where instrumentation is an inexpensive commodity and in situ data are easier and less expensive to collect.

The dissipation of wave energy in the marginal ice zone is often attributed to wave scattering and the dissipative mechanisms associated with the ice layer. In this study we present observations indicating that turbulence generated by the differential velocity between the sea ice cover and the orbital wave motion may be an important dissipative mechanism of wave energy. Through field measurements of under‐ice turbulence dissipation rates in pancake and frazil ice, it is shown that turbulence‐induced wave attenuation coefficients are in agreement with observed wave attenuation in the marginal ice zone. The results suggest that the turbulence‐induced attenuation rates can be parameterized by the characteristic wave properties and a coefficient. The coefficient is determined by the ice layer properties.

Waves can drastically transform a sea ice cover by inducing break-up over vast distances in the course of a few hours. However, relatively few detailed studies have described this phenomenon in a quantitative manner, and the process of sea ice break-up by waves needs to be further parameterized and verified before it can be reliably included in forecasting models. In the present work, we discuss sea ice break-up parameterization and demonstrate the existence of an observational threshold separating breaking and non-breaking cases. This threshold is based on information from two recent field campaigns, supplemented with existing observations of sea ice break-up. The data used cover a wide range of scales, from laboratory-grown sea ice to polar field observations. Remarkably, we show that both field and laboratory observations tend to converge to a single quantitative threshold at which the wave-induced sea ice break-up takes place, which opens a promising avenue for robust parametrization in operational forecasting models.

Observations of wave dissipation and dispersion in sea ice are a necessity for the development and validation of wave–ice interaction models. As the composition of the ice layer can be extremely complex, most models treat the ice layer as a continuum with effective, rather than independently measurable, properties. While this provides opportunities to fit the model to observations, it also obscures our understanding of the wave–ice interactive processes; in particular, it hinders our ability to identify under which environmental conditions these processes are of significance. Here, we aimed to reduce the number of free variables available by studying wave dissipation in landfast ice. That is, in continuous sea ice, such as landfast ice, the effective properties of the continuum ice layer should revert to the material properties of the ice. We present observations of wave dispersion and dissipation from a field experiment on landfast ice in the Arctic and Antarctic. Independent laboratory measurements were performed on sea ice cores from a neighboring fjord in the Arctic to estimate the ice viscosity. Results show that the dispersion of waves in landfast ice is well described by theory of a thin elastic plate, and such observations could provide an estimate of the elastic modulus of the ice. Observations of wave dissipation in landfast ice are about an order of magnitude larger than in ice floes and broken ice. Comparison of our observations against models suggests that wave dissipation is attributed to the viscous dissipation within the ice layer for short waves only, whereas turbulence generated through the interactions between the ice and waves is the most likely process for the dissipation of wave energy for long periods. The separation between short and long waves in this context is expected to be determined by the ice thickness through its influence on the lengthening of short waves. Through the comparison of the estimated wave attenuation rates with distance from the landfast ice edge, our results suggest that the attenuation of long waves is weaker in comparison to short waves, but their dependence on wave energy is stronger. Further studies are required to measure the spatial variability of wave attenuation and measure turbulence underneath the ice independently of observations of wave attenuation to confirm our interpretation of the results.