As Arctic sea ice transitions to a more seasonal regime, the marginal ice zone (MIZ) is emerging as increasingly relevant to the climate system. Within this region, the evolution of turbulent ocean eddies is tightly coupled to the fate of sea ice. Yet, most existing approaches treat sea ice as a continuum, even though in the MIZ it is composed of discrete floes whose sizes overlap those of the eddies. Here, using a coupled model system that explicitly resolves interactions between individual floes and the ocean, we show that the patterns of sea ice cover regulate the energy pathways associated with large-scale turbulence. Variations in the floe size distribution reshape both the generation and damping of ocean eddies, producing more than a twofold difference in kinetic energy between realizations with different floe arrangements. These differences arise as both the sizes and spatial organization of floes imprint on surface forcing, while the resulting turbulence reorganizes the ice into clusters and open-water regions at scales distinct from the floes themselves. Heterogeneity in the sea ice cover, not just its concentration, govern upper-ocean turbulence, underscoring the challenges inherent to the growing implementation of high-resolution Earth-system models.

We report on the development of a novel process model created to study ocean-sea ice interaction and the dynamics of the upper ocean in the marginal ice zone (MIZ), built using the Community Earth System Model (CESM). Our model uses the MOM6 ocean model and CICE6 sea-ice model as active components within CESM, on a custom ~50km x ~50km grid with a horizontal resolution of ~50m, extending to a depth of 75m (30 vertical layers). The model allows for either reflecting or zonally re-entrant boundary configurations. Atmospheric forcing is imposed through a simplified data atmosphere component that provides constant forcing over the model domain. Results from several simple scenarios are presented and compared to results obtained using the MITgcm. By working within CESM, we are able to leverage CESM’s existing infrastructure and capabilities, including the use of the Community Mediator for Earth Prediction Systems (CMEPS) for coupling between active components. Furthermore, additional model components that are already available within CESM (e.g., waves, atmosphere) can be incorporated into the process model in a straightforward way. Future work will include incorporation of a modified sea-ice component that allows tracking of individual floes utilizing a discrete element method approach.

Wind, wave, and acoustic observations are used to test a scaling for ambient sound levels in the ocean that is based on wind speed and the degree of surface wave development (at a given wind speed). The focus of this study is acoustic frequencies in the range 1-20 kHz, for which sound is generated by the bubbles injected during surface wave breaking. Traditionally, ambient sound spectra in this frequency range are scaled by wind speed alone. In this study, we investigate a secondary dependence on surface wave development. For any given wind-speed, ambient sound levels are separated into conditions in which waves are 1) actively developing or 2) fully developed. Wave development is quantified using the non-dimensional wave height, a metric commonly used to analyze fetch or duration limitations in wave growth. This simple metric is applicable in both coastal and open ocean environments. Use of the wave development metric to scale sound spectra is first motivated with observations from a brief case study near the island of Jan Mayen (Norwegian Sea), then robustly tested with long time-series observations of winds and waves at Ocean Station Papa (North Pacific Ocean). When waves are actively developing, ambient sound levels are elevated 2-3 dB across the 1-20 kHz frequency range. This result is discussed in the context of sound generation during wave breaking and sound attenuation by persistent bubble layers.

Wave-ice interactions are critical for correctly modeling air-sea exchanges and ocean surface processes in polar regions. While the role of sea ice in damping open-water swell waves has received considerable research interest, the impact of sea ice on locally generated wind-waves in partial ice cover remains uncertain. The current approach in spectral wave models is to scale the wind input term by the open-water fraction, 1-phi $1-\phi $, for phi $\phi $ the sea ice concentration (SIC), but this neglects the impact of subgrid-scale patterns of sea ice coverage in limiting fetch for wind-wave growth. Here, we use the spectral wave model SWAN to simulate local waves in realistic, synthetic fields of explicitly resolved sea ice floes over a range of SICs and floe size distributions (FSDs). We consider cases with floe sizes much larger than the wavelengths, and absent of interstitial frazil or pancake ice. Through geometric arguments, we show that the fetch available for wind-wave growth, and thus the resulting wave statistics, depends on a combination of the SIC and the FSD. The combination of geometric scaling and empirical wave laws allows the prediction of bulk wave statistics as a function of SIC, a characteristic floe size, and wind speed. We show that due to the difference in spectral character from attenuated propagating open-ocean swell, these waves may have an outsized impact on ocean mixing regimes.

AbstractWind, wave, and acoustic observations are used to test a scaling for ambient sound levels in the ocean that is based on wind speed and the degree of surface wave development (at a given wind speed). The focus of this study is acoustic frequencies in the range 1–20 kHz, for which sound is generated by the bubbles injected during surface wave breaking. Traditionally, ambient sound spectra in this frequency range are scaled by wind speed alone. In this study, we investigate a secondary dependence on surface wave development. For any given wind‐speed, ambient sound levels are separated into conditions in which waves are 1) actively developing or 2) fully developed. Wave development is quantified using the non‐dimensional wave height, a metric commonly used to analyze fetch or duration limitations in wave growth. This simple metric is applicable in both coastal and open ocean environments. Use of the wave development metric to scale sound spectra is first motivated with observations from a brief case study near the island of Jan Mayen (Norwegian Sea), then robustly tested with long time‐series observations of winds and waves at Ocean Station Papa (North Pacific Ocean). When waves are actively developing, ambient sound levels are elevated 2–3 dB across the 1–20 kHz frequency range. This result is discussed in the context of sound generation during wave breaking and sound attenuation by persistent bubble layers.

In January 2022, the strongest Arctic cyclone on record resulted in a record weekly loss in sea ice cover in the Barents-Kara-Laptev seas. While ECMWF operational forecasts skillfully predicted the cyclone, the loss in sea ice was poorly predicted. We explore the ocean's response to the cyclone using observations from an Argo float that was profiling in the region, and investigate model biases in simulating the observed sea ice loss in a fully coupled GCM. The observations showed changes over the whole ocean column in the Barents Sea after the passage of the storm, cooling and mixing with enough implied heat release to melt roughly 1 m of sea ice. We replicate the observed cyclone in the GCM by nudging the model's winds to observations above the boundary layer. In these simulations, the associated loss of sea ice is only about 10%-15% of the observed loss, and the ocean exhibits very small changes in response to the cyclone. With the use of a simple 1-D ice-ocean model, we find that the overly strong ocean stratification in the GCM may be a significant source of model bias in its simulated response to the cyclone. However, even initialized with observed stratification profiles, the 1-D model also underestimated mixing and sea ice melt relative to the observations. Extreme storms in the Arctic can significantly impact the ocean and sea ice state. In January 2022, the strongest Arctic storm on record resulted in a record loss of sea ice. The storm was well predicted by the ECMWF operational forecasts, yet the loss of sea ice was not. Here we further study the impact that the storm had on the ocean, and how well a fully coupled global climate model simulates the observed response in sea ice and ocean to the storm. We do this by nudging the winds in the model to observations. In observations, the ocean responded to the storm by cooling and mixing to full depth in the Barents Sea, releasing enough heat to melt a significant amount of sea ice. In contrast, the model's simulated sea ice and ocean response to the storm is much smaller than estimated in observations. The model's ocean stratification prior to the storm is significantly stronger than observed and is likely a source of bias, which we confirm with the use of a simple one dimensional model. An Argo float showed cooling and mixing in the Barents Sea during a record Arctic cyclone, accounting for the associated record sea ice loss A coupled GCM with winds nudged to observations shows much smaller changes in sea ice and ocean structure with the passage of the cyclone A 1-D ocean model shows that too-strong stratification in the GCM is a main source of bias in its sea ice and ocean response to the cyclone

Abstract Sea ice is a heterogeneous, evolving mosaic of individual floes, varying in spatial scales from meters to tens of kilometers. Both the internal dynamics of the floe mosaic (floe‐floe interactions), and the evolution of floes under ocean and atmospheric forcing (floe‐flow interactions), determine the exchange of heat, momentum, and tracers between the lower atmosphere and upper ocean. Climate models do not represent either of these highly variable interactions. We use a novel, high‐resolution, discrete element modeling framework to examine ice‐ocean boundary layer (IOBL) turbulence within a domain approximately the size of a climate model grid. We show floe‐scale effects could cause a marked increase in the production of fine‐scale three‐dimensional turbulence in the IOBL relative to continuum model approaches, and provide a method of representing that turbulence using bulk parameters related to the spatial variance of the ice and ocean: the floe size distribution and the ocean kinetic energy spectrum.

Observations of sea ice and the upper ocean from three moorings in the Beaufort Sea quantify atmosphere- ice-ocean momentum transfer, with a particular focus on the inertial-frequency response. Seasonal variations in the strength of mixed layer (ML) inertial oscillations suggest that sea ice damps momentum transfer from the wind to the ocean, such that the oscillation strength is minimal under sea ice cover. In contrast, the net Ekman transport is unimpacted by the presence of sea ice. The mooring measurements are interpreted with a simplified one-dimensional ice-ocean coupled "slab" model. The model results provide insight into the drivers of the inertial seasonality: namely, that a combina-tion of both sea ice internal stress and ocean ML depth contribute to the seasonal variability of inertial surface currents and inertial sea ice drift, while under-ice roughness does not. Furthermore, the importance of internal stress in damping inertial oscillations is different at each mooring, with a minimal influence at the southernmost mooring (within the seasonal ice zone) and more influence at the northernmost mooring. As the Arctic shifts to a more seasonal sea ice regime, changes in sea ice cover and sea ice internal strength may impact inertial-band ice-ocean coupling and allow for an increase in wind forcing to the ocean.

Properties of the surface mixed layer (ML) are critical for understanding and predicting atmosphere-sea ice-ocean interactions in the changing Arctic Ocean. Mooring measurements are typically unable to resolve the ML in the Arctic due to the need for instruments to remain below the surface to avoid contact with sea ice and icebergs. Here, we use measurements from a series of three moorings installed for one year in the Beaufort Sea to demonstrate that upward-looking acoustic Doppler current profilers (ADCPs) installed on subsurface floats can be used to estimate ML properties. A method is developed for combining measured peaks in acoustic backscatter and inertial shear from the ADCPs to estimate the ML depth. Additionally, we use an inverse sound speed model to infer the summer ML temperature based on offsets in ADCP altimeter distance during open-water periods. The ADCP estimates of ML depth and ML temperature compare favorably with measurements made from mooring temperature sensors, satellite SST, and from an autonomous Seaglider. These methods could be applied to other extant mooring records to recover additional information about ML property changes and variability.

The retreat of Arctic sea ice is enabling increased ocean wave activity at the sea ice edge, yet the interactions between surface waves and sea ice are not fully understood. Here, we examine in situ observations of wave spectra spanning 2012-2021 in the western Arctic marginal ice zone (MIZ). Swells exceeding 30 cm are rarely observed beyond 100 km inside the MIZ. However, local wind waves are observed in patches of open water amid partial ice cover during the summer. These local waves remain fetch-limited between ice floes with heights less than 1 m. To investigate these waves at climate scales, we conduct experiments varying wave attenuation and generation in ice with a global model including coupled interactions between waves and sea ice. A weak high-frequency attenuation rate is required to simulate the local waves in observations. The choices of attenuation scheme and wind input in ice have a remarkable impact on the extent of wave activity across ice-covered oceans, particularly in the Antarctic. As well as demonstrating the need for stronger constraints on wave attenuation, our results suggest that further attention should be directed towards locally generated wind waves and their role in sea ice evolution. This article is part of the theme issue 'Theory, modelling and observations of marginal ice zone dynamics: multidisciplinary perspectives and outlooks'.

This archive includes the data used to produced the results shown in the associated article. That data was collected during the Stratified Ocean Dynamics of the Arctic (SODA) Department Research Initiative, funded by ONR.

Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Oceans. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Evaluation of a Coupled Wave-Ice Model in the Western ArcticAuthorsVincent T.CooperiDLettie AnneRoachJimThomsoniDSamuel DaleBrenneriDMadison MargaretSmithCeciliaBitziDSee all authors Vincent T. CooperiDCorresponding Author• Submitting AuthorUniversity of WashingtoniDhttps://orcid.org/0000-0001-9697-1992view email addressThe email was not providedcopy email addressLettie Anne RoachUniversity of Washingtonview email addressThe email was not providedcopy email addressJim ThomsoniDUniversity of WashingtoniDhttps://orcid.org/0000-0002-8929-0088view email addressThe email was not providedcopy email addressSamuel Dale BrenneriDApplied Physics Laboratory, University of WashingtoniDhttps://orcid.org/0000-0002-0826-1294view email addressThe email was not providedcopy email addressMadison Margaret SmithUniversity of Washingtonview email addressThe email was not providedcopy email addressCecilia BitziDUniversity of WashingtoniDhttps://orcid.org/0000-0002-9477-7499view email addressThe email was not providedcopy email address

Unprecedented quantities of heat are entering the Pacific sector of the Arctic Ocean through Bering Strait, particularly during summer months. Though some heat is lost to the atmosphere during autumn cooling, a significant fraction of the incoming warm, salty water subducts (dives beneath) below a cooler fresher layer of near-surface water, subsequently extending hundreds of kilometers into the Beaufort Gyre. Upward turbulent mixing of these sub-surface pockets of heat is likely accelerating sea ice melt in the region. This Pacific-origin water brings both heat and unique biogeochemical properties, contributing to a changing Arctic ecosystem. However, our ability to understand or forecast the role of this incoming water mass has been hampered by lack of understanding of the physical processes controlling subduction and evolution of this this warm water. Crucially, the processes seen here occur at small horizontal scales not resolved by regional forecast models or climate simulations; new parameterizations must be developed that accurately represent the physics. Here we present novel high resolution observations showing the detailed process of subduction and initial evolution of warm Pacific-origin water in the southern Beaufort Gyre.

Understanding and predicting sea ice dynamics and ice-ocean feedback processes requires accurate descriptions of momentum fluxes across the ice-ocean interface. In this study, we present observations from an array of moorings in the Beaufort Sea. Using a force-balance approach, we determine ice-ocean drag coefficient values over an annual cycle and a range of ice conditions. Statistics from high resolution ice draft measurements are used to calculate expected drag coefficient values from morphology-based parameterization schemes. With both approaches, drag coefficient values ranged from similar to 1 to 10 x 10(-3), with a minimum in fall and a maximum at the end of spring, consistent with previous observations. The parameterizations do a reasonable job of predicting the observed drag values if the under ice geometry is known, and reveal that keel drag is the primary contributor to the total ice-ocean drag coefficient. When translations of bulk model outputs to ice geometry are included in the parameterizations, they overpredict drag on floe edges, leading to the inverted seasonal cycle seen in prior models. Using these results to investigate the efficiency of total momentum flux across the atmosphere-ice-ocean interface suggests an inter-annual trend of increasing coupling between the atmosphere and the ocean.

The retreat of Arctic sea ice coincides with increased ocean surface wave activity, and wave-ice interactions are consequently poised to have a growing influence on the Arctic climate system. Recen...

Increasing extent and duration of seasonally ice-free area in the western Arctic Ocean suggests increased air-sea coupling, specifically fluxes of momentum and heat between the lower atmosphere and the upper ocean. The dependence of these fluxes on ice concentration and its dynamical characteristics is still uncertain. As part of the Stratified Ocean Dynamics of the Arctic (SODA) project, year-long time series of upper-ocean velocity profiles were obtained across a range of ice conditions and are used to infer momentum fluxes. We consider the structure of observed current profiles as a function of sea state and ice cover. During the summer and in open water with minimal stratification, the wind forcing is in local equilibrium with surface gravity waves, and there is a direct transfer of momentum from the atmosphere to the upper ocean. The presence of ice modifies the momentum budget through both the inclusion of ice-atmosphere and ice-ocean stresses, and by damping short surface gravity waves and thus changing the surface roughness that the atmosphere acts upon. Ice presence is also associated with increased near-surface stratification, which can act to decouple the sub-surface ocean from atmospheric forcing. Our observations show frequent decoupling of a thin surface layer (<10 m depth), including case studies in which the relatively fresh surface waters formed by “ice puddles” have entirely different motion from the relatively salty water a few meters below. Ice formation in the fall affects both the ocean stratification and the ice characteristics, leading to competing effects affecting momentum transfer. Initial results across the annual cycle are presented.

The high degree of heterogeneity in the ice-ocean-atmosphere system in marginal ice zones leads to a complex set of dynamics which control fluxes of heat and buoyancy in the upper ocean. Strong fronts may occur near the ice edge between the warmer waters of the ice-free regions and the cold, fresh waters near and under the ice. This study presents observations of a well-defined density front located along the ice edge in the Beaufort Sea. The evolution of the front over a ~3-day survey period is captured by multiple cross-front sections measured using an underway conductivity-temperature-depth system, with simultaneous measurements of atmospheric forcing. Synthetic aperture radar images bookending this period show that the ice edge itself underwent concurrent evolution. Prior to the survey, the ice edge was compact and well defined while after the survey it was diffuse and filamented with coherent vortical structures. This transformation might be indicative of the development an active ocean eddy field in the upper ocean mixed layer. Over the course of hours, increasing wind stress is correlated with changes to the lateral buoyancy gradient and frontogenesis. Frontal dynamics appear to vary from typical open-ocean fronts (e.g., here the frontogenesis is linked to an “up-front” wind stress). Convective and shear-driven mixing appear to be unable to describe deepening at the heel of the front. While there was no measurable spatial variation in wind speed, we hypothesize that spatial heterogeneity in the total surface stress input, resulting from varying ice conditions across the marginal ice zone, may be a driver of the observed behaviour.